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measure the air exiting the compression element rather than the intake volume drilling cleaning and ventilation are key applications for compressed air in mining work developments in performance and reliability have been very important as have improvements in the mobility and maneuverability of the equipment today s smaller and lighter compressors can be moved more easily to the next location without the need for additional equipment to carry out the move drilling using air driven equipment compressed air plays an important role in the drilling of blastholes using techniques that combine the rotary action of drilling with the impact of a hammer injected air is used both in driving the hammer that is used to break up the rock and in blowing the debris out of the hole the air is used in techniques involving top hammer drilling where the hammer is mounted at the top of the drill shaft and in down the hole dth drilling where the intensity of the hammer action is increased by locating it on top of the drill bit rather than at the top of the drill string part of the volume of air is used to power the hammer and the rest is used to flush the hole by removing the material that has been broken apart demand for increased productivity in the benching at open pit mines has spurred the use of hole diameters larger than 127 mm 5 in in diameter dth drills can produce large diameter holes with straighter alignments than could be achieved with a top hammer top hammer drilling is however a particularly economical method that is ideal for use in good competent rock for holes of short to medium depth with little if any deviation and no requirement for large diameter holes it gives a good penetration rate for high production capacity and its energy costs are low the hydraulic rock drill delivers the impact energy through a string of sectional drill steel to the drill bit this method is fast though achieving a straight hole can be more difficult in certain drilling conditions there is an approximately 10 energy loss in each coupling joint the dth method is also commonly used and comes into its own for drilling holes that go deeper have large diameters and where hole straightness has a higher priority than penetration rate it is also chosen when drilling in extremely broken and fractured rock where the flushing requirements are very high the rock hammer is positioned directly behind the drill bit ensuring minimal power losses high pressure air is used for impact and as exhaust air for flushing the hole dth drilling is a highly reliable method of producing clean straight holes in a variety of drilling conditions however this method gives slower penetration rates than top hammer drilling dth drilling applications include blastholes in production drilling drop raise cut holes and pilot holes in raise driving and ventilation and communications holes for drainage atlas copco also developed the coprod system for use where dr

illing conditions are difficult where there is broken rock or where higher capacity productivity is required it combines the straight hole drilling accuracy of dth drilling with a speed superior to top hammer drilling the system consists of impact rods combined with drill tubes to produce high penetration rates and longer drill steel life rotation and percussion are separated optimizing the drill string for each function the impact rods are stacked so that they are flush which transmits percussion without the loss of energy that occurs in the coupling joints of conventional drilling methods the main difference between pneumatic and hydraulic drill rigs is simply whether the rock drill s hitting and rotating mechanism is driven by compressed air or by hydraulic oil the track movement can also be propelled by compressed air increasing drilling efficiency the use of compressed air is vital in the creation of the deep large diameter holes that are essential for achieving optimum blast economy in open pit mines and quarries the burden between the free face and the drill hole is dependent on the hole diameter spacing and depth being able to create largerdiameter holes can significantly reduce the number of feet to be drilled hence increasing productivity air flushing increasing power output from rock drills leads to higher penetration rates so that efficient flushing of the cuttings becomes increasingly important the flushing medium is normally air for surface drilling and water for underground drilling the flushing air comes from a pressure tank supplied by one or more compressors where the compressor is regulated to maintain the required supply air is blown down through the drill bit and the cuttings are removed via the annulus surrounding the drill shaft the cuttings can be bound by a flushing additive added to the working air or can be removed using a dust collector flushing is used to clean the bottom of the hole to prepare it for the next blow and to carry the cuttings out of the hole the first of these tasks usually gives no trouble although it is necessary to ensure that the passageways for the cuttings on the sides of the drill bit are sufficiently large and that the flushing holes in the drill bit are directed so that effective cleaning of the bottom of the hole is ensured determining air pressure and flows the air required to clear holes depends on factors including the material to be removed the drill method and the hole dimensions the amount of air required depends on the equipment and the compressed air pressure chosen the total air requirement for a typical atlas copco 89 mm 3 5 in dth hammer at 586 kpa 85 psi would be 46 l s 97 cfm this rises to 200 l s 425 cfm at 2 480 kpa 360 psi for a 150 mm 6 in hammer the airflow required for the hammer would range from 84 l s 178 cfm at 85 psi to 480 l s 1 015 cfm at 360 psi planning for the total compressed airflow required also requires othe

r aspects to be taken into account the total air requirement for a drilling task is built up from the demands of the various operations involved which can include the use of hammers rotation units feed motors dust collectors and air flushing a rig fitted with a 102 mm 4 in hammer operating at 2 000 kpa 290 psi might require 205 l s 434 cfm for the hammer itself but the operation would require twice this amount when the air for the feed motor rotation unit and dust collector are taken into account similarly a 586 kpa 85 psi operation involving a midsized rock drill could require 268 l s 568 cfm to operate the drill but it would require a further 25 l s 53 cfm for the feed motor 70 l s 148 cfm for the flushing and 65 l s 138 cfm for the dust collection falling costs time spent per foot of advance at a tunnel face has fallen markedly in recent decades for the sequential operations of drilling charging ventilation scaling mucking shotcreting and bolting see figure 9 2 2 types of compressors the many types of compressors are divided broadly into two families positive displacement and dynamic or centrifugal types the most common type of dynamic air compressor is the rotary screw which is available in oil lubricated or oil free versions piston compressors have been around since compressors were first invented but advances continue to be made to create high pressure models with advantages in efficiency ease of maintenance and reduced life cycle costs in an oil lubricated screw compressor air passes through the air inlet filter where dust particles are separated inside the screw element air is mixed with the injected oil and compressed the oil is used to seal the clearance between the rotors and the casing of the element and it ensures friction of the elements and cools the output air and screw elements a separator removes the oil from the air first through centrifugal force and then through filtration in oil free screw compressors the gap between the rotor elements is minimal there is no oil injected in the screw element the male and female rotors receive a special coating and as they do not touch there is no friction and less heat production the jacket of the element is cooled the air then passes through an aftercooler where it is cooled the condensate is then separated and drained away a dryer cools the air through a refrigeration cycle to 14 8 c 5 4 f and the further condensate that is generated is removed the air then flows through the integrated dryer heat exchanger where it is warmed by the incoming warm humid air coming from the compressor s aftercooler the final step on leaving the dryer is to filter the compressed air quality reliability is generally seen as the most important factor behind the choice of a compressor model portable and stationary systems having determined the use of rotary oil injected air compressors the mine can decide on the use for an electric

powered stationary installation or diesel powered portable units if a ready and stable electrical supply is available it might appear that the stationary installation is the preferred option but it is never that easy so additional factors to be taken into consideration include cost of diesel versus electricity stage of development is the site a greenfield or a brownfield or is it at the mining setup stage distance of the infrastructure and place of work logistics complexity of transporting pylons or diesel to the site plus criteria of storing the diesel on site and life expectancy of the mining operation many underground mines today have less need for compressed air circuits than in the past thanks to the growing use of portable compressors or compressors built into mobile equipment portable air driven equipment such as drills have become increasingly efficient and they provide great flexibility in their ability to be moved to wherever required another factor has been the advent of load haul dump vehicles their use has diminished the need for the slushers double drum hoists which were commonly used to move ore and had compressed air motors some underground mines have dispensed completely with a stationary compressed air plant though most still have a compressed air network its uses are varied it can be used for instance to blow away dirt and pipe blockages apply sprayed concrete clean tools clear or cool the air and power hand tools such as drills it can also be used as a hazardwarning system if stench gas is added typical compressed air requirements in an underground mine will be for air at 7 8 to 9 2 bar 100 to 120 psig where static compressors are being used the typical solution will involve using a combination of fixed compressors which are always either simply loaded or unloaded and ones with a variable speed drive vsd that cater for the peaks and troughs of the load cycle standby compression capacity would also be installed for wherever maintenance is required or in case of failure use of vsds minimizes the energy required to maintain the required pressure precise control of the pressure can be achieved through an external regulating system this can be preprogrammed with all the required criteria for system operation using rules to ensure optimum efficiency including factors such as ensuring that operational hours are shared between main and standby machines this external regulating system is able to obtain substantial energy savings fixed static compressors are generally sited on the surface with only the piping taken belowground this ensures sufficient air for the cooling of the compressors as well as avoiding the harsh underground environment and the difficulties of delivering such large pieces of equipment underground some stationary compressors are available that are built into standard 6 m 20 ft high cube freight containers to allow outdoor use saving the need for a s

eparate container room applications for small portable compressors which deliver from 30 to 88 l s 67 to 187 cfm in the 8 to 12 5 bar 100 to 170 psig range include driving pneumatic tools such as chipping hammers jackhammers grinding tools and rammers they are also suitable for uses that require high fad such as sandblasting more powerful models provide higher free air delivery while still remaining small enough for ease of transport and maneuvering today s small light equipment means that the operator can move to the next work point easily without needing additional equipment to transport the compressor the next tier includes heavy duty models designed for environments such as quarries these models deliver about 165 to 183 l s 350 to 388 cfm at 8 to 12 5 bar 100 to 170 psig typical uses include rock drilling where higher pressures between 9 5 and 14 6 bar 125 and 200 psig are needed there is a choice of models catering for flow rates between 233 and 400 l s 494 and 847 cfm higher pressures can be achieved through the use of twostage portable compressors capable of delivering up to 31 bar 440 psig the ability to deliver ever higher pressures has resulted in productivity gains in mines changing from a regular sized 26 bar 365 psig machine to a 31 bar 440 psig machine brings considerable benefits most machines are built for 26 bar 365 psig pressures altough it may be possible for the compressor element itself to produce 31 bar 440 psig or more other components such as seals and pressure vessels must be able to operate at the higher nominal pressure because most components may need changing to achieve such an upgrade the resulting machine will inevitably be more expensive the increased capital cost must be balanced against the reduced operating costs due to the productivity gain operations that require a high volume of air include rock drilling for this application the compressor needs to be easy to operate as well as easy to relocate for quick start up in quarries and maximum productivity compressors can also be built into vehicles to suit a customer s needs and provide air power at remote locations for instance using a truck that has a power take off from the drive train from the power take off a belt drive or drive shaft can be used to take power from the engine the engine is used to power the vehicle when it is driving and to power up the compressor when the vehicle is stationary at the site where the compressor is needed oil lubricated versus oil free compressors stationary compressors come into two broad categories oillubricated and oil free in oil lubricated compressors the lubricating oil serves a number of purposes it seals the clearance gaps between the screws and the casing it lubricates the drive between the male and female screws it assists in extraction of the heat generated during compression after the compression phase a mixture of compressed air and lubricant oil

leaves the air end and is passed to an oil separator where the lubricant is removed but part of the oil is exhausted from the compressor usually as an aerosol or in a mist form in mining compressed air is sometimes used to supplement ventilation air through the use of venturi blowers the presence of oil could be an issue in these circumstances although the amount of air supplied in this manner is generally small the air quality would generally only be an issue if a compressor were being used to supply a majority of the air in long dead headings with little other air supply if oil free air is required filters are necessary on oillubricated compressors the costs for maintaining and replacing the filters must be balanced against the smaller capital cost for the compressor compared to an oil free compressor another aspect in choosing between oil lubricated and oilfree air compressors is the total power requirements for the compressor oil lubricated compressors are not available beyond 500 kw 680 hp limited by physics and economics whereas oil free compressors can be obtained in megawatt sizes atlas copco has an installation in an underground turkish mine where about 8 mw of oil free compressors are in use this application would require 16 of the biggest oil lubricated machines but significantly fewer oil free machines more machines also mean greater maintenance costs the compressors are installed on the surface with tubing and pipes to transport the air underground oil lubricated compressors tend to be chosen when compressors need to be installed underground as they are less sensitive to the local environment as well as being easier to transport boosters today there is a growing demand in mining for much higher pressures that cannot be met by an air compressor alone typically for example a portable oil injected screw compressor delivers air at pressures between 7 8 and 31 bar 100 and 440 psig compressed air at pressures between 51 and 346 bar 735 and 5 075 psig requires a booster to increase the pressure the outlet of the feed air compressor is fed into the booster as its inlet single stage booster compressors therefore take in air at perhaps 26 bar 360 psig instead of atmospheric pressure compressing the air further to achieve the desired pressure up to 70 bar 1 015 psig multistage boosters are used to take the pressure up to a maximum pressure of 346 bar 5 070 psig booster applications include minerals exploration drilling using reverse circulation techniques and coal bed methane where drilling very deep holes up to several miles deep can be demanded other applications for boosters include nitrogen injection for mine fire suppression eliminating the risk of explosion and the risk of oxidation on valves pipes and drill bits the booster is built on a modified engine block typically a john deere or cummins equipped with booster pistons mounted on modified engine pistons and using different sizes de

pending on pressure flow the capacity of the booster is determined by the inlet pressure and the speed of the driver engine the higher the revolutions per minute the more fad the booster will displace economies of drilling in making a purchase decision people often only consider the purchase price but it is important to obtain information from suppliers about the actual operating costs of the equipment this ensures that allowance is made for hidden costs such as preventive maintenance life cycle costs manufacturers of compressors continue to carry out development work to optimize the production of air the aim is to maximize fad for the lowest power consumption as this is the main factor in driving down energy costs the purchase price is only a small part of the cost of providing compressed air the quality and service life of the compressor and its components costs of energy 70 and maintenance and the indirect costs of downtime are among other factors to take into account accurate calculation of the total cost of ownership is a complex matter and some manufacturers produce calculators to help would be purchasers of pneumatic drilling equipment take into account all the variables including factors such as annual operating hours for the equipment depreciation costs interest on financing and fuel and operator costs to arrive at total hourly costs two other key elements influencing system operating costs are operating pressure and air leakage reductions in either can result in considerable savings air leaks have been estimated to waste as much as 30 of many systems output and most compressed air systems that are more than 5 years old are estimated to have a leakage rate of about 20 of the total volume consumed even a 3 mm 0 12 in air leak is estimated to represent almost 42 000 kw h of wasted energy per year as little as 1 moisture in the oil can reduce the life of the compressor s bearings by 40 today s compressor designs avoid this through electronic control of the oil temperature system automatic control systems also play an important role in ensuring efficient operation for instance by matching use of vsds to fluctuations in flow manufacturers develop systems to improve the efficiency of air production and the quality of the compressed air recent electronic developments regulate the engine speed and the inlet air to optimize fuel consumption the volume flow rate is not a measurement of actual gas volume in a compressed state but rather of air that has been re expanded back to inlet conditions a 47 l s 100 cfm compressor takes in 47 l s 100 cfm of atmospheric ambient air through its intake and may compress it to a gauge pressure of 7 8 bar 100 psig the original 47 l 100 ft3 of air has been reduced in volume 7 8 times and it now only occupies 6 l 12 8 ft3 in its compressed state the compressor used with a top hammer rig will typically be operated for just 45 of the cycle being operated o

nly when the hole is actually being drilled for perhaps 35 of the cycle the compressor will be unloaded but still running and retaining its pressure while actions are carried out such as changing the rods for the remainder of a cycle the rig will be in transit and the pressure vessel can be depressurized appreciation of the times for loading unloading during the cycle is an important factor in calculating operating costs for the equipment a typical example is shown in figure 9 2 3 which indicates times such as 2 to 6 minutes for drilling each rod up to a minute for adding the next a few minutes for collecting the rods before moving to the next position and time for providing a collar to seal the hole the deeper the hole the greater the inlet pressure and flow that will be required to clean it maintaining a constant air speed will require increased pressure compressor flow is a function of the pressure at the compressor inlet it also depends on various factors including flushing speed distance and volumetric efficiency compressors are rated for operation in a particular range of ambient temperatures which can be an important factor in mining however a machine that can work in higher temperatures will cost more and there may be no need for the extra expense the latest advanced machines have been built to perform in a wider range of ambient temperatures including options to work at up to 50 c 122 f and to save energy though the use of features such as automated switching off of the dryer in light load conditions energy savings and heat recovery rising fuel costs and environmental issues have increased demand for energy saving equipment manufacturers continue to develop new ways of improving efficiency for instance atlas copco s compressors feature a fuel saving system that operates when the compressor is under partial loads savings are typically 10 to 20 compared to a similar machine without the system the investment cost of a system such as this can soon pay for itself in countries where fuel costs are high or where fuel supply is difficult as in remote locations energy usage is becoming increasingly important and manufacturers aim to combine the best possible fad with a reduced specific energy requirement the use of advanced computational fluid dynamics techniques in designing the equipment helps minimize internal pressure drops and drive down the energy costs there are sound economic reasons for operating a compressor at the lowest possible discharge pressure economical compression through variable speed drives the cost of compressed air can represent more than 40 of the total electrical costs therefore energy efficient solutions can bring substantial savings one of the key ways of doing this is to use a vsd which tunes the total compressor capacity from a series of stationary compressors to match the demand for air besides providing immediate energy savings a vsd can reduce overall life cycle cost

s of the compressor by an average of 22 fixed speed machines are ideal when they can run at full load for most of their operating time but where air demand fluctuates vsds can achieve savings of up to 35 the vsd enables provision of constant net pressure which provides stability for all processes that use compressed air peaks in electrical current during start up are eliminated and vsd compressors can be started and stopped without limitation another way of saving is to recover energy through an integrated heat exchanging module that makes direct use of the heat coming out of the compression element and transforms it into hot water as a form of energy uses include space heating and showers preventive maintenance proper maintenance is vital to prevent breakdowns especially in hostile environments such as underground mines the ideal is to carry out the maintenance before the machine breaks down and a growing body of evidence about component life makes it ever easier to schedule maintenance and replace parts at the optimum time manufacturers complain that compressors at mines tend to be undermaintained the equipment may be underground exposed to dusty environments and at risk of a much shorter life than in less hostile conditions many mining companies use their own maintenance crews to service the machines instead of bringing in the manufacturer s expertise this can be another contributory factor to reduced life if in house personnel have not received adequate training it takes effort to bring the machine up to the surface consequently maintenance of bigger underground machines tends to be performed in place atlas copco points out that in most industries about 50 of its compressors are regularly serviced by its maintenance crews whereas in mining the proportion is closer to 5 when machine maintenance is neglected major problems are likely to occur and operating costs increase in combination with what can be a hostile environment lack of maintenance can contribute to an unnecessarily short equipment life in a mine perhaps 3 4 or 5 years compared to twice that in other situations special options such as heavy duty filtration are available for dusty environments and trained technicians would immediately identify where these would be beneficial the lack of contact with suppliers often means that compressors are ordered without discussing the operating environment by centralized purchasing based on initial costs alone specifying extra features such as heavy duty filtration is particularly important in situations where maintenance is likely to be difficult and sporadic new technology brings advanced options for monitoring wear to help plan preventive maintenance which can help overcome the traditional shortcomings in mine maintenance some types of mining such as salt mining are particularly corrosive with a consequent impact on the life of wear parts in situations such as this there is a temptation to shun m

aintenance given that the machine s life will inevitably be short nevertheless proper service would help extend the life of the equipment compressor rental rental even of major machines can be useful in cases of short term additional demand and can be useful from a financing and tax perspective by spreading the costs and dispensing with the need to buy a major plant furthermore with a rental the supplier is responsible for all maintenance and for supplying a replacement in case of breakdown for instance atlas copco has a division dedicated to specialty rental with a focus on industrial applications and the mining sector the fleet specializes in oil free and oilinjected high pressure compressors for mining applications as well as generating sets the units deliver air at the rate of up to 755 l s 1 600 cfm with pressures up to 45 bar 650 psig high pressure compressors can be mounted in a crash frame and are used for deep drilling application deeper holes means that higher pressures are required to extract cuttings compressors are also available housed in 6 m 20 ft international organization for standardization iso containers that offer ease of transportation see figures 9 2 4 and 9 2 5 demand for a specialty rental fleet is particularly high in the united states and rentals are typically from a week to a year which is ideal for situations where the compressor needs to be constantly relocated being diesel driven there is no need for a generator making it ideal for use in remote locations this type of equipment is also brought in where there is a short term demand for extra air above that available from the permanent installation or in the case of a breakdown lowpressure rental units can be used for driving pneumatic tools breakers pneumatic pumps diaphragm pumps and general cleaning duties medium pressure units for example 9 5 bar 125 psig are used to inflate mine truck tires to power highflow pumps and to supply air to blast furnacesnecessity for treating air attention has to be paid to minimizing three contaminants that occur in compressed air solids moisture and oil residues these can otherwise contaminate the compressed air to a considerable degree leading to corrosion in pipes and resulting in costly repairs air treatment solutions can be thought of as insurance for the plant rather than simply an extra cost specification of equipment to remove moisture in particular can be thought of as insurance against corrosion malfunctions and production shutdowns without it the costs can be high untreated air may cause extensive damage and lead to serious performance degradation all plants need basic air treatment to protect equipment production processes and end products more critical applications require enhanced solutions to meet air quality requirements equipment can be specified to improve the quality of the air downstream from the compressor by removing contaminants including moisture

particles and oil the presence of these can be harmful in particular situations some form of air treatment is normally required to provide compressed air of the quality required at the point of use otherwise there could be severe effects from the contamination including damage to tools and valves corrosion and damage to equipment piping and machinery and contamination of products contaminants can cause rust and scale to form within pipelines leading to the increased wear and maintenance of pneumatic devices sluggish and inconsistent operation of air valves and cylinders malfunction and high maintenance of control instruments and effects such as spotting in paint and other types of spraying many plants need only part of the air treated to a very high quality however if the majority of the air is needed at a high quality it would make sense to treat all compressed air to the level required by the highest quality user where compressed air is supplied from a central point there may be purification equipment in the compressor room to protect the distribution system with further purification at the point of application an extensive range of purification equipment is available for both centralized and decentralized compressed air systems this allows the user to tailor the quality of air for each specific application from general purpose ring main protection through critical clean dry air point of use systems purification may also be required for decentralized applications such as operation of pneumatic equipment machinery and tools and air instruments air treatment that removes moisture and particles increases efficiency the production of dry clean air prevents corrosion clean dry air extends the life of equipment in the mine enhances system reliability and avoids costly downtime and production delays design criteria for air purity whether designing new compressed air systems or reviewing existing systems the first step is to define the compressed air purity requirements air purity requirements vary widely but can all be met with the right equipment however unnecessary levels of air purification can significantly increase the associated energy cost the quality of air required depends on the application particularly for oil free air requirements to assist in the selection of the necessary air purity a series of classifications has been developed many applications need only part of the air treated to a high quality in such cases it is generally more effective to treat all the generated air to a minimum acceptable level and to improve the quality to the desired level close to the usage point points to consider for a given application include required air quality estimated air demand required working pressure atmospheric contamination position and type of compressor intake temperature of the compressed and cooling air and condition and configuration of existing piping choice of treatment

approaches air quality requirements vary considerably from application to application to achieve the levels of cleanliness specified by iso 8573 1 2001 careful thought must be given to systems design commissioning and operation point of use purification equipment should be installed as close to the application as possible to remove the maximum amount of rust and pipe scale prior to the application filtration systems can be used with oil injected compressors to yield air of a satisfactory quality different applications have different air quality demands the iso 8573 1 standard specifies the quality of the air in terms of particle content the quantity of dust particles that the compressed air can contain as well as the acceptable oil and moisture contents a primary compressor can be fitted with different purification systems according to specific categories within iso 8573 1 and hence be suitable for different applications oil filters are extremely important for ensuring the reliability and availability of compressors heavy duty filters are available that can retain 99 of particles as small as 10 m in contrast to conventional filters that retain 50 m particles another advance in reducing component wear is the use of special oil for lubrication of rotating parts which brings about a significant extension in the life of components such changes have resulted in a doubling of the filter life which is particularly beneficial in remote locations concentrated contamination the compressor uses ambient air for compression without treatment any contaminant in the air such as dust will also be in the compressed air even with filtration some contaminants will remain resulting in the introduction of dust into equipment downstream of the compressor which could cause malfunctions compression reduces the air volume and thus increases the concentrations of airborne contaminants in the intake air consequently compressed air generally requires some form of treatment these contaminants may also be joined by other substances originating within the compressor or in the piping and hoses research indicates that dust concentrations of 173 000 particles cm3 are common up to 80 of these particles are small enough to pass through a compressor intake filter in a typical example the air volume is reduced by compression to one seventh of its original the resulting concentrations of particles such as oil and dust are not compressed and their presence will be increased by a factor of 7 thus as shown in figure 9 2 6 if there were 180 million particles of contaminant in the original volume there would be more than a billion after compression preventing blockages the presence of solid contaminants is the result of corrosion and rust plus mineral deposits all of which build up within the aftercooler storage tank and piping system contributing to this load of solid particulates are solids that bypass the intake filter of the compress

