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By R. Schuerch, C. Cimiotti, G. Anagnostou, J. Nickerson, P. Perazzelli

"This paper presents experiences gained from the construction of the Lake Mead Intake No. 3 project. The 4.7 km long tunnel was excavated with a hybrid TBM (able to operate in both closed and open mode). The tunnel crossed metamorphic and sedimentary rocks under a hydrostatic pressure of about 14 bar. During the excavation of the tunnel the TBM encountered difficult ground conditions caused by a combination of high water pressure, poor ground quality and locally low depth of cover. The adverse conditions required the TBM to be driven in closed mode at very high support pressures (10 – 15 bar) for approximately 60% of the tunnel length. The paper summarizes the main problems encountered during TBM excavation and analyzes the evolution of the TBM parameters over the entire tunnel length. INTRODUCTION The Lake Mead Intake No. 3 project is located approximately 30 km away from the city of Las Vegas in Nevada, USA. The project consists of the construction of a deeper third intake for the biggest reservoir in the United States, which is formed by the Hoover Dam. The construction of the new intake was required due to the constant drawdown of the lake level (more than 40 m in the past 20 years) and the consequent risk that the shallower intakes 1 & 2 may run dry. The project included the fabrication and positioning on the lake bottom of an intake riser, the excavation and lining of a 185 m deep shaft and construction of a 4.7 km long tunnel. One peculiarity of the project is that the water table is located about 140 m above the tunnel elevation (i.e. corresponding to a hydrostatic pressure of 14 bar at the current lake level). The tunnel was constructed using a tunnel boring machine (TBM) able to operate in both open and closed mode (Mc Donald & Burger, 2009). The present paper focuses on the TBM tunneling experience gained from the Lake Mead Intake No. 3 tunnel. The TBM excavation started on December 27, 2011 and finished on December 10, 2014 with the breakthrough to the intake structure at the bottom of Lake Mead. GEOLOGICAL CONDITIONS The assessment of the ground conditions encountered during construction was mainly based upon qualitative descriptions of the tunnel face conditions (during open mode operations) and analysis of the extracted muck (during closed mode operations)."

Jan 1, 2016

By Malcolm Ross

Of the six forms of asbestos, only three have been used to any significant extent in commerce. These are chrysotile, crocidolite, and amosite. Between 1870 and 1980, approximately 100 million tonnes of asbestos was mined worldwide, of which more than 90 million tonnes was the chrysotile variety, about 2.7 million tonnes the crocidolite variety, and about 2.2 million tonnes the amosite variety. The three principal diseases related to asbestos exposure are (1) lung cancer, (2) cancer of the pleural and peritoneal membranes (mesothelioma), and (3) asbestosis, a condition in which the lung tissue becomes fibrous and thus loses its ability to function. These diseases, however, are not equally prevalent in the various groups of asbestos workers that have been studied: the amount and type of disease depend on the duration of exposure, the intensity of exposure, and particularly, the type or types of asbestos to which the individual has been exposed. Lung cancer is caused by exposure to chrysotile, amosite, and crocidolite asbestos; however, increased risk of this disease is usually found only in those who also smoke. Asbestosis is caused by prolonged exposure to all forms of asbestos, whereas mesothelioma is principally caused by exposure to crocidolite asbestos. There is good evidence that chrysotile asbestos does not cause any significant amount of mesothelioma mortality, even after very heavy exposure. The common nonasbestiform amphibole minerals, cummingtonite, grunerite, tremolite, anthophyllite, and actinolite, which are often defined as "asbestos" for regulatory purposes, have not been shown to cause disease in miners. Chrysotile asbestos, which accounts for about 95 percent of the asbestos used in the United States, has been shown by extensive Canadian studies to be safe when exposures do not exceed 1 fiber per cm3 for the working lifetime. Chrysotile dust levels found in buildings rarely exceed 0.001 fibers per cm3. Such dust concentrations will have no measurable health effect on the building occupants. Present and future controls of minerals defined as "asbestos" and removal of asbestos from buildings and homes may cost many billions of dollars. Much of this expense is unnecessary and even counterproductive. Asbestos abatement could in fact produce a health risk to those exposed to dusts during and after removal operations overly restrictive controls could force the use of poor or dangerous substitutes, and could greatly affect the hard-rock mining industry.

