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By John C. Edwards

Carbon monoxide (CO) sensors are used in mine fire early-warning systems. Experiments were conducted by the U.S. Bureau of Mines with six diffusion-type CO sensors to determine their response to a reference CO concentration under both static and dynamic flow conditions. Static experiments were conducted with 0.5 L/min flow of 16 ppm CO in N2 through 8-and 12-L chambers. Dynamic flow experiments were conducted in two environmental chambers: One had directional flow capability of 1 m/s, and the second provided moderately nondirectional flow as high as 1.8 m/s. Reference CO concentrations of 13.5 to 19 ppm in air were used for the dynamic experiments. The results of the static experiments demonstrated that the sensors consistently underestimated the reference gas concentration. The dynamic experiment results showed the sensors provided reasonable agreement with the reference gas concentration when directional flow effects were not considered. Directional flow effects were evaluated for two sensors. One of the sensors showed a strong dependence upon the relative orientation of the diffusion tube with respect to flow direction. The second sensor did not show a dependence upon flow direction. The sensors' directional flow effect is significant for their proper in-mine utilization.

Jan 1, 2010

Provide ear protection which allows normal, unaltered hearing at low noise levels, yet protects the wearer from excessive noise. The Approach: A commercial earmuff with integral speakers has been adapted with a special amplifier so that low sound levels are not affected, but higher noise levels automatically reduced. How It Works: The discriminating earmuff developed by the Bureau of Mines has two modes of operation. In the first mode, where input sound levels are less than or equal to 83 decibels, the wearer will perceive noise at its actual level. For inputs in excess of 83 decibels, the second mode of operation begins and the sound perceived by the wearer is progressively attenuated, or reduced, as the input level is increased. A recognizable difference still exists between two adjacent sound levels enabling the wearer to differentiate between them.

Jan 1, 1975

By Edward Thimons, William A. Hertbrink

The effect of wind speed upon aerosol penetration into an idealized enclosure was studied The idealized enclosure was a painted plywood box that was 1 2X1 2 XI meters in volume Two fans supplied 1 7 m3 /min of filtered air to this enclosure at a static pressure of 2 8 mm of water The enclosure had a 7 5 cm diameter vent port which was isolated from the air flow around the enclosure To simulate holes in real enclosures, three 16-cm diameter holes were drilled on the front and back sides of the enclosure This simulated enclosure was placed in a tunnel-like structure The air flow from an ultra-light air craft was directed at the front of the enclosure The air speeds were varied between 14 and 36 km/hr as measured by rotating vane anemometer Static pressure in the enclosure was measured with an electronic manometer Two optical particle counters measured the particle number concentration of particles between the 0 35 to 0 5 µm inside and outside of the enclosure Aerosol penetration into the enclosure was computed as the ratio of the aerosol concentration inside the enclosure to the concentration outside of the enclosure The enclosure static pressures measured increase from 2 8 to 3 4 mm of water (P=00001) Aerosol penetration into the enclosure increased linearly with air velocity above 20 km/hr Theoretically estimated penetrations were correlated with observed penetration into the simulated enclosure When simple linear regression was used to model the observed penetration as a function of the estimated penetration, the value of the slope was 0 69±0 12 and the P value for the regression model was less than 0 0001 These results indicate that enclosure static pressure needs to be higher than the wind's velocity pressure in order to minimize aerosol penetration into these enclosures