or as well as particles resulting from compressor wear these abrasives range in size from microscopic to large bits and flakes particles can be removed through filters which are a cost effective means of eliminating all types of contamination with minimal pressure loss to protect the compressor from incoming dirt a prefilter is always provided in the case of piston vane and screw compressors these filters have a dirt retention capacity of around 5 m centrifugal compressors are more sensitive to incoming dirt and inlet filtration is normally in two stages retaining down to 0 2 m although droplets are visible to the naked eye particles such as coal dust may only be visible under a microscope whereas a scanning electron microscope is necessary to identify particles such as paint pigment and oil vapor particulate matter includes small solid and liquid particles such as dust smoke sand pollen mist fly ash viruses and bacteria the presence of particles such as dust can block a pipe increasing resistance to the airflow and therefore increasing energy use decreasing performance and increasing operating costs moisture can add to a blockage by forming a sludge moisture also promotes fungal and bacterial growth pneumatically controlled valves that control items such as conveying or filtration equipment may also become blocked over time with a resulting impact on the equipment they control as well as downtime for repairs with a blockage a compressor will need to be run at a higher pressure to achieve the desired output pressure which requires more energy reducing moisture water is probably the most familiar example of a liquid contaminant in compressed air when the air is compressed the density of the moisture increases water in pressurized air does not present a problem as long as it remains in a vapor state but condensed water can lead to corrosion in pipes interference with the lubrication of air tools and the risk of freezing in pipes and tools moisture is an important pollutant to consider in mining system design it causes two problems condensation which can be troublesome downstream and corrosion that can develop dry air is important for avoiding corrosion of air lines and the subsequent leaks and pressure losses replacing a long underground pipe is expensive corrosion begins to occur even before condensation is observed it destroys the interiors of both piping and equipment ultimately it leads to pipe ruptures and equipment malfunctions corrosion also introduces rust particles that can damage the equipment using the air further costs come from the shutdowns needed to reinstall the pipes and equipment condensation occurs at a relative humidity of 100 but corrosion starts even at a relative humidity of 50 when it reaches 60 there is an exponential growth in the rate of corrosion figure 9 2 7 moisture can also lead to damage in the bearings of any equipment that uses oil films for lubrica

tion there can also be resulting losses if air is used to control the filling of containers with final products valves may stick resulting in under or overfilling the corrosion caused by moisture in the air piping can drastically increase operational costs leakage translates into a loss of air capacity this means increased usage of the compressor as it works to compensate a 5 mm 0 2 in hole leaks 27 l s 57 cfm at 7 bar 90 psig to compensate for this loss of airflow capacity 8 3 kw 11 hp of additional compressor power is required which can equate to costs of thousands of dollars per year even from such a relatively small hole even a 3 mm 0 12 in hole can cause leakages of up to 10 l s 22 cfm which in terms of energy consumption equals an annual cost running into thousands of euros dollars pounds as shown in table 9 2 1 this 3 mm hole would leak 100 l s 212 cfm at 6 bar 85 psig giving a power loss at the compressor of 3 1 kw 4 2 hp for a 10 mm 0 39 in hole the energy loss would be increased tenfold humidity the maximum water content that the air can hold without condensation depends on the air temperature more can be held at higher temperatures at high air temperatures a relatively large quantity of vapor can be carried in the air but condensation occurs as the air cools moisture condenses out of the air as it encounters lower temperatures at night as the air temperature cools and the air s capacity to hold moisture is reduced dew forms the air contacts the colder surface and sheds moisture every kilogram of air contains a certain quantity of water in grams which is the absolute air humidity relative humidity is a comparison of how much water vapor is in the air compared to the vapor pressure at the ambient temperature and pressure which is the vapor capacity relative humidity is therefore expressed as a percentage if the temperature of a volume of air is raised without adding more water vapor then its relative humidity decreases the dew point of air is the temperature at which the water vapor held in the compressed air is equal to the compressed air s capacity to hold water vapor it is the temperature at which condensation starts to occur when the air is being cooled if the temperature of the air drops any lower than the dew point the additional water vapor will condense and drop out in liquid aerosol form for instance inlet air with a temperature of 30 c 86 f and a relative humidity of 50 will have a dew point of 18 c 64 4 f see figure 9 2 8 after passing through the aftercooler the air temperature may be ambient 10 40 c 104 f with 100 relative humidity treatment in a refrigeration dryer can reduce the temperature to 20 c 68 f and the pressure dew point to 15 c 5 4 f greatly reducing the likelihood of moisture droplets forming for most industrial applications compressed air can be considered dry when there is no liquid water present liquid water causes corro

sion contributes to the mineral deposits found in air pipes and washes away the necessary lubricants required in air valves cylinders and motors for every 20 c 36 f increase the capacity of air to hold water vapor doubles conversely for every 20 c 36 f decrease the capacity to hold water vapor is cut in half removing the water from compressed air can be accomplished in various ways an air receiver stores the air after the compressor hot compressed air cools in the air receiver where the condensation water is collected and separated out this is the least expensive way and though an old method it also gives the lowest degree of water separation mining applications normally feature an aftercooler aftercoolers are used in virtually all stationary compressor installations as a standard feature if the air goes in at 25 c 77 f it will typically emerge before going into the aftercooler at 90 c 194 f the aftercooler cools it to perhaps 35 to 40 c 95 to 104 f removing most of the moisture the ambient air will generally be cooler than this resulting in heat exchange between the pipe and the surroundings so that the temperature in the pipeline drops which leads to condensation optional dryers can be used to further reduce the moisture content of the compressed air to very small quantities air exits a compressor with 100 humidity and droplets of water form as soon as the temperature falls around the piping refrigerant drying is used to condense and separate a large amount of the water refrigerant dryers remove moisture from compressed air in even the harshest conditions other types of dryers include adsorption dryers heat of compression dryers and membrane dryers with the choice depending on the desired dew point compressed air network distribution portable compressors can be set up alongside drilling equipment and can supply air via a short length of hose however some mines use permanent networks fed by fixed pipelines from banks of stationary compressors the most important issue in designing a piping network is not the quantity of air but rather achieving the correct pressure to operate the equipment air pressure is reduced because of the friction in passing through obstacles such as restrictions bends and narrow passages the pressure drop increases if the air supply chain is long or if the air supply piping is small in diameter for the user of compressed air the airflow rate is of less interest than confidence that the compressor will meet the pressure needs of the work in hand machines with a low operating pressure of about 6 5 bar 80 psig are used in industries such as cement production or coal mining in pneumatic conveying and unloading or in blowing dust away this type of application demands huge amounts of air at a relatively low pressure a higher pressure of about 8 5 bar 108 psig is used for materials handling of larger items and it is a common practice to provide a single air circui

t for both uses even though the result is delays to the higher pressure use while the air supply is diverted to service a high volume low pressure application today independent lines can readily be set up to supply different pressures for divfferent types of operations which can result in considerable reductions in operating costs air distribution is the critical link between the compressor installation and the machine or tool that is using the air distribution requires an effective system of air lines and accessories particularly in harsh environments such as mines a well designed and properly maintained air distribution system should have leakage of no more than 5 of the capacity of the installation unfortunately 15 to 20 leakage is quite common the design of the air line and the choice of the fittings are important for minimizing losses pressure losses are created by restrictions such as small size couplings or hoses that are too long or too small in diameter every coupling in an installation creates a pressure loss but the losses can be exacerbated through the use of incorrect fittings specialist fittings are required in particular situations such as swivels that prevent the hose from getting in the way when working with hand tools and torque arms to reduce fatigue in operators ideally the distance between the tool and the off take should be no more than 3 to 5 m 10 to 16 ft though this is often impractical to achieve in major installations such as mines the main line distributes the air from the compressor location to the point at which the air will be used in a large compressed air system serving several zones the main line should be arranged so that each branch can be shut off without affecting the rest of the system this ensures that when working on the piping system only the branch involved has to be shut off leakage may be decreased if nonoperating units are shut off this approach also makes it possible to ensure that the most important unit is supplied with air if the compressor capacity proves insufficient for the whole system to operate simultaneously a ring main distributes the air within the working zone excessively long off takes should be avoided use of a ring main means that if an unexpectedly large air usage occurs in any service line air can be fed from two directions this reduces the pressure drop and provides level and more stable air pressure in the entire system the off take or branch line is the final part of the permanent installation and should be carried as close to the workplace as possible the users in an air distribution system are the air tools together with their air preparation units or any other equipment consuming compressed air air line accessories such as pressure regulators should be of high quality diameters and lengths of a branch line depend on the amount free air to be supplied the materials used for the pipe and couplings are also important for avoiding leakage a

nd corrosion while minimizing pressure drop along the length to ensure that air at correct volume and pressure is delivered to the work face the performance of air power tools is largely dependent on the ability of the system to supply an adequate quantity of air of the correct quality and pressure too low an air pressure reduces the performance of most air tools if the pressure is lower than the design value efficiency drops radically and productivity decreases for a system supplying hand tools that operate at 7 8 bar 100 psig the pressure should not be less than 7 1 bar 90 psig at the tool end to ensure acceptable productivity tests on a typical grinder showed that a pressure loss of 1 bar 15 psi leads to almost 30 less material removed so the worker has to work longer to do the job similarly tests with a hand drill have shown that every hole that takes 2 seconds at 7 1 bar 90 psig would take 3 2 seconds at 6 8 bar 85 psig which would lead to substantial additional operating costs over the course of a year emissions and noise directives two widely adopted requirements regarding machine emissions are the tier 3 standards in the united states and the euro 3 and 4 standards in europe similarly noise regulations continue to be enhanced to comply with national and international standards equipment from major manufacturers complies with the key international standards though customers may need to confirm equipment suitability for use in specific countries some countries have no specific requirements on either emissions or noise dust can create a considerable nuisance in drilling if not collected and it is particularly important to control particles smaller than 5 mm 0 2 in as effectively as possible the basic requirement is for the dust collector to operate with a partial vacuum which means that a suction ejector should be the final piece of equipment in the sequence larger drills are fitted with a brake ejector which dispenses with the need for a seal against the rock and facilitates collaring and allows drilling to be performed with no appreciable drop in production remote monitoring and control many mines today run a series of independent portable compressors those mines that retain a stationary surface compressor room are increasingly adopting centralized remote control to optimize the usage of a bank of multiple compressors automatic control ensures that the correct combination of machine size is automatically adopted for maximum efficiency to achieve this one or more variable flow compressors are required in the network the control ensures that each runs in its optimum range for enhanced efficiency compressor controls can consist of hard wired digital contacts or a choice of three major field bus industrial interface protocols modbus profibus and ethernet ip industrial protocol this allows the machines to be integrated easily into the control panels so that the operator can start a machine remot

ely without needing to be in the compressor room today s remote monitoring capabilities are ideal for use in mines as diagnostics and checks can be performed by experts away from the site use is made of the global system for mobile communications gsm network to relay information from the compressor to the monitoring system the system can be used by both portable and stationary compressors satellite solutions are also available and are ideal for portable compressors in locations that are outside mobile phone networks different tiers of service are available starting with a simple notification process when there is a problem the text message carries details of the problem for example a warning status due to the oil temperature such notifications can be very useful even where there are technicians on site as they receive an instant warning another option offered by manufacturers is local monitoring where the equipment is connected to a special communications box that displays the status this requires a physical connection to the box which may not be ideal in some mining situations portable compressors can be equipped with a special controller that supports both gsm and satellite networks this box broadcasts the compressor s status and its most important parameters including its gps global positioning system coordinates this means that it can be used for theft protection it can be located on maps or satellite photographs the system will send a text message if it is moved away from a set location this feature is particularly used by rental companies in checking up on their fleet locations and usage use of such a system ensures that the service operations are well planned service engineers can check on efficiency analyze any faults before visiting the site and plan predictive maintenance the machines can be monitored and analyzed with any drop in efficiency highlighted and remedied use of this kind of system also helps keep down the costs of servicing as schedules can be planned for maximum efficiency including making best use of the technician s time internet monitoring is also available for industrial scale machines a central password protected web site provides access to data about the compressors that are connected to it this approach supports both ethernet connections and all types of modems the data are refreshed every minute alarms are sent out as required and service engineers can analyze any problems from thousands of miles away if necessary introduction a mine communications system which includes communication monitoring and control is an integral part of modern mine operations and management basically a communication system is a network of devices that collect receive or transmit information with the passage of the mine improvement and new emergency response miner act of 2006 following recent mine disasters especially those at the sago mine in west virginia and the crandall canyon mine in uta

h both in the united states two way wireless communication systems between surface and underground and electronic miner tracking systems are now required in u s mines however mine communications systems are not limited to tracking miners in case of emergency the subject also includes sensing systems used for process control basics as shown in figure 9 3 1 a mine communication system mcs has three basic components the information source or transmitter such as sensors the communication pathway or network and the information receiver the technological success of an mcs depends on the successful functioning of all three components however the receiver may be passive therefore the critical components are the source and the network the fundamental nature and technology of sensors vary drastically from one to another a sensor s required accuracy precision and sensitivity depend on the need the measurement fills thus a motor stator voltage measurement would be significantly more accurate and precise than for example a semiautogenous grinding sag mill ball loading measurement however the precision of measurements is increasingly important because sensor information is increasingly being used for automatic control which will be discussed further in a later section the part of an mcs currently undergoing rapid change is the communications network although tesla and marconi first demonstrated wireless radio communication a century ago mine communication systems like most industrial communications systems have been mostly wired mines have traditionally used multiple communication networks each serving a unique purpose therefore there was a telephone network a sensor network for belt conveyors and so forth however technological breakthroughs in the nonmining world such as digital radio communications pressure for mine productivity improvements and newly legislated mine safety requirements are driving the industry toward single unified communications systems for entire mines communications systems now have options for wireless connectivity or a hybrid of wired and wireless connectivity although most successful underground networks currently employ cables transmission is mostly by means of electricity such as through phone lines or ethernet cables radio signals such as wireless networks and leaky feeder systems or light fiber optics the mode of transmission is a major determinant of a communication system s ability to meet the needs of a given purpose major transmission technologies the most popular transmission medium is radio signals because they allow wireless implementation the various radio transmission technologies are discussed later beerbower 2006 msha n d niosh n d a schiffbauer and mowrey 2006 low frequency technologies low frequency lf radio systems use the very low frequency vlf and ultra low frequency ulf bands the lf band includes frequencies from 30 to 300 khz vl

f from 3 to 30 khz and ulf from 300 hz to 3 khz lf signals are least attenuated when they travel through the earth in that sense they are best suited for underground mines however their application is limited underground because they have very narrow bandwidth that is only minor amounts of information can be transmitted as lf signals and over limited communication distances a majority of the underground emergency communication technologies that are designed to survive postaccident are lf technologies such technologies are commonly implemented as transmission from surface to underground one way though two way systems exist surface antennas are typically large loop antennas laid out over the mine area some systems one way or two way use underground loop antennas lf radio systems have a variety of advantages and disadvantages advantages signals travel through the earth communication can be in the form of voice or data communication can be broadcast to all or sent to a single miner when attached to an integral accessory such as a cap lamp receivers are always close to the miner disadvantages the transmission depth can vary most natural and human made electromagnetic noise is in the lower frequencies therefore lf radio systems are susceptible to interference from noise transmission from surface antennas can additionally be affected by foliage and the presence of workings above the current working level local noise sources can create shadow zones in a mine that is otherwise covered when surface antennas are required surface land ownership and terrain can become major issues because of the large area taken up by the antenna when an underground antenna is needed the system may not survive a catastrophe additionally underground antennas are not intrinsically safe so they would have to be turned off during events such as blasting fires or fan shutdowns with currently available technologies if a message is transmitted when the receiver is off the message is lost in a one way system there is no way to confirm whether a message has been received message length can severely impact transmission time transmission of a 32 character message can take up to 3 minutes two way systems may not have portable antennas medium frequency technologies medium frequency mf technologies 300 to 3 000 khz combine the benefits of low and high frequencies external environmental noise is not the major problem that it is with low frequencies mf signals can also penetrate the earth to some extent however because they can couple parasitic coupling to existing electrical cables and pipes their effective range can be very high existing mine conductors not only act as conduits but also as antenna dobroski and stolarczyk 1982 entries in bedded deposits can act as wave guides and extend the range a r f products 1986 mf systems have a number of advantages and disadvantages advantages signals travel through

the earth to some extent communication can be in the form of voice or data parasitic coupling can extend the range of these signals significantly these signals are not severely affected by electromagnetic noise disadvantages the bandwidth of these signals is limited very few commercial products use this technology antennas can be large making portability a problem high frequency technologies high frequency hf systems use the very high frequency vhf and ultra high frequency uhf bands the hf band includes frequencies from 3 to 30 mhz vhf from 30 to 300 mhz and uhf from 300 mhz to 3 ghz gigahertz hf signals are the least suitable for underground applications because they suffer the greatest attenuation when penetrating the earth akyildiz and stuntebeck 2006 report higher attenuation for higher frequencies with moisture content also deleteriously impacting signal propagation these limitations are also observed in vhf and uhf devices such as radios which are commonly used in mines for wireless transmissions higher frequency technologies work best in line of sight applications with vhf working best in wider mine openings and uhf performing well even in smaller openings such as 1 8 m coal seams nutter 2007 hf systems have a variety of advantages and disadvantages advantages many commercial products use this technology significant advances have been made in uhf technologies in recent years many of which are finding application in surface mines and to some extent underground mines uhf voice radios are a common industrial communication tool uhf ranges are extended by mine entries that act as wave guides hf systems are not severely affected by electromagnetic noise safety related issues are well understood the high bandwidth of these systems allow for voice and video communications disadvantages signals suffer severe attenuation when going through earth physical barriers in wireless implementations multipath effects can make the signals extremely noisy when an hf signal is transmitted it reflects refracts multipath and interferes with itself on its way to the receiver thereby reducing the quality of the signal these systems require a lot of infrastructure such as repeaters routers and cables which makes them susceptible to mine disasters ultra wideband technologies ultra wideband uwb technologies are low power short range high bandwidth communications spread over a wide spectrum of frequencies uwb technologies make use of all frequencies low to high that is their short pulses have a bandwidth of 500 ghz or 20 of the center frequency whichever is less as a result they differ from the technologies discussed previously which were restricted to a single category and therefore had a narrow spectrum however because of their higher bandwidth they have low power on any one frequency uwb systems have a variety of advantages and one disadvantage chehri et al 200

8 niosh n d b intel n d advantages uwb systems are not affected by noise from narrowband systems they do not suffer from multipath effects like higher frequencies do because their short pulses are easily identified the technology can determine the time of travel of the signal thus it is ideal for location tracking applications they support high data rates so they can support all communication needs the simple architecture of uwb systems means they can be less expensive than other technologies the disadvantage is that uwb systems have low power so they have an extremely short range around 10 m a comparison of the strengths and weaknesses of the various technologies is provided in table 9 3 1 transmission media signals to and from sensors and users can be transmitted through wired or wireless media or a combination of the two both media have their own sets of challenges wired networks can become logistically and financially challenging they may not accommodate sensor user mobility and cables can get damaged cable protection through armoring conduits or burial is difficult on a massive scale creating redundancies in wired networks can also be difficult the major challenge for wireless transmission is that the technologies with the greatest bandwidth vhf uhf do not travel through the ground very well and or have very low range uwb wired networks wired networks can transmit radio electrical or optical signals the various transmission technologies employ differing types of wiring or cable twisted multiple wire cables for electric signals coaxial cables for radio transmission signals and fiber optic cables for optical transmission signals the most common wired system is probably the leaky feeder leaky feeders are cables designed to leak radio signals i e the cable shield has holes signal frequencies can be in the vhf or uhf range considerable signal loss means leaky feeder cables require repeaters to continue propagating their signals leaky feeder cables can also serve as antennas or conductors for mf communication leaky feeder cables maintain a low voltage therefore certain low voltage communication devices need only one cable to power them and to keep them connected to the network this makes these devices intrinsically safe leaky feeders are usually used in conjunction with twoway voice radios mf vhf uhf with vhf uhf being more common because mf antennas can be large and cumbersome radio coverage depends on the frequency typically uhf voice radios provide better coverage than vhf radios to maximize the benefits of all types of radio communication technologies researchers are attempting to improve the interface between mf radios and uhf vhf leaky feeders the intent is to examine whether the parasitic coupling abilities of mf transmission will improve coverage and help create redundancies during emergencies advantages leaky feeders extend the range of the frequencies that h

ave the most bandwidth they can carry voice and data leaky feeders can power low voltage devices they can serve as a conductor antenna for mf communication disadvantages the signals that leaky feeders carry do not penetrate the earth they can be expensive they require skilled labor for maintenance and installation like all cables they can be impaired following a mine disaster also they require battery backups for emergencies repeaters are required to extend signals redundancy can be complicated to achieve the other types of wired communications systems are telephones pager systems trolley wire systems computer networks or network backbones such as fiber optic cables telephones and pagers have so far been the most important communication link in underground mines they are easy to install and are battery powered however they have significant limitations that make them unfit for emergencies or as productivity tools first communication is limited to fixed locations second although they are easy to install they can be difficult to maintain because cables can get easily damaged pagers have the added limitation that the communication may not be private although telephone lines can be used to transmit data the bandwidth is limited trolley wires are becoming obsolete as rail haulage systems become less common but they can transmit communication signals on the direct current cable that powers the trolley system therefore this method of communication is noisy however because they allow communication on the haulage way they enhance safety computer networks are a critical component of a modern mine networks are usually minewide though corporationwide networks are becoming common as well corporationwide networks would probably require a multitude of transmission media modern data transfer protocols such as tcp ip transmission control protocol internet protocol and networking technology such as ethernet allow most mining equipment especially in processing plants to be part of the mine network making monitoring and data transfer seamless however for security and optimal network management there should be a barrier between office management networks and operation safety networks pamel and pederson 2007 standard category 5 cat 5 twisted pair copper wire ethernet cables are used to connect devices in a wired ethernet network however they are noisy and subject to energy losses beyond short distances fiber optic ethernet cables are another new option for local networks though they are commonly used when transmissions occur over long distances such as for mine communication backbones fiber optic systems work by sending light signals through a clear core using the phenomenon of total internal reflection by a reflective coating cladding covering the core when the core is very thin the light travels in a straight line through the core single mode so that signal loss is minimized w

hen the core is thick the light is reflected and refracted multi mode resulting in higher losses though multi mode cables have a smaller range they can carry many more light frequencies than single mode cables in addition to the core and cladding fiber optic cables also contain multiple protective layers to add strength advantages fiber optic systems have very low losses so the repeater requirement is minimal they have a significantly high bandwidth they are not susceptible to electromagnetic radio interference fiber optic cables are intrinsically safe though optical transmitters devices that convert electrical signals to optical signals may not be electrical pulses must be converted to light pulses prior to their transmission through fiber optic cables because they do not conduct electricity fiber optic cables eliminate ground loop problems dubaniewicz and chilton 1995 and are not impacted by high voltage cables lightning and other electrical disturbances disadvantages fiber optic transmission can be expensive over short distances the inability to carry electricity along with communication signals as leaky feeders do can be a major disadvantage because many devices in sensitive areas depend on the communication cable also to provide intrinsically safe power wireless networks wireless networks employ devices clients that communicate wirelessly using the 802 11x ieee standard of uhf 2 4 ghz and 5 ghz band communication they traditionally required mobile clients to be near a fixed access point that connects directly or routes data back back haul to the wired network because a mine is constantly changing fixed access points must be continually added or relocated to maintain network integrity access points attached to mobile trailers with battery and solar power are often used for this purpose in a surface mine this reconfiguration of the network is a continuous process and can be a significant burden one mine noted that they had more mobile trailers than haul trucks and operated a large crew of technicians to support the daily reconfiguring of the network blind spots can also occur regularly resulting in missed assignments and reduced efficiencies recent advances in wireless technology support greater mobility these solutions wireless mesh networks extend message routing capabilities to each mobile node allowing messages to be routed between mobile nodes back to the closest access point each node automatically locates and configures a connection with every other mobile node or access point within its range resulting in a mesh of network connections client mesh network a small mesh network may be connected through routers to a broader network see figure 9 3 2 message routes are dynamically analyzed and selected to provide optimal throughput this mesh technology not only extends the flexibility and range of the mobile network but increases the effective throughput by allowing the me

ssage load to be distributed across the mesh load balancing high bandwidth wireless mesh networks connecting the underground mining locations to the surface are possible though they may require that routers be very close to each other in a test in the canada centre for mineral and energy dropped by 50 for each hop using tcp hakem et al 2007 tcp is the protocol computers use to talk to each other the term hop is used to describe transmission of signal from one router to the next maintaining bandwidth is not the only challenge because they are based on uhf radio signals mesh network systems have the strengths and weaknesses listed previously for vhf uhf radio systems interference from existing electrical and communication systems the existence of shadow regions and the magnification of noise when amplifiers are connected in series ortega 2007 can still impair such networks other issues with wireless networks include reflection refraction of signals from ground air interfaces multipath fading from features such as plants and rocks and lower propagation velocities in dielectric material advantages given the ease of integrating modern wireless devices with computer networks wireless devices and networks in mines can usually be easily integrated into a minewide computer network this enhances safety and productivity at least in a surface mine wireless mesh networks are easy to establish to a certain extent bandwidth is not an issue wireless devices and networks are more prevalent in the nonmining world than in mining so they are constantly being improved disadvantages wireless signals are uhf radio signals therefore they have all the disadvantages of uhf signals such as the inability to penetrate the earth and their degradation as a result of multipath effects wireless devices networks are not truly wireless because they still must be connected to a power source additionally they need battery backup for emergencies powering some of these devices requires explosion proof xp enclosures which in turn makes them cumbersome complicated battery backup systems such as those used in the northern latitudes where solar systems do not work can also come with a significant maintenance burden wireless mesh networks can require a significant amount of infrastructure especially in an underground mine very high bandwidth requirements such as for videos can be difficult to maintain across multiple hops characteristics of a mine communications network an effective mine monitoring communications and control system requires a communications network that can support all its demands desired attributes a mine communications network should have the following major attributes ability to accommodate different types of information sources and existing infrastructure ability to accommodate information source mobility safe robust and redundant survivable operation ability to expand easily ease of m

