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By Raoul Fernandez, Bernard Catalano, Guillaume Roux

The Thaumasia Joint-Venture, composed of Bouygues Travaux Publics, Soletanche- Bachy and Bessac, completed the construction of the underground section of line 2 of the Nice tramway, which comprised a 3.2 km twin track tunnel and four underground stations, in a particularly complex urban and geotechnical context. The density of the surface structures, as well as the presence of many historic buildings on its route made the construction of the tunnel even more sensitive, with a settlement threshold of Half an Inch. The joint venture faced a complex subsoil, varying from one extreme to another from highly plastic clay layers to fibrous peat and to cobbles with very high permeability, with artesian ground water, and with unforeseen anthropogenic obstacles in the tunnel section Due to the diversity of the problems encountered and their variability over short distances, the construction of the underground section of the Nice tramway, in its very sensitive urban context, undeniably constituted an unprecedented challenge.

Jun 13, 2023

Blast vibrations induce sounds within neighboring residences. A house wide vibration and sound monitoring system was installed in a West Virginia home which was subjected to blasts at varied distances and direction. Eighty-nine blast events were monitored and analyzed for this case study. Fifteen channels of data were collected including three triaxial geophones, one airblast microphone, one uniaxial geophone mounted to the wall of the house (response channel), and four microphones that recorded CD quality sound waves inside the house. Each of these channels was recorded on the same time reference and scale allowing for direct comparison of the waveforms. The response channel signal was easily separated into ground vibration induced and airblast induced movement due to the differences in their times of arrival. This response channel was then compared to the sounds recorded inside the home to determine which component of blast vibration induced the maximum sound response inside the home. Blasts at distances less than 762 meters (2,500 feet) had maximum sound responses from both ground vibration and airblast. While for blasts beyond 762 meters (2,500 feet), the maximum sound response inside the home was caused by ground vibration without exception. When airblast was identified as the dominant sound generator in the house, the peak amplitude of the sound was directly related to the amplitude of airblast. When ground vibration was identified as the dominant sound generator in the house, the peak amplitude of sound was not related to the amplitude of ground vibration. In these cases, sound amplitude was driven by the conditions present in the house such as loose items, doors, and windows creating sudden peaks from falling or slamming. In the same respect, sound amplitudes varied depending on where the sound was recorded. Different rooms generated very different sounds based on the contents of the room. Findings from frequency analysis showed that the frequency content of sounds inside the house were not related to frequency content of airblast or ground vibration regardless of source suggesting that residents would have difficulty determining the source of blast induced noise in their homes.

Jan 1, 2010

By G. Yang, M. J. McPherson, P. Mousset-Jones, G. Danko, F. Calizaya

In the last 20 years, studies on controlled flow recirculation in various countries have been carried out in both coal and metal mines. These studies have shown that in addition to economic gains, partial flow recirculation can be used to provide mine workings distant from surface access points with the required volumes of air. These studies have also shown that the operation of fans and regulators, used in a recirculation system, will induce transients in gas flow and gas concentration. Various models have been developed to explain the problem. However, most have failed to incorporate important factors such as diffusion and dispersion in the modeling process. This study examines the theoretical background of gas emission transients from caved areas in coal mines, represents the problem by a "tank-airway" network model, and provides a possible solution. The study also presents the results gained from a laboratory model constructed to evaluate the major factors affecting the shape and duration of gas flow and gas concentration transients in an airflow recirculation system. In this model, the gas injection system was rearranged to simulate the variations in gas emission rates due to changes in air pressure. Within this model, a set of booster fans and regulators were used to generate the changes in air pressure within the model. Finally, the study presents an algorithm and a computer program GASTRAN, developed to analyze the gas concentration transients and calculate the pollutant transport levels in a complex ventilation network. The application of the program is illustrated by means of an example problem.