Jan 1, 1999

GLOSSARY Acid- and toxic-forming materials. Rock or coal layers containing significant amounts of pyrite or other minerals which, if exposed by coal mining, will cause acid or toxic drainage to occur when acted upon by air and water. Add mine drainage. Any water with a pH less s than 6.0 draining from a coal mine. Water is often orange-colored because of the presence of oxidized iron. Adit. An underground mine entry at sites where coal seams are exposed at ground level. Apple core. A complete hilltop (360°) left exposed by not backfilling the highwall. Approximate original contour. The surface configuration achieved by backfilling and grading the mined area so that be reclaimed land closely resembles the general pre-mining surface configuration and blends into and complements the drainage pattern of the surrounding terrain. Area mining. A surface mining method that is carried on in level to gently rolling topography on relatively large tracts of land. Active area mine pits may be several miles long. Arid and semiarid regions. Lands, generally west t of We 100% meridian, where water use by native vegetation equals or exceeds that supplied by natural precipitation, and rainfall is insufficient to support agriculture. Annual precipitation is normally 20 inches or less. Auger mining. A mining technique often used by surface mine operators when the overburden becomes too for the coal to be mined economically using traditional surface mining methods. Large-diameter (usually 2'-4') horizontal holes are drilled as much as 300 feet into We vertical Me of the coal bed by an auger. Like a bit used for boring holes in wood, coal augers consist of a cutting head with a screw-like extension. As the auger turns, the head breaks up the coal and the screw carries it back into a conveyor that loads it directly into a truck. Backfilling. The operation of refilling an excavation using material removed during the mining process. Bench. The level or flat working area at the base of the highwall that is excavated between the exposed coal seam and the original surface of the ground. Bucket wheel excavator. A continuous-digging machine that uses a rotating vertical wheel with buckets for large-scale stripping and excavating. Cessation Order. Order to cease mining issued to a coal operator by the regulatory authority due to severity of violations, Contemporaneous reclamation. Restoration of mined land that occurs as soon as practical after coal removal. Contour mining. A mining method commonly used in eastern mountainous topography where coal is removed in a narrow strip around the hillside. The extent of the cut into the hillside is determined by the depth of overburden at the highwall compared with the thickness of the coal seam. Daylighting. A term used to describe a surface mining procedure that exposes abandoned underground coal mine workings to enable removal of the remaining coal. Daylighting is followed by land reclamation. Dragline. An excavating machine, usually used in large, flat areas, that drags a bucket (which holds up to 220 cubic yards of material) toward the machine by cables, loads it with spoil, and then hoists it wit a boom up to 350 feet long, allowing the machine to excavate wide benches by depositing the spoil hundreds of feet away from the highwall. Grading. The process of smoothing the disturbed areas of the mine site, after the coal is removed, to closely approximate the pre¬mining terrain. Haul road. Any road constructed, improved, maintained, or used by mine operators and located within the permit area. Head-of-hollow fill. See "valley rill." Highwall. The cliff-like excavated face of exposed overburden and coal in a surface mine. Hydroseeding. Planting of seed mixed in a water medium. Water, mulch, lime, fertilizer, and seed are blended and sprayed onto regarded soil.

Jan 1, 1992

To test the feasibility of hydraulic borehole mining for the recovery of phosphate ore from the deep, water-saturated deposits of northeastern Florida. Approach Phosphate ore is remotely extracted through a Bureau of Mines-developed hydraulic borehole mining system. Hydraulic borehole mining can remove underground ore deposits that cannot be economically mined by the usual open pit or underground methods. It is environmentally compatible, causing none of the surface disruption or ground water pollution usually associated with other methods of mining. Selectivity of the borehole mining system also allows economical recovery of small or discontinuous ore deposits while minimizing the removal of host rock. The hydraulic borehole mining system has been used successfully in the past to mine uranium ore and oil sands. (For examples of these and other applications of borehole mining see T Technology News Nos. 97, 95, 63, 56, and 48) How it Works A 16-inch-diameter borehole is drilled from the surface down into the buried mineral deposit, and the mining tool is installed. The borehole mining tool consists of a 12-inch-diameter pipe string and accessories capped with a three-passage swivel, and ending with a mining section. The mining section has four slurry inlets and an eductor located near the bottom of the section and a single cutting nozzle located near the top. The tool generates a high velocity water jet that erodes and slurrifies the ore. The slurry is drawn through the inlet into the eductor which lifts it to the surface where it is deposited into a slurry discharge sump. All the support equipment is located and operated on the surface; only the mining tool portion of the system is underground during the recovery operation.