aintenance ability to accommodate information sources and infrastructure a modern mine has a multitude of information sources not only can individual sources differ from each other e g a drill is very different from a methane monitor or a radio but even within a source there could be different information sources for example a mine truck may be transmitting machine health information such as engine temperature and haulage jolt information derived from accelerometers and pressure transducers although a mine communications network would ideally have the ability to accommodate different information sources this ability is often absent because vendors have developed systems optimized for different information sources atmospheric monitoring voice communications tracking etc and different mine types aboveground vs underground coal vs noncoal for example in underground mining leaky feeders are generally acknowledged to account for more than 90 of all handheld voice communications systems a new communications system also may not be compatible with existing infrastructure or systems the cayuga mine in new york united states had to replace existing fiberoptic backbone and switching hardware before a new system would work pamel and pederson 2007 mine management at the bingham canyon mine in utah required not only that a new wireless network be compliant with the industry standard but also that the communications vendor ensure compatibility with existing equipment and applications beer 2008 network and data standardization also allows proper data warehousing which is critical for mine to mill type optimization indeed chen et al 2007 report on an mcs at a coal mine in china that standardized data generation and transmission with a goal of creating a standardized data warehouse the industry is certainly headed in the direction of data standardization for example international rock excavation data exchange standard iredes 2008 is creating a standard format for mining machinery ability to accommodate information source mobility humans and other information sources are not stationary but move from one location to another in the course of their work activities thus the mcs should not only be able to accommodate their mobility but should not put any constraints on their movement in surface mines wireless mesh networks are making it easy to handle mobility though the ability to maintain high bandwidth at all times can be a problem as discussed previously in an underground mine mobility is even more of a challenge mobility related problems can be overcome by mixing technologies and making compromises for example as shown in figure 9 3 3 an underground mine could use wireless mesh networks in conjunction with leaky feeder or fiber optic cables to allow some mobility at the end of wired communication to ensure postdisaster mobility it could also have a layer of lf technologies for basic voice text commu

nications communications can also be prioritized to ensure that important communication streams always get transmitted no matter the bottleneck safe robust and redundant operation both the sources of information such as sensors and the communications network should be able to function safely under typical and atypical mining conditions including moisture dust vibrations and postdisaster conditions sensors and communications equipment that are deployed in areas susceptible to explosion must be intrinsically safe or enclosed in xp boxes there are other legal requirements as well the miner act in the united states requires that underground mines provide means for two way wireless communication between underground miners and the surface at all times including after massive disasters it also requires that miners be tracked electronically at all times and that the communication system be redundant redundancy is not legally mandated for productivity purposes though desirable it is mandated only for safety purposes thus redundancy requirements have to be met only at the level bandwidth necessary for safetyrelated communication one way of achieving redundancy is by means of a selfhealing ring type communications architecture self healing implies that the network will automatically resume transmitting communications after a fault condition occurs under normal conditions communication is one way when there is a fault in the system the architecture allows communication to loop back into itself at the location of the fault figure 9 3 4 thus enabling two way communication the self healing redundant ring architecture can be achieved in different ways in a fiber optic network the redundant ring architecture may use two fiber optic cables for the ring that is there are two rings with each node user connected to both rings which carry communication in opposite directions in the event of a fault the system connects the two rings on either side of the fault maintaining communications in an underground mine using a leaky feeder or other backbone redundancy can be achieved by closing the loop as shown in figure 9 3 5 the connection to the surface can be through an existing shaft or a borehole if none exists a smalldiameter borehole could be drilled to extend the leaky feeder back to the surface the final link to the communications center can be wired or wireless an alternative would be to use another communications network such as an mf radio the national institute for occupational safety and health niosh has recently funded research into an mf radio that may prove useful as a backup or emergency network communications system similarly nonfiber ethernet tcp ip communications can be made redundant with a ring topology many ethernet switches are available that provide ring management functionality this would allow a break in the communication infrastructure to occur switches would automatically adjust to

allow the flow of data traffic around the location of the break redundancy can also be achieved by means of wireless mesh networks especially in surface mines or hybrid wired and wireless networks an all purpose one that meets production and safety requirements at all times redundant purely wireless system can be difficult to achieve in an underground mine because of transmission problems through the earth wireless or not redundancy requires that the components of an mcs remain powered even after a disruption in power supply kohler 2008 reports battery backup durations of 8 to 96 hours for redundant systems ability to expand easily mines are perpetually evolving as the mining face moves constantly mines may also increase or decrease their production rate to reflect product demand or change their mining method in response to technological changes although it is unrealistic to expect that the communications system will not need significant changes if the mine changes drastically one can expect a communications system to accommodate minor changes and expansions easily it is good practice when installing a system to include excess capacity to handle future expansions technology upgrades or changes can be frustrating because new versions of technology do not always work properly with older versions proprietary systems can also pose challenges in that they may not integrate properly with other systems thus any additions or changes to communications systems must conform to the existing broader system the mechanics of the changes are also important for example will the changes require a significant amount of infrastructure to be moved or reinstalled ease of maintenance while considering any new technology the maintenance requirements for that technology should be fully understood in evaluating maintenance requirements one must consider the type of mine aboveground or underground coal or noncoal large or small into which the system will be installed and the level of technical expertise on its staff one should also contact mines with similar systems and ask them about maintenance issues associated with that type of network new communication system before installation prior to installing a new communications network system the following checks should be conducted schiffbauer and mowrey 2006 1 is the mine s electrical noise environment surface and underground understood that is have noise sources been identified quantified and studied 2 have signal propagation tests been conducted 3 is the candidate system safe robust redundant easily expandable easy to maintain and able to accommodate different often mobile information sources does the new communication system have any safety issues will it set off explosions or affect other monitoring systems 4 have other mines that have installed the candidate system been contacted any issues note that what works in one mine may not work in another for exa

mple many coal mines in australia are two entry mines thus line of sight problems can be easily addressed as miners are restricted to only two entries beerbower 2006 however the same line of sight limited solution will not work in a coal mine that employs multiple entries therefore before investing in a new communications system one must consider all factors as they apply to a specific mine however technical issues are not the only challenges a new system will face mine personnel comfortable and familiar with existing systems will often resist the introduction of new technology for a variety of reasons thus the new system may not be fully used until the on site personnel are comfortable with it installation of a mine monitoring system a wide variety of mine monitoring equipment is available although some suppliers may provide solutions for a range of disciplines no single supplier can deliver an integrated system that spans all disciplines and can address the vast array of mining equipment mine monitoring solutions the design of monitoring systems can vary widely depending on the mining application for example monitoring systems for underground mining differ significantly from those for open pit mining generally speaking mine monitoring systems can be divided into three main categories 1 production monitoring 2 equipment status monitoring 3 safety and environmental monitoring production monitoring a number of monitoring systems have been developed to monitor mine production these systems often concern processes that use expensive equipment as a result these systems are almost always aimed at improving asset utilization for example instrumentation systems have been specifically developed for drilling excavating loading and hauling these systems provide monitoring and record parameters such as ore produced waste removed commodities consumed and changes in equipment status production output is recorded and reported commodity consumption is reported and purchase orders for replenishment made equipment status characteristics are analyzed to identify reasons for delays or stops in production so that changes can be implemented to improve efficiency some systems provide added control functions such as dispatching that assist in optimizing the routing of equipment through the mine mining operations deploying production monitoring solutions may expect increased equipment utilization however that may not necessarily occur equipment status monitoring a focus on production efficiency often results in equipment operated in ways that are unsafe and or result in high maintenance costs monitoring systems have recently been developed that focus on improving equipment reliability and availability as well as on production output these applications monitor various critical equipment status indicators and alert maintenance personnel to the need for repairs before equipment failure occurs this facilitates a move towa

rd routine preventive maintenance these systems provide information that can be used to resolve equipment warranty claims and lead to design changes that improve reliability the financial benefits of such systems can be significant a specific case study conducted across a fleet of 65 haul trucks reported maintenance savings of more than 2 million per month and a 57 reduction in the average number of trucks awaiting repair safety and environmental monitoring personnel safety and protection of the environment are vital to maintaining mining operations multiple systems have been developed to track the location of personnel and provide voice communication solutions have been developed to track the proximity of equipment and personnel these systems alert operators when equipment distances violate predetermined safety ranges and can cause equipment to be temporarily disabled or shut down to avoid accidents sensing systems are also available to monitor weather conditions air quality ventilation systems seismic activity and slope or wall movement water handling is often a critical function in mining operations and functioning effectively requires sensors that continually monitor pump stations and water flow and are interlocked with pumping equipment switchgear monitoring systems are used to help maintain process water recycling systems and ensure that water released back into the environment meets regulatory requirements reporting and interfaces effective monitoring systems are always underpinned by effective reporting systems all monitoring system providers can generally supply a reporting system for their specific application however because no single supplier provides the entire range of monitoring systems multiple reporting systems are the usual result consequently there is a need for communication between monitoring systems reporting solutions often report against their production databases this can be dangerous if those performing data analysis create such an excessive load on the production system that it disrupts the performance of the monitoring solution additionally in order to keep the real time systems performing optimally it will be necessary to have an archiving strategy that keeps the production databases trimmed monitoring systems often use information from other production systems as inputs in turn monitoring results need to be reported and communicated to upstream systems because of the proprietary nature of monitoring systems one cannot assume that support systems such as databases will be accessible to outside systems or that interfaces are necessarily readily available interfaces are often sold separately and can be costly to have developed care must be taken in selecting monitoring solutions to ensure that databases can be accessed directly or through interfaces that will allow the various mining management and accounting systems to be integrated it is critical that the supplier provide clear a

nd accurate documentation in selecting monitoring systems preference should be given to vendors who use standard database and interface components to address these interface and reporting issues companies may wish to implement a data warehousing or data historian system that collects and aggregates data from the various mining systems into a single data store that is used for maintaining history reporting and analytics and for providing interfaces to other systems see figure 9 3 6 although there are multiple providers of data warehousing historian systems very few have been developed specifically for mining an understanding of mining operations and processes is necessary to develop an effective reporting system implementation multiple approaches to implementing mine monitoring systems can be taken prior to selecting an approach companies should develop a mine monitoring strategy that provides an overall vision and specifies the guiding principles that will be used to select and implement monitoring solutions clearly defined business requirements that articulate the scope goals objectives priorities and timelines will need to be developed for each specialty area it is vital for this process to involve representatives from each of the various mining departments or disciplines and have senior leadership endorsement and sponsorship strategic vendor approach one commonly used approach to implementing mine monitoring systems is to select a strategic vendor around which to build the mine s monitoring solution landscape this vendor is selected based on its ability to supply an integrated solution that covers the greatest number of business and technical requirements this vendor is also used as the system integrator to provide interfaces with other mining solutions that fall outside its specialty area this approach focuses on delivering a broad highly integrated solution it is important that there be wide acceptance within the overall organization for this approach because the needs of specific departments may not be completely met in order to maintain overall simplicity and greater integration between systems specific departments may be disappointed with the performance of their specific disciplines or applications because of their awareness that there may be systems available that better suit their purposes this approach places a high degree of responsibility on the vendor to deliver the overall solution it simplifies initial implementation by reducing the number of personnel required for implementation and can also simplify education and training needs for mine personnel it can reduce the mine s direct labor requirements by allowing support functions to be outsourced to the vendor this approach depends strongly on the strategic suppliers and requires that a strong business relationship be developed between the mine and the vendor to ensure that the mine s short and long term needs are considered and given priority in su

pport and future development best of breed approach this approach involves selecting a combination of monitoring solutions each chosen based on its ability to address the needs of a specific function or discipline this approach focuses on delivering solutions that can provide both breadth and depth less emphasis is given to the integration of the entire solution miner tracking systems the miner act has made manual tracking of underground miners obsolete although real time miner tracking has obvious safety benefits the benefits extend to production as well the ability to locate and speak with any miner underground quickly to call for a part immediately when needed and to control and track travel efficiently are all important functions of the production cycle in a modern underground mine system components a typical electronic system for tracking miners is composed of five major components an identification tag readers underground infrastructure a data storage unit and a data display the functions of these components are as follows 1 the identification tag is a piece of equipment worn by the miner in the majority of the systems this is an active battery powered radio frequency identification rfid tag that sends a unique identification signal at a predetermined time interval there has been considerable debate on the proper location of the tag on the miner s person this tag can be mounted in a variety of ways on a lanyard on the belt in a radio on the miner s hat or in the cap lamp assembly testing has shown that an elevated location works best away from the clutter of a miner s belt and high enough to let the signal from the tag radiate outward toward the reader 2 readers are the units that receive signals from the tags and transmit them over a network to a storage database readers may communicate either by a wired network or wirelessly via radio transmission all readers must have a wired power source 3 underground infrastructure is the equipment required to provide and maintain electrical power to the readers and facilitate data transfer to the data storage unit located aboveground underground infrastructure is composed of a wired component to provide power to the reader a battery if needed and a cable or radio transmission between readers some systems provide power and data over the same cable infrastructure 4 the data storage unit receives data from the readers stores that data in a database and may perform tag location calculations 5 the data display presents information on tag locations provides reports on which miners are underground and may contain other information useful to mine rescue operations such as emergency contacts typically the display will contain a graphical representation of the mine and the location of the readers some systems support multiple data displays for larger mine operations system selection mine type size seam height regulatory requirements numbers of personn

el and equipment underground and support are important factors to consider when selecting a tracking system mine type metal nonmetal coal and so forth is an important factor in tracking system selection coal mines in particular have intrinsic safety layout and regulatory requirements that metal mines do not a u s coal mine must have a system that is either intrinsically safe or xp can be configured for redundancy in separated entries and is approved by the mine safety and health administration msha mine size is also a crucial factor in selecting a system large mines must take into account the number of readers that will be installed in a mine and consider the maintenance issues electrical connections battery testing and replacement antenna alignment etc associated with supporting those readers seam height is an important factor if a wireless system is being considered because of line of sight limitations reader placement with redundancy in low seam height mines could be as frequent as every 20 to 25 m regulatory requirements such as the miner act and recent west virginia united states legislation require that tracking systems in coal mines have redundancy or survivability and may also specify a maximum distance between readers also referred to as tracking granularity the numbers of personnel and equipment underground are also important is making a system selection systems using low speed serial communications may have difficulty transmitting tracking data reliably during shift changes in mines with more than two working sections system support is crucial for selection local distributors with knowledgeable technical staff should be a requirement a proven track record for the support staff as well as the company is also important system types the types of tracking systems currently available can be segmented by the type of underground infrastructure used wired mesh wireless mesh leaky feeder fiber or serial the advantages and disadvantages of each type are noted wired mesh systems in a wired mesh system reader nodes are organized into a mesh topology providing redundant data and power paths via another single cable communications and power are selfhealing in the event of a cable problem advantages wired mesh systems are able to achieve redundancy survivability via interconnections between readers in different entries they can provide power and data over a single cable with no underground power connection or underground batteries in some mine configurations line of sight between readers is not required so high density of readers is not required wired mesh systems scale to any mine size and offer a lower per node cost than wireless mesh systems these systems are proven in coal mining applications one disadvantage is that these systems do not provide a voice communications option at this time wireless mesh systems in a wireless mesh system radio nodes generally with integrated reader

electronics are organized into a mesh topology to provide redundant data paths although termed wireless power must still be supplied to each node via some type of cable each node generally contains a battery to provide backup power in the event of a loss of power advantages a wireless mesh system may provide communications and tracking over a single infrastructure this system type may provide 802 11 wireless data transfer disadvantages a wireless mesh system requires line of sight between nodes redundancy requires line of sight between at least three nodes this type of system requires underground power connections and for survivability underground batteries this system type involves a much higher level of complexity than competing systems these systems require a higher level of technical competence to maintain these systems have a higher per node cost than competing systems these systems are unproven in mining applications there are scalability concerns due to per node cost and hop tohop transmission delays rfid leaky feeder infrastructure systems these systems use leaky feeder cable as a method to convey transmissions between system components generally using one of two different methods a reader can either be directly connected to the leaky feeder cable for power and communications or transmissions may be relayed over the leaky feeder using analog data radio modems with power delivered independently with a separate cable in both cases the data from the readers are routed through a device in the leaky feeder head end to the tracking system data server normally using ethernet or serial communications an advantage is that an rfid leaky feeder infrastructure system may provide communications and tracking over a single infrastructure disadvantages an rfid leaky feeder infrastructure system requires underground power connections and for survivability underground batteries a system of this type has a higher per node cost than competing systems these systems are still unproven in mining applications and have associated scalability concerns due to their pernode cost fiber infrastructure systems these systems use standard ethernet communications to connect fiber optic cables between tracking system components depending on the cable used distances of 50 km or more can be achieved at extremely high data rates 1 gigabyte s although copper ethernet connections are possible at the terminus of the fiber no intrinsically safe as defined by msha components have been developed additionally power must be supplied from intrinsically safe msha approved power supplies with battery backup capability copper ethernet can be used if the devices being interconnected are housed in msha approved xp enclosures advantages fiber infrastructure systems provide the potential for communications and tracking over a single infrastructure these systems are high bandwidth media these systems are able to co

nnect to current underground infrastructure these systems work well in mines without intrinsic safety considerations disadvantages fiber infrastructure systems require underground power connections and for survivability underground batteries these systems make it difficult to attain intrinsically safe status for postaccident use in coal mines these systems require xp boxes for postaccident use in coal mines serial infrastructure systems these systems use standard serial communications methods such as rs 232 or rs 485 generally standard copper wiring provides a communication path between system components another pair of wires provides power using rs 485 communication can allow multiple devices to be placed on the communications cable and addressed independently depending on cable lengths communication rates up to 115 000 bps baud second can be achieved for longer cable lengths rates of 4 800 bps are more common in order to maintain intrinsic safety rs 485 requires the use of barriers to isolate areas power must be supplied from intrinsically safe msha approved power supplies with battery backup capability an advantage is that serial infrastructure systems are able to use current underground infrastructure disadvantages these systems have low bandwidth their common infrastructure cannot be used in postaccident implementations xp boxes are required for postaccident use in coal mines no voice communications option is provided at this time the scalability of these systems may be of concern because of bandwidth limitations system layout most mines will install tracking readers in the travelway to cover equipment and personnel movement coal mines in the united states following clarification of the miner act will likely also be required to install tracking readers in the primary escapeway usually the intake entry typically mines will install readers at intervals of 300 to 1 500 m with the distance between readers determined by the accuracy of tracking desired regulations and cost considerations the sections delimited by the readers are typically known as tracking zones generally mines will also install readers or antennas from readers that support multiple antennas at the intersection of travelways to determine the direction of travel this is typically referred to as gating for determining the suitability of a system for a given mine it is helpful to ask the system vendor to provide a layout showing the placement of readers in the mine and aboveground areas with coverage areas electrical connections battery connections and antenna placement noted redundancy survivability concerns to achieve redundancy readers communicating via a wired or wireless infrastructure must be connected to at least two other readers or have a direct connection back to the data storage unit readers communicating via radio transmission are limited to line of sight communication and so must be within the line of si

ght of at least two other readers in coal mines where ventilation concerns require separate entries for the intake return and possibly belt each reader communicating via radio transmission must be connected to at least two other readers in the same entry to achieve redundancy for wired mesh systems readers must be connected to at least two other readers in any entry as line of sight concerns are not present integration options ideally a tracking system would use a common redundant intrinsically safe communications network with the ability to incorporate atmospheric monitoring belt monitoring and control maintenance and voice communications systems as well as general data transfer unfortunately no current communications network supports all of these capabilities in a costeffective redundant intrinsically safe configuration however ideally one should select a system that provides the level of redundancy needed with options for supporting data for some of the other underground systems needed some tracking systems support atmospheric monitoring sensors others support general data transfer summary implementation of an electronic tracking system not only improves a mine s safety infrastructure but can also have a tremendously positive impact on production many systems are being introduced to the marketplace the selection for each mine should be carefully researched to find a system that will work best under its particular conditions global positioning system applications global positioning system gps devices rely on spatial and temporal information from a group of satellites for proper functioning many major mining activities such as digging shovel or dozer rock transportation subsidence and blasthole layout are typically defined by their movements in space and time therefore there are many benefits to quantifying them accurately and automatically flinn and fileccia 2006 accurate selection of mineralized zones and coal seams by an excavator reduced need for survey work for laying out drilling patterns or marking dig areas precise delineation of static hazards better dozer control leading to more even benches and ramps and the automatic creation of as built digital terrain maps dtms gps based arrangements usually imply a gps device mounted on a mining machine that provides input to a mine operations system such as machine guidance or mine management systems the role of the gps device is simply to obtain and broadcast its spatial and temporal information in real time however this information becomes more valuable when it is used to obtain computed information such as volumes or updated mine plans or to guide machine operation therefore it is important for the gps device to be able to interact with the broader mine operations systems challenges with gpss several common problems are associated with gpss vendor equipment specific system gpss are currently vendor or machine specific and becaus

e mines use a wide variety of equipment provided by a wide variety of vendors it is very difficult to integrate the disparate systems open source gps solutions designed to be vendor and machine independent are however under development flinn and fileccia 2006 such systems will be essential for an integrated mine operations system satellite availability gps devices need access to multiple satellites typically five for accuracy this can be a challenge in remote geographical locations or deep mines under certain atmospheric events or with certain satellite positions also large equipment can hide satellites from their own gps devices zywiel et al 2005 however list the following potential solutions to the satellite availability shading problem use of satellites from other systems such as the russian glonass global navigation satellite system the advantage of this solution is that it can probably be implemented with no additional infrastructure use of pseudolites or ground based transmitters that transmit positional information an issue with these is that the transmitters would need to be moved as the mine profile changes use of advanced tracking sensors these sensors combine a gps with a laser and increase availability to up to 90 these may however suffer from line of sight limitations use of gpss combined with inertial or movement data from odometers inertial systems use gps devices for original spatial information subsequent locations are computed or determined from sensors that provide information on direction speed and so forth a disadvantage of this system is that without guidance data its accuracy declines with time latency latency is the time lag between an object being in a given position and the time when it shows up as such on the operator s screen although this may not be an issue for drills it can be an issue for shovels that use gps information during digging or for gps based proximity warning systems latency effects can be minimized by opting for high speed gps data networks and computers and or using inertial systems bandwidth lack of bandwidth can also be a problem as high bandwidths are needed to transmit complex information such as dtms between the mine management system and the gps based guidance system however with wireless mesh networks bandwidth is less of a problem improving gps accuracies seymour 2007 provides suggestions for improving gps accuracies on excavators speed and accuracy can be improved by using two antennas and two receivers instead of one and placing them in the back corners of the machinery house bucket location can be more accurately determined using tilt sensors and rope drum rotation encoders in rope shovels it is essential that these components be robust proper maintenance such as prevention of slack bearings can also improve accuracies proximity warning systems proximity warning systems pwss alert miners of the presenc

e of static or moving hazards in their immediate vicinities there are typically two types of pwss a system that detects proximity based on spatial locations as determined by gps devices and a sensor based system gps based proximity warning systems these are used in surface mines primarily to alert large truck operators to the presence of smaller vehicles in their blind zones although a properly placed mirror or video camera can do the job it may not be satisfactory because of difficulties in judging distances operator inattention to the mirror or video screen or poor visibility conditions gps based pws implementations need very accurate gpss and a good wireless network the wireless network is essential because the success of the pws depends on the ability of each vehicle to transmit its location continually to other nearby vehicles the system uses this vehicle location information to determine whether another vehicle or object hazard is within its proximity zone or bubble the presence of a hazard in the proximity zone sets off an alarm and or disables movement in a static truck miller 2005 errors in satellite or wireless network transmission or reception caused by antenna placement location latency multipath effects or other effects can seriously reduce the performance of the pws static hazards such as buildings are easily detected because their locations can be programmed into the pws the systems typically also allow defining the proximity zone or bubble one advantage of the gps based pws is that there are very few false alarms also the system can use the existing wireless network a disadvantage of this system is that unless all moving objects including humans are equipped with gps devices the system is not completely effective sensor based proximity warning systems these systems consist of source or emitter units and portable detection units the source unit is usually on a large machine while detection units are on humans or smaller mobile equipment source units consist of a loop antenna surrounding the machine or signal sources that are strategically placed on the machine examples of sensor technologies that have been used for pwss include pulsed radar ruff 2006 low power lf magnetic fields schiffbauer and mowrey 2001 and rfid ruff and hession kunz 2001 radar systems can detect humans and smaller pieces of mobile equipment however they are prone to false alarms especially if they are sufficiently sensitive to ensure absolute detection of humans direct sunlight reflections and hot equipment can generate false alarms in infrared based systems physical orientation of pedestrians can impact detection in rfid based systems though these systems usually have few false alarms as with gps based pwss as the number of persons or objects to be detected increases more tags sensors are needed increasing maintenance requirements automatic control automated controls play an important role in mining

