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Pillar design is the first line of defense against rock falls—the greatest single safety hazard faced by underground coal miners in the United States and abroad. To help advance the state of the art in this fundamental mining science, the National Institute for Occupational Safety and Health organized the Second International Workshop on Coal Pillar Mechanics and Design. The workshop was held in Vail, CO, on June 6,1999, in association with the 37th U.S. Rock Mechanics Symposium. The proceedings include 15 papers from leading ground control specialists in the United States, Canada, Australia, the United Kingdom, and the Republic of South Africa. The papers address the entire range of issues associated with coal pillars and have a decidedly practical flavor. Topics include numerical modeling, empirical design formulas based on case histories, field measurements, and post failure mechanics.

Jan 5, 1999

By J. W. Paul

This circular is one of a series of papers4 on coal-mining methods and costs which are being prepared through the sponsorship of the U. S. Bureau of Mines for the purpose of presenting information on present mining methods and certain features which govern costs, safety, and conservation. The methods employed are influenced by natural local conditions with respect to the thickness, character, and dip of the coal bed, the nature of the roof and thickness of the overbearing strata, and the means employed for roof support and its control.

Jan 1, 1929

By Bernadette Michalski

Although hydrocarbons accounted for more than 60% of Bahrain's income and more than 80% of export earnings, this island nation sustained one of the more diversified economies in the Gulf Region. The availability of low-cost natural gas for electric power has fostered the development of a significant aluminum refining and manufacturing industry with emphasis on vertical integration. The Bahraini iron pelletization plant, closed since 1986 due to financial problems, was scheduled to reopen by early 1989. Commodity Review Metals.-Aluminum.-Aluminium Bah-rain Bsc (Alba) attained record high production levels in 1988 taking advantage of favorable aluminum prices, which averaged over $2,000 per ton as compared with less than $1,500 per ton in 1987. Net aluminum production was nearly 13,000 tons over design capacity. Fewer standard ingots (52,081 tons as compared with 79,685 in 1987) were produced as Alba concentrated on higher value added products such as rolling ingots (42,324 tons as compared with 32,125 tons) and extrusion billets (60,934 tons as compared with 46,618 tons).

Jan 1, 1990

By Anatol Wojtowicz

This research program was conducted to determine if respirable coal dust emanating from a continuous mining machine can be suppressed more effectively by a high expansion foam than by the water sprays conventionally used. A high expansion foam system was developed and tested on a continuous mining machine under actual operating conditions. The utility of the system was demonstrated. Test results tend to show that foam application is more effective than water sprays in suppressing respirable coal dust. However, because of the extreme variability of the test conditions, scatter in the sampling data, and other factors, not enough data was obtained to form a firm conclusion that foam is more efficient than a water spray in suppressing respirable coal dust. Sufficient statistical data was obtained, however, to indicate that foam is more efficient than water in suppressing total float coal dust.

Jan 1, 1974

By Gary W. Krantz

Fibered, portland-cement-based gunite products were applied in the Bureau of Mines Lake Lynn Laboratory Experimental Mine using a variety of pneumatic guns and gunning crews, The demonstrated wet-mix (with silica fume), dry-mix, and surface bonding products were sampled by the Bureau and subjected to a suite of engineering analyses. Gunite flexural and compressive strength, rebound, permeability, porosity, dust loading, shooting rate, crew requirements, and cost factors were evaluated. Steel, fiberglass, or polypropylene fibers were contained in all but two of the gunires tested. Both Bureau and private testing laboratory analyses are provided for some products. Electron probe micro-analysis and X-ray diffraction analysis were performed on the silica fume fraction of the wet-mix gunite to characterize the dust. Aggregate size fraction distribution analyses were performed to provide strength relationships. Results indicate that all of the commercially available fibered-gunite materials tested can provide beneficial sealant, spall prevention, or roof stability control attributes for underground mining environments when applied by an experienced crew using a well-maintained gun, in accordance with product manufacturers' recommendations and when used for the designated purpose.

Jan 1, 1984

By Lloyd A. Morley

A guide to the development and use of an APL computer program for the analysis of load-flow problems is presented. The program is designed to provide an interactive method of load-flow study to improve underground coal mine electrical system design and safety. The theoretical basis for load-flow analysis is discussed, along with per-unit calculations which facilitate computation. Specific input/output, execution and network modification procedures are presented for using the APL program. In addition, typical results are given for examples taken from power system analysis literature.