Jan 1, 1987

By Takuya Tani, Tomoyuki Aoki, Kazuo Saskai

"The authors have proposed a unique methodology in the evaluation of rock mass stiffness for the range of five to twenty meters ahead of the tunnel face, with the use of small diameter inclinometers. The inclinometers are installed at the tunnel crown at a pre-determined constant interval, about one meter behind the face in order to obtain the slight change in inclination angles during tunnel excavation. This method was developed as a daily control measurement such that the geological condition and its possible change ahead of the face could be detected early by monitoring the trend of inclination angles. This paper describes the results of the ground stiffness ahead of the tunnel face evaluated at a mountain tunnel construction site. This stiffness is evaluated automatically and displayed visually by the current system equipped with a result display screen, together with a warning message against a weak zone when detected. 1. INTRODUCTION In a conventional planning of a mountain tunnel, according to the Japanese Standard (JSCE, 2006) seismic refraction surveys from the ground surface are performed and tunnel support patterns are then designed based on the seismic wave velocity. The resolution of the velocity profile estimated by this technique, however, is poor as the tunnel overburden becomes large. The tunnel face is therefore often encountered by unforeseeable fault zones or weak rocks. Such an unpredictable weak zone occasionally causes the collapse of the tunnel face. Clarifying the forward geological information during excavation is hence significant for safe and well-controlled construction. According to the geological conditions ahead of a face, auxiliary methods typified by forepiling and face bolting could be preliminarily prepared for prompt execution. For the purpose of acquiring forward geological information, pilot borehole drilling and seismic reflection methods represented by the TSP (Tunnel Seismic Prediction) or HSP (Horizontal Seismic Profiling) are often applied. Those exploration are carried out near the tunnel face for a couple of days. This often leads to the interruption of excavation procedure and has no small effect on the construction schedule. On the other hand, some forward ground prediction methods in the daily control measurement have been developed e.g. by Schubert et al. (1995). In this method, tunnel displacements in the direction of the tunnel axis are used together with the crown settlements. We have tested their method at a few of our tunnel projects and found difficulty in the evaluation of the forward ground condition due to insufficient resolution of the axial displacement measured by a total station theodolite that we usually use for the tunnel measurement. We have therefore developed a novel methodology of monitoring slight inclination at the tunnel crown near the face, so that the forward ground conditions can be predicted and evaluated as part of a routine measurement procedure."

Jan 1, 2016

By K. N. Han, J. J. Kellar, Y. Guan

The adsorption of zinc species onto silica in ammoniacal solutions was studied. The adsorption isotherms indicated that the adsorption of zinc increased with increasing pH. The adsorption density increased as the zinc equilibrium concentration increased up to =3.5x10-4 M. Above this concentration, the adsorption density was independent of the equilibrium concentration, and a maxima adsorption density was reached. Temperature had no significant effect on the adsorption density.

Jan 1, 1995

By Philip U. Santacroce, James H. Meinholz

One-half of the $607 million Conveyance construction portion of the Milwaukee Metropolitan Sewerage District's Water Pollution Abatement Program is completed or under contract. 12,200 m (7.5 miles) of tunnel boring machine (TBM) driven rock tunnel from 2.5 m (8.0 ft) to 9.9 m (32.3 ft) diameter has been completed. This paper presents a review of TBM performance and a discussion of the pertinent geological conditions of the area.

Jan 1, 1987

By Kegomoditswe Koitsiwe, Tsuyoshi Adachi

"This paper characterizes quarterly LME copper price fundamentals from 1995 to 2011 by analyzing the transformation of the market mechanism based on structural change perspective. Using chow test for structural change based on the least square multiple regression, we divide the price fluctuation into: Stable price period (1995Q3-1999Q2), Low stable price period (1999Q3 – 2003Q3) and Price fluctuation period (2003Q4 – 2011Q2). The results show the existence of structural breaks disproves the investigation of the full sample period as a whole. In different structural breakpoints the main drivers of copper prices changes and their impact are significantly different. Moreover, the paper examines the role of speculation in copper price fluctuations.Introduction The rise in commodities price volatility and financial and economic crisis have led to questions over the organisation of futures and physical commodities markets. Spikes in commodity prices and volatility have coincided with a surge in financial speculators in the commodity markets inspiring a polarised and hotly debate among academics and practitioners about the role of investors in the development of physical markets. In his seminal work Kaldor (1939) focused primarily on whether speculative activity in the futures markets reduces the variance of commodity spot prices. Yet, part of the literature finds that the introduction of futures contracts destabilizes the spot market. IMF (2006) studied commodities boom and its causes concluding that there is little support for the hypothesis that speculative activity affects either price levels over the long run or price swings in the short-run. The impact of speculative activity on commodity prices remains a highly contentious topic. Other market analysts take the view that the supply and demand for physical commodities remain the major determinants of market trends (Krugman 2008). It is the aim of this study to contribute to the literature by examining the drivers of copper price changes from a structural change perspective. In this context we are attempting to answer to: What are the main drivers leading to copper price fluctuations? Are these factors having the same effect in different periods or not? It is meaningful to understand drivers of copper prices and thereby, their fluctuations because it will help developing countries depending on copper export to anticipate market situation and avoid bad economic development challenges that can result from price fluctuations. Moreover, this can ensure sustainable mineral supply."

