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By P. Delogne, L. Deryck, R. Liegeois

So far as the propagation of electromagnetic waves is concerned, an underground tunnel behaves like a pipe or hollowed waveguide. Waves propagate in this tunnel with a low attenuation only if their frequency is higher than a so-called critical frequency which depends on the shape and mostly on the cross -dimensions of the tunnel and which value is in the neighbourhood of several tenths of MHz. However, when a metallic conductor is stretched along the gallery the electromagnetic characteristics of the latter are considerably modified and the effect of the cut-off frequency disappears; this is due to the fact that the gallery equipped with such a conductor works like a coaxial cable where the conductor serves as the outward conductor and the wall of the gallery as the return conductor. This is the principle of the monofilar waveguide cable which has been perfectly studied by Gabillard. Two mean characteristics of the monofilar mode are as follows: first of all, when the cable is suspended in the middle of the cross section of the gallery, the electromagnetic field occupies all the space between the wire and the walls of the gallery. When the wire is close to the wall, the electromagnetic field tends to become concentrated between the wire and the wall, with the consequence that, with the given monofilar mode power, the aerial of a receiver standing somewhere in the tunnel will capture a weaker and weaker signal. Secondly, owing to the fact that the mode of monofilar propagation uses the ground as return conductor, its power of propagation is considerably diminished; the closer the wire is to the wall the higher the attenuation, for only a very small part of the wall is utilized as return conductor. To cover great distances, everything else being equal, two or more conductors must be placed in the gallery. If the distance between two conductors of a cable is much smaller than the distance between one or other of the conductors and the walls; or again if one of the conductors surrounds the others and forms a screening, two sorts of modes appear: on the one

Jan 1, 1973

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.

Reduce the dust exposure of workers in large processing buildings at mineral processing operations, using a total mill ventilation system.

Jan 1, 1994

By James D. Sisler

Location and Age The main bituminous coal field of Pennsylvania lies in approximately twenty counties west of the mountain area which extends in a northeast southwest direction through the central part of the Commonwealth. The coal fields lie in a dissected peneplain, still in the youthful stage of erosion There are numerous V shaped valleys in the bituminous fields and the tributaries of the larger streams have rather steep gradients The main streams flow in rather narrow valleys with comparatively small flood plains. The coal beds of Pennsylvania are of Carboniferous age, and are confined to two systems, the Permain and the Pennsylvanian The latter system is divided into an upper or Pittsburgh series and a lower of Pottsville series The Peimain system is divided into an upper and lower series The Pottsville series of the Pennsylvanian is represented in western Pennsylvania by the Upper Pottsville only The upper or Pittsburgh series of the Pennsylvanian is represented by the Monongahela, Couemaugh, and Allegheny groups Geologic Structure. The rocks of the bituminous coal fields are folded into many anti clines and synclines extending in a general northeast direction across the western part of Pennsylvania The intensity of this folding in creases toward the mountain region West of Chestnut Ridge, which is in Fayette, Westmoreland, and Indiana counties, the folding is minor, and the coal beds have low dips East of Chestnut Ridge, v here folding is stronger, the basins are wider and the coal beds rise steeply on the flanks of the anticlines Geology. The bituminous coals of Pennsylvania are associated with shale, sandstone, clay, and limestone Each group has different proportions of these deposits, and the proportions vary at different localities within the same group.

Jan 1, 1928

By Harold W. Lipper

Helium production and shipment reached new peaks in 1.361. The Bureau of Mines produced 727 million cubic feet, 13 percent more than the 1960 record, and shipped 552 million cubic feet, 16 percent more than the 1960 record. Production exceeded demand for the third successive year, enabling the Bureau of Mines to add 174 million cubic feet to the volume stored underground for future use. At the end of 1961, the total volume of helium in underground storage in the Clifside gasfield was 44-7 million cubic feet. Contracts to implement a long-range helium conservation program were completed with four companies, obligating all the contracting authority of $47.5 million a year made available by the Congress. The four companies will finance, build, and operate helium extraction plants to recover from natural gas an annual average of 3.1 billion cubic feet of helium that would ordinarily be wasted when the helium-bearing natural gas is used for fuel.