be it robotic control such as a telecontrolled or remote controlled device or algorithmic control this section only discusses algorithmic control where the goal is to control a process parameter within tight limits by manipulating relevant process variables for example a sag mill may be operated to optimize power consumption by varying parameters such as feed rate and recirculating load similarly the quality and quantity of a pile of coal is controlled by acting on real time quality of coal on a moving conveyor belt as communication networks have expanded so has automatic control and therefore they are more important than ever this section discusses aspects of automatic control that are relevant to mining engineers some other aspects such as artificial intelligence are covered in chapter 9 10 factors affecting control simply speaking controlling implies manipulating controlling a set of process parameters based on process information to achieve certain goals for example in a particular process for physically segregating coal a flop gate directs a block of coal either to the wash pile or no wash pile the process parameters used for determining whether to open or close the flop gate the action being controlled are 1 the quality of the unit block of coal being considered 2 the average quality and tonnage of the no wash pile and 3 the target quality for the no wash pile such a process cannot be controlled using mathematics alone accurate real time data from the on line ash analyzer is essential if the segregation algorithm is to work as designed sensor accuracy although the need for sensor accuracy is obvious defining the required accuracy of a sensor is not straightforward especially for sensors that control processes it is important to know how often control decisions are made in the process the decision interval could be defined in units such as time time between actions being controlled or throughput every 1 t metric ton 10 t etc therefore for the previous example an on line ash analysis that is within 0 25 of the true ash content for every 100 t of coal could result in the gate flopping the wrong way up to ten times for every 100 t if the gate flops every 10 t it is possible to compensate for such errors by lowering or raising targets but at that point optimization the much touted benefit of using sensors and automated control is lost therefore for a sensor to be useful for automatic control accuracy standards have to be relevant to the function being controlled also control algorithms should be examined as to the effect of measurement errors of the process variables that go into the algorithms mine management should also ensure that sensors are properly calibrated at all times sensors are often neglected after initial installation unless they are maintained properly they can hurt rather than help optimization relevancy of process inputs in modeling sag mill power consumpt

ion ganguli et al 2006 examined the usefulness of many seemingly relevant process variables such as feed rate density bearing pressure revolutions per minute noise and recirculating load as inputs however modeling revealed that only revolutions per minute feed rate and recirculating load had any noticeable impact on electric current draw the study demonstrated that the assumption that a process parameter is relevant to the process may be erroneous there are two major reasons a seemingly relevant process parameter is found to be irrelevant the first is simply that the parameter is truly not sufficiently relevant the second and more subtle reason is that the sensor is not appropriate for the process for example its accuracy may be at such a broad or coarse level that the short term information measurement it provides is simply noise in which case any attempt to control the process using the short term measurement data will be unsuccessful note that the inability to control based on a process parameter does not make that parameter irrelevant it simply means that the data being provided by a sensor concerning that parameter are irrelevant if engineers are confident that a particular process parameter should indeed be relevant they should invest in a different sensor conversely if the sensor is accurate and is providing appropriate data then that parameter is truly irrelevant to the process validity of assumptions most algorithms whether a truck dispatch optimization algorithm or a coal segregation algorithm make mathematical and informational assumptions common mathematical assumptions include data characterization such as assuming a statistical distribution and model type assuming that a particular model still holds informational assumptions include cost figures such as the cost of processing is x dollars and values of various constants optimization algorithms that run with the wrong assumptions will not be successful however assumptions are rarely examined many figures especially cost numbers are constantly changing introduction of new mine monitoring and control systems should therefore be preceded by a thorough analysis of the benefits a mine surveyor provides services from early design and project implementation throughout a mine s life to closure surveyors deal in spatially referenced information that is information associated with known positions in space they measure angles and distances to document the positions of mining features and boundaries and present the information in the form of mine maps that information is the foundation upon which mineral resources and reserves are defined mineral and land rights secured and environmental and mining plans defined directed and monitored mine surveying has always been recognized as crucial for the efficient management and safety of mining operations because of its impact on safety the position of the mine surveyor may require authoriz

ation which is issued by regulatory bodies on the basis of education and experience recent technological advances have greatly improved the precision and speed with which spatial information can be gathered processed and stored mine surveyors must constantly supplement traditional measuring skills with new skills focusing on management processing and storage of large amounts of gathered spatial data the changing role of the mine surveyor and changes in mine surveying as a discipline are recognized by minesurveying professional organizations the international society for mine surveying ism offers the following definitions in the preamble of its statute mine surveying is a branch of mining science and technology it includes all measurements calculations and mapping which serve the purpose of ascertaining and documenting information at all stages from prospecting to exploitation and utilizing mineral deposits both by surface and underground working the following are the principal activities of mine surveying the interpretation of the geology of mineral deposits in relation to the economic exploitation thereof the investigation and negotiation of mineral mining rights making and recording and calculations of mine surveying measurements mining cartography investigation and prediction of the effects of mine working on the surface and underground strata mine planning in the context of the local environment and subsequent rehabilitation these activities involve the following the determination of location structure configuration dimensions and characteristics of the mineral deposits and of the adjoining rocks and overlying strata the assessment of mineral reserves and the economics of their exploitation the acquisition sale lease and management of mineral properties providing the basis of the planning direction and control of mine workings to ensure economical and safe mining operations the study of rock and ground movements caused by mining operations their prediction and the precautions and remedial treatment of subsidence damage assisting with planning of rehabilitation of land affected by mineral operations and collaborating with local government planning authorities ism 2009 clearly the mine surveyor plays an important role in almost all engineering activities carried out at a mine site throughout the life of a mining project from exploration to closure mine safety is always a key concern in mine surveying and deficiencies in survey information can result in direct risks to safety with the possibility of multiple fatalities finances legal status and reputation mine surveyors are responsible for accurately measuring recording and informing mine management of the position of the mine workings relative to mine design and to geological features boundaries hazards areas of restricted mining and surfaces and or adjacent workings that require protection most mine surveying legisla

tion is directed at regulating this function and ensuring that accurate mining records are kept in the absence of regulations the united nations international labour organization ilo describes mandatory minimum requirements for mine surveying in its codes of practice for mine safety ilo 1995 surveying equipment and techniques generally a mine surveyor measures geometrical elements angles and distances to determine the relative positions of survey control points benchmarks as well as terrain and underground features and presents this information graphically on a map the cartesian coordinate system is commonly used to define the positions of measured objects by means of x and y axes on the horizontal plane pointing east and north respectively and the z axis pointing in the zenith direction this system imposes specific requirements on angular and distance measurements that can be used for the calculation of position angles must be measured in horizontal or vertical planes distances must be measured along horizontal or vertical lines if a distance is measured along a slope the angle between the slope line and the horizontal plane must also be determined for many years accurate measurement of angles and distances posed a significant technical challenge over the last century however developments especially in precision mechanics optics and electronics have led to the fabrication of surveying instruments that are capable of reliable and highly accurate angular and distance measurements today s standard instruments can measure angles with an accuracy of better than 1 arc second and distances with an accuracy of 1 mm 2 ppm instruments for measuring angles are called theodolites instruments for measuring distance include tapes subtense bars and electronic distance measurement edm devices the previous strict division between these types of instrument is now blurring and these instruments are merging into one universal instrument the so called total station the past 20 years have also seen the development of new surveying instruments capable of determining position without reliance on traditional geometrical structures linked to benchmarks on the earth s surface this new technique uses the global navigation satellite system gnss as a framework of reference points and space triangulation as a means to determine the location of surveying benchmarks and ground features however because this technique uses electromagnetic signals as a carrier distances between a global positioning system gps receiver and satellites can be determined only in open areas on and above the earth s surface surveys of tunnels and underground mines must still be performed by means of classical surveying techniques detail surveying has also undergone significant technological change recent developments in laser scanners have led to instruments capable of providing reliable and almost instant three dimensional 3 d models of te

rrain and objects scanners also have application in underground mine surveying where they can be used remotely to determine the extent and volume of mined cavities without compromising surveyor safety surveying and mapping procedures in open pit and underground mines a mine surveyor is usually responsible for the following tasks conducting all mine site surveys producing and maintaining all mine site and underground level plans managing all survey related data managing landownership issues and lease tenements monitoring slope stability and subsidence effects of underground mining providing maps and spatial information to other engineering departments in most western countries national or regional state regulations establish minimal standards for mine surveys and map requirements of the extensive list of regulations the following deserve special mention u s federal mine safety and health act of 1997 section 312 amended by the mine improvement and new emergency response act of 2006 or miner act msha 2006 west virginia united states chapter 22a article 2 miners health safety and training underground mines mining laws rules and regulations west virginia legislature 2008 government of western australia mines safety and inspection act 1994 section 87 government of western australia 1994 new south wales mine health and safety act 2004 section 75 auslii 2009 south african mine health and safety regulations 1996 chapter 17 surveying mapping and mine plans sagi 1996 regional laws and regulations for all types of mines vary and in many cases are more rigorous than are national or federal laws and regulations an example of this phenomenon is the west virginia code pertaining to requirements for underground maps for deep coal mines west virginia legislature 2008 laws and regulations in most states and countries require that mine maps be referred to the national mapping coordinate system and at least two or three permanent survey monuments be established on the mine property the monuments should be described and shown clearly on the maps so that they can be found quickly and easily in case of emergency mine maps are useful not only for determining relative location but also for determining volumes of ore and rock extracted so that quantity control can be exercised and royalty payments calculated almost all mine engineering work depends on mine maps surveying and mapping of open pit mines surveys of open pit mines combine characteristics of engineering and topographic surveys the surveyor provides guidance for miners to develop mining operations according to the earlier established mine plan then surveys the progress of mining and develops maps and models representing its current state the maps and models are used for calculating the volumes and tonnages mined and for reconciling mining progress with the mine plan surveying of open pits usually involves the following activities 1 estab

lishment of a minesurvey control network 2 detailed topographic surveying of open pit and waste dumps 3 data processing to calculate mined volumes and tonnages 4 stability control surveys of open pit and waste dump slopes and 5 support surveys for earthmoving machine control systems mine survey control network a mine survey control network for an open pit mine site is a basic highly accurate spatial infrastructure for relative referencing of natural and constructed topographical features mining roads benches buildings and other structures it enables surveyors to conduct cyclic surveys for the control and reporting of mining progress determine and control the elevation and slope of working benches and haul roads determine the volumes of mined ore and waste and control and manage the mine dewatering system a control network should be linked with the national survey network to enable transfer and use of the national coordinate system in most cases the primary control network for a mine is based on triangulation and or trilateration figure 9 4 1a it is important that control point positions be 1 clearly visible from the main working areas of the mine site 2 visible from multiple other control points and 3 clear of mining activities and other disturbances that could lead to their destruction control point positions are usually determined from angle and distance measurements that can be supported by gps observation as a general guideline the horizontal accuracy of a primary control network should be 1 20 000 or better control benchmarks are usually stabilized permanently by means of concrete filled steel pillars set on concrete foundations figure 9 4 1b a primary control network can be densified with secondary and tertiary control networks by means of any combination of micro triangulation intersection and resection traversing and profile lines lower class control points can be used as stations for detailed topographical and setting out surveys the positional accuracy of such points should be no worse than about 0 2 m for such accuracy closed traverses should be 2 5 km and open traverses should be 1 km topographic surveys a detailed topographical survey at an open pit mine focuses on the locations of bench slope crests and toes berms road edges and gradients ditches and water dams waste dumps power lines buildings and other permanent and temporary structures it includes the collar positions of exploratory and blasting drill holes and information on existing cavities created by previous mining activities the following survey methods are available total station survey aerial and terrestrial photogrammetry survey gnss gps survey and laserscan survey total station survey a total station survey involves determining the directions and distances to measured points and then simultaneously calculating the horizontal and vertical positions of those points by means of the so called radi

ating method such a survey is especially useful in open pit mines where benches slopes and roads can differ significantly in elevation survey data are collected stored in instrument memory downloaded to a computer in the survey office and converted by application software into a map of the surveyed area in the past to obtain such data surveyors sighted instruments on reflectors positioned by assistants at various points of interest and the risk of falling down a slope or being struck by falling rocks was significant today s total stations do not require reflectors and can measure distances to almost any object up to several hundred meters away some total stations can be combined with gnss receivers such as the leica smartstation for rapid station positioning which is useful when a station cannot be set directly over a control point but should be done only in exceptional circumstances when a rapid survey is required obtained results must be checked later or linked back to the mine survey control network figure 9 4 2 shows a typical total station survey of a mining road and benches aerial and terrestrial photogrammetry survey mapping by aerial photogrammetry is useful for large surface operations especially those with large differences in elevation areas that are difficult to access or areas with large amounts of traffic the method provides numerous advantages including 1 real time registration of details that can be revised at a future date 2 remote and safe collection of data and 3 relatively rapid surveying of large areas major disadvantages are that final results are not immediately available but rather require weeks of data processing and that significant advance preparation is required to mark and survey control points so the method is not economically feasible for smaller mining operations the positional accuracy of details obtained by this method is in the range 0 1 0 2 m mapping by terrestrial photogrammetry is useful for high scarps and slopes with rock structures and slope deformations the method involves taking images from control points of known position with special dedicated metric cameras from images of an object taken from different locations a 3 d model can be developed for use in map creation some systems use images produced by high quality commercial digital cameras equipped with nonmetric lenses gnss gps survey current gnss receivers using gps real time kinematic rtk technology deliver relatively high positional accuracy better than 0 1 m comparable to that delivered by total stations gnss is now the survey method of choice for open pit mines and is used not only for inventory surveys but also for conducting setting out surveys positioning blasthole collars and locating mining equipment particularly dozers draglines drill rigs shovels and tracks survey data are collected stored in instrument memory downloaded to a computer in the survey office and converted by appli

cation software into 3 d models and maps of the surveyed area with wireless datacommunication systems maps can be produced in real time laser scan survey since 2000 laser scanners and associated processing software have developed into fast reliable and accurate long range surveying devices because they do not require the use of reflectors or staff at a mining face they have made the entire range of surveying operations significantly safer scans are performed from a stationary position and collected data are transmitted directly to the surveying office alternatively some scanners can be mounted with gnss receivers on the roofs of four wheel drive vehicles figure 9 4 3 shows a laser scan of an open pit mine data processing as mentioned previously survey data are collected stored in instrument memory and downloaded to a computer in the survey office where specialized surveying software manipulates the data performs calculations and creates 3 d digital models and maps mining regulations often require that maps be created to specific standards with respect to typically a scale or map coordinate system in recent years constantly updated 3 d digital models have replaced classical mine maps among the many surveying software packages available today most popular are the so called general mine design packages for creating geological models mine designs and plans the following are particularly popular gemcom surpac gemcom software international datamine studio 3 datamine corporate limited vulcan maptek and carlson survey carlson software three dimensional digital models of mining operations enable relatively easy calculation on a personal computer of the volumes of waste and ore that have been mined most of such models use triangulated irregular networks tins to represent the original topography and working levels of a mine rock volume between mine levels is calculated by taking the difference between solids with the base at an arbitrary level e g 0 m and the top at the mine level represented by the tin figure 9 4 4 volume can also be calculated from a block model by summing the volumes of individual cells representing these deposits slope stability surveys modern open pit mining operations increase in efficiency as the ore to waste ratio increases usually leading to maximization of pit wall slopes however steeper slopes pose greater risk to personnel and mining equipment due to increased potential of slope failure to uphold the required safety standards and reduce risk to an acceptable level many open pit mines must develop a holistic slope monitoring program cawood and stacey 2006 such programs should distinguish the following three slope monitoring stages 1 overall monitoring of all pit walls and adjoining areas 2 focused monitoring of potential instability areas and 3 detailed monitoring of areas with earlier detected instability or failure monitoring techniques should also take in

to account the expected mode of slope failure there are four major modes of failure in open pits 1 circular failure with large rock movements along vertical planes at the top of failure and horizontal movement in the toe zone 2 planar failure with rock mass movement along an existing geologic discontinuity such as a bedding plane parallel to the slope face 3 wedge failure when two sets of flat failure surface planes intersect and dip out of the wall moderate vertical and horizontal movements are expected 4 toppling failure when vertical or near vertical structures dip toward the pit wall large horizontal rock mass movement is expected at the top of failure the relative locations of control stations and targets used in a slope monitoring network should be selected so as to be maximally sensitive to expected rock movement traditionally specialized geotechnical and surveying methods were used for slope stability monitoring however recent developments in satellite and terrestrial remote sensing technologies have significantly impacted the methods currently used monitoring on a large scale can be done using interferometric radar technologies if the primary concern is vertical movement subsidence of areas adjacent to slope crests or bench areas of large open pit slopes satellite based interferometric synthetic aperture radar insar can be used to detect these movements jarosz and wanke 2004 insar images can easily cover large areas of the whole open pit mining operation ground based radar systems also using interferometric technologies recently became the tools of choice for continuous monitoring of wall faces the most successful and popular systems are slope stability radar by groundprobe australia and movement and surveying radar by reutech mining south africa reeves et al 2001 mchugh et al 2006 these systems can provide continuous measurements of rock movement across the entire face of a slope wall with submillimeter accuracy real time processing of collected data enables confident tracking of slope movement and management of risk while optimizing safety and productivity monitoring on a smaller scale or of distinct targets can be done using classical surveying techniques control stations must be established at stable locations from which targets placed on pit walls are observed station stability must be ensured and controlled stations should be erected as concrete pillars set into bedrock or into a stable foundation stations should be linked by means of a control network with other stations located far from the mining area and considered to be stable repetitive surveys once or twice a year must be performed to check the stability of the control network for continuous monitoring of wall targets automatic high precision total stations can be used such robotic total stations are programmed to automatically measure directions and angles to targets and transmit data to a control computer in the survey offi

ce data are processed in real time and information regarding target movement is reported out if movement is greater then the earlier defined critical value an alarm is triggered enabling timely withdrawal of mining personnel and equipment automated slope monitoring systems are offered by major producers of surveying equipment as well as by independent developers the most advanced and popular are the leica automatic deformation monitoring system geomos by leica geosystems and slope monitoring software from softrock solutions western australia support surveys for equipment and machine control timely and accurate positioning as well as monitoring of mining equipment is increasingly important to efficient mine operation the following activities are highly influenced by equipment positioning drilling where accuracy is critical to efficient blasting operations dragline positioning where accurate and efficient movement of overburden material is critical for strip mining elevation gradient control where continuous assessment of ground movement must be performed and adjusted in real time grade control where 3 d mapping of mineral deposits and control of ore digging and loading are required track assignment where mining haul trucks must be directed to the right place at the right time and each load of ore or waste depending on its quality and characteristics must be dispatched to its proper destination accurate equipment positioning can be achieved by means of gnss receivers using rtk technology however the vertical accuracy of a standard rtk gps system is two to three times less than its horizontal accuracy with vertical standard errors of 0 01 0 02 m such accuracy is sufficient for most mine sites other than finish graded roads that require tolerances of just a few millimeters such greater tolerances can be achieved by combining a rotating laser with a gnss system accurate positioning of a dozer blade can be obtained in the horizontal position by using an rtk system and in the vertical direction by using a laser collimation plane lasers with a 10 m vertical swath increase this range even farther allowing multiple machines working at distances up to 300 m linear and 10 m vertical from the base station to receive grade corrections such systems provide the tightest machine controls technically available the leading machine control systems have been developed as collaborations between manufacturers of mining equipment and providers of gps receivers a computer aided earthmoving system caes combines gps the united states s global positioning system and glonass russia s global navigation satellite system positioning with an onboard display for the machine operator and wireless ip internet protocol communications between the machine and the office graphical and textual cut fill information provided to the operator eliminates the need for most survey staking caes can be used for haul road and bench con

struction and maintenance production dozing leach pad construction and maintenance reclamation ore grade control material identification and coal load out terminals it is designed to be used on scrapers loaders dozers shovels motor graders hydraulic excavators and track type tractors data on the status of each machine are sent wirelessly to the control office for monitoring by mining supervisors figure 9 4 5 surveying and mapping of underground mines in an underground mine surveys are typically performed in dark confined and often wet spaces and special equipment and methods have had to be developed to comply with underground safety regulations mining drifts drives and tunnels tend to be long and narrow requiring the use of traverses as the main survey control control points are generally located in the back roof rather than in the floor where they are less subject to heavy traffic and less vulnerable to damage for use in the dark instruments must have illuminated cross hairs targets and reading systems other adverse conditions to which instruments are exposed include dripping water high velocity ventilation air high temperature dust strong electromagnetic fields and mine gases and therefore only safety certified equipment can be used hart and parrish 1995 areas that are unsafe to access may require the use of specialized equipment that can be remotely controlled horizontal and vertical control deep mine surveys must be performed in 3 d and underground and surface surveys must be correlated if a rescue borehole is required between the surface and a specific underground location or between two underground locations survey data and survey marks must provide sufficient reference to enable accurate directional drilling the location of mine workings must be accurately controlled especially in relation to mining lease boundaries and other important surface features such as highways railroads power lines gas lines wells and historical buildings adjacent mine workings must be surveyed and presented in the same coordinate system to eliminate unintended breakthrough that could lead to disastrous gas or water inrushes maps of all surrounding mines and other relevant areas must be reviewed and fitted to the master map of the mining operation before the start of any mining project a job made difficult because all too often adjacent mines highways departments railroad companies gas companies surface landowners or mineral owners use different coordinate systems chrzanowski and robinson 1981 recommended that surveys be performed at three levels of accuracy 1 creation and survey of a primary control network for the mining area and permanent workings 2 survey of mine headings and development areas and 3 survey of short traverses necessary to map active mining areas in the united states and many other countries the first level of survey a primary control network is generally tied to the

second or third order of the u s national geodetic survey ngs network and must adhere to the same accuracy specifications in many cases the configuration and geometrical characteristics of the mine entrances require use of traverses as an underground control network traverses usually have many short 40 50 m traverse legs and direction is difficult to maintain it is advisable to perform surveys using quality theodolites or total stations that are maintained and checked regularly when an underground control network extends over a large area and traverses are long with many legs the use of gyro theodolites may significantly improve their directional accuracy the surveying and mapping of a control network is often performed by a specialized external contractor traversing with total stations in the backs classical traversing equipment used for surveying in underground traverses is not too different from that used on the surface electronic total stations the primary angle and distance measuring instruments enable automatic reading and storage of directions and distances distances are measured electronically with the help of edm devices that are coaxially mounted in a telescope for use underground instruments should be protected from dust and moisture for use in gassy mines instruments must be certified for use in such environments that is they must be explosion proof most theodolites and total stations today have been properly sealed at the factory and can be used in such environments if for safety reasons edm devices cannot be used a steel tape can be used for distance measurements underground survey stations are usually stabilized in the backs of underground drives by the following means to protect them from damage standard spads driven into wooden plugs set in holes drilled in native rock spads are hooks for attaching plumb bobs and have defined spots for sighting power driven studs driven directly into rock by a stud gun using an explosive charge adhesive spads attached to the rock by adhesive plastic cement or epoxy spads with clamps attached to steel arches or roof bolts survey stations should be identified with brass aluminum or plastic tags it is important that tags are permanent and that metal tags not be attached directly to survey stations to prevent corrosion identification numbers on the tags can be either 1 sequential assigned to stations as they are created regardless of location or 2 position coded to identify station location level drive or station number modern theodolites and total stations are equipped with optical or laser plummets for fast easy centering over or under the control point if laser plummets are not permitted standard plumb bobs can be used when hung from a spad in the roof the bob can be illuminated by a cap lamp held behind a translucent screen or sheet of paper small reflectors and targets can be attached directly to spads and conventional reflectors c

an be used on forced centered traverses most underground leveling is performed while traversing due in part to time constraints generally by means of the trigonometric leveling technique vertical angles can be measured with high accuracy and thus trigonometric leveling provides similarly accurate results during traversing and leveling it is important that instrument height and target or signal height also be measured accurately measurements collected at an underground traverse station are shown in figure 9 4 7 traversing with total stations in the walls wall station traversing although the back provides a secure location for control points it presents a number of disadvantages for mine surveying the most obvious of which is the difficulty of installation and access locating control points in backs in a modern highvolume underground mine usually requires lifting apparatus to heights of 5 m in contrast locating control points in walls makes installation and access easier faster and safer because a theodolite cannot be set under a control point wall station traversing requires use of a surveying technique other than that used for classical traversing rather the resection technique free stationing with all available distances and horizontal angles measured is used to determine instrument position wall mounted points are observed from a temporary instrument station located in the drive wall station traversing has become popular in underground mining operations particularly in western australia and it is important that surveying professionals have an indepth understanding of the methodology accuracy and limitations of the technique the instrument and target are shown in figure 9 4 8 the surveyor secures a target to the wall by inserting a target stem into a wall sleeve mounted in a drilled hole the method requires specially designed target prisms that retain a central position regardless of their rotation total station instruments must be coaxial that is distances and angles must be measured along the same line of sight and software must be able to determine instrument position from resection observations by means of the least squares best fit calculation method analyses of wall station traverse accuracy suggest that for optimal directional accuracy a configuration must have acute triangle geometry jarosz and shepherd 2004 temporary instrument stations located normal or near normal to wall stations decrease the accuracy of bearing transfer if acute triangle geometry is not always possible the surveyor should take additional observations to the previous and next instrument station to add rigidity to the survey structure and use forced centering when observing consecutive instrument stations ensuring that the initial triangle geometry is acute figure 9 4 9 recent experiences suggest that wall station traversing significantly increases the safety of surveying operations in modern underground mines with la