Jan 1, 2017

By Bonn J. Macy, David A. Gulley, William A. Vogely

INTRODUCTION Some of the most famous and graphic environmental incidents have arisen from mineral extraction, including oil spills, the Reserve Mining asbestos tailings case, Kaiparowitts surface mining and coal combustion, and other environmental causes celebre. The remote location of much of the mining industry to some extent reduces the human health hazards from pollution, but often times the pristine locale in which mining is conducted provides a sharp contrast to the impacting industry. This prompts questions as to what the research literature says about the true costs and benefits of environmental compliance. We survey the state of this knowledge. Where possible, we discuss studies focused on mining and related industries, such as primary metals production. In many cases, how- ever, the studies pertain to the economy as a whole. For present purposes, the mining industry is defined as companies engaged in the production and refinement of minerals, including metals, fuels, and nonmetallics (e.g., phosphate, sand and gravel). There are several stages in mining, with environmental effects occuring at every stage. The exploration stage comprises the period from initial prospecting to the point where the deposit has been located and delineated in sufficient detail to permit development decisions to be made. Geophysical and geochemical surveys, diamond drilling programs, and exploratory stripping and excavation are activities that may be employed during this stage. Some forms of prospecting are relatively benign, al- though even airborne surveys and motor vehicles generate noise pollution. Roads and the passage of vehicles and equipment affect land surfaces and vegetation, and attract heavier backcountry use. Clearings, stream crossings, and borrow pits can lead to increased erosion and sedimentation of streams. Geological survey grids disrupt vegetation and appearance. Moreover, prospecting can involve the excavation and stripping of overburden, resulting in soil and vegetation disruption as well as in- creased sedimentation of streams and lakes. The effects of exploration are often temporary, and frequently less severe than for other activities. Nevertheless, exploration-related impacts vary with the intensity and type of exploration effort, and can be significant. During the development stage of mining, shafts are sunk, pits excavated, buildings erected, and transportation facilities established. Dust, noise, and other socioeconomic and environmental impacts are generated by the relatively large and sudden influx of people, equipment, and activity. Surface disturbance and solid waste are generated by development, and liquid wastes form when mines are dewatered. The extraction phase is associated with a variety of environmental impacts. These impacts may differ for surface and underground mines. In surface mining, surface disturbance is obviously a major consequence. Piles of overburden and waste accumulation mar land surfaces. Wind and water erosion tend to spread the dis-

Jan 1, 1985

By Michael L. Nave

An existing coal mine's raw coal 60 inch conveyor system had become productivity bound by a capacity of 3,500 tph. The existing conveyor drives were fixed speed wound rotor induction motor drives installed in 1983. The fast track upgrade installed variable speed medium voltage variable frequency drives to speed up the conveyor to a capacity of 5, 000 tph. The installation took place over a one week system shutdown during Christmas 2000.

Jan 1, 2002

By Ralph J. Holmes

INTRODUCTION Although sampling techniques used by the mineral industry continue to improve, sampling is still an area which is often neglected. Frequently, sampling and sample preparation requirements are left to personnel who do not fully appreciate the significance and importance of sampling. Consequently, plant evaluations are often based on seriously biased samples, leading to mass balance problems and incorrect assessments of plant performance. The basic rule for correct sampling is that each particle of ore or concentrate must have an equal probability of being collected and becoming part of the final sample for analysis. If this is not the case, bias is easily introduced and the sample is not representative. For example, when ore is travelling on a conveyor belt, the lumps may come to the surface. Consequently, a grab sample taken from the top layers only will contain a greater proportion of lumps, i.e., the sample is biased. There seems little point in making major investments in precise analytical equipment, if the sample provided to the analytical laboratory is not representative in the first place. This paper describes the sources of plant sampling errors, reviews the methods of estimating their variance, presents some worked examples, and provides some practical advice for reducing sampling errors and their variance. SAMPLING BASICS It is generally accepted that the discharge point of an ore or concentrate stream is the most suitable sampling location. The stream can be intersected at regular intervals, and representative samples, referred to as increments, can be obtained by taking a complete cross-section of the ore stream. On the other hand, sampling devices that take part of the stream on an intermittent or continuous basis, e.g., a bleed from a pipe, may introduce serious bias, and should be avoided at all cost. Increments may be taken at completely random times or tonnages during the sampling operation, in which case it is called "random sampling". However, as shown below, random sampling results in the largest sampling variance, so it is preferable to divide the ore or concentrate stream up into strata of equal time or mass and take one increment from each stratum. This operation is called stratified sampling and may be either systematic sampling, in which increments are taken at the same point in each stratum, or stratified random sampling in which the increments are taken at random within each stratum. Systematic sampling results in the smallest sampling variance, provided periodic variations in quality or quantity are not present which may coincide with, or approximate to, any multiples of the proposed sampling interval. In such cases, it is strongly recommended that stratified random sampling within fixed time or mass intervals be carried out.

Jan 1, 1991

By P. Ollivier

The ore-processing plant of the Soremib mine Pour a (Burkina Faso) has now been in uninterrupted operation for 3 years. Ores from the oxidized and non-oxidized zones of the deposit are processed together in one flotation unit. About 60% of the gold is free and is recovered in a gravity processing unit. The residual gold in the flotation concentrate is processed on the spot by cyanidation and carbon-in-pulp.