Jan 1, 1991

Currently the challenge that our society faces is to combine the economic activity for the continuously increasing needs of our expanding population with the necessary environmental integrity and the humanistic social concerns. In this paper, the methodologies that should be applied by the progressive mining industry in order to fall within the frame of the sustainable development are summarized. The Sappes project, an advanced gold mining project in north-eastern Greece, is presented together with the approaches adopted by Thrace Minerals S.A.

Jan 1, 2003

By Jeffery Leavy, Ken Davis, Kirk H. McDaniel

The Waste Isolation Pilot Plant (WIPP) is a United States Department of Energy facility located in southeastern New Mexico. It is designed for the safe disposal of transuranic radioactive waste in deep geologic salt beds. Westinghouse TRU Solutions, LLC, the managing and operating contractor, undertook a project to simulate the processes at WIPP in order to identify bottlenecks and optimize available resources. The activities simulated in the model included the receipt, processing and disposal of radioactive waste underground, the mining of new areas for future waste disposal and the transportation of salt out of the mine. The complexity of the processes and the interactive requirements between processes required the use of advanced modeling techniques. The simulation model includes a huge number of locations and path network node points, with movement to and from the locations controlled using parameters rather than explicit routing. Information for the timing and sequence of the mining and nuclear waste emplacement operations is brought into the model via spreadsheets. Arrays in the simulation model keep track of past and future events that occur. Routing to the multiple possible positions in the underground mine is done using attributes, and system functions within ProModel in order to allow for a highly flexible sequence of planned events and to reduce the level of effort in creating the ProModel processing. Considerable use of subroutines in the simulation model is utilized for parametric decision-making that is repetitive. This presentation describes the modeling techniques used to accurately simulate the surface and underground operations. The surface and underground operations are considerably different, thus they will be treated in their own sections.

Jan 1, 2002

By O. Ozcan, J. D. Miller, Z. S. Nickolov

The production of soda ash from trona (sodium sesquicarbonate, Na2CO3•NaHCO3•2H2O) resources has completely displaced the production of synthetic soda ash in the USA. Further, the utilization of other trona resources is under consideration in China, Turkey, etc. Recent research has been concerned with the development of flotation technology for the trona industry. In this regard studies on the flotation behavior of sodium carbonate salts: trona, sodium carbonate monohydrate and decahydrate, as well as the flotation behavior of sodium bicarbonate, are reported for both cationic (dodecyl ammonium hydrochloride) and anionic (sodium dodecyl sulfate) collectors. It has been found that strong flotation of sodium bicarbonate (NaHCO3) can be achieved with 100% recovery, while the other sodium carbonate salts do not float well. These results have been explained by FTIR analysis of aqueous solutions of Na2CO3and NaHCO3in a range of concentrations from very dilute to saturated conditions. The changes in the shape of the O-H stretching band of water are correlated with the flotation behavior of Na2CO3salts and NaHCO3. In addition, the absorption band of the carbonate ion at ca. 1385 cm-1is used to monitor its interactions with water and/or other ions in solution. The infrared results demonstrate thatNa2CO3acts as a water structure maker, leading to an extensively hydrated surface that accounts for the poor flotation of most sodium carbonate salts. In contrast, NaHCO3does not have this characteristic and consequently complete flotation is possible with both cationic and anionic collectors. These results support the previous water structure analysis for soluble salt flotation of alkali halides and other oxyanion salts.

Jan 1, 2003

By G. Brooker

The back-filling operation at Olympic Dam mine supports a 9.8 million tonne per year (Mtla) underground Longhole Open Stoping operation. It involves a combination of Cemented Aggregate Fill (CAF), Surface Rockfill and Underground Rockfill. The fill material is introduced from the surface via bore-holes into the top of the stopes. Due to the deleterious effects of the dust and the thickness of the atmosphere in the stope it is not possible to view the filling process. The need for a means to measure the filling process is driven by the stopes, which have both rock and CAF fill placed in them. The large volumes and high relative cost of CAF makes the minimization of CAF fill a business priority. Incorrect filling can lead to the sterilization of ore reserve. The use of millimeter wave radar to view through the haze to give real-time data on the relative positions of the different fill masses is being developed as an in-stope fill control device. This paper reviews the salient points of the technology and its potential use in the back-filling operation at Olympic Dam. The broader potential of this technology for use in the mining industry by 'seeing' through water and dust laden environments such as that found in stopes and ore passes is discussed.