Jan 1, 1962

By R. Karl Zipf

Use of Salamon's stability criterion in underground mine design can prevent the occurrence of catastrophic domino-type pillar failure. Evaluating the criterion requires computation of the local mine stiffness and knowledge of the post failure behavior of pillars. This paper summarizes the status of the practical use of this important criterion and suggests important research to improve our capabilities. Analytical and numerical methods are used to compute the local mine stiffness. Work to date in computing local mine stiffness relies mainly on elastic continuum models. Further work might investigate local mine stiffness in a discontinuous rock mass using alternative numerical methods. Existing post failure data for coal pillars are summarized, and a simple relationship for determining the postfailure modulus and stiffness of coal pillars is proposed. Little actual postfailure data for noncoal pillars are available; however, numerical models can provide an estimate of post failure stiffness. Important factors controlling postfailure stiffness of rock pillars include the postfailure modulus of the material, end conditions, and width-to-height ratio. Studies show that the nature of the failure process after strength is exceeded can be predicted with numerical models using Salamon's stability criterion; therefore, a method exists to decrease the risk of this type of catastrophic failure. However, the general lack of good data on the postfailure behavior of actual mine pillars is a major obstacle. Additional back-analyses of failed and stable case histories in conjunction with laboratory testing and numerical modeling are essential to improve our ability to apply the stability criterion.

Jan 5, 1999

Track and control the tram maneuvers of continuous mining machines by developing and evaluating a laser sensor system. Background Progressive technology has the potential to greatly improve mine-worker safety, helping to create a safer, better working environment for mine workers by keeping them away from the dangerous face area. To benefit from such technology, the Bureau is investigating remote, computer-assisted operation of mining systems for underground, highwall, and surface mining applications. A cornerstone for computer-assisted operation is an effective guidance system. Since there are no guidance systems on any commercial continuous miners (CM's), the Bureau it-self developed and tested a laser-based sensor system, based on a commercial sensor called Lasernet. The laser-based guidance system employs four laser scanning sensors at fixed locations in a mine entryway to report the angular coordinates of two cylindrical retro-reflective targets mounted on a CM. Using triangulation, a real-time microcomputer system processes the sensor data and updates the xy position and heading (h) of the CM five times per second. Using a simple control algorithm and communications interface to the CM control computer, the system also controls rotational and translational tram maneuvers.

Jan 1, 1992

By Richard G. Geyer

One aspect of a program to improve the chances of survival following coal mine disasters is the development of a communications system which will allow surviving miners to make their circumstances known to rescue teams. Various communications techniques can be considered, including electromagnetic systems, acoustic systems, and hybrid systems. The electromagnetic and acoustic systems would be independent of existing mine communications systems and set up specifically for use in emergencies. Hybrid systems might use a short emergency link to existing telephone systems in the mine. Many variations are technically possible, and the primary task is in evaluating the relative merits of each, so that the most workable system can be selected.

Jan 1, 1973

By Robert C. Hickman

"INTRODUCTION The Big Four fault and the Sandy Creek fault, with several cross faults, traverse the Stalion-Curnel fluorspar prospect in a northeasterly direction. The Big Four mine, about three-quarters of a mile northeast of the prospect, is the only active mine in the immediate area.A resistivity survey was made of a portion of the prospect by the Division of Geophysical Exploration, Bureau of Mines, in May and June 1946. As a result of this survey, five holes were drilled by the Bureau of Mines during the period from October 8 to December 16, 1946. Two Longyear No. 12 Junior Straitline diamond drills were used for the work.ACKNOWLEDGMENTSIn its program of investigation of mineral deposits, the Bureau of Mines has as its primary objective more effective utilization of our mineral resources to the end that they make the greatest possible contribution to national security and economy. It is the policy of the Bureau to publish the facts developed by each project as soon as practicable after its conclusion. The Mining Division, Lowell B. Moon, chief, conducts preliminary examinations, does the actual investigative work, and prepares the final report. The Metallurgical Division, Oliver C. Ralston, chief, analyzes samples and makes beneficiation tests.The project was under the supervision of Mitchell H. Kline, chief, Raleigh Branch, Mining Division."