Jan 1, 1998

By Donald C. Moore

Introduction Asamera Minerals (US) Inc. and its joint venture partner, Breakwater Resources Ltd., discovered ore grade gold mineralization on their 20 km2 (5000 acre) Wenatchee, WA land position in February 1983. Due to the high grade nature of the discovery ore and the known reserves of ore in the "B Reef' and "B West" zones previously outlined by other companies, a decision was made to construct a mine/mill operation near the known ore occurrences. Further drilling in the discovery area quickly expanded known gold occurrences to more than 3.6 Mt (4 million st) with tentative in-place ore grade of 7 g/t (0.25 oz per st) and minor silver values. Based on existing knowledge of the ore body and the rapidly increasing ore reserve, a decision to build a 1.8-kt/d (2000-stpd) mine and mill complex was made in the second quarter of 1983. A schedule was devised to begin immediate mine development, shaft sinking, environmental and land use permitting, and mill and tailings dam construction (Fig. 1). Meeting the scheduled startup date, April 1, 1985, required a fast track schedule in all areas. To this end, Asamera purchased the Oracle Ridge Partners concentrator. This was an assemblage of new equipment designed for use as a copper concentrator in southern Arizona. The purchase contained all of the major mineral dressing equipment - crushers, screens, rod and ball mills, etc. and an engineering package. It did not include most of the other required items, such as buildings, conveyors, pipelines, tanks, and pumps. At the same time, core samples were sent to two independent process development laboratories for initial flowsheet development. Due to the refractory nature of the carbonaceous ore, cyanide leaching was not feasible. Flotation was selected as the concentration process. Further testing showed that autoclaving of the flotation concentrate followed by cyanidation would result in overall recovery of about 85% gold. A mine manager was hired to begin assembling an operations staff, hire an environmental consulting firm, and begin mine development. Environmental and land use concerns were major obstacles due to the mine's close proximity to a city of 20,000 people. These concerns had to be rapidly defined so as to mitigate any adverse impacts from and mining processing operations. Baseline data dealing with weather, air and water quality, and sound were measured before start of mine construction. Concentrator and flowsheet development remained static until October 1983 while definition drilling and mine development proceeded. In late October, a process engineer was hired to coordinate development of a process flowsheet, purchase the remainder of the concentrator equipment, prepare a concentrator construction contract, finalize concentrator detail engineering, and combine environmental and process requirements with a tailings dam design. Process development There were only 17 months remaining to mill start up from the hiring date of the process engineer. Therefore, the process flowsheet had to be finalized rapidly. To accomplish this, samples of drill core from the highest grade (and therefore potentially the most commercial) ore zones were sent to an outside metallurgical laboratory to confirm beneficiation tests on the flotation process. Test results again showed that flotation would provide about an 86% gold recovery. Therefore, all further testing was concentrated on flotation and autoclave/cyanidation of flotation concentrates. Focusing on a well known process such as flotation was important in accomplishing the rapid design and construction of the concentrator. If, during these next phases, we were continually changing design concepts, layout, and process flow, the mill startup would have been delayed many months. Once a process flowsheet is selected the process engineer must obtain the process criteria needed to design the beneficiation system. For example, it was known in early December that the Oracle Ridge rod and ball mills were too small to grind 1.8 kt/d (2000 stpd) of Wenatchee ore. A decision had to be made to purchase a large, used ball mill and convert the Oracle Ridge ball mill to a rod mill. The process engineer must be cognizant of the process criteria needed to size and select equipment. If not, the process engineer must use the professional services of the equipment manufacturing companies to review the requirements that the equipment is asked to perform. For the Wenatchee system, this resulted in the adaptation of a ball mill to a rod mill with a weight limit of grinding rods to protect the mill bearings and drive trains. When a decision is required, the process engineer has to present the facts and options in a manner that allows a rapid decision. This information must include costs, equipment availability, and effect on the construction schedule. At the Cannon mine, there were process development details that resulted in decisions similar to the ball mill purchase. These included an increased flotation residence time from eight to 25 minutes, an increased thickener area requirement, a high pressure tailings pumping system, and area constraints in plant layout. All of these decisions had to be timely and required assistance from manufacturers' service engineers, and knowledge of the alternate costs and effects on construction completion. Equipment procurement It was decided in early 1983 to build the ore milling facility with Oracle Ridge equipment, augmenting it with used equipment

Jan 2, 1989

By Sandeep Upadhya, Marc Morgan, Baljinder Bassi, James Fletcher, Mike Deevy, Nishant Nayan

"In order to protect public safety in the event of a deliberate fire attack, underground rail authorities are increasingly considering the need to design for arson-initiated fire scenarios. Where typical design fires for modern rolling stock mean a peak fire size is reached after 12 minutes, an arson-initiated fire reaches its peak within 2-3 minutes. We present the innovations required to successfully incorporate this requirement on a recent design-build project. In stations 3D modelling is used to optimise smoke reservoir designs, smoke chimneys, station boxes and tunnel geometry to allow coordination with structural requirements. In tunnels, novel coupling of one dimensional network modelling and 3D Computational Fluid Dynamics (CFD) is used to improve assessment of complex fire scenarios. Finally, the impact on tunnel structures is assessed through comparison with standard time-temperature curves and risk of explosive spalling. INTRODUCTION An increasing regulatory environment and the appreciable influence that terrorist incidents have had on public safety policy have motivated the need to protect against large arson fires, especially in civil structures and public transport systems. With a greater reliance of a growing urban population on underground subway systems, design of such infrastructure is continually being reassessed and developed worldwide. Underground rail authorities are paying increased consideration to the design of fires - with properties beyond the upper regions of growth and intensity - amongst arson fire studies. Use of fire hardened materials on modern rolling stock means fires caused accidentally can be expected to develop relative slowly. However, recent experiments involving large initiating fires (as would result from an arson attack) have shown rapid fire growth rates and flashover leading to greater maximum heat release rates, Hadjisophocleous (2012), White (2010), and Lönnermark, et al. (2015). This paper describes the challenges and innovations required to complete a detailed design to control smoke from such aggressive super-fast growing fires. Computational modelling is used to demonstrate the required smoke control design by configuring the mechanical exhaust system combined with careful coordination with the architectural and structural design. The design objectives are to provide tenable egress paths in accordance with NFPA 130 (2014) and fire-fighting access. Finally, analysis of the design fire is used to inform the tunnel lining design, reducing the risk of explosive spalling, protecting the asset in the event of a severe fire."