Jan 1, 1977

By Robert H. Peters

How can employees be stopped from engaging in unsafe work practices? It is often easier to prevent employees from performing unsafe acts through manipulations of the work environment than through various training or motivational programs. Therefore, it is important that accident prevention programs seek to identify the reasons for the unsafe behavior and to redesign tasks and the work environment (e.g., tools, equipment, physical surroundings) in order to remove employees from sources of harm and to prevent situations from arising that would prompt them to perform unsafe acts. Unfortunately, in the mining industry the work environment is often innately hazardous, rapidly changing, and difficult to predict, making it very difficult, perhaps impossible, to fully protect the employee by environmental manipulations. Therefore, it is important that effective methods be identified for influencing mine employees to work safely. Various strategies have been used to convince employees to avoid unsafe acts and/or adopt self protective behaviors. The intent of this article is to provide guidance to mine operators concerning the use of four techniques for influencing mine employees to work safely: (1) employee surveys, (2) incentives, (3) fear communications, and (4) disciplinary actions.

By William Seymour, L. D. Schmidt

A preliminary survey of coke and steel plants conducted by the Bureau of Mines in cooperation with the Office of the Solid Fuels Administrator for War and with the advice of the Coke Production Committee indicated that production of pig iron could be increased. appreciably if present blast furnaces were supplied with a more uniform coke.4/ Nonvarying percentages of ash , sulfur , and fixed carbon in the coke , together with uniform physical characteristics , such as size , strength , and porosity , would aid the blast -furnace operator greatly in his trial - and - error methods of obtaining maximum production . With nonuniform raw materials he must employ certain factors of safety in operation , such as an excess of coke , an excess of limestone , and operation of the furnace below the maximum rate . Even so , he often has trouble from iron not being up to specifications , hot tops , high blowing pressures , furnace hanging up , etc. The more uniform his raw materials (of which coke is probably the most important) , the nearer to ideally can he run his furnace and thereby save raw material and increase production . One cause of nonuniformity of the coke produced by ordinary American plant practice is the prevailing lack of precise control of the bulk density ' of the coal charge in the byproduct oven . This report summarizes the available information on the subject of bulk density of crushed coal and its control . It includes brief reviews of some of the literature , some results obtained at plants visited by the authors , and results of a few preliminary tests made at the Pittsburgh Station of the Bureau of Mines .

Dec 1, 1943

By L. J. Prosser, A. T. Iannacchione

From 1991 through 1995, 44 miners out of a total workforce of less than 2,000 were fatally injured in the stone industry. Of these, 12 occurred at underground mining operations with nine deaths resulting from roof or rib falls. A safer environment can be achieved by evaluating the nature of the hazardous ground and by developing more efficient and effective ground-control strategies Roof and rib conditions were observed and assessed in 33 underground stone mines in Illinois, Indiana, Kentucky, Maryland, Missouri, Pennsylvania and West Virginia (Fig. 1). Hazard assessment indicated that the ground failures that occurred under moderate to substantial overburden. i.e., >30 at (100 ft), were caused by stress concentrations and geologic strictures. Ground failures near the surface are caused by solution (water) processes. Selection of the mining horizon and mine-layout decisions tremendously influence ground stability.

By Sean Gallagher, Thomas G. Bobick

The Bureau of Mines performed a pilot study examining the effects of posture on back strength and Maximum Acceptable Weight of Lift (MAWL) on six healthy male subjects (M = 32 years + 4 SD). Six hack strength measurements (3 static and 3 dynamic) were made while the subjects were kneeling and standing. In addition, these subjects (who were unaccustomed to lifting in these postures) volunteered to participate in a study of psychophysically determined NAWL in both postures. Results of the back strength tests showed a significantly lower peak torque per body weight output in kneeling versus standing hack strength measurements for five out of six test comparisons (p < .05). Subjective estimates of lifting capacity in the kneeling posture were significantly lower than those for the stooped posture (p < .05). The results of tests of hack strength and lifting capacity in these two postures provide useful information to consider in determining the physiological and psychophysical stresses imposed by these

By Stephen P. Signer

This paper presents an overview of laboratory and field tests on approximately 250 fully grouted roof bolts instrumented with strain gauges in order to study loading behavior. Laboratory work included pull tests, time-dependent tests, and shear tests. The field tests were conducted in 14 different mines extracting different commodities. However, because of the focus of this publication, only the results of tests in 9 coal mines are reported here. In the field tests, all but 14 bolts were loaded by rock movement; these 14 bolts were tested using pull gear. The variables studied included anchorage length, mechanical interlock, time-dependent behavior, shear, installation load, loading rate, and maximum load level. Such information will improve the understanding of the behavior of resin-grouted bolts, which in return will enhance the safety of miners by reducing the occurrence of rock falls. The influences of geology, overburden depth, entry width, mining-induced stresses, and bolt spacing are not described.