Jan 1, 2001

By L. Blain

In practice, geochemical analyses can be grouped in two broad categories according to their aim. Those that seek to determine the exact chemical composition of geological materials fall under the heading of assays, whereas applied geochemistry concerns itself with the detection of anomaly contrasts. Recent trends have blurred the distinction between both approaches for many users, as methods that were traditionally used for assays are being adopted in applied geochemistry and assays make increasing use of instrumental techniques. Nevertheless. it is important to keep a clear distinction between the two types of analyses because it has immediate practical consequences, cost is the most obvious, as well as fundamental implications. In the broadest terms, the goal of geochemistry is to strike an optimal balance between throughput and accuracy, at the lowest reasonable cost, while assays strive for accuracy. Traditionally, complete silicate analysis has been the concern of assayers whereas exploration geochemists have been more interested in base metal analyses where acid extractions of the elements, without dissolution of the silicate matrix, has been the norm. This kind of distinction is less realistic now, especially with the growth in lithogeochemical studies, and some overlap in methodology is unavoidable. However, where such overlaps occur the distinction remains in the emphasis of the work. A commonly used example is that although HF acid preparations are used by both, the emphasis in applied geochemistry is on sample throughput and batch analysis, whereas assayers are more concerned with the range of elements to be determined (Thompson and Walsh, 1983).

Jan 1, 1993

By Omar A. Muhtadi

8.1 INTRODUCTION Several methods currently exist by which gold may be recovered from a pregnant leach liquor. Two of these methods are discussed in this chapter, the Merrill-Crowe (zinc cementation) process and the carbon adsorption process. These two methods represent the most frequently used techniques for gold extraction and are, -in fact, used almost exclusively in U.S. heap leaching operations. Because of the efficiency and ease of use of these two methods, it is extremely likely they will continue to be quite prevalent within the gold mining industry in years to come. The remainder of this chapter includes information on the history of the two processes, descriptions of the actual processes, criteria to consider in selecting a recovery process, and commercial design and construction considerations for both of the gold recovery methods. As with other chapters in this book, some fairly technical information is presented for the benefit of those readers needing a greater level of detail. However, the overall intent of the chapter is to provide an overview of the processes likely to be used in gold extraction, thus giving the reader a firm basis for more technical research into the topic, should this be needed. 8.1.1 History of Zinc Cementation During the late 18901s, zinc cementation was introduced for the precipitation of gold and silver from cyanide solutions. This occurred at about the same time as the introduction of the cyanidation process, the history of which is recapped in Chapter 1. The initial cementation process involved introduction of a gold-bearing cyanide solution onto a bed of zinc shavings. It proved to be quite inefficient because the reaction rate was very slow. The zinc quickly became "passive", inhibiting further gold deposition. Shortly after this first introduction, zinc precipitation was improved by adding a lead salt (usually lead nitrate) to the zinc. This allowed a zinc-lead couple to form on the surface of the shavings, eliminating passivation of zinc surfaces and thereby allowing continued deposition of gold. Further improvements were shortly forthcoming. The first of these involved the use of zinc dust rather than zinc shavings. This provided a much

