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By Brad Murray

Evaluating the performance of a shielded tunnel boring machine (TBM) can be difficult because the ground cannot be observed directly and in relation to the TBM attitude within the excavation. It is difficult to determine whether performance problems are caused by ground loading, steering issues, fine muck packing against the shield, or migration of annular grout around the shield. The Arrowhead Tunnels Project in Southern California uses strain gauges on its shielded hard rock TBMs to detect shield strains early and correlate them with tunneling conditions, thereby increasing the chances that problems will be correctly diagnosed and addressed to optimize TBM performance. The frequent automatic measurement of shield strain has also been valuable by confirming whether remedial methods used to free the machine after stoppages are effective. This paper discusses the qualitative interpretation of characteristic strain patterns on the Arrowhead Tunnels TBM shields and discusses installation details and special considerations for setting up a strain measurement system.

Jan 1, 2008

By Geoffrey Fosbrook, Donald Phillips, Anil Parikh

The Second Avenue Subway is a $16.8 billion project planned by the Metropolitan Transportation Authority (MTA) in New York City. It will reduce overcrowding and delays on the Lexington Avenue Line, improving travel for both city and suburban commuters, and improving access to mass transit for residents of the East Side of Manhattan. The project is a new, two-track, 13.5 km (8.5 mile) subway extending from Lexington Avenue at 125th Street in Harlem on the north end of Manhattan, to Water Street at Hanover Square in Lower Manhattan. The first phase of construction includes rock tunnels from 92nd Street to 62nd Street and connection to the existing 63rd Street station, three new stations, and track and systems from 105th Street to 63rd Street, allowing service between 96th Street and Brooklyn via an existing Broadway Line. The following describes the Project in detail, discusses the construction challenges addressed in the design, and the initial design/build contract to be awarded in 2005. A discussion of the planned mined construction of two rock caverns and a cut-and-cover station construction are also included.

Jan 1, 2005

By Vladimir Admek, Paul W. Jeran, Michael A. Trevits

It has' been found that lithological conditions over the Pittsburgh Coal bed cause the subsidence coefficient to vary within the area of the subsidence trough. This precludes the use of European developed predictive models, which are based upon a constant subsidence coefficient. Regression analysis of the distribution of subsidence coefficients from 11 Bureau of Mines, U.S. Department of the Interior, longwall panel studies on the location relative to the edge of the panel has yielded a third degree polynomial equation. This equation has been incorporated into a BASIC computer program for use on a personal computer that allows users with no previous knowledge of the theory of subsidence to predict vertical movements over typical longwall panels in the Northern Appa1achian Coal Basin.

Jan 1, 1986

By Sam H. Patterson

Australia has led the world in bauxite production since 1976, and only the Republic of Guinea has larger bauxite resources. India has a small integrated aluminum industry, and deposits containing more than 1 Gt (billion metric tons) of bauxite were discovered in the 1970's. The Peoples Republic of China has large bauxite resources scattered in several regions, but it is a monohydrate type that is difficult to process for aluminum. Indonesia and Malaysia both have long histories of bauxite mining, and both have limited resources of high-grade bauxite. Districts containing bauxite resources in the 10 Mt to 150 Mt (million metric tons) range are scattered in countries along the eastern rim of the Pacific Ocean, on islands in this ocean, and on the western and northern rims of the Indian Ocean.

Jan 1, 1982

By J. Geisler

When addressing Germany’s resource supplies, we need to distinguish between those domestically available and imported ones. Resource extraction ostensibly competes with the designation of protection areas. However, the parallel existence of wildlife and plant life, and operations in the areas used for resource extractions is continually underestimated. The European Commission has compiled guidance documents facilitating the extraction of resources from protected areas. With regard to resource productivity, the market appears to be the appropriate instrument for minimising resource consumption. Policy makers are now called upon to create a legal framework leading to a consensus accepted by society.