Jan 1, 1983

By T. M. Barczak

Many of the support concepts currently used in the United States originated in South Africa. These products include the Hercules Crib1, Propsetter, MX Prop, Rocprop, and Spider Prop. Another recent development has been the introduction of hydraulic prestressing units, such as the Jackpot system, to various U.S. standing support systems. Several other prop-type supports with similarities to systems used in South Africa are in use in U.S. coal mines. Some exciting new developments that improve the installation and yield performance of props are also underway. In addition to prop-type supports, crib-type supports and single-unit systems such as the Can support are also frequently utilized in longwall tailgates in the U.S. The goal in U.S. support development is to enhance roof support capability while alleviating material handling barriers to reduce injuries associated with support handling and installation. Support products are generally full-scale tested at the National Institute for Occupational Safety and Health (NIOSH) in the unique Mine Roof Simulator load frame. The performance testing protocol is designed to simulate the full range of load conditions that occur in underground mining to identify the performance deficiencies and limitations of the support products. Once the products complete the performance evaluation, they are implemented into the NIOSH Support Technology Optimization Program (STOP). STOP is a window’s based software program that was developed by NIOSH for facilitating the design of standing roof support systems. STOP has become an industry standard to compare the performance capabilities and facilitate the application of these support products into various mining conditions. The purpose of this paper is to provide an overview of the support design and application philosophy in the United States.

By J. W. Pall

The method of mining bituminous coal in Pennsylvania cannot be treated in an extended manner in this publication since this would require more space than justified. The general plan of operation of most mines is on the room and pillar system, using double entries from which the rooms are driven In the early mining in the Pittsburgh coal bed the "checkerboard" plan was much used, but this entailed a large loss of coal in the blocks of coal that were left standing. In recent years there has been a tendency towards the adoptions of the panel, room and pillar method, also the block system, which ad mats of concentrated mining within a relatively small section of the mine It is not unusual to use 4, 6, or 8 parallel entries for the panel development. The longwall advancing method has been tried in some of the thin beds of the central coal field, but so far it has not passed beyond the experimental stage. The average extraction' of coal throughout the State is 714 per cent, but it is estimated that 15 5 per cent of the loss is avoidable, so the actual extraction should approximate 87 per cent. Pennsylvania is exceptionally well provided with means of transportation by trunk lines, branches, and by intra State railroads, among which are the Pennsylvania, Baltimore & Ohio, New York Central, Buffalo, Rochester & Pittsburgh, Western Maryland, Bessemer & Lake Erie, Pittsburgh & West Virginia, Pittsburgh & Lake Erie, Erie, Monongahela Division, and Montour railroads, all of which reach some of the bituminous mines The Monongahela River furnishes water transportation for Allegheny, Greene, Fayette, and Washington counties During 1923 the coal traffic on this river amounted to 18,709,084 tons, and of coke, 385,426 tons Coal is moved on the Allegheny River also, the total in 1923 being 911,178 tons s.

Jan 1, 1928

This chapter defines light as a type of energy, and tells how different features of light are measured. It 1s important to understand the units of light measurement because they are used throughout the rest of the book. But more Important, this will help you to understand the "regs" and how to get the best out of the lighting you have available! By the time you complete this chapter, you should know what candle-power, foot-candle, and foot-lambert refer to, and you will also be able to tell why the helmet that the new miner wears appears orange to human eyes. Light that you "see" is really radiant energy that hits the retina of the eye. Radiant energy moves out from a light source much like a series of bullets from a number of machine guns being fired at the same time in all directions.

Jan 1, 1976

By E. D. Gardner

"It has only been in recent years that the proper ventilation of metal mires has received serious consideration. Increasing temperature and humidity with greater depth in some of the larger mines of the West prevented the efficient operation of the mines and made the installation of mechanical ventilation systems necessary. Doors that interfere with tramming are generally needed to control properly the mechanically induced air currents and are one of the inherent disadvantages of the system. In fact the necessity for the use of doors in the main haulageways has discouraged the installation of mechanical ventilation in some metal mines.A number of mining companies in Arizona are using ventilation doors which can be opened and shut mechanically by the motorman without leaving his seat or stopping his train, end thus interfere very little with the transportation of the ore. The Copper Queen Branch of the Phelps-Dodge Corporation at Bisbee introduced these ventilation doors and adapted them from those in use in the company's coal mine at Dawson, New Mexico. Other mining companies have installed the same type of door and it is now being used in a number of districts in Arizona.The doors at the Calumet and Arizona mine in the Bisbee district are representative of those in use. The doors at this mine are substantially built of 2-inch lumber, are air tight, are well placed and have two openings or passageways. The main door, which is used for the motor trains, is 5 feet wide by 6 feet high and is opened by compressed air and closed by a counterweight. At the side of the motor door is the man door, which is 16 inches wide by 5 feet high and is opened and closed by hand."