Jan 1, 2016

By w. Chruscielewski, T. Domanski

INTRODUCTION Concentration of radon 222Rn and its decay products occuring in the Polish mines of metal-ores call for the necessity of systematic radiation control /Do8la/ both of the working environment and of the miners' personal exposure. The attempts at introducing a system of radiological protection in mines, similar to the ones existing in X-ray or isotope laboratories, took several years and consisted of development of the methods for control of concentration of radon and its progeny in the air, as well as the methods for measuring individual exposure. It was accepted that the assessment of both transient concentration in the air and of personal exposure are basic elements of the control system, which should be implemented independently of each other. Concentration measurement serves to detect and to determine those areas in mines where there is intensive radon emanation, and where current control of the effectiveness of technology introduced to deacrease the concentrations is necessary; personal dosimetry results in the assessment of the actual exposure of miners to radiation. PRINCIPLES OF THE SYSTEM The assessment of working environment is based on concentration measurements of the potential radiation energy of radon alpha decay products. Decentralized assessment is carried out by the special dosimetric service operating in each mine. Dosimetrists are equipped with portable radiometers, type RGR-11, made by the institute of Nuclear Research, Warsaw. The radiometer is presented in Fig. 1. Measurement of filter activity is performed automatically according to Markov's method /Ma62/ or any other method. Simultaneously to potential energy measurement the dosimetrists are measuring the dust concentration in the air and ventilation rate. Ventilation service looks for correlation between those indices and the concentration of radon daughters in the air. Derived Air Concentration /DAC/ for concentration assessment was accepted to be 6.25 10-6 Jm-3 /0.3 WL/ according to ICRP recommendation /Publication No. 24/ /ICRP77/. If environmental measurements reveal potential energy concentration exceeding the value of 0.3 DAC at working places, the miners employed there are subject to individual control of personal exposure. Individual exposure measurement is carried out centrally by the Institute of Occupational Medicine in [Lodz] for all metal-ore mines. Miners who are to be included in the control scheme are referred by a mine management to the Institute where they are registered and assigned a dosimeter. A passive dosimeter with

Jan 1, 1981

By Stanislaw Wasilewski, Zdzislaw Krzystanek

The CMC-3 new generation system for continuous methane monitoring enables on-line measurement of methane concentration within the range of 0-100% CH4 with a great autonomy of operation. In principle the system has been worked out in the asspect of hazard detection in mines endangered with rock and gas outbursts. But after last crash in the Halemba colliery, according to the recommendation of the after-accident committee, the system was directed to this colliery for operational tests. The paper describes construction and functions of this system and gives some results of tests conducted at the Halemba colliery. The results point out the necessity of using monitoring equipment of continuous operation in mines of high dynamics of methane emission. INTRODUCTION Commonly used in Polish coal mining the methane monitoring systems of CTT/63/46 Up or CMM-20 and CMC-1 type are based on cyclic measurements with 4-minute repetition of measurements. This period has been stated sufficient from viewpoint of methane emission dynamics under normal exploatation. In these systems, automatic switching-off electrical power is performed by the surface station, i.e in case of detecting exceeded concentration value the station generates control pulse signal which actuates the switchng-off devices CRA and IZZO. Such a way of disconnection causes a considerable time delay, up to several minutes, in electric power break at hazardous areas. In the methane monitoring system with the new CMC-3 station, the different phylosophy of operation has been applied. Measurement of methane concentration is performed in a continnous way. In case of exceeding the alarm value, immediate control of the IZZO unit directly by methane monitor follows and consequently energy break without necessity of communicating with the surface station. Alarm values are set directly in methane monitor. The system ensures central powering of underground equipment from the surface, and in case of power failure the methane monitor equipped with battery operates autonomously for about 12 hours. Such an extention of the methane monitor funtionality has been achieved thanks to the use of internal microprocessor controller. The system with the CMC-3 station has been worked out in the aspect of methane hazard detection in mines exposed to gas outbursts. But after last gas explosion, according the desicion of the After-accident Commitee, the system was installed in the Halemba coliery where it underwent operational tests. Besides