Mar 1, 1948

By R. Karl Zipf

The sudden, violent collapse of large areas of room-and-pillar mines poses a special hazard for miners and mine operators. This type of failure, termed a 'cascading pillar failure' (CPF), occurs when one pillar in a mine layout fails, transferring its load to neighbouring pillars, which causes them to fail, and so forth. Recent examples of this kind of failure in coal, metal and nonmetal mines in the U.S.A. are documented. Mining engineers can limit the danger presented by these failures through improved mine design practices. Whether failure occurs in a slow, non-violent manner or in a rapid, violent manner is governed by the local mine stiffness stability criterion. This stability criterion is used as the basis for three design approaches to control cascading pillar failure in room-and-pillar mines-the containment approach, the prevention approach and the full extraction mining approach. These design approaches are illustrated with practical examples for coal mining at shallow depth. Cascading pillar failure {CPF) in room-and-pillar mines can go by many other names, such as `progressive pillar failure', `massive pillar collapse', 'domino-type failure' or 'pillar run'. In this kind of failure when one pillar collapses the load that it carried transfers rapidly to its neighbours, causing them to fail, and so forth. This failure mechanism can lead to the rapid collapse of very large mine areas. In mild cases only a few tens of pillars might fail; in extreme cases, however, hundreds, even thousands, of pillars can fail. CPF can have catastrophic effects on a mine, and sometimes these effects pose a greater risk to health and safety than the underlying ground-control problem. Usually, the CPF induces a devastating air blast as a consequence of the displacement of air from the collapse area. An air blast can disrupt the ventilation system totally by destroying ventilation stoppings, seals and fan housings. Flying debris can seriously injure or kill mining personnel. The CPF might also fracture a large volume of rock in the pillars and immediate roof and floor. In coal mines and certain other mines this can lead to the sudden release of large quantities of methane gas into the mine atmosphere; a methane explosion might result from the CPF. CPF is at the far end of the spectrum of unstable pillar failure. At the other end are slow `squeezes' that develop over days to weeks and, because of their slow progress, do not pose an immediate danger to mining personnel. There is ample warning time for men and machinery to get out of the way of the failure. In a CPF, however, the failure progresses so rapidly that men and equipment cannot be evacuated in time. Significant seismic energy is released as a consequence of the rapid failure and collapse. CPF should not be confused, however, with coal-mine bumps and rockbursts. In some cases the damage can appear similar, but the underlying mechanics are completely different. As will he shown later, the mechanics of CPF depend on the applied vertical stress and the post-failure, i.e. strain-softening, behaviour of the pillars. In a CPF pillars shed their applied load rapidly and have very little residual strength after failure. The collapse itself may release significant seismic energy, but otherwise the mine is seismically quiet. Alter a CPF the openings in the affected mine workings have usually closed completely. In contrast, coal-mine bumps and rockbursts occur in seismically active mines. Research has shown that coal-mine bumps and rockbursts are seismic events induced by mining that damage underground mine workings. Bumps and bursts are thus a subset of a much larger set of mining-induced seismic events.[ Only some of these seismic events damage mine workings; fortunately, most do not. The mechanisms by which a mining-induced seismic event can lead to a damaging coal-mine bump or rockburst is still a significant research area.2 After a bump or rockhursr the affected mine workings may or may not be completely closed. For example, in the coal-mine bump described by Soler and co-workers2 the mine workings remained open even though the pillars were destroyed during the bump event. Because CPF differs from a coal-mine bump or rockburst, the design approaches to control their occurrence also differ. The design recommendations developed here apply to CPF and not to bump- or burst-prone mines. Cascading pillar failure examples Unfortunately, CPF has occurred in room-and-pillar coal, metal and non-metal mines. The most infamous example is the Coalbrooke colliery in South Africa, where 437 miners perished where [si >1 3at1ttsumsus7car kky vArtMixiL7i nesafr tramwsamn ures] on 21 January, 1960.1 Table I summarizes the mining dimensions of 13 examples of rapid pillar collapse in U.S. coal mines. All occurred during the 1980s and 1990s, and all happened suddenly or without significant warning. Most resulted in air blasts and damage to the ventilation system. Table 2 gives the mining dimensions of six room-and-pillar metal and non-metal mines in the U.S.A. where failure occurred in all probability by the CPF mechanism. The collapse areas can be huge. Fortunately, some of these failures gave advance warning. At the lead-zinc mine slabbing from pillars and roof falls began four weeks prior to the main collapse.3 At the copper mine considerable rock noise and smaller failures preceded the main collapse by five days.5 At the copper-silver mine it is not known if nature provided a warning.6 Evidently, the trona mine collapsed without warning.7,8 Rock noise and other failure warnings preceded the silica mine collapse by three weeks. v The presence or absence of warnings at the salt mint is not known. to Most of these collapses induced a substantial air blast; damage to the ventilation systems was limited, however, to bent airdoors and a few downed stoppings, except at the trona mine where extensive damage to the ventilation system resulted.