Jan 1, 1988

By Roderick G. Eggert, John E. Tilton

During much of the 1970s and 1980s, world metal consumption grew more slowly than during the 19505 and 1960s. The slowdown contributed to surplus capacity and low real prices because actual consumption was consistently less than expected as new mining and mineral processing capacity came on stream. Over the last year or so, however, world metal consumption has picked up noticeably, raising the question, Has metal demand returned to the long-run growth rates more typical of the 1950s and 1960s than of the 1970s and 1980s? This paper examines this possibility and, more generally, assesses the factors that will shape demand for the major metals over the longer term. TRENDS IN METAL CONSUMPTION The extent to which metal consumption has recaptured the brisk growth rates typical of the 1950s, 1960s, and early 1970s is shown in Figure 1. This figure traces the consumption of crude steel, primary aluminum, refined copper, refined lead, and refined zinc between 1960 and 1987 for the western world, consisting of the OECD countries (including the United States), and the developing countries. Consumption increased in 1987 for all five metals, and preliminary data for the first six months of 1988 suggest even more substantial increases, at least for the United States (U.S. Bureau of Mines, 1988). However, Figure 1 also shows that the recent increases in consumption are not untypical of similar surges during earlier periods of economic expansion and thus may reflect only cyclical or temporary factors. In short, the available data are unable to provide a clear indication of whether recent increases in metal consumption reflect the beginning of a new era of faster growth or simply a cyclical and temporary upturn associated with the expansionary phase of the business cycle. Consequently, to pursue this issue, we are forced to examine the underlying forces that will shape metal demand trends over the next decade. The approach we have taken involves two steps. The first examines the prospects for overall economic growth. The expectation is, the faster the economy expands, the faster the production of metal-containing goods grows.2

Jan 1, 1989

By Charles D. Litton

Introduction The successful performance of a mine-wide fire detection system depends upon its ability to detect the presence of a fire rapidly and reliably. It should be sufficiently rapid so that there remains enough time to either safely evacuate a mine or successfully extinguish and control the fire or both. It should be reliable so that false alarms are minimized without sacrificing sensitivity or time response. Systems should also be durable enough to withstand the mine environment over long periods of time while maintaining a high degree of re1iability. Maintenance and calibration of the system should be simp1 e and not require the expenditure of excessive time and manpower to keep it operational. Sensitivity, reliability, and durability of mine fire sensors and their electronic support systems have been the subject of significant Bureau research within recent years. The bulk of this type of information, along with the reports from which the remainder of this paper is derived, can be found in the Bibliography. It suffices to say that there exist commercially available systems for use in mines. This paper addresses a strategy for the use of such sensors and systems. Many factors influence the design of a mine-wide fire detection system, such as the potential sources and modes of ignition, the types of combustibles involved and the quantities avai1able for fire growth and flame spread. Mine air ventilation influences the growth and spread of a fire and also serves to transport the products-of-combustion to other areas of a mine remote from the fire. Fire sensor alarm thresholds place limits on the sizes of fires that can be detected. The time to respond to a detected fire, either in terms of evacuation or control and extinguishment, place additional time constraints on the design of fire detection systems. These factors interact with each other, often in complex ways, and it is the definition and understanding of these factors and their interactions that hold the key to the design of adequate and re1iable fire detection systems. Our level of understanding of the problem has increased dramatically within recent years and it is the intent of this paper to discuss the progress that has been made and how the information can best be used to improve the level of fire detection in underground mines.