Jan 1, 1993

By Britta Schoesser, Zdenek Zizka, Markus Thewes

"The support pressure of a slurry shield corresponds to the in situ earth and groundwater pressure to ensure the stability of the tunnel face. The support fluid (bentonite suspension) penetrates from the excavation chamber into the pore space and transfers the support pressure to the granular structure of the soil within this zone. At the same time, the cutting tools rotate periodically with the cutting wheel and remove the penetrated soil up to a certain cutting depth at the face. Shortly after the tool passing, the penetration process starts again. Both, the support pressure and the soil excavation, act in the same direction at the tunnel face, but they are subject to different cyclic intervals. This relationship between the time needed for the transient penetration process and the interval of the cyclic passage of the cutting tools at a local point at the face is examined and the impact onto the global face stability is discussed. INTRODUCTION Slurry shields are usually deployed for excavations in soft ground. The main application range is in non-cohesive soils (DAUB Recommendations 2010). In non-cohesive granular soils, the tunnel face stability is one of the key design issues. The slurry shields make use of pressurized bentonite suspension (slurry) to support the unstable tunnel face. To support the tunnel face effectively, the slurry pressure has not only to counter the groundwater pressure, but also has to be transferred into an effective stress to support the soil grains. In general, the pressure transfer can be achieved in two ways: (1) with a thin flexible membrane or (2) a penetration zone. The membrane (1), called filter cake, creates a thin impermeable layer from bentonite particles directly on the tunnel face, and enables a transformation of excess slurry pressure into effective stress. In case of penetration zone formation (2), the excess slurry pressure is transferred onto the soil skeleton along the entire penetration depth by shear stresses between slurry and soil grains. These theories, presently applied to assess the pressure transfer on the grains within slurry shield tunnelling, are originating from diaphragm wall technology, e.g. Müller-Kirchenbauer (1977), Kilchert and Karstedt (1984). They assume that the support pressure transfer mechanism is built-up instantaneously on the whole tunnel face and is not damaged or influenced by the interaction with excavation tools. These assumptions are valid for conditions during the excavation of diaphragm wall trenches whose bottom is excavated and the walls of the trench are supported. At the tunnel face of a slurry shield, the support suspension acts on the same area as the soil excavation. Hence, the conditions on the tunnel face are transient (time dependent) due to the time period needed for the penetration process of the slurry and the periodical damage of the pressure transfer mechanism by excavation tools (Fig. 1a)."

Jan 1, 2016

By T. Lupek, S. Plaum

"The execution of classical building services in underground mining operations is more truth than myth. From small concrete foundations for conveyor belts to the construction of huge workshops for large machinery maintenance, nearly every operation requires building services. By creating such fixed facilities, these services ensure the efficiency of the production. A distinction must be made between fixed facilities which directly enable the production and auxiliary facilities which only indirectly support the production. The construction costs of such auxiliary facilities are often roughly estimated because they do not immediately contribute to mineral extraction. The research project ‘Development of a systematic cost-calculation method for building services in underground mines’ seeks to address the question: ‘Can the construction costs concerning fixed auxiliary facilities be neglected e.g. within a prefeasibility study?’ The presentation will show the monetary relevance and significance of these auxiliary facilities and introduce a guideline for cost estimators. PROBLEM DEFINITION The overriding interest of an underground mining operator is to exploit the commodity with the maximal quality by minimum cost and time expenditure. If a new operation shall be installed, it has to promise profitability. Therefore, predictive economic feasibility studies are performed in advance of installation. Herein, all cost expenditure for installation and operation of the future underground mine is determined and compared to the expected income by selling the raw material. The described interest of the mining operator is the starting point of the research project ‘Development of a systematic cost-calculation method for building services in underground mines’. While economic feasibility studies for future operations are focused on the profitable exploitation of raw materials and the efficiency of the accompanying necessary production processes, auxiliary actions are only considered rudimentary. Necessary production processes, as well as auxiliary actions regularly require classical building services, which are normally performed in construction business on the surface in the same manner. By performing building services like masonry or concrete works in underground mines, fixed facilities shall be set up in order to enable or support the raw material production. Production enabling fixed facilities are varying from small concrete foundations for conveyor belts or other infrastructural elements to upstream processing plants situated in the mine workings. While such fixed facilities are essential parts of the production process chain, supporting facilities underground shall increase the efficiency of the mining operation. Workshops, control rooms and social installations are only a few examples for supporting facilities. Those could be situated on the surface as well, but the efficiency increases significantly by installing them underground. Especially supporting facilities are evading from the main interest of the mine operator, since they are only indirectly connected to the production process. The building costs are oftentimes only roughly assumed."

Jan 1, 2017

By Eric Leung, Stephen G. Hardcastle, Andrew Dasys

In today's economic environment, Canadian mines can ill afford to neglect their ventilation systems as they can consume 30- 40% of the electricity used in underground mines. In addition, Canadian mines can incur significant heating costs. For mines to be their most cost efficient they must embrace existing and emerging technology to optimize the use of their air; namely, maximizing its work in diluting and removing pollutants, limiting leakage, and avoiding the unnecessary consumption of costly fan pressure all the while ensuring the health of their workforce. Furthermore, in Canadian mines which are heavily dieselized there is great interest within the industry to convert from a rigid quantitative approach to ventilation, based upon engine size, towards a more flexible qualitative approach that provides credit for Clean engine technology" and permits ventilation supply to be driven and based upon pollutant demands. In the future, there is even the possibility that ventilation will only be required to supply oxygen to diesel equipment as the underground hands-on workforce is replaced by surface workers and tele-operation. Such changes will allow mine operators to minimize their electrical usage and operating costs, for in its simplest form the cost of running a fan is proportional to the quantity3; therefore, reducing current ventilation demands or limiting increases brought on by more stringent legislation, can produce very significant cost savings. CANMET, through ventilation surveys and use of its modern 3D-CANVENT ventilation simulator, have been demonstrating to the mining industry how ventilation can be optimally delivered at reduced costs. El-Equip with their leaky-feeder communications and MultiVENT monitoring and control system have facilitated mines to control fans and hence costs, and also monitor such ventilation parameters as pollutant concentrations. These two parties are now combining their efforts to develop an integrated air management system which will be demonstrated at CANMET's Experimental Mine Val D'Or, Quebec. With such an air management system, the ventilation engineer will have: 1) a simple to use simulator to design and test ventilation scenarios; 2) remote controls of fans, doors and regulators to implement changes; and 3) real-time monitoring of airflow, pollutant concentrations, and both vehicle identity and location to show whether changes are necessary. It is only when all three are available, that a mine's ventilation system can be operated at minimum cost.

