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By M. K. Larson, J. P. Dunford, E. G. Zahl, T. M. Brady

Researchers at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health, Spokane, WA, have collaborated with three Western longwall coal mines in an on going effort to develop technologies that will aid in providing safe and stable working areas. The goal of the research described here is to develop a stress monitoring system that will provide immediate information to mine managers for making daily safety decisions as areas of poor ground are mined through. Initial work has focused on answering preliminary questions regarding the reliability and use of stress change patterns. Research is concentrated on monitoring horizontal stress because horizontal stress is transmitted over long distances through stiff strata, thus allowing an extended length of entry to be monitored. This paper presents an explanation of the concept, key results from field tests at two mine sites, and a proposed process for implementing a monitoring system. System design layouts, instrument use, data collection and interpretation methods, and processes to present findings to mine staff are described. Additional validation and correlation with actual failure mechanisms are required before this approach can be recommended at ongoing operations. However, initial results indicate that this approach shows promise in mines prone to bumps and roof falls associated with large stress changes. In particular, analyses of measured changes in horizontal stresses appear useful.

Reliably measure stress chan¬ges in order to assess stability of mine openings. Approach: A durable, permissible, sensor and readout system have been developed and tested. How It Works: The stress sensing element is a taut steel wire which is, vibrated at its natural frequency, If the tension on the wire is changed because of deformation of the sensor housing, the natural frequency of the wire changes. This effect is similar to decreasing or increasing the pitch of a violin string by loosening or tightening it. Because the stress sensor electrical output is a frequency signal, rather than an amplitude signal, its accuracy is unaffected by the resistance of the signal wire, or other attenuation. Signal wires can be a mile or longer without affecting accuracy. When a button is pushed on the readout box, the sensor wire is electromagnetically excited and vibrates at its natural frequency. That signal causes a readout in illuminated digits. (By referring to calibration chart and the previous reading, the user knows the change in stress.) This system is permissible. To install the sensor, a slightly oversize hole is drilled into the mine pillar. Next, a special tool is used to both position the sensor and wedge it in place. Figure 1, shows the sensor and its integral wedge and hole-fitting piece.

Jan 1, 1976

Investigate the use and placement of lightweight concrete to improve ground control technology in deep mines where deformation occurs under heavy ground conditions and where there is danger of rock bursts. Approach Investigations of lightweight concrete properties and placement methods were conducted in the laboratory and in the field. Three test sections were completed: a monolithic, portal-type structure with integral walls and arch constructed aboveground; an underground test section constructed in a mine drift using plywood forms; and a test section constructed in a mine drift using an air-supported formwork. In the two underground test sections, the light-weight concrete was placed using a piston pump with concrete discharge line. A cooperating mine also used lightweight concrete, in the density range of 25 lb/ft3, to replace timber blocking in a raise preparation structure (the enlarged area across a vein where chutes and manway access arc placed). Other experiments included the use of precast lightweight concrete blocks in situations where ground support was needed, such as fur mine, ventilation doors, stoppings, and barricades.

Jan 1, 1990

By David S. Yantek

A-weighted sound levels around vibrating screens in coal preparation plants often exceed 90 dB(A). The National Institute for Occupational Safety and Health (NIOSH) is actively developing noise controls to reduce noise generated by horizontal vibrating screens. A 121-microphone, 3.5-meter-diameter array was used to perform beamforming to determine locations of significant noise radiation on the screen. Below about 1 kHz, the screen body was found to be the most significant noise source. The beamforming contour maps showed several key locations on the sides of the screen and the feedbox are the most significant contributors. Operating deflection shape (ODS) analysis was used to examine the screen behavior under actual operating conditions. This information is helpful in determining how to modify the screen body to reduce the noise radiated by the screen below 1 kHz. The analysis showed modal vibration patterns on the sides and feed box were the main contributors to noise. The results show several areas on the screen sides and feedbox that can be modified to reduce noise.

Jan 1, 2009

Oil from shales has long been a source of fuel in foreign countries; however, in the fuel economy of the United States this source is classed as a reserve for future needs. In fad, shale oil has never been produced here in quantities necessary to establish oil-shale utilization as a sustained industry. The first known resources of stored energy that man endeavored to utilize were probably wood and water, and from these he directly obtained heat and power, respectively. With the evolution of man came the search for and the development and use of other natural fuel resources, the series progressing through the solid, liquid, and gaseous fuels until today those of one type can be converted into another, depending upon the use for which they are intended. The most important fuels are those that appear naturally in the most concentrated, conveniently obtainable, and usable forms. With the discovery of each new and more concentrated fuel there has been an appreciable increase in the importance of and number of devices for converting these fuels into energy.