Aug 1, 1921

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 T. Christos

The explosive oils, nitroglycerin (NG) and ethylene glycol dinitrate (EGDN), were extracted from dynamites by a halocarbon solvent and were then determined by high-pressure liquid chromatography. Separation was achieved by liquid-liquid chromatography on a column packed with Durapak-Carbowax 400/Corasil II and the eluted NG and EGDN were detected with a double-beam ultraviolet detector.

Jan 1, 1973

By Marilyn Biviano

This analysis was conducted in response to concerns raised by the Chairman of the Energy and Commerce Committee of the House of Representatives regarding the potential impacts on automobile production, GNP and employment resulting from embargoing south African supplies of the platinum-group metals, platinum and rhodium. This analysis should be considered an addendum to the recently released study in which the direct economic costs I of a U.S. embargo on selected South African strategic and critical materials are estimated. The estimated GNP and employment impacts result when a mineral shortage reduces domestic industrial production and are in addition to the direct costs estimated in the earlier study. The direct cost to this nation resulting from a decision to embargo six south African strategic and critical minerals was estimated at $1.85 billion per year during the 1988-1992 time frame of the study. The estimated direct costs include the costs to U.S. consumers resulting from higher strategic mineral prices, lower mineral consumption, and the cost of developing higher cost domestic mineral resources. A large proportion of the costs result from the shortage of the two metals: platinum and rhodium. The average direct annual cost of embargoing is estimated at about $1.4 billion for platinum and $384 million for rhodium.2

Jan 1, 1988

By Michael J. Sapko, Eugene M. Bazala, Eric S. Weiss, Kenneth L. Cashdollar

The data presented in this report are the results, to date, of an ongoing Pittsburgh Research Center Disaster5Prevention research program on the explosion hazards associated with blasting operations in noncoal mines. Laboratory and experimental mine tests have shown that oil shale and sulfide ore dusts can be ignited given the proper predispersed dust concentrations, particle size, and kerogen or sulfur content. Methane (CH) gas may also4be present in deep oil shale formations and can pose a significant added hazard to underground blasting operations. The most common explosive used for blasting in oil shale had been ANFO, a combination of ammonium nitrate and fuel oil; blasting in sulfide ore had used ANFO and/or dynamites. Tests conducted at the cannon gallery at Lake Lynn Laboratory near Fair chance, Fayette County, PA, provided a means of evaluating the relative incendivity characteristics of new and existing explosive products. Three explosives—a pumpable emulsion-ANFO blend, a packaged water gel, and an emulsion blasting agent—exhibited low-incendive qualities compared with other more highly incendive products such as ANFO and some dynamites. Based on the data collected during numerous full-scale blasts in oil shale and sulfide ore mines, the low-incendive products significantly reduced or eliminated the ignition hazards while at the same time providing effective fragmentation of the rock. Based on the positive results from the gallery and field testing, low-incendive explosives, coupled with good blasting procedures, show promise in reducing dust and/or gas ignitions associated with blasting operations in oil shale and sulfide ore mining applications.