Jan 1, 1997

By Kenneth A. Grace

Introduction The 1980s have not been kind to the mining industry, especially in the United States. As mineral commodities prices plunged, marginal producers were squeezed out and then major players were forced to cut back or close down operations. Base metal miners suffered the most. Gold was all that glittered. As had been the case throughout min¬ing's history, exploration activity was an early victim of these depressed conditions. Mining companies had to economize drasti¬cally and exploration was deemed a nones¬sential activity. Funding for new explora¬tion ventures dried up as mining was seen as a poor investment. A national magazine even proclaimed the death of the industry. Indeed, ignoring matters of independ¬ence of supply and the relationship of min¬eral production to national security, it was argued that mining was but a small cog in the overall scheme of things in the United States. The industry made a relatively small contri¬bution to the gross national output. We were becoming a service industry economy, re¬member? But what of those countries where mining plays a major role in the economic well-being? In some, mining is the national economy. In a few specific cases, special conditions actually brought prosperity. Copper production in Chile is one example. There, high grade copper, low production costs, and a technically advanced industry reaped the benefits of mine closures else¬where. In most other cases, however, par¬ticularly in the lesser developed countries, whole economies were devastated. This article will show what one major mineral producer, Canada, did to ensure the survival and even growth of its minerals exploration activity during these lean years. Background While Canada is among the world's mining leaders, mining is not its dominant industry. Still, it plays a far more important role than in the United States. It is a major earner of foreign exchange, currently accounting for about 25% of the total value of exports. Through spinoffs and a multiplying effect, it is a significant employer. In the far north, particularly, mining is the major nongovernment industry and a leading factor in the opening up of frontier territory. The industry cannot be allowed to die because it is often the main economic underpinning for vast, remote areas. Thus, exploration for new deposits cannot be cur¬tailed significantly without it having a long¬term negative impact on the very fabric that melds such a large, sparsely-populated ex¬panse of country into a nation. Over the years, Canadian governments have employed various means to encourage the development of new mines. Often, these incentives were tax-oriented, such as the three-year income tax holiday that applied to new mines in the 1950s and 1960s. The advantage of the tax connection is that any such incentive policy can be applied across the board to the 10 provinces and two territories that make up the federation of Canada. This is important because mining, except for the two federally-administered northern territories, comes under provincial government jurisdiction. Mining taxation is a complex give-and-take between the central and provincial authorities. In Canada, expenditure on mineral exploration is an allowable cost against reve¬nue for tax purposes. This works well pro¬vided there is some revenue from which to deduct. New exploration companies, those with no income from mining activities, de¬rive little benefit from this type of tax provi¬sion. Similarly, in times of depressed prices and reduced or nonexistent profits, the tax deductibility of exploration spending loses its value even for the major mining compa¬nies. To encourage exploration in Canada during the lean years, a different sort of incentive was required. The instrument used during the 1980s was again tax connected. It became known as flow-through financing or, simply, flow-through shares. When it assumed its final shape, it worked dramati¬cally. Flow-through shares Flow-through shares are so-named because they permit tax benefits earned by a corporation to 'flow-through' to the share¬holder. Basically, when an investor buys a flow-through share and the proceeds de¬rived by the company from this transaction are used for Canadian exploration, the in¬vestor can claim a deduction for tax pur¬poses as if the exploration expenditure was made by him personally. Flow-through shares go back to the early 1970s when Canada revamped its mineral income tax law. At that time, it permitted full deduction of exploration and development expenditures and provided for an automatic depletion allowance of one¬ third of operating profits from mining. There was also the three-year income tax holiday for new mines. New legislation replaced the depletion allowance with an earned depletion arrange¬ment whereby one dollar of depletion was earned for every three dollars spent on ex¬ploration and development. This earned depletion was `banked' during a transitional period (to 1974). After that it could be deducted from resource profits up to a maximum of 25% of such profits in any one year, with the excess carried forward. To promote exploration and mine de¬velopment in Canada, the earned depletion allowance plus the continued deductibility of exploration and development expendi¬tures permitted the recovery of risk capital before taxation. The three-year tax holiday, however, disappeared. Also, mining com¬panies that did not reinvest in exploration lost the depletion allowance benefit.

