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By R. A. Lohnes, S. M. Levorson

As part of research to develop a coal handleability index that predicts the ease with which coal will flow through a handling system, comparative tests were conducted with a Johanson Indicizer and a low-stress triaxial apparatus on 12 coals at a variety of gradations and moisture contents. The lndicizer test provides a rapid method for generating data associated with coal handling characteristics. The arching index measured with the Indicizer is a function of the geometry of the apparatus as well as the properties of the coal. The handleability index determined from triaxial data is a more direct measure of coal characteristics. The handleability index shows a wider range of values than the arching index and, therefore, appears to be more sensitive to coal variations. Neither the arching index nor the ratholing index, as measured with the Indicizer, agreed well with the handleability index. This is attributed to differences in sample preparation as well as to the tests themselves.

Jan 1, 1993

By M. H. Foroughi

In this paper, the compressive strengths, failure modes and acoustic emission behaviors of cubic coal specimens containing bedding planes at various inclinations are considered. Test results showed that the compressive strengths and the modes of failure of coal specimens depend on the inclination of the bedding planes. From the acoustic emission (AE) measurements, the count rate detected through a low-pass window (AE (L)) was compared with that through a high-pass window (AE (H)) in each test. The results of accumulated AE history were compared with AE signatures of others. It is shown that the AE signature of coal depends on the inclination of the bedding planes, and the AE signatures can be classified into three groups. Each group corresponds to a particular mode of failure, namely, slip on the bedding planes, fracture across the bedding planes and fracture extension through the bedding planes. The parameter r, defined as the ratio of AE (L)/ [AE (L) + AE (H)], is plotted against the stress for each test. Test results showed that r also depends upon the inclination of the bedding planes.

Jan 1, 1999

By Roshan B. Bhappu

In situ mining and extraction is one of the Frontier Technologies that is destined to play an increasingly important role in the recovery of metals and minerals in the future. This premise is based on increasing costs of labor and energy, increasing awareness of environmental considerations and decreasing ore grades in the United States. Up to now, in situ mining has been successfully applied to a few favorable situations for the extraction of some evaporites, copper and uranium. However, because of its unique technical, environmental and economic advantages, this versa tile technology will find broader applications for the recovery of above commodities as well as for others which are currently extracted by hydrometallurgical means. This paper traces the development of in situ mining and extraction; stresses its dependence on interdisciplinary science and engineering; discusses its theoretical, practical and economic aspects; and finally presents potential applications of this Frontier Technology.

Jan 1, 1985

By Norbert Patzelt, Johann Knecht, Wolfgang Baum

High pressure roll grinding (HPGR) is a mature but still expanding comminution technology. In the metals mining industry, HPGR is slowly gaining acceptance as a cost-efficient, high-throughput alternative for plant optimization. The increasing need to treat ores with progressively lower grades, complex mineralogies, refractory metal occurrence and variable rock types requires an energy-efficient comminution technology that reduces metallurgical problems inherent in conventional crushing and grinding, while stabilizing leach and flotation circuits and increasing metals extraction. This paper will summarize our latest HPGR pilot test results for gold and copper projects in the United States and South America and their confirmation through the first HPGR operation in copper mining. This paper will also stress the use of the high pressure grinding roll as a metallurgical tool. The application of HPGR for the treatment of heap leach SX-EW ores, semi-refractory gold ores, waste rock material and concentrator feeds will be illustrated.

Jan 1, 1998

By R. Hogg, R. H. Weiland, P. Bunnaul

The dewatering of flocculated clay suspensions by compression in a centrifugal field was investigated. The results were analyzed with respect to the direct applicability of centrifugal dewatering (as in solid-bowl centrifuges) and indirect applications to gravity sedimentation systems. An important objective of the study was to evaluate the self-weight effect using centrifugal forces to simulate consolidation of deep sediments. Experiments were conducted in which the sediment mass and initial structure were maintained constant while the effective sediment weight was varied by centrifuging at different speeds. The relationship between the limiting sediment density and the applied consolidation stress was found to be the same for both gravity and centrifugal consolidation, indicating that small-scale laboratory tests can be used to predict consolidation in deep beds. The effects of the initial structure were also studied using controlled variations in flocculation conditions. The results imply that, for the flocculated suspensions studied, the longterm consolidation behavior is relatively insensitive to the actual extent of flocculation.