Jan 1, 1938

By F. W. Wood

ORIGINAL experimentation in specially designed arc-melting furnaces and a comprehensive review of technical literature have helped with an understanding of electric arcs as used in metallurgical applications. Results relevant to the distribution of electric potentials and currents, temperatures, pressures, the consumption of electrodes, the identities of particles participating in electrical conduction, and the modes and mechanisms of discharge are presented and discussed. Present knowledge of high-current arcs is insufficient to test pertinent theoretical suggestions. However, the chief doubts concern the identities and the liberation or formation of current-carrying particles. It seems that either (1) novel formulations of existing concepts are needed, or (2) essentially new concepts must be recognized to explain observations. An analysis of the situation has led the authors to favor the latter possibility and to suggest the existence of supplementary conducting particles. The conduction of current by the streaming of charged agglomerates is postulated. Another outgrowth of analysis is an equation for the arc potential as a function of current densities in the arc. In lieu of conclusions, the potentialities of practical applications and specific needs for fundamental clarification are summarized.

Jan 1, 1965

By M. Orchin

THIS PAPER is concerned with two aspects of the behavior of coal: (1) Dispersion by solvents atmospheric pressure and high temperature and (2) the destruction and regeneration of the coking properties of coal. Several pure polycyclic compounds and a coal-tar fraction were found to extract 95 percent of the organic material of a bituminous coal. About 20 percent of the extract was soluble in benzene, and this fraction contained the ?coking principle? of the coal. From an extensive chemical spectroscopic, and x-ray study of the benzene-soluble material, some conclusions could be drawn concerning the composition and structure of this fraction of coal. A possible commercial application of the extraction technique is in the preparation of low-ash carbonaceous material for the manufacture of electrode carbon.

Jan 1, 1951

By D. S. Kingery

Experiments initiated by the Bureau of Mines on August 26. 1969, and recent work of others, have demonstrated the effectiveness of ventilation for controlling concentrations of respirable coal mine dust. Substantial reductions in dust concentrations have been attained by increasing the volume and rate of air movement across the face and by controlling the airflow pattern. Ventilation experiments conducted by the Bureau using high-pressure fans as auxiliary ventilation units showed that lace-generated dust could he effectively controlled in five mines employing continuous mining machines. Additional data was obtained on industry installations in two mines using similar ventilation systems. By maintaining an airflow approaching 100 fpm across the entry, the experimental system reduced the concentration of respirable dust by factors as great as 6.4. In all mines where the system was used the face-generated dust concentrations were reduced to below 3 mg/m3. Total respirable dust in two cases was above the 3 mg/m value because of the dust content of the intake air. In some mines. depending upon the type of coal being mined and other dust control factors in use, it was possible to Obtain concentrations of less than 2 mg/m Although the technology for the application of the dust control system investigated is readily available, it is evident that additional engineering studies should he made in each mine where the system is to be applied.

Jan 1, 1969

By Raja V. Rarnani, Robert L. Frantz

"Scientific, engineering, and biomedical research teams synergystically developed major topical research areas in the Respirable Dust Center. Descriptions of their interactions and resulting accomplishments demonstrate how cooperative research within and among these study groups benefits the overall respirable dust research and practical application needs of the mineral industries.The development of a state-of-the-art small animal inhalation exposure facility suitable for studies of fresh and aged coal mine dust, a major goal of this research group, will contribute toward the GTCRD goal of advancing the understanding of causative mechanisms for the occupation-related lung impairments and the airway diseases of mine and mill workers. Such understanding includes improved definition of the role of various aspects of the lung environment (e.g., surfactant and the mucociliary system) in the disposition and toxicity of respirable dust, comprehensive characterization of the role of the pulmonary alveolar macrophage (PAM) and its secretory products on the development of dust-related lung disorders, and an expanded search for methods to reduce the toxicity of respirable dust both before and after it enters the lung. The National Academy of Sciences has recommended, in Measurement and Control of Respirable Dust in Mines, that respirable dust research should include study of the behavioral and constitutional factors affecting individual susceptibility to workers' pneumoconiosis occupational disease and the development of methods for detecting the potential onset of pneumoconiosis earlier and more conclusively than can be done using X-ray methods. These recommendations have guided the research group in its goals of establishing and disseminating a scientific protocol for standardizing the inhalation testing for all research objectives within the Generic Center which involve small animal exposures and implementing the infrastructure necessary to make lung tissues obtained during inhalation studies available to all researchers within the Generic Center."