Jan 1, 1986

By R. O. Burt

Gravity concentration - the separation of minerals according to their relative density - is one of the oldest forms of mineral processing. Even though modern technology has developed a range of other processes, gravity concentration remains as one of the most important methods employed for mineral separation. The range of minerals recovered covers a wide spectrum, from andelusite to zircon, from coal to diamond, from gold to industrial mineral. The long history of gravity concen¬tration, along with a still imperfect understanding of the various mechanisms involved has resulted in a series of ingenious engineers developing, some¬times perfecting and sometimes rejecting, a wide range of equipment, suited for a variety of different duties. 'Selection' in the context of gravity separation, is primarily the choice of the right type of equipment for the separation in hand; 'sizing' of the correctly chosen unit is, more often than not, determining the appropriate number of units required to suit the throughput. The accent of this chapter will, therefore be 'selection'. A brief description of the major types of gravity concentration equipment will follow a discussion of the factors which determine the selection of the correct unit. CLASSIFICATION OF GRAVITY CONCENTRATION EQUIPMENT All concentration equipment has a primary function and a secondary function. The primary function is the efficient separation of the constituent minerals into two or more discrete phases; the secondary function is to effectively cause the discharge of these discrete phases into separate compartments (Aplan 1975). For maximum efficiency of operation, the forces which effect the primary function should not also result in the secondary function occurring; in such cases optimum operating conditions required for the primary function, separation, may have to be compromised to ensure reasonably efficient operation of the secondary function, product discharge. With gravity concentration, the primary function is effected by the relative movement of minerals of different density in response to gravity and one or more other forces, the latter often including the

Jan 1, 1986

Marble has been recognized as a valuable natural resource ever since ancient times. Due to its peculiar aesthetic and technical characteristics as well as the lithotype uniqueness, it has widely been appreciated over the past centuries. In present times its production and demand are enjoying an increasing trend, with comparatively high market prices. All this considered, marble can be included among these natural resources whose exploitation provided, and still provides, an important contribution to the growth of the economic system. Nevertheless, there is at least one more important reason that makes marble a valued resource. For ages, marble represented one of the most important raw materials for sculpture sand architectural masterpieces, which constitute part of the cultural heritage of mankind. With this in mind, the value of marble is strictly related to its extraordinary capability to preserve cultural heritage and therefore to convey civilization from past to future generations. In other words, the role of marble should be recognized as being of the utmost importance in order to attain an overall objective of ?cultural sustainability?, that is, the assurance of the inter-generational flow of the cultural heritage capital. To achieve this sustainability goal, the priorities should be to protect and preserve the world?s artistic and architectural historical heritage, which require restoration works. In this field, a very il task is entrusted to the extractive industry: this industry, in cooperation with historians, art experts and public authorities, is in charge of detecting and supplying historical stones for restoration purposes, taking into consideration that, in order to restore a monument in a correct way, the same lithotypes the monument was made from are needed. These marbles are often no longer in production, so that it becomes necessary to find the location of the original quarries, as only there is it possible to extract even the small quantities of stones that are needed. In this case, the stone, located in its geological context, could have such valued characteristics as to be considered an important public asset and consequently a resource to be preserved and protected even beyond the market conditions. This important task should be carried out by the public administration through a targeted intervention of territorial planning and monitoring, which could include the support for the specific extractive activity.

Jan 1, 2003

By Samuel M. Cassidy

The exact date of man's first use of coal is lost in antiquity. The discovery that certain black rock would burn was undoubtedly accidental and probably occurred independently and many times in the world over thousands of years. It is quite likely that these independent discoveries were made when primitive man chanced to build camp fires on exposed ledges of a black rock, then was amazed when it caught fire. The Chinese recorded the use of coal 1100 years before the Christian Era and from the Bible we learn that King Solomon was familiar with coal in what is now Syria. In Wales, there .is evidence that the Bronze Age people used coal for funeral pyres, and it is known that the Romans used this fuel. There are other ancient references. So the knowledge that coal would burn, and even some uses of that knowledge, go back thousands of years. However, practical and consistent use of coal seems to date to England in the Middle Ages.