rge drives however it requires the use of modern coaxial theodolite and zero constant reflectors distance measurements must be accurate to 1 mm 2 ppm and angular measurements must be accurate to 5 detail surveys the details of underground drives drifts and tunnels are derived from control stations established in mining structures in most cases detail surveys are conducted concurrently with control surveys traditionally the method of chains and offsets was used to perform detail surveys the procedure is as follows stretch a reference tape between traverse stations measure offsets to the right and left walls at regular intervals 2 3 m with a short tape measure vertical distances to the roof and floor with surveying staffs poles note the details distances and offsets of existing features it is sufficient to approximate the perpendicularity of offsets due to their shortness and the measurement accuracy 0 05 m higher accuracy 0 01 0 02 m is required in drives or tunnels with permanent roof and wall supports prepare a sketch of the survey in approximate scale in cases such as when rebuilding a tunnel or drive prepare a detailed cross sectional survey for a reference line it is traditional to use a plumb line attached to a spad installed in the roof measure offsets at different elevations between the plumb line and the walls today total stations with reflectorless edm devices are used almost exclusively to perform detail surveys the procedure is as follows survey a few lines strings of points running at different elevations and representing the outline of the structure of interest download the collected data from instrument memory to a computer in the survey office for processing plotting and in most cases creation of a 3 d model of the structure the newest surveying technologies use laserscanning devices for fast continuous collection of detailed and accurate transverse profiles when the device is moved massive deposits mines extracting massive deposits are surveyed almost exclusively in 3 d total stations are used to survey access and development drives laser based monitoring systems are used to survey cavities and stopes in the latter case with the instrument inserted into the stope by means of a boom the motorized surveying head scans the opening with the help of a laser rangefinder a total station can determine the position of a device by tying it with positions of existing control stations special inspection and surveying devices are also available to survey inaccessible vertical shafts and orepasses jarosz 2008 collected data are converted to 3 d models with the help of specialized computer software these models are linked with other models of development and access drives to provide a 3 d model of the whole mine such models enable creation of on demand plans and cross sections in any scale or projection tabular deposits relatively thin tabular deposits are traditionally surveye

d in two dimensions with the projection plane parallel to the deposit such surveys should be performed in coal mines or mines from which metalliferous reef type deposits are extracted as in the gold mines of south africa using chain readings and orthogonal offsets to provide detail the procedure is as follows for a reference line use a steel dip tape stretched between strike gullies or drifts use orthogonal offsets and triangulation to relate the position of the dip tape to spads installed in the gullies use a short tape and a surveying stick to measure offsets between the tape and the stope face also measure the width height of the face if the deposit is on an inclined plane reef reduce the distances measured along the dip to true horizontal distances in the survey office create a horizontal map and use a planimeter to determine the areas between face positions and the volumes extracted recent developments enable 3 d surveying of thin tabular deposits by means of electronic total stations combined with data collection and display hardware and software the results of an underground survey can be viewed in real time on a ruggedized laptop computer thick tabular deposits extracted by room and pillar mining are surveyed almost exclusively with total stations the surveying procedure is similar to that used for access and development drifts as described previously setting out surveys setting out surveys provide direction and grade for mine drives extensions and tunnels and are crucial to mine development the following are common methods for performing this type of survey grade sticks two spads are placed at a set distance in the backs and wooden poles are suspended from the spads marks are placed on the poles in such a way that when lined up the marks indicate the direction and gradient the gradient is transferred to the development face grade chains the method is as above but chains are used instead of poles and small rings attached to the ends of the suspended chains are used instead of marks strings and grade pegs two sets of pegs spaced 5 10 m apart are placed in the sidewalls of a drive at calculated levels strings are run between the pegs to create an inclined plane with the design gradient the gradient is transferred to the development face direction and grade lasers for a short extension of direction and grade a small laser is positioned in the wall opposite the development heading the laser is inserted into a sleeve cemented into a hole drilled into the rock in such a way that the laser beam projects the direction and gradient for new development a drilling pattern is marked at the heading for a long extension a larger laser is mounted in a special enclosure attached to the back of a drive in both cases a total station is used for laser setup the direction and grade of the laser beam should be checked regularly today lasers are used almost exclusively to determine direction and gr

ade hydrology is an imprecise science developed by empirical observations by many people over the course of 3 000 years complex nonlinear systems are involved many of the factors that go into the computations are probability based time variable imprecise or uncertain identifying and quantifying the risks associated with system failure usually sets the level of effort that is justified more precise calculation methods are evolving but considering the uncertainty of the data approximations are commonly used the locations quantities and detrimental effects associated with water in the operating areas are continually changing as the mine development progresses this effect renders the precise calculation of the performance characteristics of the pumping system at any particular point of limited operational value computer based systems hide the complexity of the calculations and allow more rapid solutions of the empirical equations complex computational fluid dynamic calculations are usually justified only if the costs and development times are substantial for example a manufacturer of a new class of pumps could justify the effort because upfront computer modeling may well reduce the cost and time needed to build prototypes however a mine engineer trying to decide if that pump would have sufficient capacity to pump from his pit probably could not justify that level of computation some factors from the mine planning process are predictable with reasonable precision for example the hydrostatic lift necessary to pump water from a planned shovel face is predictable because engineers design the elevations of the pit face and pit rim in advance changes in these factors are predictable as long as mine operations follow the plans the size and shape of the drainage basins that contribute to the runoff into the mine area are measurable in advance but other critical factors affecting the quantity estimation of runoff are difficult to measure accurately meteorological factors climatology and actual rainfall can vary significantly from the predictions changes in land use and development over time reduce the predictive ability of long term rainfall monitoring and flow gauging station data these can show up as drift in the mean runoff levels and intensity over time because removal of ground cover and construction of paving tend to limit infiltration and reduce the concentration time some examples of these factors follow natural basins and channels are nonhomogeneous in their ground cover slopes soil type and moisture content the variability of rainfall intensity over a basin increases with the size of the basin larger basins are subject to locally heavier precipitation intensities most precipitation records are point measurements rainfall gauges are small samples of the larger precipitation event spatial variability of storm patterns makes even nearby locations difficult to predict without on site data streamflow gaug

es are better indicators than rainfall gauges where these records are available because of the integration of the runoff from the upstream basins as long as the characteristics have not changed over time historic observations used to determine the probabilistic frequency of rainfall events are uneven in some places reliable precipitation records may have recorded the variability over several centuries while in others only for decades in the case of some greenfield developments no historic data may exist at all in semiarid regions empirical methods are commonly used to predict rainfall runoff events which make it difficult to quantify the magnitude of potentially damaging high return period storms such as 100 year or 500 year events coverage is definitely better in the developed world than in remote areas mine dewatering team few people think of mine dewatering at a surface operation as a major issue when compared to other production tasks such as fragmentation loading hauling crushing or milling if neglected however no other operations are possible in the mine mine dewatering requires applying knowledge from many fields to create practical cost effective and efficient systems to manage the water this chapter discusses practical field methods that provide sufficient levels of accuracy and precision to limit risk the objective is to put tools in the hands of the engineers and technicians to manage mine water inflow and accomplish production effectively and economically all of the following specialists have a role to play in managing water but it is the role of the generalist to understand the big picture and know when to call the experts mining engineers overlap and coordinate with other specialty engineering disciplines to develop a cross disciplinary engineering approach to the issues involved with prediction collection and handling of water in mine workings meteorologists track the data related to historic precipitation patterns utilizing rainfall measuring stations streamflow gauges radar satellites and modern database systems that supply the data to predict probable precipitation values and the associated statistical risks civil engineers hydrologists predict the runoff recurrence and design the surface drainage controls storage basins and conveyance structures mechanical structural engineers provide the expertise to design pumps pipelines and mechanical aspects of pumping stations including concrete supports and pump engineering electrical instrumentation engineers design the electrical power distribution instrumentation and controls required to run interlock and control pump stations and dewatering systems environmental engineers provide the knowledge of federal state and local regulations for obtaining permits prior to commencing operations they assist mines to predict evaluate and mitigate pollution from operations land legal and water rights professionals manage t

he legal aspects of obtaining permission to extract and use specific water quantities for industrial purposes they also help miners manage disputes over historic ownership and water rights law government agencies fund and manage the basic research and development that provide much of the background hydrology data available in the united states the national weather service and the national oceanic and atmospheric administration noaa collect and distribute much of the precipitation data that are critical for predicting runoff the u s geological survey provides a database of streamflow records for drainage basins and groundwater levels in monitoring wells located throughout the country review of surface hydraulic calculations this sections gives a brief outline of the process of designing a runoff control system for a mine the process can be broken down into a series of estimates required to scope the problem detailed explanations for these estimates are in chapter 16 4 precipitation storm events to determine the amount of protection necessary for the various mine operations structures the risk level of the proposed structure can be estimated based on failure consequences the appropriate design storm point precipitation frequency ppf event can be selected from noaa or other sources to determine precipitation amount and intensity noaa 1980 basin runoff calculation using the rational method or one of a number of computational runoff calculating models u s army 1971 basin characteristics for each basin in the watershed are measured shape area channel length ground cover and relief ppf from the design storm for the area is applied a measure of precipitation millimeters or inches that falls within the storm period e g 25 mm or 1 in of rainfall in 6 hours expected once every 10 years peak flow rate q time of concentration and total runoff volume are calculated routing network is designed using the flow information from the individual basins the runoff protection network can be designed this may consist of a number of structures to route the water from the source to the discharge point open channels culverts detention and sediment control basins spillways weirs and flumes the u s army corps of engineers hydraulic engineering center hec 2009 tools are helpful as is the american iron and steel institute handbook spindler 1971 safety aspects of dewatering water in mine workings presents a number of hazards to the safe operation of the mine sudden precipitation events result in rapid high volume runoff into surface mines along the road network and over the pit rim water allowed to run over highwalls can cause erosion bringing down debris talus and raveling thereby creating hazardous conditions to mining operations below ponding erosion and degradation of the haulage surfaces and working benches mean that all operations slow down to maintain control of the equipment slides and rockfa

ll risks increase when water percolates into cracks in the highwall in cold climates ice and freeze thaw cycles increase the risk of raveling and rockfalls as the freezing water swells inside the fractures wedging the blocks apart ice builds up where water seeps out of the highwall when these overhangs fail and fall they can cause extensive damage especially if the ice mass is large seasonal thawing causes these ice buildups to break loose and rain rocks and ice into the pit drainage control maintenance should be conducted prior to the arrival of seasonal precipitation in areas where this is predictable such control measures include filling surface cracks around the pit perimeter and diverting runoff from the pit rim to limit water infiltration regular inspection of ditches culverts and drainage channels for damage and cleaning away debris to allow maximum water flow should become standard operating procedure scheduling of major construction or modifications should allow for completion during the dry seasons avoiding critical system downtime on dewatering systems high volume precipitation events cause flash flooding particularly in mountainous areas and arid climates such as in the american southwest proper planning of the pit location and associated mine facilities must take into account drainage protection significant storm runoff can be controlled by properly designed drainage controls that direct runoff away from the pit to prevent problems before they occur in pit haulage roads and benches should be sloped to prevent ponding and direct water through perimeter ditches to sumps for collection culverts must be adequately sized to convey water where roads intersect drainage crossings emergency planning contingency plans must exist to protect personnel from entrapment if flooding from sudden inflow of runoff results in loss of the main access route this can happen if the haul road washes out or slides off the wall because of slope failure ensuring that the pit designs include emergency evacuation routes must be part of the mine planning process surface mines usually have more than one escape path from the pit ramping down to start a new bench in the pit bottom commonly called drop cutting can be particularly hazardous during monsoon season it may be necessary during intense precipitation events to abandon mining equipment in the drop cut and evacuate personnel to a safe location until the runoff subsides escape route planning is even more important in underground mines that may be subject to rapid inundation if old flooded workings exist in the area mine pumping systems cannot keep up with storm runoff in real time due to extremely high inflow rates that are usually at least one to two orders of magnitude higher than economically feasible pumping rates in severe events power may be disrupted and sumps designed to capture the entire runoff volume of a particular design storm can be overwhelmed most dewatering s

ystems cannot function during heavy rains and must be shut down to prevent damage from excessive sediment and debris floating barge pumps handle these events much better than fixed pump stations as long as their sumps can handle the runoff after significant precipitation operators may have to excavate mine sumps in order to recover the original volume lost due to sediments washed in from erosion of the roads and walls above pumps may be inundated or buried under sediment and may need to be replaced before pumping from the pit can resume impoundments an embankment that impounds water at a level above its previous channel elevation creates a potentially hazardous condition failure of the impoundment can release a tremendous amount of stored energy which is then directed at anything below embankments dams and diversion dikes require higher than normal safety factors if that structure s failure could lead to loss of life or significant property damage this higher safety factor is based on risk assessments of downstream structures and populations periodic inspections monitoring and maintenance of operating impoundments must be carried out to ensure that the structure remains safe and its operation is within its designed limits the size of the impoundment often determines the frequency and level of inspections required by the permitting agencies knowing the applicable regulations can reduce the costs of monitoring and inspections for example under the u s mine safety and health administration regulations for coal mining embankments larger than 6 m 20 ft high and ones with a capacity exceeding 24 670 m3 20 acre ft require inspections every 7 days impoundments only slightly smaller have less onerous inspection requirements msha 1977 dam breaks are now rare because of regulatory vigilance imposed in the wake of significant disasters in the past the potential damage from a failure can be very high due to the high volumes of water that can be released in a short time and the proximity of population and structures downstream when impoundments fail investigations into the causes usually find that the fault lies with improper design construction operation inspection and or poor maintenance practices slope failures into impoundments evaluation of the potential for slope failure should be part of the design criteria for all deep sumps adjacent to highwalls backfilling operations into flooded pits create the potential for dump failures to produce large damaging waves the volume of sumps built under slopes with a history of stability problems should be as small as possible shallow sumps with large surface areas are preferred to smaller deep water sumps miners working near large in pit ponds and sumps must be extra vigilant if any risk exists of slope failure into the water procedures for real time monitoring of wall stability can mitigate the hazards to provide advance warning if raveling develops if personnel are required

to work near the shoreline of sumps shallow areas such as old ramps are most hazardous because a wave approaching from deeper water can rise significantly an example of slide induced waves occurred at the valdez creek mine in the alaska range united states during backfilling into a previously mined pit when a dump failed and created a very large wave the area a long sinuous valley 67 m 220 ft deep by 457 m 1 500 ft wide and 1 6 km 1 mi long was concurrently collecting tailings and dump material from the stripping operations the pit had a standing water pond 53 m 175 ft deep against the toe of the dump mine dumping was from the original pit rim elevation in a single lift about 24 m 75 ft above the water surface tension cracks developed behind the dump crest and a large section 18 m 60 ft thick slid into the water the dump material displaced the water at the toe resulting in a wave 11 to 12 m 35 to 40 ft high that hit the wall across the pit at the far end of the valley 1 6 km 1 mi away the wave was still more than 2 m 6 ft high where it damaged a pump station fortunately no one was hurt but the potential for severe injury existed for anyone working on the ground near the surface of the pond as a historic note in 1958 the largest wave ever recorded at 533 m 1 750 ft high was caused by a slope failure into deep standing water in a fjord in lituya bay alaska bbc 2000 access safety and maintenance planning heavy machinery deep water limited access and people in close proximity create significant safety challenges that must be mitigated when considering floating barge applications long term sumps must have access structures designed into the system these can include floating gangways complete with handrails cableways and pipeline flotation systems anyone working around the barge must wear appropriate flotation protective devices whenever the barge and pump draft are too deep to allow the barge to be pulled close to shore docks may need to be built in sumps with shorter design lives the barge may be accessed by boat providing that its weight limits and stability are not exceeded as a work platform the following are important factors to be considered servicing plan for pump control maintenance weight and center of gravity for the barge crane reach limitations and control access requirements occasional operator access for pump maintenance support for pipelines and electric cables to account for water level changes moving equipment and machinery on barges creates the possibility of capsizing the barge to avoid tipping major shifts in the center of gravity during maintenance or operations need to be carefully planned special marine engineering expertise may be required to identify hydrodynamic stability and buoyancy issues before construction or major component replacements buoyancy control adjustments can be accomplished with air chambers that allow the deck level adjustments

pipeline supports must include additional buoyancy where the discharge pipe connects to the barge to compensate for the weight where the pipe rises above the water lifting plans weight and crane capacity site access must be designed to allow pumps motors and other equipment to be successfully lifted from the barge to transport equipment onshore pump and barge draft requirements may limit the ability to drag the barge close enough to the bank for service the slope of the sump bank frequently causes the barge to run aground well before it is close enough to shore to enable convenient access for small steep sided sumps this is less of a problem due to the higher wall angles large sumps or pit lakes require the development of standard operating procedures that include the weights of the barge pumps switchgear and pipe fittings that will need to be placed both during construction and changed later during maintenance cycles some sumps have access limitations that preclude using shore based lifting equipment in these specialized cases it may be necessary to employ sky crane heavylift helicopter services to fly the equipment to the operating location generous factors of safety are needed to account for the barge weights that will increase when mud water logged floats and scale accumulate over time the suction force that has to be added to the weight to break free of the mud if the barge settles to the bottom should not be underestimated the critical factors in these plans are the crane locations reach limits and estimates of the weight that must be lifted bank stability is also a concern in sumps with fluctuating water levels in pit water control the primary objective of the in pit water control network is to expeditiously convey water through the workings to the temporary collection sumps for removal without adversely affecting the mining activity runoff sources include the point sources from groundwater infiltration streams entering the pit and rainfall collection on the surfaces inside the pit s perimeter factors that water control system designers must consider as engineering trade offs are the cost performance designs involving the pump capacity pipeline diameter power requirements system duty cycle and number of lift stages large capacity pump pipeline systems with few stages are designed to run intermittently compared with smaller systems with larger sumps that run almost continuously the large system has a higher factor of safety to handle unusually large inflows but comes at a higher capital cost than the smaller system which accepts higher risks of being overwhelmed in infrequent precipitation events but handles normal dewatering needs better smaller redundant parallel pumping systems can provide the surge capacity of a larger system while increasing system availability increasing sump capacity is one of the least expensive ways of reducing risk without sacrificing the efficiency of the pumping system ind

irect costs of water in the pit water in the rock fractures adversely affects the geotechnical stability of the pit walls mining pits at the steepest stable pit highwall angles is the most profitable because it lowers the stripping ratio proper water control increases the pit wall stability thus maximizing the wall angles preventing water from infiltrating the fractures in the rock is critical to maintaining maximum stability horizontal drain holes drilled to intercept the fractures can successfully reduce the pore pressure water in the mine working areas causes inefficiency in all materials handling operations water buildup at the oreloading face degrades the crushing and conveying efficiencies dewatering efforts should move the water to local sumps that follow the loading equipment close enough to prevent digging in wet ore fines and water combine to form a highly abrasive grinding medium that destroys moving parts excessive moisture can cause backsliding on inclined belts where the feeders drop ore onto a moving belt the steeper the belt the worse the problem becomes when conveying saturated material water seeps out of the muck running down the belt until it spills and builds up in the drives and under the rollers particularly in cohesive ores with many fines wet material causes a buildup in chutes resulting in plugging and costly downtime slabs from material buildup on the walls of the chutes can break off fall onto the belt and cause adverse wear or torn belts haulage road runoff control haulage roads act as arcs in the flow network in the pit because they are continuous and interconnected and lead from the pit s upper reaches to the bottom working levels making them ideal channels for water haul truck tires are becoming one of the major costs of mining wet roads tire slippage and sharp rocks are primary causes of premature failure drivers must reduce their speeds to maintain control under wet road conditions maintaining good drainage control prevents visibility degradation and reduces spray from haulage roads muddy conditions create poor traction resulting in increased stopping distances for mobile equipment properly designed haul roads should be crowned or slanted to prevent ponding on the road surface crowned roads with at least 2 cross grades have fewer problems than surfaced roads without drainage grades with washboard ruts because the road surface retains most of its strength by having the cross grade eliminate standing water perimeter ditches concentrate the water and direct it down toward the sumps on long ramps the water volume can build up significantly before it reaches the bottom as smaller tributary streams and rivulets join the main flow it is desirable to divide the flow before the water accumulation gets deep enough to overflow the ditch into the haulage lane where the ditch is located on the pit side of the road creating holes in the berm allows part of the runoff to escape the dit

ch and sheet flow down the wall reducing the size of the ditch necessary for the remaining portion of the flow the water flows over the highwall travels to the next lower area in the pit and from there to an intermediate sump or another berm relief on its journey toward the bottom switchbacks in the haul road present challenges to handling the water collected in the ditches along the highwall haul roads usually have superelevated curves raising the outer edge of the road perimeter if the straight road section is crowned or sloped back toward the highwall water runs in a v ditch between the road and the wall when approaching the switchback the ditch elevation increases as the road nears the superelevated curve and the water escapes the ditch running across the active traffic lanes to continue downhill the result is erosion of the travel surface creation of washboard ruts and tendency of the water to meander over the entire road surface several ways are suggested to mitigate these problems a trench between the highwall and the superelevated curves should be created to allow water to continue past the curve and cascade over the wall this has the effect of moving the water off the road but does so by directing it to the pit bottom most pit designs do not allow enough width to accomplish this because the trench takes up too much room diagonal swales grooves or water bars should be cut into the road surface prior to the curve to force the water to cross the road at a designated location aggregate can be selectively placed and compacted to prevent erosion in these designated water crossings approach transitions must be gradual enough to ensure no adverse effects on the speed of trucks traversing the swales the most expensive way to move the water is to divert the ditch into a culvert running under the superelevated fill the culvert can run along the same route that the trench would have taken but without the width penalty alternatively the culvert can cut the corner under the lanes thereby diverting the water to the inside edge below the switchback continuing the v ditch down the road the culvert entrance design usually involves a small sump but must prevent water from backing up and flooding over the road there is a width penalty to construct this and sufficient fill depth must be available under the road to prevent the weight of a loaded haul truck from crushing the culvert pipe sumps sumps capture and temporarily hold runoff to allow for sediment control and for pumping the clarified water properly designed water collection networks concentrate the accumulated runoff as high in the pit as possible sumps can be located in a pit bottom a wide spot in the bench along the wall or at a switchback along a haul road obviously pumping costs increase with the elevation difference between the sump location and the discharge elevation sumps should be large enough to ensure that the active volume will keep the pum

p running for a reasonable period efficient sump design matches the pump capacity to the inflow rate for normal groundwater infiltration reducing the need for periodically cycling the pump if a sump has low or infrequent flows it may not be in the right place in such instances it may be necessary to combine the inflow from other ditches to increase the utilization or consider eliminating the sump by rerouting flows elsewhere removal of expected sediment and debris must be part of any sump design the extent of the cleanout structure depends on the planned life of a sump the velocity of the water in the approaches and the presence of sediment traps in channels sediment traps have weirs and larger flow cross sections in the channel which slow the water flow allowing the entrained solids to drop out of suspension sumps collecting runoff from high intensity storms can rapidly fill with sediment if the velocities are erosive because of steep channel grades or easily eroded soils it is easy and advisable to inspect the sumps periodically to ensure that necessary capacity exists slope stability effects must be part of the design and location of the sump geologic structures known to have stability issues should be avoided long term sumps on the highwalls are a source of water infiltration that percolates into the rock resulting in an increase in the pore pressure along the fractures this increases the probability of slope stability problems as mentioned in the safety section groundwater the review of surface hydraulic calculations section discussed handling runoff water from meteorological sources that originated outside the mine this section will give a brief outline of the process of identifying quantifying and controlling groundwater infiltration into the mine groundwater infiltration from aquifers water filled cavities or other sources exists in nearly all mining operations a more detailed treatment for these issues is found in loofbourow 1973 and in chapter 16 4 the process can be broken down into a series of estimates required to scope the problem depending on the status of the project premining feasibility studies the subsurface geologic structure and hydrology of the deposit are mapped and understood exploration wells are drilled to locate and quantify potential water resources for processing and potential mining hazards the wells are tested to model flow rates porosity temperature and chemistry looking for possible adverse issues the quality and chemical makeup of the water are assessed in order to design the treatment methodology the interception strategy is chosen for handling the predicted water inflow rates interception wells in the aquifer are pumped to dewater outside the mining area inflow outside the mine perimeter is blocked by reducing porosity inflow into the mine is accepted and handled along with other water sources mine development phase predictions from the pre mine fe

asibility studies are verified the flow outside the mine perimeter is blocked through grouting freezing or other methods to reduce porosity of aquifers or fractures identified as high risks water is intercepted and drawn down using well fields preventing quality degradation and avoiding treatment issues mine operation groundwater infiltration is routed into sumps and handled through the in pit pumping systems water quality issues are treated along with affected run on water prior to discharge or reuse pump system redundancy and capacity are maintained to handle unexpected changes in flow rates see the valdez creek case study later in this chapter interception well fields and blocking structures are maintained and expanded as mining progresses through the reserve the presence of groundwater in a mining claim has both beneficial and detrimental effects on the economic viability of the operation all mining operations and processing plants need water to function and it must be imported if insufficient supplies exist on the property however groundwater intercepted in the pit is usually in the wrong place with inconsistent flow rates and may have quality problems that must be handled before it can be used in the process the main objective in mine dewatering is to economically capture the water route it around the operations with minimal disruption and store it for beneficial use or failing that treat the water prior to discharge wet drilling and blasting drilling under wet conditions is more expensive and less productive than if the operation is dry one method of limiting the effects of water on the drill bench is by digging perimeter trenches into the bench this is particularly useful in deposits that have considerable water present in the rock but relatively low permeability perimeter trenching would not be effective if the ore is highly porous because this allows water intercepted by the trench to recharge back into the drill pattern even if it is not possible to pump or drain the perimeter trench it may lower the local water table sufficiently drawing the water from the bench s upper couple of feet to improve the conditions for starting the hole collaring fracturing from blasting the previous bench is usually sufficient to provide the additional permeability to draw down the local water table from the drill area to the perimeter trench the permeability in the unfractured surrounding rock is lower preventing excessive flow from the walls back into the drilling area if the bench conditions are wet redrilling is often required and may or may not be successful because the same water conditions that caused the initial problems still exist it is not uncommon to drill a pattern while drop cutting only to find that 90 of the holes are collapsed or plugged by the time the blast is scheduled after the good holes are loaded and shot to create additional porosity to pull down the water table redrilling sta