Jan 1, 1995

By A. W. Khair, S. J. Jung

"A fundamental study of fragment size distribution and characteristics of fracture pattern is presented for the dynamic penetration of a conical bit into coal block. In this paper, damaged zones during crater formation and fragment size distribution were studied. Bit with a sharper tip angle and a smooth body configuration performed better penetration. Results suggest that in coal cutting the trend should be toward the face cleat direction using a sharper angled tip bits which consumes less energy for an optimum range of penetration depths, thus attaining maximum cutting efficiency and reducing fine fragments.1. INTRODUCTIONMuch research in the past has been done on energy requirements and mechanism of energy dissipation for ideal rock fragmentation in cutting process. However the mechanisms of energy dissipation or failure criteria for rocks in cutting process in order to evaluate the efficiency of energy requirements in specific rock fragmentation is not well understood. The formation of a crater in rock under the impact blow of a bit has been observed experimentally (Hartman, 1959). It is known that directly beneath the edge of the bit the rock is crushed into fine powder, toward the sides of the crater it chips out into relatively large fragments. (Sikarskie & Cheatham, 1973). Singh et al. (1967) investigated the cratering process under the two different conditions of static and dynamic loading. They found that the amount of energy consumed per unit volume of crater is unequal for the two different loading conditions. A complex network of fractures often extends downward and laterally into the rock below the bit. The surface of the specimens showed that the dynamic loading damaged larger area then the static loading."

Jan 1, 1989

By A. Wahab Khair

"This paper presents an analysis of fracture mechanisms in coal subjected to bi-axial state of stresses, indentation of laterally confined coal specimen. Coal specimens were loaded to failure by the straight wedge indenters at various lateral confinement pressures. Strain distribution and acoustic emission characteristics of coal specimens under stress were recorded. The influence lines of vertical forces acting on the horizontal straight boundary of the coal specimen for each type of wedge indenter have been established using holographic interferometry technique. The effects of wedge indenter angle, confinement pressure, and coal anisotropy on fracture types, failure modes, and post-failure conditions were studied. The results indicated that combined application of holographic interferometry and acoustic emission monitoring techniques is not only suitable ·for studying deformability of heterogeneous and microscopically discontinuous material under stress but it also enhances the mode of fracture during the post failure stage. INTRODUCTIONOne of the relevant processes in the coal cutting technology is the application of indentation theories. Since most cutting tools in the coal industry are wedge shaped most of the indentation research is found for a wedge shaped tool.A wide range of behavior is found in different rocks subjected to the wedge penetration. A rock which is elastic brittle at standard pressure might become elastic plastic at high confining pressure (Gnirk and Cheatham, 1963). It was also observed that some rocks will merely be crushed and indented by a wedge whereas others will crack and form chips, furthermore the existence or non-existence of chips depends mostly on the geometry of the indenter, type of rock and the depth of penetration (Evans and Murrel, 1958). However, coal cutting technology is mostly explained by models which use rigid wedge to penetrate into a brittle material in which both crushing and chipping will occur (Evans and Murrel, 1958, 1962)."

Jan 1, 1988

By Anu Martikainen

Utilization of belt air in underground coal mines has been discussed extensively during the last decade. The Final Report of the Technical Study Panel on the Utilization of Belt Air and the Composition and Fire Retardant Properties of Belt Materials in Underground Coal Mining formed by the Miner Act of 2006 recommends research on leakage, use of booster fans, and escapeway safety. This paper discusses the role of ventilation modeling in evaluating primary escapeway pressurization in a three-entry development system to improve emergency escape in a coal mine using belt air. The intake entry of the NIOSH Bruceton Experimental Mine was pressurized using a 1.1 m (42 in) diameter, 37 kW (50 hp) fan. The work details air movement in the simulated three-entry system and the resulting leakage patterns. Three mine ventilation software packages were compared to analyze their performance in predicting the airflows and leakage conditions with different fan settings. NIOSH researchers found that the measurement results correlated well with the results of modeling.

