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By Joseph Kuti

Longwall mining is the term used for the underground extraction of a wide and deep panel of coal. Such a panel may be blocked out by one or more entries on either side ("head" and "tail") of a longwall face. If all the entries are pre-driven, the panel extraction is termed longwall retreat mining. With one exception, all the longwall faces in the United States are of this type.1 Prior to the general decline in the rates of production with Continuous Miners, the development of the multiple entries generally kept ahead of the longwall extraction rate. This is no longer the case: longwall extraction rates far exceed the rate of development. In addition to this problem, in newly established mines, the development of a haulage and bleeder system based on multiple entries results in a lead-time of three years or more before longwall mining can be applied.

Jan 11, 1979

By Joseph Kuti

Longwall mining is the term used for the underground extraction of a wide and deep panel of coal. Such a panel may be blocked out by one or more entries on either side ("head" and "tail") of a longwall face. If all the entries are pre-driven, the panel extraction is termed longwall retreat mining. With one exception, all the longwall faces in the United States are of this type3 Prior to the general decline in the rates of production with Continuous Miners, the development of the multiple entries generally kept ahead of the longwall extraction rate. This is no longer the case: longwall extraction rates far exceed the rate of development. In addition to this problem, in newly established mines, the development of a haulage and bleeder system based on multiple entries results in a lead-time of three years or more before longwall mining can be applied. This is one reason why earlier projections and much of the optimism attached to longwall mining as a principal "savior" in the energy crisis should be viewed with some caution. The alternatives to retreat mining with multiple entries are: Modified retreat mining- where the tail-entry is being formed during the mining of-the panel ("2"-system). Some form of advance mining-where the head-entry or both head and tail entries are being formed as part of the longwall extraction process. These methods are well-known and well-established. Variants of them are being practiced in Canada, Central and South America, but not in the US. It is primarily the laws governing ventilation-conceived for room and pillar mining which prevent the rapid development of these techniques. Another aspect of longwall mining is that it requires a systematic and consistent approach in organization, roof control, ventilation and transport. It is for this reason that compliance with health and safety regulation is fairly well ensured if the longwall system has been well laid out and is subsequently well-run. Nevertheless, a management mentality raised in the great flexibility of the room and pillar system cannot always come to terms with the degree of forward planning and rigid discipline required to successful longwall mining. Research, development and other investments in the partial aspects of longwall mining are always of interest, but no massive trend to longwall can be expected realistically unless these major stumbling blocks in the basic law and basic approach are effectively removed.

Jan 1, 1980

By Joseph Kuti

Longwall mining is the term used for the underground extraction of a wide and deep panel of coal. Such a panel may be blocked out by one or more entries on either side ("head" and "tail") of a longwall face. If all the entries are pre-driven, the panel extraction is termed longwall retreat mining. With one exception, all the longwall faces in the United States are of this type. (1) prior to the general decline in the rates of production with Continuous Miners, the development of the multiple entries generally kept ahead of the longwall extraction rate. This is no longer the case: longwall extraction rates far exceed the rate of development. In addition to this problem, in newly established mines, the development of a haulage and bleeder system based on multiple entries results in a lead-time of three years or more before longwall mining can be applied. This is one reason why earlier projections and much of the optimism attached to longwall mining as a principal "savior" in the energy crisis should be viewed with some caution.

Jan 1, 1978

By Owen Kreilis

By the time coal was discovered in Newcastle, Australia in 1791, it was already a most important industrial commodity in European countries. Coal was the first mineral to be discovered in Australia and the first to be mined. Today, coal remains Australia's most important mineral in terms of local use and international trade. The first mechanized longwall in Australia began operation in 1963. It contained self-advancing hydraulic supports and was installed at Coalcliff Colliery, located in the Southern Coalfields of New South Wales. After nine months and production of 53 kt (58,000 st), the unit was withdrawn, largely because of uncontrollable roof weight and with the problems of airborne dust and large coal still unsolved. Basically, roof support was insufficient. The European design of the Coalcliff longwall was inadequate for Australian conditions. Another type of support with modifications was installed and began operation at Kemira Colliery at Wollongong, New South Wales, in 1964.

Jan 1, 1995

By Milan Lipensky

A variation of the longwall retreat system using friction props developed in coal mining is used extract a sedimentary manganese deposit at the San Francisco mine, Autlan, Jalisco, Mex. The Compania Minera Autlan, operating the mine, is partially owned by Bethlehem Steel Co. Roof control problems under a number of mining and strata conditions that defied uniform theoretical approaches led to a variety of experimental approaches that subsequently resulted in practical mining systems. Geologically, the area is one of considerable volcanic activity. The rocks are nearly flat-lying to moderately dipping conglomerate, tuff beds, inter-bedded porphyritic sills and felsitic lava flows. The formations overlying the manganese horizon are badly fractured and vary in thickness from 50 ft at the collar to 1400 ft in the deeper parts of the mine.