rts again under wet conditions like this it can take a month to develop a 152 m 500 ft long drop cut that might take only a week if the bench were dry although factors such as energy density detonation velocity or energy distribution usually dominate the decision about the explosive type the presence of water in the blastholes prevents using the least expensive blasting agents commonly used ammonium nitrate and fuel oil anfo blasting agents will not detonate or will misfire if the powder gets wet water resistant emulsions must be used if the water cannot be removed but they are nearly twice as expensive to use as dry hole anfo based products of equivalent energy blasthole dewatering with hydraulic driven pumps can offset some of the emulsions costs if the water infiltration rates are slow enough pumping the holes and using impermeable polyethylene sleeves allows the placement of inexpensive water sensitive anfo in areas that otherwise would require emulsions the cost of the sleeves adds to the blasting costs but significantly offsets the cost of using expensive emulsions case study valdez creek groundwater control between 1993 and 1995 cambior alaska s valdez creek mine in the alaska range was reaching the end of the mine s reserves this large placer gold mine operated year round above timberline in a remote subarctic stream valley this mine operation s primary defining challenge was groundwater infiltration flow in valdez creek ran year round across the entire length of the mining claim and continually recharged the subsurface aquifer groundwater flowed through the gravel deep in the deposit year round although the pit walls froze solid to a depth of 3 to 4 6 m 10 to 15 ft blocking the flow during the winter blasting occasionally breached this frozen wall resulting in sudden inflows of water and sediment into the pit the inflow increased during the annual spring breakup with a significant spike in water volume as the walls thawed draining the water held back during the winter management scheduled closing of the mine by freezeup in the fall of 1995 due to reserve exhaustion and marginal economics the company was under pressure to limit spending particularly on fixed infrastructure that it would have to abandon or scrap at closure the remote location required more time and logistical effort than most mines to make major improvements adding incremental diesel powered pumps was feasible with some notice weeks but adding highdensity polyethylene hdpe pipeline capacity was difficult expensive and required a long lead time months the mine experienced increasing water inflow rates in 1993 the pit had an approximately 69 l s 1 100 gpm inflow with a pumping capacity of 82 l s 1 300 gpm by mid 1995 the inflows had increased to 454 l s 7 200 gpm pipeline and pumping capacities were barely adequate for initial conditions surges overwhelmed the system flooded the pit floors for weeks and interrupt

ed ore production until the inflow subsided the initial 20 cm 8 in diameter pipeline was not adequate beyond about 63 l s 1 000 gpm requiring two pumps in series to keep up and maxing out pipeline capacity because the surge capacity of the system was limited the mine added a second 20 cm 8 in pipeline flows increased in 1993 to nearly 126 l s 2 000 gpm by freeze up interrupting production more frequently management agreed to fund an upgraded 30 5 cm 12 in diameter pipeline because it was essential to regain control over the water in the pit this pipeline was in place before breakup in 1994 the new pipeline worked well for about a year before it was deemed insufficient to keep up with increasing demands the inflow tripled over this period to 391 l s 6 200 gpm the pumps that were on site or readily available had to be pressed into service even though they were not well matched the system started with one large diesel powered pump and then added a large electric slurry pump and finally an additional large diesel pump in series two of the pumps operated at poor efficiencies well beyond their curves due to flows above their designed flow rate only one pump was still operating on its curve adding the second and third pumps in series to the pipeline resulted in smaller incremental flow increases extremely high flow velocity in the pipe approaching 6 m s 21 ft s resulted in high friction head losses 3 m 10 ft of loss per 30 5 m 100 ft of pipe causing the hydraulic grade line hgl to exceed 10 slope pumping in series adds the pressure of the last pump to the discharge pressure of the previous stages so the sequential order of the pumps is important pumps like pipelines have maximum design internal case pressure ratings to avoid overpressuring and cracking the cases additionally the discharge pressure exceeded the recommended working pressure for the hdpe pipeline which was operating at a reduced safety factor the operating point for this system was only possible because it pumped cold near freezing water doubling allowable working pressure the last incremental 63 l s 1 000 gpm required additional pipeline capacity 6 months before closure because no additional funds were available the pump crew salvaged the original 20 cm 8 in diameter pipeline from the 1993 pit and relocated it to the final pit two pumps in the series pushed the incremental flow up the wall extending production nearly to the end of the mine s life ultimately the lack of a pump caused abandonment of a portion of the final ore face in the last 3 months the pit filled with water because of the lack of a 189 l s 3 000 gpm capacity cross pit pump and the availability of a short pipeline to move water from the shovel loading area this inundation resulted in the loss of approximately 3 000 to 4 000 oz of gold contained in ore that was uncovered and awaiting haulage to the wash plant the mine lost the water battle in l

ate summer when an additional 442 l s 7 000 gpm inflow occurred through the pit wall immediately forcing the operation to abandon production efforts and to commence reclamation when considering the increasing magnitude of the water inflows over a short period the mine did an outstanding job managing the pumping problems with limited resources available it managed to mine more than 95 of the planned tonnage from the final pit even with seriously deteriorating pit water conditions specialized pit pumping problems because mines are located where economically recoverable minerals are found they are frequently in inhospitable locations with extreme climates mountainous areas have high relief topographically controlled rainfall and steep channels that cause erosive flow velocities jungles frequently add extremely high rainfall and seasonal monsoonal patterns arctic areas have extremely cold climates ice glaciation and permafrost deserts defined by low annual precipitation can be very hot sahara high altitude and cold antarctica atacama in chile or dry with most of the annual precipitation in a few intense storms arizona s sonoran desert in the united states each of these climates has unique challenges that affect the dewatering system designs arctic conditions and permafrost permafrost is the condition in the soil below the seasonal active layer where the temperature never rises above the freezing point of water this is not a problem by itself but if the soil contains moisture and fine grained soils it tends to create thick lenses of clear ice permafrost that exists in foundation areas must either be kept frozen or removed if the conditions that formed the permafrost such as ground cover and shading are changed thawing is possible fine grained soils must be removed from the foundations of the pump stations and replaced with coarser nonwicking material any source of heat such as flowing water in pipelines must be insulated to prevent thawing around the pipe if the ground thaws the bearing capacity may be lost causing collapse of the overlying structures buried pipes in frozen ground can melt an annulus around the pipe that changes the permeability of the soil in the case of an impoundment sump or artesian well this can result in uncontrolled flow outside and around the pipeline above about 60 latitude permafrost may exist in all subsurface areas unless the area has been tested and been found to be clear even in areas generally free of widespread permafrost there may be sporadic permafrost containing clear ice lenses in local areas cold climate areas without permafrost have seasonal freeze thaw cycles that occur in the active layer depending on the severity of the climate these can affect ground support stability as much as 3 m 10 ft below the surface haulage traffic can push the frost line considerably deeper than usual up to 5 m 18 ft under the roadway because of increased compaction red

uced moisture content and the complete elimination of snow or ground cover in permafrost areas most pipelines are installed aboveground in insulated utilidors for small diameter installations pumps valves and other control stations should be enclosed heated and insulated to prevent freezing steel has a much higher heat transfer rate and is usually much thinner than hdpe so the pipes will begin to form ice at the fittings and flanges quicker the pump crew should be equipped with a propane fired burner to thaw valves that have frozen in place water standing in dead zones will freeze rapidly preventing the actuation of the valves desert pumping deserts uniquely challenge pit dewatering operations in several ways extreme swings in seasonal rainfall require system designers to consider both too much and too little water water is usually but not always in short supply except when flooding occurs the sources are frequently deep wells drilled into alluvial valley deposits and may require long overland pipelines to bring the water to the mine site because the supply is usually short the systems design must avoid waste or contamination wherever possible the temperature range of deserts has extremely wide variations both seasonal and diurnal electrically operated pumps need additional care to ensure that insufficient cooling does not shorten component life evaporation and reusing water can cause undesirable concentration of contaminants it is necessary to derate the hdpe pipe working pressure for conditions above 22 8 c 73 f the working pressure ratings must be reduced 50 at 60 c 140 f pipe lying in the sun while empty or with the water not flowing can quickly reach this temperature pressure surges on start up can cause the hot pipeline to rupture anchoring pipe along narrow rights of way prevents thermal expansion cycles from expanding and deforming into sinusoidal loops snaking causing pipe encroachment onto the road deserts frequently experience large temperature swings exceeding 22 2 c 40 f daily allowing the pipe to lie in the sun with no flow to stabilize the temperature simply exacerbates thermal expansion issues alkalinity or other mineral content of the water in the sumps increases with evaporation recycling increases this effect because limited freshwater sources are available for dilution because of arid conditions to prevent processing issues the buildup of dissolved minerals must be managed bleeding a small split off the main process stream and replacing it with fresh makeup water may prevent undesirable concentration of minerals if the quality reaches unacceptable levels it may be necessary to segregate water for less critical uses for example haul road dust suppression seasonal monsoon rains can create an excess water volume that overwhelms the sump capacity storage reservoirs should be as large as practicable to capture and hold the excess runoff for use during the dry season if too much

water becomes a problem an alternative to pumping from the pit can be spraying water into the air to enhance evaporation this sometimes becomes a dilution issue with large collection areas on top of the leach dumps in solvent extraction electrowinning circuts pump selection most surface mine dewatering systems use centrifugal pumps because of their wide range of operating characteristics the required head h and flow rate q will determine the pump design scheme operating pumps in parallel allows additional flow capacity beyond what is practicable for a single pump and provides system redundancy higher head requirements than single stage pumps develop can be handled by utilizing multistage pumps driven from a single shaft or by using several single stage pumps in series extremely high head applications such as grout pumping or underground dewatering may require positive displacement pumps piston diaphragm variable cavity or gear pumps the flow pulsates because of the periodic nature of the pump mechanisms and requires dampening to prevent shock damage to system components see issue water hammer section later in this chapter systems employing positive displacement pumps require more care matching the system s power flow and pressure capacity to the required operating point and are less flexible in changing conditions than centrifugal pumps centrifugal pumps commonly available centrifugal pumps have head ranges up to about 107 m 350 ft in single stage configurations with flow rates up to 681 m3 h 3 000 gpm pumps are available that have capabilities exceeding these but are less common centrifugal pumps can be grouped into the following categories based on their configurations end suction pumps use a single open suction eye from the side of the impellor with the drive motor on the other side these are the most commonly used single stage pumps but have high net positive suction head required npshr double suction pumps use a manifold to route suction from both sides of the impeller the drive motor axis passes through both sides of the pump case and can be driven from either side these are moderate npshr pumps vertical turbines use multiple stages driven from a common shaft and generate very high discharge heads these usually mount through a horizontal deck with the motor above and require that the suction bell be submerged under the barge or in a deep well these pumps require the least npshr because the suction and the first pump stages are submerged pump curves the primary source of pump data is the manufacturer s data sheets manufacturers will usually supply a line card showing ranges of each family of pumps they offer covering a wide range of head flow requirements this is the tool most designers use for preliminary screening of the specifications to find a pump with the appropriate capacity for the application after a general pump family is selected it is time to get the detailed data specificati

ons from the manufacturer the following are some of the most important specifications that the system designer must determine from the manufacturer s pump operating characteristics curves total dynamic head tdh flow q range requirements revolutions per minute rpm motor rotational speed driver type coupling and efficiency power npshr system operating point example figure 9 5 2 is a typical system head curve system curve showing the pressure flow characteristic curve for a pumping system this system consists of a single stage pump with field variable rpm the pipeline system has both a hydrostatic head elevation lift of 52 m 170 ft and friction losses that increase as the flow rate increases a family of curves that are rpm dependent represents the pump s tdh versus flow rate q output the system curve lines represent the head and flow relationship of the pipeline valves and fittings the system curve intersects the left side of the chart where q is 0 at 52 m 170 ft total static head the pump must develop at least this amount of tdh to overcome the hydrostatic head and begin pumping water as the system curve moves right with increasing q the curve starts to rise as friction losses increase the difference between the total static head and the system curve is the energy either lost to friction in the system or used accelerating the water column in the pipe velocity head the pump system operating point is the intersection of the system curve and the pump tdh curve point a where the 1 800 rpm pump curve and the system curve intersect at 88 m 290 ft tdh pumping 170 l s 2 700 gpm this pump works at its best efficiency point bep at a q of around 177 l s 2 800 gpm ideally the designer would select a pump for the system that matches the operating point as close to the bep as possible because of internal pump dynamics the efficiency is not only a function of q but there is usually a shift in efficiencies when changing the rpm pump efficiency is overlaid on the pump curve and resembles a bull s eye with the bep in the center each pump is designed to work within a particular flow range centrifugal pumps have a limited ability to continue to pump water past designed upper limits for the pump family flow in a pump has a maximum point beyond which tdh drops off rapidly above 659 m3 h 2 900 gpm the efficiency drops and by 1 022 m3 h 4 500 gpm the pump s tdh begins to fall rapidly at zero flow the tdh rises to the maximum head that the pump can develop deadhead pressure 98 m 320 ft however the pump is doing no work so the efficiency is zero all of the input energy is wasted as heat throttling there are several ways to change the system flow to accommodate variable demand in a fixed speed system such as one driven directly by an electric motor the most common way to reduce the flow is by installing a control valve in the discharge pipe the system head curve is modified by partially clos

ing a valve shifting the operating point from a to a as the valve creates additional frictional losses and reducing the flow from 613 to 454 m3 h 2 700 to 2 000 gpm the pump is still working hard but the energy lost across the valve causes the hydraulic efficiency to drop in a variable speed system similar changes in the operating point require reducing the pump s speed from 1 800 to 1 600 rpm which would shift the pump curve this would move the operating point from point a to point b at tdh of 75 m 245 ft affinity laws manufacturers design pumps for particular operating ranges but within these ranges the curves can be shifted speed changes are practical methods for modifying the operating characteristics of pumps when the applications change in the field the effects of changing the speed ratio between the original operating point and the new pump speed n1 n2 are shown in table 9 5 1 as can be seen the flow ratio changes are linear with the speed ratio head is a squared function and power requirement increases as the cube speed ratio changes are most useful when coupled to a variable speed motor keep in mind the old rule of thumb for rotating machinery that if you double the speed the maintenance costs go up eightfold impeller sizes trimming ratios d1 d2 have the same effects as changing speed ratios but are more difficult to change after manufacturing this capability allows adjusting fixed speed pumps to match the required operating point of a long term installation without sacrificing the efficiency that a throttling valve would cause limited adjustments by reducing the impeller diameters can be done at the mine site machine shops but this requires that the pumps be disassembled increasing impellor diameters is not possible without obtaining a new impeller from the manufacturer efficiencies suffer if the impeller diameter is significantly reduced from the original diameter casada 2006 pipelines pipelines are the hydraulic analog of wires in an electrical system like the electrical system the pipelines have carrying capacity flow rate q voltage capacity pressure ratings and resistance to flow hf frictional losses practical graphical solution for rapidly designing pump locations one of the most straightforward ways to lay out a pipeline and locate booster pumps along the route is a graphical cross section this process works because all factors in the dimensional analysis of the bernoulli equation reduce to length the sum of these factors represents the total energy in the system or the hgl the topography is drawn in cross section along the actual proposed route figure 9 5 3 scaled to compare the pit surface elevations against the hgl in the pipe system when the hgl intersects the topography the system has used all of the available energy and as a result water will no longer flow by using cross sections in this manner it is readily apparent where to install booster stations along the pipeli

ne route system designs use the high pressure pipe in the bottom and lower pressure rated pipe less expensive as the elevation increases the required pressure ratings drop as the pipe elevation increases internal pressure decreases and the hf slope in the hgl flattens the first pipe connected to the discharge of pump a has the highest hgl is at the lowest elevation has the highest internal gauge pressure and thus has the thickest walls required to resist bursting the highest pressure rated pipes have the smallest inside diameters and the greatest frictional head losses hf beginning at the sump the hgl is at the water surface elevation entrance and suction side losses reduce the hgl further in the pump inlet piping npsha the pump adds energy to the system raising the hgl by the tdh of pump a continued plotting of the hgl in each pipe segment shows hf as percentage slope related to the pipe friction losses until the hgl reaches the discharge location sumps pumps and discharge locations are included along the pipeline route the point where the topography intersects the hgl is the maximum elevation that the available tdh energy from pump a can push the water the booster pump b is placed at an accessible location along the pipeline below the elevation of the hgl topography intersection the additional tdh from pump b raises the hgl sufficiently to arrive at the tank with no further booster pumps required the residual pressure in the line above the minimum necessary to reach the tank will accelerate the flow from the pipe end at the discharge the hgl consists entirely of velocity head as the pressure head drops to atmospheric and delta elevation term falls to zero after the pump locations have been determined it is possible to increase the safety factor by systematically placing the booster pumps at lower elevations than the profile indicates note that pump b is placed on a bench well below the hgl topographic intersection from pump a this accounts for future wear in the pumps and scaling or system degradation as well as for approximations in estimates of the minor head losses this method assumes that the entrance shock and fitting losses are minor compared with the elevation change in the system if this is not the case more precision should be applied to the npsha analysis of the pump inlet structures pipeline material selection selecting the appropriate pipeline materials for pumping projects involves balancing many competing characteristics the factors that determine which material is best for any given project include the following pipe material characteristics corrosion resistance electrical conductivity chemical compatibility thermal expansion cost availability lead time logistics pipe materials metal carbon steel stainless steels copper ductile iron bell and spigot corrugated steel pipe csp plastic pipes polyvinyl chloride hdpe masonry vitrified clay concrete

precast composite hdpe lined carbon steel grouted steel hdpe pipe ease of construction joining labor skills available weight ductility strength pressure ratings temperature high density polyethylene the invention of hdpe pipe is among the most influential products to appear in mining since 1960 its unmatched combination of low weight strength flexibility ease of installation and corrosion resistance revolutionized pumping processes in mining hdpe pipe has many advantages over steel pipe for use in the harsh mine environment it is much more flexible than steel allowing installation in areas where it would not be practicable to install steel pipe hdpe pipe is resilient and often more suitable in the mine pit environment than are metal or concrete alternatives occasionally heavy equipment can be driven directly over hdpe pipes although it is necessary to protect the pipe from damage with a thin layer of fine material or conveyor belting before driving the equipment across the pipe the pipeline should be depressurized to limit the transfer of hydraulic pressure to other locations in the system an hdpe pipe will crush flat and then begin to rebound immediately after the load is removed attempting this with any rigid pipe results in permanent deformation or crushing hdpe is resistant to most chemicals and is not subject to corrosion crucial characteristics when dealing with acidic or caustic leach solutions the main alternative material to hdpe for these applications is expensive stainless steels cathodic protection systems are not required for buried installations because the hdpe pipelines are nonconductive and not subject to galvanic corrosion these characteristics give hdpe pipelines a design life of 50 years service when buried the low density of hdpe makes it an ideal material to connect floating barges to the shore and its flexibility allows it to follow the barge as the water level changes hdpe is slightly less dense than water trapped air gives it enough buoyancy to float the pipe out to barge pumps hdpe pipe is the easiest material to work with in the field because of its low melting point joining hdpe requires specialized fusing machines that combine the three operations of the fusing cycle 1 milling the pipe ends 2 melting the surfaces and 3 fusing the ends together typically pipe larger than 6 in diameter arrives at the job site as a truckload of 12 2 to 15 2 m 40 to 50 ft long segments the assembly process is considerably faster than welding steel pipes semiskilled workers with field fusing machines can make three to four joints per hour because hdpe pipe is flexible and light the pipe bed preparation requires little work and small forklifts or backhoes are the largest pieces of equipment necessary to handle the pipe segments when it becomes necessary to make repairs a chain saw is usually sufficient to cut out the damaged section and replace it with a new one usin

g the fusing machine when repairs are necessary in areas that are too tight to excavate fully it is possible to slip an electrofusion coupler over the ends of the broken pipe this sleeve system allows repairs in inaccessible locations and contains its own internal heating elements a generator is connected to an electrofusion controller which melts the collar onto the pipes sealing the ends several characteristics limit the applicability of hdpe pipe in some situations hdpe is limited to moderate pressures with the upper end of its range limited to design pressures less than 2 068 kpa 300 psi for sdr 6 pipe the larger the sdr the lower the pressure rating due to thinner pipe walls common working pressure ratings range from 207 kpa 30 psi for sdr 40 pipe to 1 758 kpa 255 psi for sdr 7 3 pipe steel pipe on the other hand has thinner walls and is useful for extremely high pressures additionally the maximum depth of burial for hdpe is shallower than for that of steel the pressure ratings of hdpe pipe are temperature dependent because hdpe is a thermoplastic with a low melting point the designed pressure rating temperature is for a pipe at 23 c 73 f and has a service factor of 2 the working pressure needs to be derated 50 for pipes installed at 60 c 140 f and increased to 200 working pressure rating for installation at 4 c 40 f as the temperature of the installation diverges from 23 c 73 f the allowable pressure ratings continue to move toward both extremes ultimately the pipe becomes brittle at very cold temperatures crystallizing at about 101 c 150 f and softens and loses its strength as it approaches its melting point other pipe materials other materials have characteristics that make them the choice for some circumstances composite grouted steel pipelines combine concrete grout or other masonry material as a liner inside steel pipe these are useful in slurry pipelines tailings or culverts carrying large amount of debris where the main issue is erosion resistance galvanized csp is one of the major culvert manhole and sewer construction materials zinc galvanizing offers corrosion protection allowing longterm installations at competitive costs combining welded steel pipelines with a liner of thin hdpe has the advantages of corrosion resistance of the hdpe and the pressure ratings from the strength of the steel pipe pipe joints usually use bolted raised face steel flanges and inner smooth hdpe flanges to prevent the corrosive fluids from contacting the steel these double layer pipelines allow for integral leak detection by installing sample ports in the outside steel line anchors point loading and thrust blocks anchors need to support the weight of the pipe water and live loads developed by the flow in the pipelines these axial loads can be quite large where pipes hang from supports high on the side of pit walls the pipe walls must also be strong enough to hold these loads between a

nchor points the wall s strength determines the maximum distance between anchors pipes need support at pump stations and wherever they are attached to pumps valves or other fittings it is poor engineering practice to allow loads from the pipe s weight to transfer through the flange bolts case deformation due to external loads may reduce internal clearances causing unacceptable wear or binding in valves and pump impellers thrust blocks are designed to help pipes resist the forces developed when water flow changes direction or velocity for example the thrust from an uncontrolled fire hose nozzle calculations for the thrust block must counter the changes in the momentum of the water stream the impulse momentum changes result from the forces applied to the water and resisted by the thrust block confined stress due to temperature changes pipelines subject to changes in temperature will expand or contract proportional to the length of the pipe and the temperature change hdpe pipe is particularly problematic in this regard because it has a coefficient of expansion six times higher than steel and its flexibility makes it less able to resist bending stresses warming pipelines can deflect into sinusoidal loops snaking and this may result in them moving off the designed right of way placing piles of earth on the pipe at regular intervals called point loading serves to control the lateral movement if the temperature is high during installation shrinkage occurs as the pipe cools this can result in pulling the pipe completely out of fixed pump stations tanks or concrete anchors as an example of these issues using plexcalc ii a 41 cm 16 in diameter sdr 15 5 pipe can be installed without taking into account thermal expansion hdpe has a thermal expansion coefficient of 9 10 5 in in f performance pipe 2003 note for a 22 c 40 f temperature swing a 914 m 3 000 ft pipe changes length by 3 3 m 10 8 ft hot installation at 27 c 80 f cooling to 4 c 40 f is the short term temperature change induced by pumping cold water into an empty pipe and will result in a tensile force of 107 kn 24 000 lb force trying to pull out the fittings the change associated with cold installation at 4 c 40 f warming to 27 c 80 f will result in a compressive force of 160 kn 36 000 lb force if the pipe is constrained and must be guided at 49 m 160 ft intervals to prevent buckling field flow measurements the two necessary measurements that indicate the current operating conditions of a pump are the pressure head and the flow rate q the intersection of these two parameters defines the operating point on the pump curve many types of pressure gauges are available to obtain the head but measuring the flow is more difficult for permanent installations flow measurements use preinstalled devices in the pipeline at strategic points to monitor flow these include mechanical rotating vanes hot wire transducers differential pres