By Thomas V. Falkie, R. Venkataramani

Underground coal winning operations can broadly be classified as conventional, continuous, and longwall mining. In conventional mining, the operations of cutting, drilling, blasting, loading and hauling, and roof support are performed in that sequence in each working face in a work area. The major difference between continuous and conventional mining is that the coal is cut and loaded by a continuous miner in the former, thereby combining the unit operations of cutting, drilling, shooting, and loading into one. Longwall applications have been viewed with great interest in recent years, and although at the end of 1970 there were only 37 longwall installations in the U. S. with combined production of less than 4 percent of underground total, there is no question about the growth potential of longwall in the United States. Increased capacity, versatility, and power characterize continuous miners today. Although continuous miners have outsold conventional gathering-arm type loading machines for some years, the latter, in the new extra-high capacity types, are continuing to find wide use. Whether the mining system is continuous or conventional, the haulage units may include six-wheel articulated shuttle cars, tractor-trailer units, or extensible belt and bridge-conveyor systems, all tending to increase the productivity of the face units. The decision as to which to choose - continuous or conventional mining - is complicated, and both systems are capable of high production rates. Most continuous miners in use today have a revolving pick-mounted drum to cut the coal and a gathering arm loading unit. Functionally, there is little difference between the loading unit in a

Sep 1, 1972

Reduce rockfall fatalities and injuries by using innovative blasting practices to reduce damage to the rock at the excavation limits with little or no increase in cost. The Problem Falls of highwall have been a leading cause of fatalities, injuries, and equipment damage in the surface mining industry. Although the number of highwall falls is not great, when such an incident does occur it is about 14 times more likely to be fatal or result in severe injury and damage to equipment than other types of surface mine accidents. Overbreak or damage to the rock from poor or improper blasting practices is a major factor contributing to rock falls. Presplitting or cushion blasting is the technique most often recommended for improved wall control. This type of blasting however, adds to drilling and blasting costs and is not universally accepted by the industry. Air gap presplitting techniques, also called air decks, are currently being used in some mines as a less costly alternative to conventional presplitting. Approach Blasting can cause highwall damage, but proper blasting techniques have been shown to reduce the magnitude of rockfall problems. In preventing rock falls, it is important to maintain the natural strength of the rock structure to the greatest extent possible. Improved blasting practices have three main advantages: 1) they are preventive rather than corrective in nature; 2) they are cost effective; and 3) they have a very low impact on the mining operation when properly implemented. New ways of evaluating highwall integrity, such as seismic refraction tomography, were investigated.

Jan 1, 1991

Provide a more efficient method of cooling hot working environments in deep mines than is possible with single stage spray coolers or cooling coil heat exchangers. Approach Pass warm mine air through several stages of horizontally oriented water sprays fed by the chilled water supply of the mine. How It Works This concept extends the capabilities and potential applications of the coolers described in Technology News nos. 71 and 93. In this multi-stage design, hot ventilation air is cooled while passing through horizontal water sprays. Air enters the cooler through a diffuser section which slows the airflow and distributes it evenly across the cooler with a minimum of pressure drop. This ensures uniform exposure of the warm air to the cool water and consequent high thermal efficiencies. In the three-stage cooler shown, cold mine service water is sprayed from the first water stage manifold on the downwind end of the cooler. Slightly warmed water from this spray stage is collected in a sump, pumped and then resprayed through the second stage manifold. The process is repeated again for the third-stage. An overall counterflow heat exchange effect is thus achieved by exposing the hottest incoming air to the warmer, third-stage water spray first and to the coldest, first-stage water spray last. Wave plate eliminators can be employed between stages of water sprays to increase thermal efficiency or at the outlet to minimize the water discharged into the mine ventilation air. Cooled air can then be ducted to hot work spaces or simply released

Jan 1, 1985

By W. H. Ode, W. A. Selvig

Investigations have shown interesting relationships between primary-tar and light-oil yields and chemical analyses of coals. These studies have been based largely upon results published by the Bureau of Mines in connection with its survey of the gas-, coke-, and byproduct-making properties of American coals. This paper gives the results of a similar correlation in which the range in rank and type has been extended to include nearly all classes of coal, the object being to determine relationships that are significant in predicting tar and light-oil yields from chemical analyses of coals. The yields of primary tar and light oil are important in two fields of coal utilization, namely, combustion and carbonization. It is generally recognized that the principal cause of smoke produced upon burning coal is incomplete combustion of tar and light-oil vapor released during burning. The greater the tar and light-oil yields of a coal, the greater is its potential smoke-producing property. During the present war, development of new sources of fuel oil has been emphasized, especially where the supply of petroleum products is limited. One possible source of a substitute fuel is the tar and light oil that can be obtained by low-temperature carbonization of coal. In both England and Germany large quantities of low-temperature tar and oil are being processed as a source of liquid fuels. It is obvious that primary-tar and light-oil yields are of paramount importance in the selection of coals for such use.