Jan 1, 1995

By S. J. Knoll, D. F. Scott, T. J. Williams

Highly stressed rock in stopes continues to be a primary safety risk for miners in underground mines because it can result in failures of ground that lead to both injuries and death. Spokane Research Laboratory personnel investigated electromagnetic (EM) emissions in a deep under-ground mine in an effort to determine if these emissions could be used as indicators of impending catastrophic ground failure. Results suggest that (1) there is no increase in the number of EM emissions prior to recorded seismic activity, (2) some EM signals are generated during blasting, (3) interference from mine electrical sources mask seismic-generated EM signals, (4) EM emissions do not give enough warning (compared to seismic monitoring) to permit miners to leave a stope, (5) the distance an EM signal can travel in the rock is between 17.7 and 39.6 m (58 and 130 ft), and (6) current data acquisition systems do not differentiate between EM signals generated from seismic activity and random mine electrical noise. These results preclude monitoring EM emissions as precursors of impending catastrophic ground failure.

Jan 1, 2004

By Y. M. Jiang

From underground instrumentation data and from direct observation of longwall panels, it was demonstrated that growth of the main-roof overhang causes an extremely high roof weighting on the face supports. This can result in catastrophic effects on the supports when the roof-weighting intensity far exceeds the support capacity. In this paper, a comprehensive study was conducted on the characteristics of main-roof breakage and its effects on shields at different locations along the face. The study was based on monitored shield data, theoretical analysis and finite element analysis. With the help of theoretical analysis and numerical modeling, stress distribution and redistribution in the main roof were analyzed to define the main-roof failure modes and to understand the maximum roof-weighting intensity imposed on the shields. From this study, it was found that the effects of main-roof breakage on shields are chiefly related to the shield's initial-setting condition and to the final failure mode of the main roof.

Jan 1, 1996

By Z. T. Bieniawski, D. A. Newman

The Geomechanics Classijication (RMR System) (Bieniawski, 1979) was modified for entry and roof support design in underground coal mines. Adjustment multipliers were introduced to incorporate the influence of high horizontal stresses and the roof support reinforcement into the existing classification system. Sixty- two case histories of standing and fallen mine roof were collected from two mines in the northern Appalachian coalfield. Twenty-seven engineering and geologic parameters were recorded for each case. A partial correlation analysis was carried out on the cases to establish which parameters have a significant im- pact on the stand-up time of supported coal mine roof. Survival analysis, a statistical technique used in medical research to assess the effect of a drug or treatment on a patient's life expectancy, was conducted together with stepwise multiple regression to derive values for the adjustment multipliers. A practical example is included to illustrate the application of the modified Geomechanics Classification to underground coal mine design.

Jan 1, 1987

By Joaquin Marti, Peter A. Cundall

This paper reports on some recent work in which several schemes were developed to model jointed rock under high stress, with particular reference to the phenomenon of "block motion" observed during dynamic loading of underground structures. Three approaches were made, corresponding to an increasing relative importance of internal block deformations as compared to rigid block movements. The first one uses distinct element method and assumes internally rigid blocks, which can break, repeatedly, whenever an empirical crack criterion is met. In the second approach each block is allowed three degrees of freedom to deform internally. The third approach, still in the development stage, permits arbitrary deformation of all blocks, which are internally decomposed into finite-difference zones and automatically rezoned during slip to preserve the calculation accuracy on joints. The last two schemes allow arbitrary constitutive relations for the intact rock, and all three schemes permit the geometrical arrangement of joints to be arbitrarily complex, in contrast to normal Lagrange, finite-difference programs, which are unsuited to model discontinua.

Jan 1, 1979

By Khosrow Bakhtar, Robert E. Cameron, Arfon H. Jones

The use of rock simulators in rock mechanics research greatly expands the scope of the problems that can be investigated with physical models. However, the exact reproduction of full scale conditions, or absolute simulitude, is not obtainable on a small scale model. For this to be possible, the scales of length, time, and pressure (or mass) must be changed without altering the theoretical equations that describe the behavior of materials concerned. In using rock simulants for physical modeling of structures designed in rock, the geometry of full scale structure is reduced to a size suitable for the available testing machine. This will require the strength related properties to be scaled down. Simulation should be representative of the in situ conditions. Complete simulation will require that friction parameters and the stress ratios be matched exactly between prototype and model. The procedure involved in application of physical modeling for rock mechanics research is discussed in the following pages. Background, theoretical approach, and anticipated benefits to the research community are also elaborated.