sure manometers with orifice plates ultrasonic flowmeters and numerous others the common factor is that these devices except the ultrasonic flowmeter must be inside the flow to function the ultrasonic flowmeters are portable and use transducers strapped to the outside of the pipe all of these instruments measure the flow velocity v calibrating them for measuring q requires knowledge of the inside diameter of the pipe to calculate the flow area a q va is used to calculate the flow rate pipe discharge drop method the simplest flow measurement method is the pipe discharge drop which can be used any place where the pipe protrudes from the bank and the flow discharge drops freely by gravity figure 9 5 4 this measurement method uses projectile kinematics to calculate the velocity of the discharge stream the only instrument necessary is a calibrated stick for measuring the horizontal distance x from the mouth of the pipe to the point where the stream drops a fixed distance y a folding carpenter s ruler is a perfect tool for this measurement the ruler is moved until the distance from the top of pipe to water flow at the pipe end is y x y and the flow depth are recorded as a fraction of the pipe diameter y is corrected for the wall thickness and compensated for the discharge running at less than full pipe flow to obtain the actual stream drop modeling instrumentation controls and power bearing in mind the limitations of the accuracy of the hydraulic predictions previously discussed an understanding of these highly complex systems requires simulation and modeling it can be difficult to calculate the complete state of even the simplified system used in the simplified control system example section given the construction costs tied up in systems that perform poorly simulation is essential to design an effective pit dewatering system consider the piping network flow diagram as an interconnected series of arcs and nodes analogous to electrical networks many of the computer based pipe network modeling systems force designers to break the system down into basic components and assign characteristics to each before running iterative passes until the system operating point is found dewatering systems do not operate as disconnected discrete components wood and lingireddy 2010 hydraulic networks simulations are based on the same mathematical relationships that govern electrical networks the hydraulic equivalent of kirchhoff s laws the sum of flows into and leaving any node equals zero the sum of pressure drops around any closed loop equals zero hydraulic simulations use specialized boundary nodes that have fixed pressures or act as flow sources or sinks control system components like the electrical network hydraulic networks contain other components besides pipes wires and nodes connections that transform the pressures and flows components are specialized arcs that connect one or more nodes and transform

the pressure accumulate flow or perform other specific functions table 9 5 2 shows some of the common modeling components in the hydraulic system their electrical analogs the functions they perform and the number of nodes they connect to other components because water is noncompressible under ordinary conditions communication and feedback are necessary between different parts of the network the problem is that unless water accumulation components such as tanks or reservoirs exist somewhere in the system the volume flowing into the system must be the same as that which leaves to ensure this happens without incident the components at the end must be able to communicate and control the components at the beginning of the pipeline in order for this to happen the system must contain the following components hydraulic sensors detect fluid levels pressures and the presence or absence of flow sensors detect the mode state of pumps valves control positions and system demands actuators motor controls and relays control the active components in the system communication links collect the inputs transmit them to the command and control component and send command signals to the actuators the controller the brains of the system executes command and control logic evaluates inputs and sends appropriate commands to the actuators over established communications links simplified control system example complex control relationships can be derived from the simplified network shown in figure 9 5 3 which contains a pump drawing water from a sump and pumping it uphill through a second pump to a tank for the following description it can be assumed that pipeline from pump a discharges directly into a tank feeding pump station b hydraulic sensors are necessary to measure the state of the hydraulic network and should be able to detect if the sump contains enough water to prime the pump fill the pipe and deliver sufficient water to the tank the system should have a sensor to detect if the tank needs water or if it is too full and therefore about to overflow when pumping flow sensors would tell the controller if flow exists downstream from the pumps in order to avoid damage in the simplified system only one actuator is necessary to turn on each pump the mode sensor to supply the feedback that this has occurred could come from an additional set of contacts to supply the binary state of the starter to the controller as an input on or off communication links carry the inputs from the sensors and outputs from the controller the controller is physically connected to these links and to the distant sensors and actuators through wires running to the controller other options require that radio links wireless computer networks or other telemetry hardware carry the signals these have the advantage of not requiring physical cables although they increase the complexity and potentially the cost of the communications netw

ork the command and control system controller is the intelligence behind the pumping system the controller takes the inputs from the hydraulic and state sensors and the feedback from the actuators and applies the preprogrammed control scheme to create the appropriate action commands to the actuators a controller can be as simple as a manual switch operated by an employee when activated it sends power to the motor and an indicator light showing the pump status remote operations controllers rocs allow the system controller to be located almost anywhere as long as the radio communication link is reliable rocs sometimes supply both the programmable controller and the radio hardware in the same box simplifying system design most of the modern controllers use some type of a programmable computer based system programmable logic controller plc systems are the most commonly used type of industrial controller programmers program a plc using a simplified language called ladder logic that uses simple constructs to simulate signals that enable contacts timers and sequences to create the appropriate output for each system operation systems that are more complex run on larger computers incorporating powerful programming languages that can create internal simulation models capable of controlling entire water handling networks with many components and interrelationships when the pump network has more than one stage in a series it becomes necessary to interlock the pump stations and holding tanks intermediate tanks receiving water from below and supplying water to a local pump pushing up to the next stage must balance the flows to avoid overflowing the system normally tanks in this sort of configuration use three level sensors to feed information to the controller about the tank level state 1 high tank level sensor shuts down the lower stage pump the tank is full 2 low tank level sensor shuts down the next stage pump the tank is empty 3 mid tank level sensor starts the next stage pump in the series when the tank has enough water to pump without quick cycling this allows both stages to pump simultaneously for part of the cycle improving the system s efficiency pump station designs design of pump stations must balance a number of competing constraints in the pumping system especially the availability of electric power the design life of the pump station at a particular location will determine the effort that goes into its layout and construction the access quality and space availability for the station may also limit the selection deciding on the type of motor to drive the pump is among the primary design constraints selecting the appropriate drive system depends on several competing characteristics under normal circumstances diesel is generally the more expensive power source than electricity however at remote sites whereutility company electric power is not available it may be less expensive to run the pumps from die

sel engines than to use the same fuel to generate electricity for electric driven pumps diesel driven pumps diesel driven pumps are convenient to use for self contained trailer mounted pumps that operators can deploy quickly this makes diesel pumps the choice for pumping water out of the shovel loading faces or other in pit situations where the sump must move every time the pit advances the most effective pit dewatering crews have a number of these pumps covering a wide performance range the variable speed operation inherent in the design of the diesel power plants allows considerable flexibility in the varying performance of the head and flow rates at the operating point of the attached pump the main disadvantage of diesel engines is that they require operator access for daily fueling and engine servicing this requires maintaining an access road capable of carrying fuel trucks to the pump station as well as a turnaround area the energy conversion efficiency of the best diesel engines falls far short of comparable electric drives high efficiency low speed diesel engines have thermal conversion efficiencies of more than 50 compared with electric motor efficiencies in the mid to upper 90 range when using diesel engines automation is not as viable as when using electric motors some diesel engines can operate remotely with sensors controlling the starting and stopping but these features do not account for the fine tuning that diesel starting and shutdown procedures usually require the engine speed must usually be set manually although pneumatic dashpot controls may allow automatic operation requiring a complex feedback system if the operating point is not constant electrical motor driven pumps one of the most critical parameters that determines pump performance is the rotational speed at which the pump operates as discussed in the affinity laws section changes in the pump s discharge head are proportional to the speed ratio squared maintenance costs for rotating machinery are proportional to the speed ratio cubed doubling the speed raises the maintenance costs eightfold the lowest rpm that meets the required operating point is the most reliable low speed pumps usually cost more and are proportionally heavier than the higher speed pumps to achieve the same performance so the initial costs versus operating costs need to account for these factors motors for common pumping applications are usually three phase induction motors with power ratings ranging from 4 to 224 kw 5 to 300 hp the rotational direction of the motors must match the designed rotation because centrifugal pumps can only run in one direction when using a threephase powered system reversing any two phases to the motor changes the motor s rotation direction the number of poles p in the stator windings and power line frequency f determine the motor s synchronous speed synchronous speed 120 f p 9 5 10 induction motors produce torque at any speed less

than synchronous so the motor s armature runs slower synchronous motor rpm ratings appear odd because of the armature lag for example a four pole motor whose synchronous speed is 1 800 rpm may run at 1 750 rpm in synchronous motors the more the motor speed lags behind the synchronous rate the more current it consumes and the more torque it produces this effect is highest during startup when the motor s current can be up to 10 times larger than the normal running current starting requires special attention in order to prevent excessive current causing undesirable voltage fluctuations in the incoming power grid soft start motor controllers are necessary on the larger motors particularly if the installation is at the end of a long power line soft starters can also control the system s ramp up speed thereby effectively acting to control the dynamic shock effects to the system see the issue water hammer section electric driven pumps are more suited for fixed installations that move infrequently such as booster stations or floating barges the selection of the electric pump operating point requires more engineering than does the variable speed diesel driven pump the highest efficiency installations couple the pump directly to its drive motor so the electric motor s speed must match the pump at the desired operating point field speed adjustments are limited to changing drive pulley ratios if the pump is belt driven otherwise adjustments to the pump operating point involve throttling valves in the discharge pipe network with a commensurate loss of efficiency ratios not obtainable by changing the number of poles are possible by using belt or geared drive systems if variable speeds are necessary variable frequency drives vfds can be economic for smaller pumps up to about 56 kw 75 hp vfds change motor drive speeds by electronically converting the line power frequency supplied to the motor thus making a wide range of output speeds possible however this comes at a significant cost both in acquisition and efficiency automatic operation is easy to design into these pumps because numerous types of level switches or instruments for switching electric signals are available start up against an empty pipeline may present problems keeping the pump on the curve because there is little backpressure until the water rises enough to prevent cavitation a damaging condition caused when internal pressure falls below the vaporization point of the fluid see the issue cavitation section vfd motor controllers are available that can control the start up speed profile gradually increasing the pump output pressure as the pipeline fills pump stations with electric drives do not have to maintain regular access for daily operations which makes electric pumps suitable for installation in difficult terrain and confined areas the major constraint is that power lines or flexible trailing cables have to be run to the pump s location from

the motor control panel the starter panels and other controls must be located where operators have access but these can be some distance from the pump booster stations pumps capable of handling large variations in the suction lifts are well suited for pumping from sumps but often do not have high head discharge pressures this is where the pump system frequently combines booster pumps in a series with sump pumps fully utilizing the best characteristics of both fixed booster pumps maintain constant discharge heads because the hydrostatic lift to the discharge location does not change fixed boosters stations may be in line or tank fed with level controls that cycle the pumps to match inflows tank fed booster pumps are normally designed to maintain the water level above the suction eye of the pump ensuring a positive suction head floating barges the decision to use a floating barge system is usually a good fit when pumping the water from a long term sump with fluctuating levels due to irregular or seasonal inflows water elevation changes result in changing pump static lift conditions that can affect the pump capacity this can happen in very deep ponds where the surface elevation drops significantly during the life of the system to the point where the static head exceeds the dynamic head capacity of the pump booster stations may be required but can be added later if the barge pump s initial capacity is adequate when properly designed barge pump installations do not suffer from suction head issues npsha because the pumps maintain a fixed distance between the pump inlet and the water surface this is a dramatic improvement over trailermounted pumps that have to be moved down the ramp each time the water surface drops by between 3 and 4 6 m 10 and 15 ft increasing sump levels float the barge whereas the trailer pump would risk inundation barge pumps are much less labor intensive to operate but their installation and maintenance costs are likely to be higher minimum water depth must be maintained in the sump to account for the pump and barge draft requirements to avoid grounding the pump or sucking debris and rocks into the system minimum clearance must be maintained between the suction inlet and the sump bottom the suction line must be located deep enough to avoid the formation of vortices that suck air into the inlet screen or pipe this is detrimental to performance and can cause the pump to lose prime in horizontal centrifugal pumps the flexible suction lines must be weighted to prevent the screen from floating too close to the surface but they must also be supported to keep it out of the bottom sediments bottom clearance issues can be a problem with vertical turbine style pumps because the intake depth is fixed by the design distance between the pump intake and the barge deck this style of pump is more likely to ingest debris if the sump s water depth drops to the minimum necessary to float the barge with proper bar

ge design the pump intake can be kept at a safe distance from the bottom by keeping the pump intake pipe shorter than the bottom supports of the barge thereby leaving sufficient clearance the use of a vortex prevention collar around the suction intake can allow the suction to be closer to the surface than the flow would otherwise allow this collar is essentially a fin that prevents the streamlines that are approaching the suction line from rotating the depth required above the suction hose to prevent the formations of vortices is dependent on the pumping rate mcnally n d ssue air locking pipelines air in the pipeline can consume all available pump energy trying to push the air against the hydrostatic lift an example is the force needed to push a balloon down to the bottom of a swimming pool the air s buoyancy resists the flow in the pipe when flowing water tries to push the entrained air bubbles down from a local topographic high to a lower elevation under less extreme air conditions the fluid in the pipe can flow under a relatively stable air pocket even in the flat lying areas of the pipe air bubbles restrict the cross sectional area increasing the flow velocity and friction losses in the pipe eliminating air from all overland pipelines prevents loss of pumping efficiency turbulence increases the friction losses and gas compressibility robs the system of energy converting it to heat air release vacuum breaker combination valves should be used at all significant topographic high points on the pipeline profile these valves are usually large ball check valves with a floating ball and must be installed vertically air release function allows the air bubbles out of the pipe where they naturally accumulate the ball falls from the seat while air is present allowing the trapped air to escape from the pipeline when the water rises into the valve body the ball moves up into the seat to seal the valve if the flow conditions drop the internal gauge pressure into vacuum the ball check falls back allowing air into the pipe and preventing suction collapse this is necessary to prevent vacuum conditions where the flow is intermittent or where the pipeline profile significantly declines in elevation particularly when using hdpe or other flexible pipelines pumping over a ridge frequently results in the hydraulic flow regime changing from pressurized flow hazen williams equation to open channel flow in a partly filled pipe manning s equation the pipeline flows with the pipe full until reaching the maximum elevation of the section depending on the flow rate either the pipeline will develop a steady open channel flow or will begin cycling the trapped air bubble as previously described an air release vacuum breaker valve will allow air into the pipe thus smoothing the flow and should create a stable open channel flow the pipeline may convert back to full pipe pressure flow near the bottom of the hill computations of the

parameters in this sort of mixed flow regime are complex it is usually sufficient to be aware of the potential issues when evaluating a pipeline in rolling topography issue cavitation cavitation occurs wherever the local flow conditions reduce the absolute pressure below the fluid s vapor pressure rapidly moving water creates low pressure areas particularly when passing through structures that result in flow area reduction resulting in formation of bubbles velocity increases at flow control valves restrictions in the cross sectional area or around the ends of rapidly moving components as they reduce the pressure causing the fluid to begin vaporizing the bubbles themselves are not damaging but after the restriction the fluid slows and the pressure rises above the vapor pressure this causes the bubbles to collapse suddenly resulting in localized shock waves and pitting cavitation occurs most frequently at the suction eye of the pump impeller behind the impeller tip and on the downstream side of valves where this collapse zone exists it occurs on pumps when npsha is less than npshr due to the design of the inlet piping failing to maintain a proper positive suction head fittings and elbows too close to the pump inlet can cause the restrictions and turbulence leading to excessive friction losses cavitating pumps frequently sound as if they are pumping gravel even though no sediment is present in the fluid issue priming priming the pump is the operation that removes the air from the pump body and fills it with fluid centrifugal pumps cannot handle much air in the pump chamber below 0 5 is usually acceptable but above 6 by volume the pump s capacity is seriously degraded removing air from the pump chamber is necessary to allow positive suction lift to develop selfpriming pumps usually have a vacuum pump to remove air from the pump case allowing external atmospheric pressure to push the fluid into the intake foot valves check valves at the end of the suction pipe hold the prime by keeping water from draining back into the sump when the pump is turned off issue insufficient suction head many pumping problems occur when the pump is located too far above the water surface of the feed source the elevation difference between the suction eye of the pump and the water surface varies as the sump level changes the pressure of the fluid must be higher than the vapor pressure at the suction eye of the pump at the operating temperature or cavitation can result methods to solve problems on the suction side of the pump include the following lowering the pump closer to the water surface of the sump reducing the static lift ensuring that the pipe is clear and the suction screen is not blocked reducing the length of the suction hose and increasing the diameter of the suction piping both of which reduce friction losses in the intake piping ensuring that the suction side fittings are not leaking air ingestion can bre

ak the priming ensuring that the pump is not cavitating cavitation can have the same effects as air ingestion limiting the pump efficiency ensuring that the foot valve is holding to maintain prime po z figure 9 5 5 simplified net positive suction head dewatering surface operations 761 reducing the number of fittings and keeping them as far from the pump as practicable to limit the friction losses in the suction line ensuring that the pump is operating near the bep splitting the load by using several smaller pumps in parallel instead of a single large pump issue minimum flow centrifugal pumps must have sufficient fluid flow to avoid overheating pumps convert the mechanical energy from the drive shaft into various forms including hydrostatic pressure head fluid kinetic energy velocity head and heat friction losses fluid flowing through the pump carries the heat from the mechanical and hydraulic losses in the system if the system is prevented from flowing by closed valves insufficient suction head or insufficient discharge head pressure to overcome the system s static head most of these losses are converted into heat eventually causing the water inside the pump casing to boil explosions are possible if the pressure due to vapor expansion exceeds the maximum casing pressure rating significant damage will occur to the pump impeller from cavitation at temperatures well below the normal boiling point as the temperature increases the vapor pressure of the fluid increases resulting in more cavitation this has the same effect of operating the pump with insufficient npsh by increasing the necessary static pressure required to prevent vaporization issue sediment debris and screens the primary source of debris entering the pumping system is through inadequately maintained intake piping the first line of defense is to install an appropriate screen over the suction pipe to prevent large solids from entering the pump suction the suction hose should be kept above the sump bottom to prevent the flow from sucking debris onto the screen during construction pipe segments must be inspected and cleaned before they are joined when dragging pipes into place the ends act as a scoop and can pick up a surprising amount of rocks and debris which require flushing before closing the section large rocks will migrate along the flow and jam against valves preventing them from properly actuating pipe that has been stored outside should be inspected prior to construction for animals that have moved in in line screens traps or cleanout fittings should be installed periodically in the pipe and located to protect valves pumps regulators or other sensitive fittings drains and cleanout fittings should be placed where the discharge during cleaning does not cause damage when the pipeline runs through hilly country it is important to ensure that the pipeline has sufficient drain valves installed at logical topographic l

ow points to allow flushing of the system this allows removal of sediment buildup in pipe systems before blockages occur and is particularly necessary if the pump system handles turbid runoff or slurry because the solids will pass through the normal intake screen but may settle in the pipe issue pressure bleed through check valves in a high lift multistage system pressure can bleed through check valves causing excessive hydrostatic pressure in the lower stages and resulting in pipeline ruptures when the pump system starts systems can experience problems with pipe segments splitting in the bottom stage of a series of pumps because of starting pumps against excessive hydrostatic head this can be a problem when using pumps in a series without an atmospheric pressure break between stages check valves are designed to allow flow in only one direction when holding pressure against the upstream face the valve closes preventing backflow and holding the differential pressure across the valve pitted faces or improperly sealed valves allow small water seeps that can equalize pressure on both sides because water is incompressible this can happen with little seepage volume over time in systems that have almost no trapped air the lower stages of the pipeline are the most likely to experience pipe rupture because the pressure cascades through multiple stages above the dynamic head from starting the lower pump is added to an already overpressurized pipe segment indications of this problem show up in hdpe pipe sections that have been repaired numerous times the solution is to design multistage pumping systems with transfer tanks between the stages at atmospheric pressure more area is necessary for the pump stations and the system will be less efficient but the starting sequence and dynamic interactions are easier to control an alternative would be to install accumulator tanks to allow expansion against a compressible air bladder costs due to the cost of designing and building pit dewatering systems efforts to keep water outside the pit are usually a good investment intercepting and diverting water at the pit rim is less expensive than pumping from the bottom of the pit the direct pumping costs include power infrastructure and required space designated for the pump stations and pipeline rights of way pit water may also require treatment before discharging off site indirect costs can be significantly higher because of the effects that water has on productivity reducing highwall stability and safety hazards that the operation must mitigate direct cost example of hauling wet ore increasing moisture content increases the density of the material adding to the costs of haulage and conveying if the dewatering crew can lower the moisture content of the ore from 4 to 2 by improving water control at the shovelloading face a mine processing 89 290 t 100 000 st per day saves 1 786 t 2 000 st of excess water previously hauled to the cr

usher daily this is the equivalent of pumping 21 l s 333 gpm of water out of the pit using the most inefficient of pumping systems the haul truck if haulage costs 0 75 t on an annualized basis this reduces annual operating costs by 548 000 the inflow of water can affect the cost and progress of underground mining limiting the mining methods used and presenting hazards mine dewatering has effects both on the groundwater table which is usually a shared resource and on the environment receiving any discharge although many mines have been worked successfully beneath perched underground reservoirs streams lakes rivers and seas there are also many examples of catastrophic inrushes experts such as hydrogeologists hydrologists and pumping engineers can contribute to the success of mining projects and should be consulted when appropriate the general objective in the control of water in underground mining is to permit safe efficient work with acceptable consequences the most common method of control is pumping where an impervious cover above a mineral deposit can be maintained it may not be necessary to draw down the groundwater aquifer provided accesses including shafts can be developed by grouting ground freezing or casing many salt potash and coal mines are of this type pregrouting with cement slurries can reduce the hazards of serious water inrushes and minimize delays during shaft boring or sinking whereas cover grouting using chemical grouts can reduce inflows to underground development as part of any mine plan an overall water balance is essential to ensure that enough water is available and that surplus water is managed and disposed of in an acceptable manner sources of water the main sources of water encountered in underground mining are inflows of surface water through natural geological conduits mine openings and boreholes inflows of groundwater through the natural permeability of the rock and from secondary fracture permeability mine service water such as water used for drilling and dust control sprays and drainage from hydraulic backfill although prediction of the volume of mine service water is straightforward the magnitude of natural inflows sometimes can be difficult or impossible to predict until mining takes place nevertheless experienced engineers geologists and hydrologists are able to make satisfactory predictions in many cases so that appropriate control measures can be put in place sudden inrushes of water or mud can arise from heavy rainfall events via mine openings or surface subsidence and caving zones unplanned connections to the sea lakes rivers swamps clay deposits wet cover tailings dams and water dams connections to water pockets such as caverns in carbonate rocks and fault conduits magmatic water if mining near a volcanic caldera and connections to adjacent flooded mines impact of water on operations the presence of water in underground

mines impacts virtually all operations and activities its main beneficial effect is in the control of dust in drilling and during rock transportation it also serves as a transport medium for hydraulically placed backfills and sometimes as at the mcarthur river uranium mine in saskatchewan canada as a medium for transporting ore the negative effects of water include the following increased heat transfer from the rock in hot mines freezing in very cold mines increased humidity causing less comfortable working conditions and reduced labor productivity reduced ground stability due to water pressure corrosion of plant equipment and ground support elements requirement for more expensive explosives spillage from trucks and conveyors water and mud rushes from orepasses and other sources erosion of roadways particularly ramps the need for special precautions for mining in the presence of water under pressure increased power consumption for pumping and ventilation all of these impacts add to the cost of mining and in extreme cases may be the difference between profit and loss predicting water inflows prediction of water inflows requires an understanding of the climatic and hydrogeological factors plus any existing humancaused conditions such as abandoned boreholes and nearby flooded mines and the effects of planned mining work many sites present no significant water problem but this should never be assumed it is difficult to predict groundwater flows into underground mines as they are dominated by structural controls that usually cannot be identified from exploration drilling hydrogeologists have access to sophisticated numerical modeling tools but experience shows that these models often fail to accurately predict inflows to an underground mine because of the lack of data particularly in the early stages of a project to maximize the reliability of predictions data should be collected at all stages of a project or mine development each mine should have an efficient data management system which covers the collection storage and distribution of the data to the relevant people the data to be collected at each stage of a project or mine should be determined by a group of competent persons prior to work commencing for example the following is a checklist for the collection of information required for the prefeasibility stage of a mine project topographical information rainfall quantity and intensity data river flow and flood level history tidal levels and flows earthquake frequency and strengths climatic conditions including temperature humidity and evaporation rates surface water runoff characteristics groundwater characteristics including levels salinity temperature recharge discharge and general flow directions hydrogeological conditions including geological units and their permeabilities and storage and general geological features faults information on soil and rock types

their characteristics depth of weathering and so forth for design typically a 1 in 100 year event is considered reasonable assuming such records exist for the location but the expected life of the operation needs to be taken into consideration a short duration mine is less likely to receive such an event than one that has operated for decades but many mines have much longer lives than initially expected the decision should be based on a risk assessment and a realistic consideration of the consequences of the scenario selected the runoff coefficient must be selected carefully because high intensity events are more likely to occur when the ground is already wet from normal precipitation thus initial abstraction is small there is also a trade off between storage capacity and pumping rate once the inflow volume of the worst case scenario has been estimated the option exists to divert the inflow to available storage and pump it out slowly after the event or to cope by matching the pumping rate to the expected inflow rate the best option is usually somewhere between these two extremes of course storage capacity must be empty if it is to be relied on in an emergency hydrological studies and modeling hydrogeologists petroleum engineers and civil engineers all start with darcy s 1856 observation that velocity of laminar fluid flow through sand is directly proportional to the permeability of the medium and the hydraulic gradient hydrogeologists find pumping tests useful in predicting the performance of water wells petroleum reservoir engineers test within much deeper wells and on cores taken from them to forecast production of oil and gas civil engineers concentrate on soil moisture and the effects of pore pressure on stability efforts to calculate flow to tunnels shafts and underground mines are made difficult by complex geology and lack of data in simplest form the water table below which the ground is saturated is nearly a horizontal plane in a succession of layers of diverse permeability there may be multiple water levels artesian water is trapped under a layer of comparatively low permeability so that water rises above the ground surface where permeability is irregular or discontinuous the water level is similarly erratic where water feeds into the ground the water table is higher and groundwater flows from such points to lower points of discharge the slope of most natural water tables is gentle which usually mimics land surface and the motion of flow is slow the water table or piezometric surface is depressed by pumping a well the resulting gradient causes flow toward the well the simplest analysis such as the theis solution theis 1935 is based on an ideal aquifer homogeneous isotropic and horizontally infinite and a perfect well which is open to the full thickness of the aquifer or is very long compared to its diameter and thus receives water by horizontal flow the depression is an inverted con