Jan 1, 1981

By A. M. Marabini, G. Belardi, V. Alesse, M. Acosta

Sotiel mine is situated in the Iberian Pyrite Belt in southern Spain, some 40 km north of the port of Huelva. Although mining operations at the site date back to Roman times, the present mine came into production in 1983 and 5.6 million tonnes of ore had been extracted by 1993. The orebody is volcano-sedimentary and consists of fine grained copper, lead and zinc minerals in massive pyrite surrounded by slates and volcanics. Prior laboratory research had resulted in the synthesis of a new collector, belonging to the MercaptoBenzoOxazole (MBO) class that acts selectively towards Cu and Zn minerals after activation with CuS04. The MethylMercaptoBenzoOxazole (MMBO) version of this collector had been used for the laboratory flotation of Cu minerals and sphalerite activated by CuS04. This resulted in identification of the optimal physicochemical conditions for laboratory-cell flotation of the two minerals from samples of complex sulphide ores, and subsequently the reagent has been tested in the Sotiel plant (Spain). The plant has three flotation sections. With conventional re-agents, the first section yields a Cu concentrate grading 21% with a total recovery of 29%, and the second one yields a 40% Pb concentrate with total recovery of 34% and a 47% Zn concentrate with total recovery of 78%. Application of the new synthetic reagent in the copper and zinc circuits produces a more selective process with a decrease in re- agent concentration grade and recovery are increased by 2 and 9 points respectively in the case of Cu and by 1 and 3 points where Zn is concerned. Moreover, the penalty elements in the Cu concentrate are halved.

Jan 1, 1995

By Bryce Sullivan, Cliff Baratta, Ehsan Alavi, Timothy Dobbs, Lisa Mori

"Soil conditioning is one of the main factors in successful application of EPB machines in tunneling projects, which involves changing the characteristics of the ground in order to make it suitable for the tunneling process. Selection of the type of conditioner mainly depends on soil type, properties of the tunnel boring machine, and most importantly geological condition. Proper EPB tunneling and soil conditioning in ground above water table is challenging. This was encountered in Northgate Link Extension Tunneling Project in Seattle, WA. In order to improve the tunneling operation, a novel algae-based encapsulated oil was used as a conditioner and as a result the operation of the TBM was improved significantly. This paper reviews the traditional soil conditioning measures that were adopted in University Link and Northgate Link projects in Seattle, WA and compares the results with results when using the encapsulated oil additive. INTRODUCTION Soil conditioning agents are used in EPB tunneling to transform the excavated soil into a workable paste with the desired hydrological and mechanical properties. Reducing wear, power consumption, friction, adhesion, and improving the face stability and material flow are some of the benefits of using soil conditioners in EPB tunneling. Soil conditioning is performed by injecting foam, polymer, water, and bentonite to the tunnel face, excavation chamber and screw conveyor. Selection of conditioning agent mainly depends on soil type, geological condition (groundwater and soil permeability) and TBM features (injection points, open or closed cutterhead, type of foam generator, etc). The most widely used soil conditioners are foam and polymer and in some cases due to existing conditions, clay dispersion or anti-wear additives are also used (Milligan 2000, Langmaack 2000). Foam. Foam is created by dispersing air in a surfactant solution. A different combination of surfactant type and foam parameters should be used for different soil types. Laboratory tests on virgin soil should be performed to identify the best surfactant and foam parameters for the specific soil type (Langmaack 2000). The foam parameters can be described as follows:"

Jan 1, 2016

By Henry G. Healy

Observation well (Hydrographs are shown for these selected wells) Contour represents the height, in feet referred to mean sea level, to which water would have risen in tightly cased wells that penetrate the major water- bearing formations in the Floridan aquifer, July 6-17, 1961. Contour interval 10 and 20 feet, changing at mean sea level. [ ] Extent and distribution of flow areas vary with fluctuations of the piezometric surface, particularly in areas of heavy Relatively small areas of artesian flow are not included immediately adjacent to and paralleling the coast and many of the major rivers and springs