Jan 1, 1989

By Nicholas S. Lynn

Introduction Borne out of the need for reductions in capital expenditure and increased production, several new and innovative carbon systems have been developed for small precious metal heap leach operations throughout the United States. Perhaps the most important aspect of these systems is the carbon column. Though diverse in design, these columns can be categorized into three basic types. The first is known as the gravity flow type or Cortez type. As the name indicates, solution flows via gravity, throughout 4 to 6 columns which are arranged in a normally stepped con- figuration which is conventionally upflow in design. The second type, known as the vertical column, is an arrangement whereby flow is established through pressurization in an upward manner, throughout 4 to 6 columns in a vertically stacked configuration. This arrangement is typically intended for use with small portable heap leach operations and employs a semi-continuous mode thus preventing gravity from occurring. The third type and newest development in carbon columns is an arrangement whereby the solution flows throughout 4 to 6 columns placed in a side by side configuration and pressurized by a single feed pump (Figure 1). A unique aspect to the third type, is that the adsorb and desorb cycles are accomplished in the same column, due to a fixed carbon charge. An in-depth analysis is warranted due to numerous advantages of this arrangement, and is therefore the subject of this paper. Advantages and Variations One advantage to the third type of carbon column is the fact that initial capital expenditures and operating man- power requirements are reduced. Another advantage is that the system can be made fully portable up to a 0.0315 m3/s (500 gpm) capacity. Systems of this nature are operational at several sites. Above this flow rate, the system's portability is one which can be maintained, but disadvantages (i.e. larger diameter carbon column and greater weights) far outweigh the advantages. There are several variations in each of these systems which allow for unique operation. For example, carbon columns made highly portable, can be moved from unitized heap leach operations to central stripping facilities. Although this method has been used in Colorado, transportation of these units has been known to be quite cumbersome. If distances exceed 5 km (3.2 miles) then special front-end loaders are required. This limits heap locations to within 5 km (3.2 miles) of the central processing facility. Another example transports the carbon charge from the heap leach locations to a centralized processing facility; this method is quite effective. For the past 5 years one mine has employed this technique of transporting carbon in 907 kg (1 ton lots), in DOT containers, towed by company pick-ups. This operation uses a vertical column with a 907 kg (1 ton) carbon charge. A third example uses static carbon columns with fixed carbon charges. Carbon Adsorption System The carbon adsorption system (Figure 1) is fed by a single preg solution feed pump. This feed pump pushes the preg solution through all four to six fixed charged carbon columns, which are on line. The sequencing of the carbon columns is achieved using valves. Expansion of the carbon charge is dependent upon the carbon selected. The carbon typically used is a 6 x 12 mesh size, with a nominal flow rate of 0.00135 - 0.00138 m 3/s (22-25 gpm) per square foot of carbon, based on a 40% bed expansion. With 8 x 16 mesh size,

Jan 1, 1987

BP Minerals America (BPMA) has completed its $400 million modernization of Kennecott Utah Copper's Bingham Canyon mine. Modernized facilities include the in-pit crusher, conveyor, ore storage area, concentrator, ore pipe-line, and tailings pipeline. With modernization, Kennecott will achieve substantial cost reductions. Bingham Canyon is now one of the lowest cost copper producers in the world. And the mine will continue to provide jobs and income in Utah for another 30 years or more. The Modernization Project began in February 1986. The work took 33 months. In late 1987, the construction force peaked at 1100 workers. Kennecott Utah Copper now employs a permanent work force of 2100 employees. Less equipment and more efficiency The modernization work has increased the scale of the facilities that transport and process copper ore. A large, continuous transport system has replaced multiple haulage units. Fewer but larger pieces of equipment have replaced many crushing, grinding, and flotation units. The result is less maintenance, fewer employees, and improved metal recoveries. About one-third of the $400 million modernization project is directed at improving ore movement by eliminating rail transport. The new concentrator accounts for the remaining two-thirds of the modernization investment. The modernized plant was started up in stages. In February, ore was fed to the crusher. By the end of March, the three grinding lines were operating and the flotation circuit was producing copper concentrate. In July, the design through-put rate of 70 kt/d (77,000 stpd) was reached. October saw the achievement of targeted metal recoveries that corresponded to the fully modernized operation. It is estimated that Bingham Canyon will annually produce 181 kt (200,000 st) of refined copper, 9.3 t (300,000 oz) of gold, 71 t (2.3 million oz) of silver, and 5.4 kt (12 million lb) of molybdenite. Current Bingham Canyon production is about 97 kt/d (107,000 stpd) and a similar amount of overburden. Some 70 kt/d (77,000 stpd) of ore are processed through the in-pit crusher and 27 kt/d (30,000 stpd) of ore are transported by rail. The Bingham Canyon mine has yielded more than 11 Mt (12 million st) of refined copper. In 1863, precious metals - silver-bearing lead - were first discovered in Bingham Canyon. What was once a mountain is now a huge open pit. In fact, the mine is the world's largest man made excavation. The pit is some 4 km (2.5 miles) wide and 0.8 km (0.5 miles) deep. Since the pit began operating in 1906, more than 4.5 Gt (5 billion st) of material have been removed. Modernized facilities Electric 21 m3 (27 cu yd) or 23 m3 (30 cu yd) shovels are used to load the haulage trucks. Both 154 t (170 st) and 181 t (200 st) trucks are used to haul the ore to a mobile, in-pit crusher. The crusher replaces three crushers located at the old concentrators. There are two dumping locations at the new crusher, which can handle two trucks a minute. The 1.5 x 2.7 m (60 x 109 in.), 745 kW (1000 hp) Allis-Chalmers gyratory crusher reduces the ore to 254 mm (10 in.) size or less and delivers it to the conveyor. The crusher and conveyor systems are capable of handling 9 kt/h (10,000 stph) of ore.

Jan 11, 1988