e symmetrical around the well its slope decreases logarithmically to the radius of effect where the depression is not measurable if permeability is not uniform the cone is distorted where water is only in fractures it is discontinuous as a well is pumped the drawdown increases until the well is dewatered or until because of the steepening gradient the rate of inflow balances the pumping and flow becomes steady figure 9 6 1 as the cone expands its shape may be changed by masses of higher or lower permeability or by recharge or barrier schematic profiles in figure 9 6 2a show the extreme effect of a barrier surrounding a shaft being deepened those in figure 9 6 2b show the effect of an irreducible recharge e g on a shaft being sunk in the center of an island the cone around such a shaft expands normally in stages 1 and 2 but its shape is changed by a barrier or continuing recharge the void space within a soil or rock is referred to as its porosity the amount of water that can be stored within the porosity and subsequently released is referred to as effective porosity or sometimes coefficient of storage the total porosity of shales and clays is very high generally greater than 25 and in some cases 50 but the water is absorbed in the crystal structure and cannot be removed easily whereas the intergranular spaces are typically so small that movement of water under usual conditions is negligible unless huge areas are considered most of the porosity of coarse sandstones is effective as storage close spaced open fracturing can give dense rock important storage capacity but it is rare solution cavities can provide storage in otherwise dense limestone and dolomite some lava contains ash erosion surfaces and tubes with high permeability and more or less storage weathered surfaces of most strong rocks are likely to carry water induration hardening closes pores and fractures the amount of water that can actually flow through and from the rock mass and into the mine depends on the permeability of the rock mass and more importantly the presence and permeability of flow paths such as faults shears and bedding plane breaks these are generally not measureable before mining hence the limited value of modeling pumping tests can sometimes yield limited guidance pumping tests are made by pumping water from a well at a sufficient rate long enough to lower the water level measurably in several observation wells which should be at prescribed locations with respect to the pumped well the pumped well should penetrate the entire aquifer and in usual tests receive water freely from all of it in thick aquifers this may not be possible but useful conductivity data could still be obtained the time and cost of pumping tests generally limit the number that can be made on a project hence it is difficult or impossible to determine properties of more than one part of a complex rock mass indicate uniformity of any part of t

he mass or establish averages that can be used with confidence where these points can be determined in other ways and where the test can be set up to provide the information needed there is no better source of data pressure tests with packers are water injection tests in some ways the reverse of pumping tests but they can be made in holes of usual diamond drilling size and the packers can be set to test any interval of open hole and can be reset repeatedly figure 9 6 3 generally the water pressure at the section under test can be between 1 1 and 2 5 the hydrostatic head without danger of opening fractures where permeability is high there is an advantage in testing at a low pressure difference to limit pipe friction and the likelihood of turbulence where it is low a higher pressure difference provides a measurable inflow more quickly packers may fail to seat where erosion of weak rock has enlarged the hole and water can leak around them through fractures or connected pores such leakage can be reduced by using long packers by making successive tests below a single packer near the bottom of the hole as it is deepened and by testing below double packers a series of tests can be checked by a single test of the same section of the hole leakage around packers or through pipe joints leads to overestimating inflow however any mud or grease caked on the walls of the hole would have the opposite effect borehole flowmeter surveys may be used to measure water flow patterns within a well the flow log reveals zones of water entry and exit and allows flow contributions from individual zones to be measured spinner flowmeter logs are used during well pump tests to measure hydraulic conductivity with very low flow rates the spinner flowmeter may be insufficiently sensitive the heat pulse flowmeter may be used in a stationary mode at selected depths to detect linear flows down to 1 mm s holes can be cleaned by swabbing i e pumping by repeatedly lifting a column of water above plastic cups on a wire line inside a string of casing or tubing which may extend 100 m or more below the water level in the hole measurement of the rate of water level recovery after swabbing is a negativepressure test the swab can be run inside tubing on which packers are set to determine inflow from the interval between them and to sample the inflow a series of tests between packers efficiently expanded and contracted from the surface can be made at the rate of one to three tests per hour packer tests take time for lowering and recovering the packers and setting up for each test drill stem tests are made with a special tool lowered into the hole on a string of drill pipe above the tool is a packer which can be expanded to close off the bottom of the hole the tool can be placed between two packers to test the section enclosed a pressure transducer and data logger can record the pressure increase as the tool is lowered the shut in pressure in the test

section pressure changes during the test and pressure decrease as the tool is being removed to start the test a valve is opened permitting fluid to flow from the ground through the tool into the empty pipe and a sample is recovered potential production can be calculated from the rate of flow and the recorded bottom hole pressures each normal drill stem test calls for a trip into and out of the hole with a string of tight pipe use of tracers tracers are put into a groundwater system at some point and used to indicate the direction of water movement and in some cases its approximate rate by being recognized at a point or points downstream none of the many tracers is ideal under all conditions a tracer should be recognizable after dilution generally with portable equipment in some cases in test holes be unimpaired by physical chemical or bacteriological reaction and adsorption with the water being tested or rock in contact with it at least until recognized move with the water be convenient to use reasonably available at moderate or low cost easily soluble in water and require no elaborate equipment or procedure and present no environmental hazard or cause anxiety to anyone fluorescein an extraordinarily intense coal tar dye usually is purchased as a red orange powder when dissolved in water it is a brilliant green one part in 40 million ordinarily is recognized by sight one part of good quality fluorescein in 5 to 10 billion parts of clear water can be recognized in a colorless tube about 1 cm or less in diameter by 1 m long with a black rubber stopper or other black bottom a number of tubes can be mounted side by side in a rack examination should be made by good white light in front of a white reflecting surface tubes containing 0 to 0 002 ppm of fluorescein can be used comparatively fluorescein is not affected by carbonic acid but is made colorless by contact with peat acetic acid and mineral acids it is unaffected even by long contact with limestone sand silt montmorillonite and other common clays its vivid color gives fluorescein a special advantage where it is desired to make results evident to all observers other dyes fast crimson congo red methylene blue and so forth may be used similarly chloride ion or salt is recognized in test holes by decreased resistance to electric current or chemically providing dilution is not too great dense solution may be trapped in low spots otherwise salt solution seems to move at the same rate as the water it is obscured by any natural brine and changes the permeability of some clays bromide nitrates and other ions are also used dextrose recognized chemically is not adsorbed and moves at the same rate as water but is attacked by soil bacteria and is more easily lost in dilution than radioactive isotopes radioactive isotopes are said to be recognizable in concentrations of 10 18 but are generally precluded because of public sensitivity to t

heir use the normal application is to place the tracer in a possible water source and watch for it to appear in the mine for example a tracer may be added to mine water discharge to show whether it is returning into the mine this may be impossible if the suspected source is a very large body of water if the mine is flooded the tracer could be put in the mine and water pumped behind it to cause the tracer to be observed at the surface although the results could be inconclusive control and collection of water planning for the control and collection of water must consider all possible sources under normal conditions as well as the possibility of extreme events control of surface water the following measures can contribute to management of inflows to an underground mine shaft collars and ramp portals can be built on elevated ground or surrounded by earth or rock bunds bunds should have a uniform level with no low points that could lead to failure where a portal is built within an open pit it should be elevated above the floor of the pit surface earthworks should not unintentionally impede or divert natural stream and sheet flows shafts should be pregrouted and imperviously lined rivers can be diverted lakes and swamps drained and streams cleared and straightened to reduce direct inflow and recharge intakes including stream beds can be covered with rolled clay or concrete water can be intercepted in shallow wells or caught in water rings in shafts slopes should be cleared and drains built trees should be planted in low flat areas to increase evapotranspiration the mine should have a procedure that will be followed to manage the effects of extreme weather events for example with normal rain work should be continued but awareness maintained if cyclonic rains are in the area the situation should be monitored continuously on weather radar and crews withdrawn from high risk areas if there is flooding potential work should be stopped all crews withdrawn and the situation monitored until danger has passed management of drilling in a situation that could pose a threat to future mining operations e g holes from a dry lake bed or frozen lake all drill holes should be fully or partially grouted during exploration hydrogeology data should be recorded for future planning needs when working underground in areas suspected of containing high pressure underground water the hole should be drilled using appropriate equipment and procedures exploration drill holes must be cemented in some areas to prevent migration of water from different aquifers if the hole is left unsupported any soil or weak rock soon caves partly plugging the hole and hiding it after which treatment from the surface can be difficult if an underground working is connected to a hole to which water has access it may enter perhaps with gas at such volume and pressure that sealing from below is difficult the practice at one salt min

e is to leave a 45 000 t pillar centered on the mapped location of each hole the capacity of high pressure water to ravel weak rock and if it carries grit to erode strong rock and metal must not be overlooked an extreme example of the problem was the inundation and loss of the diamond crystal salt mine at lake peigneur in louisiana united states in 1980 when an exploration drill hole broke into the workings even without being connected to workings wet holes can decrease stability by permitting water to saturate and weaken clay shales and raise pore pressure some holes if kept open could be used for observation of water levels treatment geological testing telephone or electric lines driving raises and so forth exploration holes generally should be plugged securely before abandonment or if needed for communication or observation pipe or casing should be set through all weak or wet ground prevention of inrushes a risk assessment is required to identify the necessary precautions to manage potential sources of inrush prior to mining beneath surface water near underground water sources or old workings water should be drained or pumped to below the current working level if this is not practical a minimum safe approach distance should be determined and maintained the maximum flood levels should be determined for all mining areas access to an underground working should be constructed above the expected maximum manageable flood level in that area in flat land sheet flooding to a depth of only 100 200 mm can rapidly erode a channel into an underground mine and flood it surface water should not be allowed to pond or accumulate near mines and should be drained or pumped away where this is not possible adequately designed and constructed bunding must be in place and the freeboard monitored the migration of water under the bund should also be monitored no structures dams tailings dams storage facilities mine infrastructure roads or rock dumps should be built over the footprint of any underground workings if any potential exists for caving to the surface adequate crown and shaft pillars should be provided and monitored notably rock dumps can be a significant water source for deep infiltration underground dams water storage facilities slimes dams or any other storage facility that might be damaged and cause an inrush should be properly designed and located so they are not influenced by mining induced ground movement where mining activity is close to the base of oxidation or the surface the area should be fenced or barricaded and bunded allowance should be made for the angle of repose of the possible breakthrough area if tailings or surface water storage facilities overlie an underground mine a risk minimization program should emphasize water diversion groundwater drainage and sound slope stability practice monitoring should include checking the stability of structures on a regular basis maintaining adequate

storm freeboard and having diversion structures to deal with an overflow tailings should not be used to fill surface subsidence above working mines because of the potential for liquefaction and inrush through a relatively small subsidence opening this was the cause of the 1970 inrush at mufulira mine in zambia which caused the death of 89 miners backfilling backfill is used with many mining methods and may be used to reduce the risk of subsidence and some forms of inrushes planning should ensure that stope voids are sufficiently filled so that caving is minimized controls are in place to prevent the fill material from liquefying during placement or remobilizing due to subsequent water inflows and ground vibration fill strength is adequate to ensure stability during adjacent mining or pillar extraction fill should be drained so that it cannot remobilize and filling schedule limits the accumulated void space in the mine design of backfill may include tests for particle size water retention characteristics field capacity volume abrasiveness transportation systems fluidity the possibility of liquefaction and the need for additives such as fly ash cement and gypsum during hydraulic filling of voids monitoring should include pressures behind the barricades bulkheads ponding on the fill surface the barricade bulkhead integrity and drainage rates and vertical filling rate draining underground water in some cases making initial openings in tight ground to drain conduits or masses of wet rock has advantages but the procedure may be complicated by one or more of the following conditions high pressure water hot water or dissolved gas weak ground unstable in contact with water flowing under high pressure mud and grit causing or increasing erosion uncertain location of wet ground or conduits uncertain rate of inflow to indicate the water s location pressure and perhaps something of the rate of flow pilot holes usually are drilled ahead of development openings cover drilling which is drilling in advance and to the sides of the heading with multiple holes may be necessary for safety tapping can be accomplished by developing an opening into the water source where water occurs in small conduits in a rock strong enough to resist erosion the heading can be continued until the desired inflow is obtained if water is carried by a well defined clean conduit this may still be a good approach but drilling and blasting the last round is tricky and unless a pressure door has been built only friction in the conduit and in the heading restrain the inflow with more time and cost tapping can be controlled by driving to a safe distance from the wet ground cutting a drill station and drilling many radiating holes the safe approach distance depends on the geology water pressure and knowledge of location where high pressure is expected and especially where it could erode the collars of the holes work mus

t be protected by drilling an oversize collar hole and cementing a collar pipe with a bypass tee and a full opening valve drilling is completed through this valve water is drawn from many points throughout a sizable rock mass which may be important to minimize erosion because these holes are short head losses of 10 to 40 m per 100 m may be acceptable in this range each 50 mm diameter hole may produce 4 to 8 l s and each 75 mm diameter hole 12 to 24 l s it may be worthwhile to utilize the pressure of tapped water to reduce the pump head this can be done by piping water under pressure directly or through a settling tank or kettle to the pump suctions if the concentration of sand and solids in the water is significant then effective settling and regular cleaning of the pressurized settling tank can be a problem grouting grouting may be used to reduce the water flow into workings but flow reduction is usually accompanied by a pressure buildup behind the grout which can be dangerous in drive and tunnel construction it is good practice to grout and then drill release holes after tunneling passes the area arranging for the water to be drained toward sumps grouting can be used to control water in shaft sinking and tunneling rarely stoping in weak or fissured wet ground reduce or stop flow past underground plugs and bulkheads reduce leakage from reservoirs especially under dams consolidate and strengthen ground plug a conduit through which work has been flooded and make concrete for plugs and so forth with or without preplaced stone limitations are notable the grout operator controls the nature of grout and the rate at which it is injected into the prepared hole the operator can limit the pressure and in some cases influence the movement of water in the spaces to be filled generally the operator s picture of these voids and what happens in them is vague after the grout has left the pipe into which it is pumped it goes where it wants to unseen although the existence of clay in voids interferes with cement grouting appreciable water movement interferes with all kinds although new grout materials have increased the range of conditions in which grouting can be used a degree of uncertainty persists the usual procedure is to drill the ground through casing anchored sufficiently to withstand the pressure to be used test permeability and inject a grout that should be chosen and used in accordance with the conditions and objectives conduits below the water table should be grouted before a heading reaches them thereafter water movement is much more difficult to control deep holes usually are grouted in stages i e the hole is drilled until a degree of permeability is found then grouted after the grout has set the hole is drilled out deepened and again grouted a method of stage grouting from the bottom up has been developed for grouting alluvium where walls are to be built grouting should prece

de walling if at all possible if not grout pressure must be kept as low as possible pressure against the ground must exceed hydrostatic ordinarily it is not allowed to exceed the calculated vertical stress in special work it may be desirable to open fractures by pressure exceeding the in situ stress after grout pumping is begun it usually is continued without interruption until the planned sealing off pressure is reached dyes can be mixed with grout to tag various stages of injection grouting effectiveness is tested by drilling new holes between or near holes that have been grouted the degree of confidence in the result depends partly on the uniformity of the ground and partly on the nature of subsequent work cement grouts do not enter the smallest fractures or pores finer than those of coarse sand prior treatment of the ground and admixture of sodium silicate and bentonite improve penetration but even with this help pores of medium sand are a limit bentonite decreases strength but improves the pumpability of cement slurries and gives body it also acts as a dispersant reducing or preventing bleed or separation of water neat cement slurries do not set unless the cement particles are brought together at a specific gravity of about 1 5 setting time is reduced by use of high early strength cement by the addition of calcium chloride and somewhat more by the use of special fast set additives high pressures and temperatures also shorten setting time sawdust shredded plastic and similar materials can be added to help plug large openings as far as the delivery system and the size of the openings permit fly ash sand and fine gravel can be added to reduce cost without sacrificing strength powdered aluminum reduces or counteracts shrinkage but where the grout sets under high pressure its effectiveness is questioned the water cement ratio is important in controlling the behavior of cement slurries in grouting deep holes that cut openings of various widths the usual practice is to start with a thin slurry e g 5 1 water to cement or even 10 1 by weight in the expectation this will get into the smallest possible openings average slurry on one series of shaft pregrouts was 4 1 and water was reduced to 1 1 where possible cement slurries of about 0 5 1 can be pumped slurries can be made to stand under water at 20 to 30 from horizontal trial runs should be made with unusual mixtures acceptance of a large quantity of grout without pressure increase generally indicates that grout is running through a sizable conduit out of the ground that was intended to be grouted remedies may include thickening the slurry adding bridging materials such as sand or chopped plastic reducing the rate of pumping and letting the hole stand for several hours where large quantities of cement grouts are to be used for an extended time labor may be saved and slurry quality improved by mixing at a central plant with bins weighing devices

water meters agitators and pumps with pressure slurry can be pumped through around 1 5 km of 25 to 50 mmdiameter pipe while the plant and the grout operator are connected by telephone for short jobs a batching plant and truck mixers are useful reciprocating simplex or duplex grout fitted slush pumps are usual compressed air drive is convenient because of its flexibility for low pressure centrifugal pumps can be used which usually are fed by gravity from agitators ground freezing ground freezing has been used extensively for groundwater control and excavation support in mining and underground construction since the late 19th century the ground is frozen using coolant pipes to convert soil water into ice the resulting frozen material is strong enough to allow a shaft to be sunk through deep saturated soils the coolant which flows through pipes installed in boreholes can be brought to temperatures well below 150 c once the ground has been frozen much less power is required to maintain it in a frozen condition drainage system design mud and silt from blasthole drilling fill decant water road traffic in wet areas and flow through caved or weak ground are problems in many mines even where the natural permeability of rock is low the drainage system must cope with the suspended solids load of the water drains alongside rail development at gradients of 0 5 1 0 require frequent local sumps and associated ongoing cleaning particularly if hydraulic fill is used rubber tired equipment causes more mud to enter the drainage system and requires gradients of at least 2 favoring a free flowing system designed to minimize settlement before the main mine sump drainage should be via a dedicated system of side or center drains boreholes pipes and designated storage areas it should not be directed into old stopes passes or other workings unless a risk analysis has been conducted for the potential of an inrush the benefits of controlling mud and water may include easier maintenance of track ballast or road surfaces substantially improved tire life neater cleaner and safer traveling ways less water percolating to any lower work and lower cost less congestion and less loss of time for cleaning pumping stations should be located to ensure sufficient emergency storage below the station which gives time to carry out emergency pumping repairs at maximum expected flow rates there should be a contingency plan for inrushes due to pump failure including emergency evacuation procedures rising mains should be placed so that they can be regularly inspected to ensure no premature failures the mine drainage system should be recorded on a suitable plan such as a long section or isometric plan of the mine so that it can be understood as a system contingency planning each site should have a contingency plan which is enacted when a lead indicator exceeds its threshold value the contingency plan which is the responsibility of t

he mine or project manager is a response plan that defines levels in the lead indicator that would trigger escalating responses including possible damage reduction those responses including evacuation procedures ongoing monitoring requirements and types and sources of emergency support available in addition the plan should be reviewed annually when there is a change of scope in the mine or following any major incident when the plan has been enacted clarification and settling systems sumps are 1 accumulators to partially equalize the continuously changing rate of inflow and increase the regularity of pump operation 2 reserve storage in which water can be held during short power interruptions and periods of suddenly increased inflow and 3 settlers in which some suspended solids can be removed where pumping is substantial the higher efficiency of separate settlers or clarifiers is advantageous clarification removal of suspended solids from mine water may allow the use of more efficient clean water pumps which is especially important in deep mines with large volumes of water to be removed all clarification systems utilize gravity sometimes assisted by inertial and or mechanical means to separate the solids from the liquid neutralization of acidic water can also be done at the settler the most commonly used settling systems are described in the following paragraphs horizontal sumps long development openings are used with horizontal sumps relying on laminar flow and retention time to allow the solids to settle to the bottom with clean water discharging over a wall at the end or into a launder figure 9 6 4 the sumps must be periodically cleaned so multiple sumps in parallel are the usual layout with one sump cleaned at a time either by pumping out as a slurry or removal by a loader baffles have been used to control velocities and improve settling but their value is questionable and cleaning is more difficult the main advantage of these sumps is their simplicity and the absence of any mechanical devices they are essentially labor free except for cleaning their main disadvantage is low efficiency requiring large excavation volumes which makes them unsuitable for high water flows to enable cleaning with mobile equipment often the wall is destroyed and then rebuilt vertical sumps vertical sumps also rely on gravity and retention time to settle out the solids they are circular in shape sometimes with a cone at the bottom to facilitate mud removal figure 9 6 5 their height is typically the distance between two sublevels the dirty water flows in via a central pipe which discharges at about one third of the cylinder s depth and clean water rises for removal via a ring launder around the top flocculants may be added to improve the settling characteristics of fine solids mud collects at the bottom and is removed at regular intervals allowing continuous operation these settlers are more compact th

an horizontal sumps are much easier to clean and do not have to be removed from service for cleaning the large diameter 5 10 m vertical openings require reasonable ground conditions and are typically lined with fibercrete or concrete multiple units can be accommodated in close proximity to the pumping station and the settled mud can be gravity fed to the mud removal system vee settlers vee settlers evolved to maximize the benefit from addition of flocculants to achieve high throughputs in relatively small excavations the settler has three internal compartments two for initial settling and one for mud storage and thickening figure 9 6 6 the dirty water is introduced under a floc bed in a v shaped compartment the clear water rises and is removed via a launder while the finer solids are captured by the floc bed which overflows into the central compartment where it thickens for eventual removal coarser solids settle in the vee compartments and are periodically released into the central compartment via drain cocks which may be automatically operated the sludge in the central compartment thickens and is drawn off for separate disposal maintenance of a stable floc bed is the key to successful performance of these settlers this is facilitated by dividing the long settlers into shorter compartments the overall capacity can be adjusted by varying the number of compartments in operation lamella plate settlers in lamella plate settlers the dirty water flows across a stack of parallel inclined plates as the particles settle onto the plates they slide down and out of the stream because the vertical distance between the plates is small even small particles can settle out relatively quickly provided the flow velocity is low these devices are more commonly used in processing operations where space is at a premium mud handling systems thickened solids from settlers can be removed from the mine in a variety of ways this material sludge often contains valuable minerals particularly in a gold mine with coarse free gold and should be delivered into the processing stream typical removal systems include mixing with other rock the sludge can simply be mixed with either ore or waste depending on its value and removed by the normal materials handling system this can be quite messy but may be satisfactory if the quantity of material is small filtering the sludge may be dewatered to produce a moist cake by a filter press or vacuum filter for removal by the normal materials handling system or separately if desired injection the sludge may be injected into the rising main such that the clear water pumps remove the sludge without being damaged by it the velocity in the rising main must be sufficient to prevent settling of the coarsest particles pumping if the solids are sufficiently fine they may be pumped out by suitable slurry pumps hydraulic displacement this method uses the head of a column of clear water suppl

emented by some additional pump pressure if required to displace the thickened slurry to the surface the system was developed in south africa and is used at mount lyell atkinson 1982 where the discharge tunnel is sufficiently lower than the shaft collar to eliminate the need for pumping except for the flushing cycle figure 9 6 7 pumping systems the design of pumping systems of even moderate capacity presents complications that require specialists but should be guided by those who are fully acquainted with broader plans and objectives of the work the need to pump any inflow of water with complete reliability means at least one capable pumping unit plus one equal spare in a three unit system any two should be able to pump the maximum inflow the greater the number of units the less the percentage of spare capacity but beyond some point a larger number of smaller units will cost more and will have lower efficiency where only brief pumping interruptions can be permitted duplicates of all essential parts must be provided including power supply pipes and valves positive displacement pumps are capable of handling dirty water and can greatly simplify the underground handling of water before it is pumped in general pumping for shaftaccess rail mines is optimized with centrifugal pumps the steeper gradients and greater volume of mud generated by mobile equipment in trackless mines favor the use of positive displacement dirty water pumps high speed centrifugal pumps are capable of high efficiency provided close tolerances are maintained they are vulnerable to wear by grit and essentially are clear water pumps therefore means to remove suspended solids before pumping are an important consideration unlike most positive displacement pumps centrifugal pumps can be rotated without fluid flow because the power demand is least when no water is pumped large pumps generally are started with discharge valves closed flow also is limited or stopped if 1 discharge pressure is not sufficient to force water into discharge pipe as from extreme impeller wear 2 passages anywhere in the pump system are plugged or 3 pressure in the suction is insufficient cavitation develops in the intake of impellers if pressure there drops below the vapor pressure of the fluid so that the fluid boils the formation of bubbles reduces the capacity and efficiency of the pump and their collapse damages it to determine the potential for cavitation it is necessary to calculate the difference between the total head on the suction side of the pump close to the impeller and the liquid vapor pressure at the operating temperature design of pump stations objectives for designing a pump station usually include the following enough units of all essential components should be provided so that any one can be repaired while others handle greatest expected flow ordinarily this requires spare units with appropriate valves and crossovers and a crane capable