Mar 1, 1944

By John N. Murphy

INTRODUCTION It's a pleasure to be with you and to share in this opening session for the 27th Annual Institute on Mining Health, Safety, and Research. As we come together today, I would like to reflect for just a moment on the past Institutes. Much of the progress in Mine Health and Safety has been the subject of presentations and discussions at the previous Institutes, either by identifying the issues, proposing techniques to overcome the problems, or presenting new findings to address important issues for the mining industry. May I extend our thanks and congratulations to VPI and to the planners and organizers of all of these Institutes for their important contributions to our mutual goals of improving mine health and safety. In the time available today, I would like to accomplish two objectives: 1. Provide my assessment of the current status of the Mining Health and Safety Research Program; and 2. Share with you the continuing need and direction for the Mining Health and Safety Research. MINE HEALTH AND SAFETY RESEARCH TODAY Mine Health and Safety Research was conducted formerly at four geographical locations within the USBM, specifically: Pittsburgh, Spokane, Twin Cities, and Denver. Although the Twin Cities and Denver Centers were closed, we have been successful in relocatingfmaintaining much of the core competencies to conduct a responsive, multidisciplinary Mine Health and Safety Research Program. The current staff at Pittsburgh and Spokane directed toward Health and Safety Research totals 397. This includes Lake Lynn Laboratory, about 60 miles southeast of Pittsburgh, where large-scale mine fire and explosion research is conducted. With the closures and transition we have worked to maintain the core competencies necessary to address Health and Safety issues. In some cases we have made arrangements to provide the requisite core competencies through external organizations. An example is the reassignment of the diesel particulate instrumentation capability from Twin Cities to Pittsburgh. In the case of diesel emission control, due to the cost of relocating laboratories and the lack of the appropriate skills at Pittsburgh or Spokane, the emission control laboratory is now being operated in Minneapolis through a contractual arrangement with the University of Minnesota.

By M. R. Geer

The ever-increasing need to guard against stream pollution has intensified interest in the problems of handling and disposing of flotation tailing. Therefore, the Bureau of Mines investigated the possibility of using crushed washery refuse to adsorb the free water in thickened flotation tailings on a bench scale and then in a pilot plant because the conventional methods of disposing of coal flotation tailings--impounding them or filtering them so they are dry enough to be conveyed to the refuse dump--are sometimes either impractical because of space limitations or costly because of low filter capacity. Most of the refuse samples tested were of similar mineralogical composition and exhibited similar water retention capability. The amount of crushed refuse required to adsorb the water in a particular tailing was influenced greatly by the fineness of the solids in the tailing and hence the percentage of solids to which it could be thickened. The ratio of crushed refuse to tailing solids required to provide a mixture dry enough to be carried on an inclined conveyor belt varied from 2.4 to 6.4. Several chemical agents that were tested were very effective in turning the free water in tailings into a stable gel. Fly ash also was very effective in adsorbing water.

Jan 1, 1968

By Dennis R. Dolinar

The danger to personnel, equipment, and pillar structure created by the spalling of a coal rib can be minimized by installing rib bolts. To assure that a configured support system will maintain a coal rib, the U.S. Bureau of Mines developed a rib bolt system based on a nonpreventable failure concept. A statistical equation quantitatively relates the amount of rib retained to the bolt spacing and the width of the spalled material. Laboratory test results show that the equation accurately predicts the amount of material retained and confirm the validity of the support concept. The examination of rib bolting at a coal mine experiencing rib sloughage provides evidence that the effectiveness of the support can be related to the failure pattern of the spalled material. An analysis of roof and roof support reaction to rib sloughage at the mine indicated that the rib sloughage had little effect on roof stability. Although supporting ribs might not affect roof stability, laboratory test results indicate that the material retained by the support can sustain a load up to 20 pct of the intact compressive strength of the material.

Jan 1, 2010