Jan 1, 2011

By J. H. Bassarear, P. F. Thomas

Large-scale equipment can reduce both capital and operating costs for concentrators. Large semiautogemus (SAG) mills can be effectively utilized in big mills but they must be kept fully loaded to tab advantage of their great potential. With varying hardness ores, controlling throughput is difficult and careful design must take this into consideration. A variable speed drive on large primary semiautogemus mills can overcome this problem to a considerable degree. This paper provides a base case using standard accepted technology of two wound rotor single speed 4476 kW (6000 hp) motors to drive the primary SAG mills of a hypothetical 36,364 t/d (40,000 stpd) typical porphyry copper mill. One other fixed speed drive will be described and jive variable speed drive configurations will be reviewed. Capital costs for the entire grinding circuit, from crusher product to flotation feed, were developed for the base case and each of the alternatives. A technical evaluation comparing the advantages and disadvantages of each drive is presented.

Jan 1, 1987

By Jeffrey R. Kelly, Paul M. Kubera, Richard A. Howk

Mixing of solid-liquid slurries is a unit operation that is widely encountered in the minerals processing industry. Applications may range from simple slurry storage in open tanks to complex chemical reaction systems under extreme conditions of temperature and pressure. The specific process requirements dictate both the degree of mixing required and the type of agitation employed to achieve the desired results.' Many continuous-flow process applications feature tanks operating in series to provide a discrete number of stages and a known residence time for the slurry. Because these tanks operate at a constant level in an overflow mode, the mixer must maintain uniform solids concentration and size distribution throughout the tank; failure to achieve uniformity results in accumulation of coarse solids in the tank, ultimately leading to a process or mechanical failure. Downward-pumping, axial-flow mixing impellers are widely employed to produce uniform solids suspension. The specific impeller type, number, size, and power draw is a function of each given situation. The use of high-efficiency, fluid-foil impellers (Figure I) has evolved as a recognized standard for these flow­controlled applications. Recent small-scale experimentation and full-scale experience has demonstrated that, when uniformity is required, capital and operating expense can be minimized by employing an additional upper impeller pumping in the upward direction.

Jan 1, 1995

By D. William Tedder

Several bauxite residue sands and muds produced by Bayer plants in the U.S. and overseas have been fractionated using dry and wet magnetic separators. The magnetic sand fractions typically contain about 60 wt% iron and the bulk of the radioactivity in this waste. The muds are more difficult to process than the sands, but some fractionation is possible using a combination of flotation and magnetic separation techniques.

Jan 1, 1984

By Y. Luo, S. S. Peng, C. T. Holland

Introduction A well-designed mining plan is one that minimizes cost and mining induced problems and maximizes recovery of the coal reserve. To minimize the negative effects on surface structures caused by ground subsidence due to underground mining activities, two kinds of practices are commonly employed by mine operators. One is the support technique, which leaves an area of coal unmined or partially mined beneath the structure to be supported. The other is the protection technique, which protects the structure when it is subsiding with the ground by taking advantage of the ground subsidence process (Luo et al., 1992). In designing the supporting technique, the only currently available method in the US is the one stated in the Pennsylvania Underground Coal Mining Rules (1985). However, the size of the support area designed by this method will be excessively large and result in a wasteful use of coal reserves when the overburden depth is more than 350 ft. A more scientific method is proposed in this paper for designing the support area. This method is based on a large amount of subsidence data collected throughout a number of major US coal fields and the authors' experience with monitoring and protecting surface structures that have been undermined by longwall panels. It considers the critical deformation indices that a structure can tolerate, and depth and height of underground extraction. A support area designed by this new method will not only assure the safety of the structure to be supported but will also maximize the extraction of the coal reserve. Design of support area using the Pennsylvania rules The Pennsylvania Underground Coal Mining Rules (1985) state that no underground mining activity should be permitted beneath structures where the overburden depth is less than 100 ft. An exception to these rules is provided for mine related openings that provide access to the surface for such as entries, shafts, boreholes and site-specific variances for entry development. If the overburden depth is greater than 100 ft, the mine operators should utilize either of the following: •Extraction techniques that provide for planned subsidence in a predictable and controlled manner, or •Support techniques designed to prevent subsidence damages to features identified as: •Public buildings and non-commercial structures [ ] customarily used by the public, including churches, schools and hospitals • Dwellings, cemeteries, municipal public service operations and municipal utilities in place on April 27,1966 •Impoundments and other water bodies with a storage capacity of 20 acre-ft or more • Aquifers, perennial streams and water bodies that serve as a significant source for a public water supply system, and •Coal refuse disposal areas. The support techniques require that a support area be left beneath the surface structure or feature to be protected (Fig.1). The support area should consist of coal pillars, with their size and pattern being such that their bearing strength is maximized. The total coal extraction within the support area should be limited to a maximum of 50%. The support area should be rectangular in shape and determined by projecting a line at a 15° angle from the surface to the coal seam with an offset distance of 15 ft from all sides of the structure. For a