Jan 1, 1986

By C. Patrick

Annually, the US coal industry generates and must dispose of over 200 million st (180 million t) of coal refuse, expanding a major environmental problem. The purpose of this research was to investigate the feasibility of utilizing coal refuse as an aggregate in concrete. This paper reports on findings of the initial phases of a project to determine the viability of replacing traditional concrete blocks with refuse blocks for use in ventilation stoppings in underground mines. Refuse, collected from three active preparation plants in eastern Kentucky, was used as the primary as aggregate in the preparation of concrete cylinder. Stress-strain analyses on the refuse cylinders yielded compressive strengths of from 59% to 77 % of the control-group strengths. Low variability within the groups was found while significant differences between the groups existed. On-going determinations of the effects of weathering on the refuse cylinders is being conducted and will be completed in early 1995. The research results are favorable for the future direction of the overall project objectives.

Jan 1, 1997

By W. B. Beerbower

Resin bolting has enjoyed wide acceptance for coal mine roof support. Beginning in 1973, the first year of significant resin bolting in coal mines, we estimate that 2.5MM resin bolts were installed. This grew to 7MM resin bolts in 1974 and 13MM in 1975. Resin bolts are currently being used in over 300 coal mines throughout the major coal producing areas of the U.S. and barring major work stoppage we expect more than 17MM will be installed in 1976. Although not a cure-all, the number of unintentional roof falls occurring in many mines has been dramatically reduced as a result of converting to this "new" method of support. 1 The improved anchorage strength of resin bolts provides better roof support. (Slide #1) This anchorage strength provides a mechanism to resist changing roof stresses along the entire length of the fully grouted resin bolt, thereby assuring stabilization of rock strata over long periods of time. The ability to resist roof displacement is borne out by readings obtained from strain gauged bolts. These findings can be summarized as follows.2

Jan 1, 1977

Relatively few longwall mines in the U.S. operate under multiple seam conditions where the two seams are less than 200 ft apart. This paper describes the experience of six that do. These operations are located in PA, WV and UT, and include examples of both undermining and overmining. Some operate above or beneath their own workings, others are in historic mining districts and must contend with abandoned mines that are decades old. The lessons that these mines have learned cover a broad range of topics, including: • Whether to stack gateroads or place them under old gob areas; • How to size pillars and select artificial support to cross longwall stop lines; • How to use yield pillars to minimize multiple seam stresses and coal bump potential, and; • When to anticipate the creation of pathways for gas, water, or oxygen between current and abandoned gobs.

Jan 1, 2007

By Matthew J. DeMarco, Anthony T. Iannacchione

Coal bumps have presented serious mining problems in the U.S. throughout the 20th Century. Fatalities and injuries have resulted when these destructive events occur at the working face. Persistent bump problems can result in abandonment of large reserves or lead to premature mine closure. Through the years, a1ternative techniques such as artificial supports, extraction sequencing, destressing, pillar design changes and specific pi1lar retreat practices have been successful1y imp1emented to mitigate coal mine bumps. Several techniques have evolved for room-and-pi1lar operations that control the way the roof rock breaks, regulating the manner in which stresses are redistributed in the mined section. Special mine layouts employed in longwall mines have also proved to be successful in safely redistributing or containing excessive loadings. However, with ever increasing production rates, greater overburdens and new mining systems, the need to evolve even more effective bump control designs will continue to challenge the U.S. coal mine industry.

Jan 1, 1992

By James J. Scott

Introduction Friction Rock Stabilizers, trade name Split Sets, are presently under research and development by Ingersoll-Rand Company and Dr. James J. Scott, inventor. Conceived in 1953, the system is a patented process undergoing extensive field and laboratory testing. The author has published papers on the Split Set System earlier (References 4, 5, 6) The Split Set System holds promise to be a revolutionary development in the field of ground control. The system produces an interior reinforcement to a rock mass which: 1. Is simple in its concept. 2. Adjusts to the degree of restraint needed to match rock properties. 3. Provides a yieldable support and, later, a more rigid support as it is needed. 4. Pre-loads the rock in compression to increase stability. 5. Is a full-contact, fully tensioned device to resist rock loads. 6. Minimizes the stress concentration effects inherent in many interior support devices. 7. Improves safety for the miner. 8. Is cheaper than a grouted system. 9. Offers the rock mechanics engineer an opportunity to design in a fashion not before possible.