Jan 12, 1964

By P. J. Conroy, E. A. Curth

INTRODUCTION In June 1962, the first attempt at longwall mining in Illinois was initiated by Old Ben Coal Company in their No. 21 Mine. Longwalling was continued intermittently using various supports until April 1970. During this period, longwall mining techniques were used on separate occasions at six faces within Mine No. 21. However, due to various problems that developed at each location the faces were eventually terminated. The most significant problems concerned the support systems and roof conditions that were present in the mine during each attempt. Between 1965 and 1972, similar conditions were met by Freeman Coal mining Company during four attempts at longwall mining in their Orient No. 5 and Orient No. 6 mines. In 1975, the U.S. Bureau of Mines and Old Ben Coal Company entered into a cost-sharing agreement to demonstrate the application of longwall mining in Illinois. The first phase of the demonstration was to conduct a premining investigation to review previous attempts at longwall mining, perform rock mechanics tests, and establish support requirements based on the lnvestigation results. The information obtained during the demonstration at Old Ben's No. 24 has been utilized to optimize subsequent face equipment and panel geometry. Mining of the first panel began in September 1976 and was successfully completed in May 1977, and two additional panels were mined under the cooperative agreement. Currently, Old Ben Coal Company is the only longwall mining operator in Illinois. In addition to the face in Mine No. 24, five longwall faces are being operated in four other mines.

Jan 1, 1981

By Daniel Barkley

Underground coal mining in Illinois has a lengthy history dating back to the early 1800?s. High extraction underground mining has played a significant role in production through out this time. Modern mechanized longwall mining methods were introduced in the 1960?s and have been in continual use ever since. Regulations governing subsidence from underground coal extraction and the mitigation of resulting impacts to surface structures and surface land initiated in 1983. Despite the history of experience with subsidence, recent plans to longwall in Illinois have stirred public emotions and strong opposition. Anti and pro longwall groups formed and divided a community over the potential economic benefits new mining ventures could bring verses the potential problems associated with longwall mining in productive flat farmland. The debate culminated in a county wide referendum vote on the use of longwall mining. This paper provides an overview of the history of underground mining in Illinois, the controversy that has risen in central Illinois regarding longwall mining, and the efforts to educate the public about regulations that govern longwall subsidence.

Jan 1, 2007

By R. H. Foley

It is difficult to consider any seam as unsuitable for longwall mining operation for something like 95% of British coal is produced by this system. The following is a brief report on how they do it-their techniques and equipment. Depth of working in British mines varies from about 150 ft to more than 3000 ft, with the average being about 1300 ft. Average seam thickness is approximately 40 in., but working seams vary from 16 in. to as much as 14 ft.

Jan 8, 1965

By N. T. Avard

THE Joggins coal field, Cumberland county, Nova Scotia, is on the easterly side of Chignecto bay, at the head of the bay of Fundy. In area, so far as proven, the field extends easterly from the town of Joggins about fifteen miles to Chignecto. The distance across the outcrops of the several seams exposed is approximately one mile. HISTORY Early records of coal mining in this locality are somewhat obscure, but it is known that prior to 1750 the French settlers were mining coal for their own use from the seams which outcrop in the floor of the bay adjacent to the shore, where, at low tide, the reefs are bared for a mile or more. Coal was also mined from the seams outcropping in the cliffs. It is known, too, that at Joggins coal has been mined commercially for over one hundred years. At first, all shipments were made by water, but in 1882 a railway connecting with the Intercolonial railway at Maccan was built to serve this field. GEOLOGY Due to the abundance of fossils in the strata forming the Joggins cliffs, this area was for many years a mecca for geological students from all over this continent. A 'sunken fcrest' in the shoreline was of particular interest but, due to constant erosion by the sea, this has apparently been all washed away. On the Joggins shore, the cliffs stand sixty to one hundred feet high, and six workable coal seams, with numerous smaller ones, are there exposed. Others outcrop in the reefs extending from the shore toward the bed of the bay. In working underground, fossilized trees are often found immediately overlying a coal seam, and standing at right angles to the pitch of the seam. This is said to be an unusual condition. In most cases, the bark of the tree is a fine-quality coal, with high carbon content, whereas the pulp has turned to 'stone'. There is a definite tendency for the coal to run out, or turn to shale. One seam, workable two miles from the shore, has almost completely disappeared in the outcrop at the shoreline. ? It was thought that a large area could be mined under the bay from an opening near the shore, but the first submarine level had to be abandoned at a distance of 4,000 feet, where the coal became very dirty and shaly, and the mine able area to the westward became more restricted as the mine was developed to the deep. This tendency is common to all seams.