Jan 10, 2000

By A. T. Iannacchione

Underground stone mining represents an emerging sector for the U.S. mining industry. As this expansion takes mines under deeper cover and as more efficient mining methods are utilized, adequate stone pillar design methods will become more important. It is the purpose of this paper to examine current design practices and to discuss issues for safe mine layouts so that a rational first approach towards balancing the demands for increased production can be weighed against increased risk to worker safety from rib instabilities and pillar failures. Seventy-two stone mine pillar designs were examined. Pillars with width-to- height ratios below 1.5 and subjected to excessive stress levels appear more likely to fail. When width-to- height ratios fall below 1 .O, defects in the pillars, such as through-going discontinuities, can have a significant influence on stability. Discontinuity persistence, dip, material properties, and orientation are important factors controlling pillar strength. The influence of discontinuity dip, a characteristic easily identified in the field, was examined so that its presence could be accounted for in developing generalized guidelines for pillar design.

By Eric Zahl, John Dunford, Hamid Maleki

Coal bumps are defined as sudden failures of rock and coal near entries that are of such a magnitude that they expel large amounts of material into a mine opening. Coal bumps are influenced by geologic conditions, the geometric design of coal mine excavations, and the sequence and rate of extraction. Researchers from private industry and the National Institute for Occupational Safety and Health have studied mechanisms of violent failure and have identified individual factors that contribute to coal bumps. In an attempt to develop tools for assessing coal bump potential, the authors initiated a comprehensive study using information from 25 case studies undertaken in U.S. mines. Multiple linear regression and numerical modeling analyses were used to identify the most significant variables contributing to coal bumps (excluding bumps related to fault-slip). Twenty-five geological, geometrical, and geomechanical variables were considered initially. The most important of these variables were then identified as (1) energy as calculated using the mechanical properties of the strata, depth of overburden, and joint density, (2) mining method, (3) pillar factor of safety, and (4) stress gradient and yield characteristics.

By R. Raines, S. P. Signer

Researchers from the Spokane Research Laboratory of the National Institute for Occupational Safety and Health installed 39instrumented, fully grouted bolts at six test sites in a trona mine retreat panel to study mine roof stability for the improvement of workplace safety. Variables at each test site included bolt spacing, bolt length, roof span, and location in the panel layout. At most test sites, two rows of instrumented bolts were installed, one in or near the intersection created during development and the other in or near the intersection created during second-pass mining. The most significant factor affecting bolt load was roof span. The highest loads were on the bolts installed in the intersections of the 6-m-wide entry. Mining-induced stress resulting from panel layout was the next most significant factor affecting bolt loading. Minor variations in bolt loading could be attributed to changes in bolt spacing and bolt length. Gas pressure release in the immediate roof contributed to some bolts showing compressional loading during gas bleed-off.

By R. C. Wang, W. M. McKewan

The behaviour of wire ropes used in mine hoisting is not well understood. In an effort to improve this understanding, the structure of round-strand wire ropes was analysed. This report provides a generalised mathematical model that completely describes the geometry of the wires. It consists of two sets of vector equations and is valid for any round-strand wire rope. One set of equations is used to trace the paths of wires that have the form of a single helix. The other is used for the paths of double helical wires. The specific model for a 33-mm 6x1 9 Seale, IWRC, right regular lay wire rope was presented as an example. The paths and the geometric properties of the wires which include the path length per lay of strand, the curvature, and the torsion were determined from this model. In future work, the model could be used to conduct stress analysis for the wires in the deformed rope at a given rope strain and also to study the effect of wear and breaking of wires on strength loss for the various round-strand wire ropes used in mine hoisting.

By Richard O. Kneisley

Microseismic activity observed in both the laboratory and underground indicates that a quiet period, associated with the closure of existing fractures and strongly influenced by coal seam microstructure, occurs prior to coal bumps. Field studies conclude that coal mine bumps occur against a background of this so-called microseismic calm. This Bureau of Mines report summarizes microseismic activity associated with face bumps and floor bursts in a deep, western U.S. coal mine. Results conclude that while bumps are often accompanied by panel-wide increases in microseismic activity, bumps are not only preceded by a localized decrease in activity, but occur within these quiet zones. The results of this study concluded that microseismic activity may be applicable to the global detection of potential bump-prone zones, but that future studies are necessary to confirm these findings and to improve the techniques for evaluating stress control effectiveness.