By W. F. Hughes

The thermodynamics of an electromagnetic field-fluid interaction system is discussed. A review of the thermodynamics of linear media (the permittivity and permeability taken as functions of density and temperature) is presented; then an extension is made to nonlinear media (the permittivity and permeability taken as functions of the fields). Expressions for thermodynamic properties and reversible work are derived and the first law of thermodynamics for magnetohydrodynamic flow is discussed.

Jan 1, 1968

Objective To develop a passive, inexpensive technique for monitoring explosion overpressures within sealed areas in underground coalmines. Background From 1994 to 2000, seven explosions of methane and/or coal dust occurred within the worked-out, sealed areas (gobs) of underground U.S. coal mines. These explosions, believed to have been started by lightning, destroyed many seals and caused much damage external to the sealed area. One gob explosion went undetected until the mine operator reopened the sealed area and discovered the damage. Fortunately, these gob explosions did not cause any fatalities or injuries. Because lightning occurs in just about all mining areas, several questions arise. Could gob gas explosions be occurring in other sealed areas and going undetected? If so, what is the magnitude of the resulting explosion overpressures? The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) undertook a study to identify and evaluate passive measuring devices to monitor and quantify the overpressures associated with such explosions. This work was done in parallel with full-scale explosion experiments for evaluating the strength characteristics of seals used for isolating areas in underground coal mines. Approach Evaluation studies were done in PRL's 20-liter explosion test chamber and in the full-scale Experimental Mine at Lake Lynn Laboratory to evaluate the response and accuracy of various commercially available automobile tire pressure gauges to overpressures generated from gas and dust explosions. The first series of tests was done in the 20-liter chamber, which is used to study the explosibility and inerting of fuel dusts and gases. Data from the tire pressure gauge tests were compared to the pressure-time data obtained from the 20-liter chamber 's traditional electronic strain gauge pressure transducer recorded on a high-speed data acquisition system. To evaluate the tire pressure gauges, the valved inlet (tip) of the candidate pressure gauge was removed and the body of the gauge was cemented with epoxy into a 0.25-in pipe elbow and attached to the outside of the test chamber. A second series of tire gauge evaluation tests was done at Lake Lynn during explosion-resistance testing of seals used in underground coal mines. Full-scale seals (20 ft wide by 8 ft high)were constructed as one wall of a 2,000-ft3 chamber and exposed to a series of methane explosions. Average overpressures ranged from20 to 80 psi. The seals were built with various strength materials ranging from 7 to 48 in thick. The modified tire gauges are attached on the outside of the chamber to a 0.25-in NPT pipe that extends into the chamber (figure 1). The axis of the gauge is mounted at a right angle to the plane of the seal to minimize the coupling of any seal movement to the stem of the gauge that may cause inaccurate readings. The internal explosion pressure history is recorded with a strain gauge pressure transducer mounted inside the chamber. Methane is injected into the chamber, mixed with air, and ignited with an electric spark located at the geometric center of the chamber. Maximum explosion overpressures are recorded and compared with the tire gauge pressure.