Jan 1, 2010

"A bed, British Columbia, Canada, coal, carbonizingproperties B 510Pa., coal, washing characteristics RI 4941A' bed, Pa., coal, washing characteristics RI 4834"

Jan 1, 1960

"D bed, Ky., coaL, washing characteristics RII 5140coking coal, reserves, estimate RI 5037Pa., coal, washing characteristics RI 4834, 4941D bed mine, Ky., coal, washig characteristics"

Jan 1, 1960

"M bed, Matanuska valley, Alaska, coal carbonizingproperties B 510M spectral lines, low-energy, study RI 5538Mab shaft, Leadvile district, Colo., investigation RI .1518Maberry process, for aluminum chloride TP 321"

Jan 1, 1960

"Qatar, crude petroleum, production, annualdata MY 1949-51Quality mine, Ark., coal, carbonizing properties TP 667washabilty study RI 496N. Dak., lignite, grindabilty as function ofmoisture, tests, results RI 5167"

Jan 1, 1960

By James D. Noll, M. Eileen Birch

A monitoring method for diesel particulate matter was published as Method 5040 by the National Institute for Occupational Safety and Health (NIOSH). Organic and elemental carbon are determined by the method, but elemental carbon (EC) is a better exposure measure. The US Mine Safety and Health Administration (MSHA) proposed use of NIOSH 5040 for compliance determinations in metal and nonmetal mines. MSHA also published a rule making for coalmines, but no exposure standard was provided. A standard based on particulate carbon is not considered practical because of coal dust interference. Interference may not be a problem if an appropriate size-selective sampler and EC exposure standard are employed. Sub micrometer dust concentrations found in previous surveys of nondieselized, underground coal mines were relatively low. If a large fraction of the sub micrometer dust is organic and mineral matter, sub micrometer EC concentrations would be much lower than sub micrometer mass concentrations. Laboratory and ?eld results reported here in indicate the amount of EC contributed by sub micrometer coal dust is minor. In a laboratory test, a sub micrometer EC concentration of 31µg m 3 was found when sampling are spirable coal dust concentration over three times the US compliance limit (2mg m3). Laboratory results are consistent with surveys of nondieselized coal mines, where EC results ranged from below the method limit of detection to 18µg m 3 when size-selective samplers were used to collect dust fraction shaving particle diameters below 1.5µm sub micrometer EC concentrations were ?7µg m3. In dieselized mines, sub micrometer EC concentrations are much higher.

Provide a central source of subsidence reference in formation for industry, academia, and government agencies interested in improving subsidence prediction and analysis under U.S. mining conditions. Approach Develop a comprehensive bibliography about mining related surface subsidence and store this information in a computer file. Make specific references accessible through a key word retrieval program. Supplement these key word identifiers by entry of author's name, title of publication, subject of text, or sponsor of publication. How It Works Requests for subsidence in-formation are made by phone or mail to the Bureau of

Jan 1, 1982

Provide the mining industry with an easy-to-use means of accurately predicting surface subsidence caused by longwall mining in the northern Appalachian Coal Basin. Approach The Bureau of Mines developed a subsidence prediction model using the novel approach of a variable subsidence coefficient. This approach had to be used because of the resistant strata types which commonly occur within the relatively thin overburden material typical in northern Appalachia. Such resistant strata precluded the use of the popular European methods that assume homogeneous overburden or overburden behaving as homogeneous from a subsidence point of view. The model is available in a BASIC computer program for use on most personal computers. The user has the options of obtaining individual subsidence calculations or may choose to develop a subsidence profile using an average overburden value. The program output can be generated in graphic or tabular form showing the location of the surface point with respect to the longwall panel edge, overburden depth, and the subsidence value.

Jan 1, 1986

By Keith A. Heasley, Timotlly M. Barton

Historically, the surface subsidence over underground coal mines has been predicted using empirical profile or influence functions which have little or no connection to the actual mechanics of the subsidence- Without a mechanistic basis, establishing the exact site-specific parameters to use in these empirical methods has been problematic. A practical subsidence predictive method based on mechanics has the appealing capability of allowing the determination of site-specific parameters from fundamental properties of the overburden with minimal field calibration work. This paper presents a case study where a mechanics-based, boundary-element program is used to calculate the surface subsidence associated with several panels of a Northern Appalachian longwall coal mine. The program used in this case study is called LAMODEL, and it incorporates a frictionless, laminated overburden into a general purpose displacement-discontinuity code primarily designed for calculating the stresses and displacements in coal mines or other thin seam or vein type deposits. In this paper. the program is used to calculate both the underground convergence and the resulting surface subsidence at three longwalls. The subsidence results from the model are compared with field measurements and analyzed The results from the case study in this paper demonstrate that the laminated model with calibrated properties can easily provide fairly accurate subsidence predictions and is fairly flexible for fitting measured subsidence. However, additional subsidence predictive case studies are recommended in order to ultimately evaluate the potential of the laminated overburden model for practical subsidence prediction