Jan 1, 1989

By Gerrit V. R. Goodman, Fred N. Kissell, Charles D. Taylor

In This Chapter [Methane emission peaks Exhaust line curtain or duct The spray fan system Dust scrubbers with blowing ventilation Dust scrubbers with exhaust ventilation The ventilation of abnormally gassy faces Methane detection at continuous miner faces Ventilation and methane detection at bolter faces and Reducing frictional ignitions] This chapter gives guidelines for preventing methane gas explosions at continuous miner sections in coal mines, both at continuous miners and at roof bolters. The need to control peak methane emissions is particularly stressed. Emphasis is also placed on ventilation principles, monitoring for gas, and reducing frictional ignitions. METHANE EMISSION PEAKS Methane emission from the coal at continuous miner faces varies considerably. Plotted on a chart, methane emissions consist of a series of peaks and valleys corresponding to the cutting cycle of the mining machine, with the methane concentration spiking as the machine cuts into the coal (Figure 3–1) [Kissell et al. 1974]. These methane peaks can be substantial. For this reason, efforts to safely dilute the methane must focus on the level of the [ ]

Jan 6, 2006

By Thomas M. Barczak

Purchasing a new set of longwall shields requires a substantial investment. A poor shield design can lead to economic hardships, safety concerns for the mine workers, and closure of the mine. This paper addresses several key points that should be considered in the procurement process: (1) understanding your goals and the logic in selecting a higher capacity shield, (2) the importance of completing performance testing before production shield fabrication begins, (3) making sure performance testing is properly done, (4) measuring load(stress) development during performance testing, (5) testing a shield to failure, and (6) the value of buying extra shields. In addition, several challenges are proposed for consideration in future shield designs. These include (1) 100,000 life-cycle expectancy, (2) improved hydraulic diagnostic capability, (3) smart load control by optimizing setting pressures, (4) lubricated link joint design concepts, (5) composite material applications to reduce shield weight, (6) incorporating periodic weighting predictive algorithms into the data-processing software, (7) advanced component load measurement on two to three specially instrumented shields to detect loading in the structural components, and (8) constant set leg cylinder design.

Jan 10, 2000

By Anthony Iannacchione

One of the more pressing engineering problems for deep longwall mines in the Southern Appalachian Basin is to design longwall systems that will eliminate catastrophic coal pillar failure from the working environment. The purpose of this study is to quantify the behavior of a particular size abutment pillar prone to burst or bump. Because the 24.4-111 (80-ft) square abutment study pillar is within the pillar size commonly used in this region, understanding the behavior of this pillar should aid in future efforts to design optimum mining strategies. This research has attempted to construct the pillar stress and roof-to-floor convergence profiles in order to evaluate the ultimate strength, deformation modulus, visco-elastic deformation, and violent failure characteristics of the pillar during longwall mining. This information reflects the overriding influence of the local geologic characteristics on bursts, provides the field measurements needed to verify concurrent modeling studies, and suggest some basic mechanisms associated with the coal pillar bursts discussed in this paper.

By R. Karl Zipf

MULSIM/NL (multiple seams, nonlinear) is a new U.S. Bureau of Mines boundary-element-method (BEM) program for calculating stresses and displacements (is., convergence) in coal mines or thin, tabular rnetalliferous veins. This manual gives detailed operating instructions for MULSIM/NL and illustrates its use with several practical examples. While this manual concentrates on the practical aspects of actually running and using MULSIM/NL, another companion report titled "MULSIM/NL- Theoretical and Programmer&apos;s Manual" provides mathematical and programming details to those engineers and programmers who need to fully understand the FORTRAN program or desire to alter and enhance it. MULSIMINL analyzes one to four parallel seams that have any orientation with respect to the Earth&apos;s surface. Three main features distinguish MULSIM/NL from its predecessors: (1) nonlinear material models, (2) multiple mining steps, and (3) comprehensive energy release and strain energy computations. MULSIM/NL has six material models for the in-seam material including (1) linear elastic for coal, (2) strain softening, (3) elastic plastic, (4) bilinear hardening, (5) strain hardening, and (6) linear elastic for gob. The multiple mining step capability enables the user to simulate a changing mine geometry. Finally, MULSIM/NL performs comprehensive energy release rate calculations.

Jan 1, 1992