Jan 1, 1994

By Kenneth W. Luke

In the development of the ultimate pit limits for a narrow ore body, pa¬rameters necessary in the design of a functional, or working, pit become highly sensitive factors in the determination of ore reserve levels and their associated waste to ore stripping ratios. Through the use of geologic cross sections, ore reserves can be roughly calculated by utilizing a straight line approximation for pit wall slopes. The optimum position of the pit floor can be substantially altered from such a preliminary design though with the introduction of functional mining parameters, such as a ramping network, and working bench heights, berm widths, and bench to bench wall angles. Originally a computer program was developed to quickly evaluate changes in cross-section pit design with minimal alteration of input data. After developing a satisfactory technique of cross-section evaluation which incorporates working mine parameters, an optimization algorithm, or procedure, was developed and included in the program to eliminate much of the tedious manual decision-making required in determining the optimum location of the pit floor on each cross section. Optimization in this case implies the maximum profit pit. When pit and processing costs are defined or hypothesized, this computer program can be used to design the maximum profit pit, constrained by the recognized functional mining parameters. A second way of stating the optimization is that the program can be used to develop a pit design which minimizes waste stripping at any desired ore reserve level. The basic method of cross-section evaluation parallels present manual methods. Program input is a combination of data obtained directly from cross sections developed for, geological interpretation and pit design parameters selected by the mine planner. As a result it is easy for the mine planner to comprehend what the program is accomplishing, and thus participate in the development of the computer assisted design.

Jan 1, 1971

By Y. Théberge, V. Svalbonas, M. Fresko, E. Stopper

For many gearing applications, calculations carried out to AGMA standards are comprehensive. For very large gears, the elastic nature of the gear and pinion structures begins to play a larger role in determining the load distribution along the teeth. Various factors affecting the stiffness of the gear and pinion sets have been studied through FEA models for actual configurations. In particular, the effect of gear shape, load location, unsymmetrical structures, etc. have been studied in the unaligned and field aligned conditions. Analysis results show that the load distribution factor is highly sensitive to pin-ion stiffness, which affects gear structure design.

Jan 1, 2004

By S. Orr

Flow in heaps and dumps is a two-phase flow phenomenon, though for many applications it could be simplified as unsaturated flow. Unlike saturated flow (typical of ground water flow), where permeability is independent of other hydraulic parameters, unsaturated flow permeability depends on the degree of saturation and/or on capillary pressure. Several recent field studies suggest that flows in heaps and dumps tend to concentrate in preferred pathways, bypassing much of the ore. Different preferential flow phenomena are triggered, promoted and influenced by different heap structures, by pretreatment, by the composition of the leach solution and by application rates and schedules. The structure of heaps and dumps is determined and affected by every stage of their construction -from blasting to crushing to conveying and stacking of the material. History of heap construction and operation combined with monitoring, mapping and certain field tests can reveal patterns of flow and transport in a given heap and can shed light on the physical mechanisms behind it. Such insight can provide a first cut on heap leaching enhancement by either eliminating or bypassing physical barriers to flow and leaching. Based on the understanding of the heap structure, advanced flow and transport models can be constructed and further enhance the insight. This insight is essential for understanding cause and effect and can provide a basis for decision making. Further, based on the physically-based models, an intelligent control agent, such as MRDS1, can learn and build a self-learning representation (or a model) of the complex heap leaching system, followed by dynamic optimization and planning of heap leaching and heap rinsing.