Jan 1, 1966

By K. K. Cheng, Z. M. Chen, A. L. Mular

INTRODUCTION Since the nineteen fifties, process engineers have been seriously concerned with process models for various purposes (1,2,3). Models serve as subroutines to mathematical flowsheets which simulate circuits of interest. Simulators can serve to increase process know- ledge, assess circuit performance, investigate flowsheet modifications, evaluate new flowsheets, perform off-line optimization, and compare alternative control strategies. This chapter describes a methodology to develop a simulator of a bulk Cu-Mo circuit comprised of roughers, scavengers and 3 stages of cleaning. The simulator was employed to evaluate the influence of water addition at circuit points and to estimate the optimal number of cells for each stage in the circuit. DESCRIPTION OF CIRCUIT Figure 1 is a flowsheet of the Brenda Mines Ltd. (located near Peachland, B. C.) bulk Cu-Mo flotation circuit as simulated prior to an expansion/renovation which involved the installation of large, new flotation cells. Referring to the flowsheet, feed to rougher cells includes fresh feed, scavenger concentrate and 1st cleaner tailing. Rougher con, 1st cleaner (sect ion 2) con and 2nd cleaner tailing are fed to 1st cleaners (section 1). 1st cleaner (section 1) concentrate and 3rd cleaner tailing serve as 2nd cleaner feed, while 2nd cleaner concentrate is fed to the 3rd cleaners which produce a final bulk concentrate. Table 1 lists cell types and specifications important to the circuit. DEVELOPMENT OF MODELS To develop flotation cell models a systematic procedure was employed (4). This involves the selection of responses and factors, proposing models to be fitted, the acquisition of raw data, the statistical adjustment of raw data, fitting models to adjusted data and testing the adequacy of fitted functions. Responses and Factors Responses of interest included recoveries, concentrate grades and concentrate solids/water flow rates for each stage. Factors that influence these responses, such as reagent addition rates, air flow rates to cells, solids and water flow rates to stages and feed grades were not manipulated during the sampling period. Thus, the investigation was limited,

Jan 1, 1986

By E. Harrison

The Greens Creek Ore Bodies are located approximately 18 miles southwest of Juneau, Alaska in an area on Admiralty Island classified as a non-wilderness national monument. An area-wide stream sediment geochemistry program targeted the deposit in October of 1973. Today, after 37,000 meters of combined surface and underground diamond drilling, three ore zones are known to exist with total reserves approaching 4.1 million tonnes. Lying within moderately folded metasediments of an undetermined age, these orebodies are thought to be of seafloor exhalite orgin and contain unusual and impressive amounts of gold, silver, lead, zinc and copper.

Jan 1, 1986

By Clinton Strachan, Dirk J. A. van Zyl

11.1 INTRODUCTION This chapter outlines some of the selection and design considerations for leach pads and liners. Leach pads and liners are generally chosen to provide the required or desired levels of low permeability and foundation conditions at minimum cost. The selection and design of a particular liner depends upon its anticipated use and performance, and what materials may be available. A leach pad is the firm base for a heap. When geomembrane liners are used, the pad is the firm, compacted foundation upon which the liner is placed. In the case of a clay liner, the clay liner is usually also the pad. It is important to consider the design of a pad or liner in terms of a system. The "leach pad system" consists of the prepared foundation, bedding layer (if used), liner (s), seepage collection or detection layer (if used), and cover layer. Foundation preparation is necessary to ensure a stable base for the rest of the leach pad system. A bedding layer is used to protect a liner from being punctured by large angular fragments in the foundation material. A seepage collection or detection layer, consisting of well-drained material and (sometimes) pipes draining to a collection sump, is included when a double liner is used. A cover layer on top of the liner can serve the following purposes (van Zyl and Strachan, 1986): • Preventing of ultraviolet light exposure to sensitive geomembranes; • Limiting evaporation from compacted clay liners and thereby eliminating cracking of such liners; • More efficient collecting of leachate; and • Protecting the liner from damage during heap construction. Economic evaluations of alternative liners for a project must include the overall system. For example, a geomembrane liner may require different foundation preparation and cover material selection and placement than a clay liner. Liners can be made of compacted clay onsite, amended soil, or geomembranes. Geomembrane is a generic term that has been proposed to replace many terms, including synthetic membranes, polymeric membranes, plastic

Jan 1, 1988