Jan 1, 1977

By Caren Caldwell, Leslie Thompson

1.1 Biological Process Description Pintail Systems, Inc. (PSI) has developed and in partnership with their clients in the mining industry has applied biological remediation processes for detoxification of spent ore and process solutions from heap leach operations. Contaminants that are treated to mine closure levels or drinking water standards include cyanides (weak acid dissociable and total cyanides), thiocyanate, nitrates and heavy metals. Biological processes are both site-specific and ore-specific processes. PSI specializes in isolating indigenous microorgan­isms from spent ore and process solutions and augments them in the laboratory for enhanced bio-detoxification in the field. Bioaugmentation in the lab is a key to successful heap bio-detox in the field. In PSI's bioaugmentation processes native microorganisms are isolated from the spent ore environment and are tested for contaminant remediation capacity. A majority of the indigenous microbes will be tolerant of the spent ore environment but will not contribute to contaminant metabolism. Indigenous enrichment or biostimulation of these non-working microbes by adding trace nutrients can competitively inhibit the working microbes. For this reason PSI focuses on the bioaugmentation process where non-working microbes are discarded and the working population is enhanced through stress, mutation and exogenous enrichment before it is re-introduced to the heap and process solutions.

Jan 1, 1997

By B. (Manas) Das

Rock characterization for geotechnical purposes using the microhardness technique is discussed in this paper. The concept of rock characterization and its steps are logically developed. The geotechnical properties should be functionally tethered to the technological problems for characterization. The overriding geotechnical concern is rock mass stability. The important factors in this respect are rock properties, structural discontinuities, ground water, field stress, temperature and technological factors. The rock properties are the primary factors and the other factors generally affect rock properties. Of the rock properties the strength and elastic properties can form a basis for rock characterization. The microhardness technique can provide these two properties. Study on coal shows that the microhardness impressions can be used for this purpose. On the basis of this study coals of all ranks can be divided into distinct geotechnical groups. The details of these are discussed in this paper.

Jan 1, 1986

By William A. Kneller

A considerable range of composition exists in rocks that have been described as chert, jasper, or flint. Their composition may be opaline, chalcedonic, quartzose, or mixed. Certain cherts, when incorporated in concrete, are known to possess nondesirable thermal and chemical properties. The inability of chert to withstand thermal shock above the freezing temperature of water is an example of such a property. Cryothermal reactions may cause disintegration of concrete, due to repeated cycles of freeze and thaw. Thermal properties are significant because small temperature changes may cause inordinate expansion and resultant fissuring of concrete. Freezing of entrained water in chert may cause excessive physical failure in concrete. Some cherts react chemically with alkalies liberated during the hydration of the cement, with resultant cracking and deterioration. Sources of concrete aggregate in Ohio have been viewed with suspicion because they contain considerable chert derived from Middle Devonian and Pennsylvanian carbonate rocks. Light-colored porous cherts from the Middle-Devonian Colum- bus Limestone exhibit the least freeze-thaw durability of the samples studied. Denser cherts may also yield to freeze-thaw stresses, but tend to be more susceptible to thermal shock. Cherts rich in opaline and chalcedonic silica usually exhibit alkali-aggregate reactivity.

Jan 1, 1966

By M. M. Veiga, M. Koehoorn

This paper reports on recently completed research that investigated the health fabric of mining communities in British Columbia (BC), Canada. The project, funded by two national funding agencies and the BC Government, and supported by numerous provincial organizations, marked a collaboration between mining engineering and health researchers. The study employed mixed-methods. First, a quantitative phase merged census, mining industry and health data to investigate the relationship between declining economic conditions and health outcomes (mental illness and stress-mediated cardiovascular disease). Second, a qualitative phase investigated community health issues associated with the mining boom-bust cycle from the perspective of health and social service providers working in a northern BC coal mining community. Third health research findings were disseminated to potential knowledge users in the hope of enhancing mine impact assessing and integrated mine planning. The paper provides a synthesis of the research methods used in this project, and highlights the main indicators used and key findings. It concludes by identifying recommendations, and future research needs considered to be of particular importance to the health and sustainability of mining communities in BC, Canada and around the globe.

Jan 1, 2011

By J. L. Fuentes

The so called 'SISCOM' is a General Purpose, microprocessor-based Monitoring and Control System, developed by AITEMIN to meet the requirements of Spanish Mining Industry in - the field of automation and data -transmission. Typical applications -are automatic control of pumps, compressors, fans and conveyors, as well as environmental monitoring and production monitoring. In relation with the last, the - System has been succesfully installed in a full section roadheader and in a mechanised steep coal face. In both cases, the main objective is to get information about running times, down times and causes, -and monitoring of other important parameters such as ventilation, methane content, power consumption..etc. Measurements concerning the face behaviour from a geomechanical point of view are also monitored. These are different pressures and stresses. All data is transmitted to the - surface and on-line analysed by a -desk-top microcomputer. The paper shows the system structure and the requirements that have - been considered on its design. Attention is given to the mechanical data acquisition problem, involving special development of some transducers. The information provided by the surface microcomputer is shown and its utility discussed.

Jan 1, 1986