Jan 1, 2003

By D. Zaharaki

The optimisation of geopolymer synthesis was studied bymixing low Ca electric arc ferronickel slag with kaolinite, sodium silicate solution, sodium hydroxide pellets and water. The pulp was heated at low temperatures and left for curing at room temperature. Through statistical analysis it was shown that the factors with the most statistically significant effects on the compressive strength of the produced geopolymers are slag particle size and aging period. XRD and FTIR studies provide useful information regarding the progress of geopolymerisation mechanisms. Finally, studies regarding the durability and structural integrity of the produced geopolymers were also carried out.

Jan 1, 2006

By Pramod C. Thakur

Coal is a major source of energy in the world today and will, undoubtedly, continue to be so for the next few centuries. Naturally, a great number of studies has been made of its physical and chemical properties. Unfortunately, the work on technical properties which influence the mining of coal and the consequent yield of inflammable gases and respirable dust particles has not progressed at a comparable pace. Coal is a brittle material. Irrespective of the mechanism of breaking coal, some dust is always produced. In mining parlance dust is defined as solid particle, smaller than 100 microns (micron = 10-6 meter), in size Coal dust, when raised into a cloud, creates two well known hazards in mines, namely, the coal dust explosion and Coal Workers' Pneumoconiosis (CMP). The latter is, perhaps, the greatest environmental hazard in U.S. coal mines today. In this context it is not only natural but also necessary to investigate the proneness of a coal seam to respirable dust production. It has been established that the amount of dust produced is a function of two groups of variables (1), (2), viz. (1) Material dependent variables, e.g., moisture content, compressive strength, hardness, etc. (ii) Breaking mechanism dependent variables, e.g., type of machine, depth of cut, etc.

Jan 1, 1973

By M. I. Brittan

A technique has been developed that analyzes routine mill operating data to determine the key operating parameters responsible for gold losses to tails. These parameters represent the prime operating variables having a dominant effect on gold recovery. The technique quantifies these effects for the specific plant being analyzed, providing a tool to optimize recovery and costs and so enhance the mine?s cash flow. The quantitative relationships generated will be different for each ore and plant: every case is site-specific and has to be treated on its merits. Examples are provided to illustrate the considerable metallurgical and financial benefits which can be realized from optimization. The examples are taken from case studies of mills in four major gold mining districts of the world.

Jan 1, 2010

By Michael Michaylov, Elena Vlasseva

On the basis of well known and widely used in mine practice retreat longwall mining system, physical and mathematical models of air leakage dynamics have been created. Flow is assumed viscous-inertial and considering natural anisotropy of porous media of a gob area. As a result of modeling pressure and leakage distribution and velocity field can be defined. Thus the model presented in this paper can be used as aerodynamical prediction of gob area characteristics.

Jan 1, 1995

By R. W. Smith, D. L. Taylor, K. A. Altman

The importance of metallurgical information in reaching appropriate decisions during the development of mining projects is demonstrated. A financial analysis is calculated using a simulation that includes random number generators. The results are compared to the results of a traditional sensitivity analysis. The traditional analysis is shown to have the potential to overestimate the value of mining projects. The type of statistical distribution selected for the random number generator affects the results significantly. The statistical method of analysis provides insight into the amount of metallurgical testing to be completed and verification of how representative the samples are.