Jun 1, 2001

By Forrest T. Moyer

THE SAFETY record of the mineral and mineral-fuel-mining-and-processing industries retrogressed slightly in 1964, as indicated by the 3-percent increase in the frequency rate of all injuries. A slight improvement in the fatality rate was more than offset by the less-favorable rate of occurrence of nonfatal injuries. The overall-operating activity of these industries was lower in 1964 as measured by slight declines in employment and total man-hours of worktime. Injury Experience.-The rate of occurrence of all disabling work injuries in the mineral industries was 18.00 per million man-hours. This overall rate in 1964 comprised frequencies of 0.29 for fatal injuries and 17.71 for nonfatal work disabilities, which compared with respective rates of 0.30 and 17.20 in 1963. Fatalities totaled 538 or 30 less than in 1963. However, the total nonfatal disabilities of 33,151 in 1964 was 492 higher than in the preceding year.

Jan 1, 1965

By Lloyd A. Morley, Robert Stefanko

The most time-consuming research segment was assembling the ref¬erences. These are provided immediately after the conclusions but are divided into two categories. The first is directly applicable publi¬cations, correspondence and personnel communications. The second listing contains those publications that are not directly tied to the research but where a probable application exists. In both listings, all important USBM publications are provided. The reference numbers used in the report apply only to the first reference portion. Further¬more, it should be noted that all entries are not used but are retained to help anyone who wishes to look further into different or allied areas of this research topic. Explosion-proof enclosures have been researched since approxi¬mately 1906. Even so, little is understood about the mechanism by which they are effective. Due to the voluminous literature published, there is a good probability that the assembled list is still incomplete. The literature search took the following directions. Work was first directed to reviewing the several references assembled by the Department of Mineral Engineering - Mining Section prior to the present project year. As a result, some duplications and inapplicabilities were found and eliminated. The primary sources of the previous search were the commonly available and usually superb library listings, such as Engineering Abstracts. Because these sources have enormous content on all subjects, they were cross-checked in the first semiannual period several times by different individuals to make sure all normally avail¬able literature were uncovered.

Jan 1, 1974

By A. R. Mumford

The fuel economy ot a. plant m be better than ite anxious friend.a J'ealize. A watchful a-aper1.ntend.ent of a Goverment plant, kn.owing that improvements in plant equipment bad. been made since hie atOkel'e were installed, was almosi per­ suaded to aubatitute a new t.,pe. The Bul'eau. of Mines was asked to aaoertain the a.cti.i&l performance ot the old stokera and tound. the plant alr doing from three to five per cent better than was promieed for the new egp.ipment. Tbe va.1.ue ot accurate knowledge of plant perfoimarice, am the need. ot eqm.pment to weigh and measure quantities is thus demonstrated. The boiler and ,tour ett1c1enc, was found to be 75 per cent, and the overall efficiency of the boiler, etoker• and economize, wae 78 per cent. Both records are high, and are to be attributed to ce in operation, to good working condition of the plant, and to the low rate ot evaporation, which was only aboui two-third., et the botler'e rated. capacity. The plant teated conaiated ot two la.boock & Wilcox boiler, tired b1 means of over teed 1toker1 and equipped wi t,b. a fuel economiaei- 1n the uptake. The bo1lel'a ,upplied ateam to two large water pump being used only intermittently.

Jul 1, 1922

By S. H. Katz

Tar and suspended matters are removed from manufactured gas used for domestic and industrial purpose.