Jan 1, 2000

By G. S. Dobby, N. J. Contini, S. W. Wilson

Scale-up and simulation of flotation columns requires construction of mathematical models which employ, as a minimum, rate constants for quantifying particle recovery in the collection zone as well as split factors for quantifying froth zone performance. To date, measurement of these rate parameters has proven to be difficult, due to the interdependent nature of the collection and froth zones. This paper describes a technique for making these measurements. The method requires recovery data from two modes of operation: countercurrent and cocurrent. In cocurrent flow slurry is fed at the bottom of the column and tailings are withdrawn a short distance below the froth interface. Countercurrent mode is conventional operation. The critical difference is that particles which are dropped out of the froth in cocurrent mode are immediately lost to tailings, while in countercurrent mode the particles are subjected to recollection. Fitting of the measured recoveries to the equations that describe flotation in the two modes yields rate constant or recovery values for both the collection and the froth zones.

Jan 1, 1988

By John D. Smart, John W. Sager

The following paper is an evaluation of the instrumentation programs on recent Corps of Engineers tunneling projects. The authors have first-hand knowledge of the NORAD Cheyenne Mountain Complex (NCMC) Expansion Project. Information on the other projects comes from conversations with those directly involved in the instrumentation programs and from referenced reports. The specific objectives of this paper are: (1) to state the purposes of the instrumentation programs, (2) to discuss the benefits gained from the instrumentation, and (3) to present conclusions from this study that will provide guidance to those planning instrumentation on future projects. Presentation of detailed descriptions of the projects and instrumentation data is limited to that necessary to the accomplishment of the above objectives. NCMC EXPANSION PROJECT The NCMC is located at a depth of approximately 800 feet in Cheyenne Mountain near Colorado Springs, Colorado. For the current expansion project new chambers were mined to accommodate a new diesel power plant and associated cooling and air handling equipment. During 1971 some 55,000 yd3 of granite were mined through existing access tunnels for this expansion. A model of the new excavation is shown in Figure 1. The light shaded areas are new openings, and the dark areas are portions of the existing operating complex. The large chamber to the right is the power plant chamber and has a span of 67 ft, a height of 50 ft, and a length of 172 ft. The other large chamber on the lower level is the cooling tower chamber and has a span of 38 ft, a height of 45 ft and a length of 185 ft. The small chamber on the upper level has a span of 20 ft and is 27 ft high and 140 ft long. Other major excavations are the 18 ft diam air tunnel

Jan 1, 1997

By James R. Craig

The Central and Southern Appalachians were the major sources of gold in the United States throughout the first half of the 19th century and have continued to yield gold to the present day. Small amounts of gold were probably extracted by the Indians and the Spaniards but the first documented report of gold in the region was made by Thomas Jefferson who found a four pound lump of gold ore, which yielded 0.85 troy oz., in the Rappahannock River of Virginia in 1782. Gold was subsequently discovered in North Carolina between 1793 and 1799, in Virginia in 1806, in South Carolina in 1827, in Georgia in 1829 and in Alabama about 1830 (Becker, 1894-5; Pardee and Park, 1948). The gold belts of the Central and Southern Appalachian Piedmont and Blue Ridge Provinces are shown in Figure 1. The superimposed circles indicate the mount of production from some of the more productive and well known areas. Although North Carolina produced far more gold than the other states, the most significant concentrated area of production is the Dahlonega District in Georgia which yielded more than 500,000 troy ounces. After discovery, gold production increased rapidly as shown in Figure 2. Production was at its maximum between 1830 and 1852 with combined totals generally exceeding 30,000 troy ounces per year. Production dropped sharply after the California gold rush in 1849 as experienced miners moved westward in search of bigger and easier stakes. After the Civil War briefly halted gold mining in the Appalachians, production rose to an average of about 8,000 ounces per year from 1865 until 1878 and to an average of about 13,000 ounces per year from 1881 until 1915 when it again fell to near nil (Pardee and Park, 1948). Minor resurgences occurred in the 1930's and 1940's. Although there has been no reported production in recent years, it is likely that "weekend panners" still remove hundreds of ounces from streams annually. The total reported production for the area through 1959 is in excess of 2.5 million troy ounces.

Jan 1, 1981