Jul 1, 1922

By George Bockosh

Mr. Bockosh is an electrical engineer with the U.S. Bureau of Mines In Pittsburgh, and has devoted the last two years to research on underground illumination. He formerly was a mine maintenance foreman and worked two years underground. He is a graduate of the University of Pittsburgh, where he is now working toward his masters degree in mining. When Congress first legislated light in American coal mines, it was a little like mandating a walk on the moon before the first satellite had been put in orbit. It was never a question, of course, of whether it could be done. But no one knew quite how. It's one thing to string a few light bulbs, and quite something else to provide uniform, sufficient, safe and reliable illumination, with fixtures that will hold up under some of the toughest conditions in the world - in the life-and-death circumstances of a craggy, black cavern filled with dangerous, moving machinery. In fact, in 1969 when Congress originally mandated illumination standards for the work places of underground coal mines, no one even knew just how much light was needed. That question was answered within a year by the National Bureau of Standards. In a study commissioned by the U.S. Bureau of Mines, the Bureau of Standards determined that underground mine should be illuminated with a light intensity of 0.06 foot-lamberts, a measurement of light reflected from surfaces in the lighted area-as opposed to foot-candles, a measurement of light from the source of illumination-in order for miners to adequately see what they are doing. That study was followed by more detailed research done at the Bureau of Mines' direction by the Research and Development Department of the Naval Ammunition Depot in Crane, Ind. This work evaluated the specific lighting needs of miners engaged In more than 100 different job tasks in all three types of coal mining- conventional, continuous and longwall. The Naval Depot report brought forth nearly 300 pages of detailed lighting data and concluded that proper illumination of mine work areas would serve more than just the cause of mine safety.

Jan 1, 1976

Provide minx operators with means for evaluating dust generation and bit wear effects on Production without costly and extensive underground testing. Approach Develop personal-computer-based cutting system models that will simultaneously evaluate machine, Coal seam, and mine-operator-controlled parameters for their interactive effects on dust generation, bit wear, and Production by either a longwall shearer or a continuous miner. How It Works CSM Programs have been developed to analyze relative dust generated by a double-drum, ranging arm, longwall shearer and a continuous miner. These interactive programs Provide relative dust, culling forces, and production values for any given set of mining machine parameters, specific seam conditions, and operator-controllable parameters. Expanded versions of each program provide a dynamic evaluation of the effects of bit wear, over time, on production.

Jan 1, 1989

By R. Larry Grayson, Douglas F. Scott

Data on health-related illnesses and disease in the mining industry are scarce, and information on rates and costs is not readily available. Substantial amounts of research are being directed to addressing these issues, including work at the National Institute for Occupational Safety and Health’s (NIOSH) mining health and safety laboratories in Spokane and Pitts-burgh. This paper briefly discusses the current status of some miner health-related issues, including those involving coal dust, silica dust, diesel particulate matter, asbestos, noise, lead, welding fumes, and skin disorders, as well as research and other activities aimed at protecting miners from occupational illnesses and disease.

By R. V. Ramani, R. Stefanko, G. W. Luxbacher

1 9 THIS IS A DIGITAL COMPUTER SIMULATION OF THE VENTILATION SYSTEM OF A MINE LOCATED IN WASHINGTON COUNTY; PENNSYLVANIA. THE VENTILATION SURVEY ON WHICH THIS SIMULATION IS BASED WAS RUN FROM OCT. 27-30 AND ON NOV. 2;1976 IN THE ACTIVE PORTION OF THE MINE INBY COMBS SHAFT AND THE INACTIVE PORTION AROUND AND INBY DONAHOO SHAFT. FOLLOW-UP SURVEYS WERE THEN RUN ON FEB. 18 AND FROM MARCH 7-11;1977 TO INCLUDE THE MAIN HAULAGE SYSTEM OUTBY THE ACTIVE AREAS 0F THE MINE. ALL SURVEY DATA WAS NORMALIZED TO A STANDARD DENSITY OF 0.075 POUNDS/CU.FT. PRIOR TO THE CALCULATION OF INPUT PARAMETERS FOR THIS SIMULATION.

Jan 1, 1977