Jan 1, 1944

By A. B. Szwilski

"The various elements of longwall mine design are reviewed, particularly as they apply to condition s in the coalfields of the Plains region of Alberta. The following recommendations are made: (1) optimum panel lengths of 1000 to 2000 metres; (2) face lengths of 100 to 150 metres; (3) the use of retreat methods; (4) the restriction of floor undulations to less than 15 degrees. IntroductionThis article considers the elements of longwall mine design and is part of a short study that has been made of the feasibility of longwall mining in the Plains region, Alberta, Canada. The Plains region, with about 20 million tonnes, accounts for more than 80% of the coal resources of Alberta. The coalbearing strata in the Plains region cover an area of about 95,000 square miles. The geological formations dip very gently toward the southwest and, from a mining point of view, may be considered horizontal. The depth of the coal seams varies from several metres to over 650 metres. However, it is not anticipated that underground mining will be extended beyond the depth range of 25 to 250 metre s.The coal seams in the Plains region have been subject to many small mining operations in the past. The majority of these small mines were limited to a depth of about 50 metres, working mainly by room-and-pillar methods, although hand-filled longwall mining was often used.The development of new underground mining operations in the Plains region will have to be on a 'start-from-scratch' basis, especially regarding the installation of equipment. Longwall mining is more mechanized than any other method of mining and requires careful attention for the selection of new and expensive equipment. There have been many proven longwall advance and retreat systems in Europe and North America; mining conditions in the Plains region are more similar to those in the United States. Therefore, it will be essential for new mining pro jects in the Plains region to commence with proven system s and equipment; in time, perhaps an experimentation process could be attempted as experience is gained.Generally, the coal face is the key factor in mine productivity, which depends a great deal on equipment reliability, training and experience of the operators. The original design of coal faces must be flexible enough to cater for potential improvements so that running time can be increased."

Jan 1, 1980

By Donald D. Born

Mine No. 95 is located in Harrison County about 5 miles west of Shinnston, WV, with coal properties covering the northwest corner of Harrison County and the southwest corner of Marion County and with adequate Pittsburgh seam reserves to support the mine for many years. The mine was opened in 1967 and was planned, projected and operated as a room and pillar mine. It is located on a spur branch of the Baltimore and Ohio Railroad, has rail loading facilities and shipped by rail during its development stage. In 1972 it was converted to a mine mouth power station supplier and now transports coal by conveyor belt directly to the Harrison Power Station of Allegheny Power System. In 1971 the first longwall unit was installed in a selected area of the mine and immediately an orderly system of planning was developed to overcome the restrictions associated with longwall mining. The first was the development of the technique necessary for the plugging of abandoned oil and gas wells that existed in the area. With the assistance of the Morgan- town Energy Research Center of the Bureau of Mines, this restriction was overcome and thus opened a great potential for longwall mining in northern West Virginia. Other restrictions that had to be considered for longwall planning were dwellings and other improvements, snap top zones, water courses, and adequate bleeder systems, and the handling and treatment of mine drainage. In 1975 the second longwall unit was installed and soon therefore became a total longwall mine.

Jan 1, 1986

By Keenan. Albert M

The challenge of mining coal seams having a pitch of 30 degrees is one not frequently found in the United States, due primarily to the scarcity of such deposits. However, in the Thompson Creek District in Pitkin, Colorado, such a challenge exists to produce high quality medium volatile coking coal, and development of a longwall system is underway. The deposits under consideration are those of the Anschutz Corporation Inc. of Denver, Colorado, which are not in a virgin state. The properties were originally mined by the Colorado Fuel and Iron Corporation from 1894-1907, and by the Thompson Creek Coal and Coke Corp. from 1953-1966. Approximately five and one half million tons of coal have been mined by the above companies, attesting to its quality. The cessation of operations in both instances was occasioned by economics. Both companies employed a room and pillar system of mining, but being denied the use of high capacity mining and loading machinery because of the excessive pitch of the coal seam. This resulted in an unfavorable productivity expressed as output per man-shift, and thus the high cost of production occasioned by hand loading and semi-mechanization dictated cessation of operations. The specific location of these deposits are in Pitkin County,

Jan 1, 1971

By Ernest A. Curth

An estimated 49 billion tons or 29 percent, of the coal reserve base to a depth of 1,000 feet in the eastern United States fall in the 28- to 42-inch range. Often left out as a consequence of selective mining, it is a paramarginal source that will become increasingly important. At present, all active thin seam longwalls are located in the Eastern Coal Province, and a number of operations have been suspended due to the erosion of the market for metallurgical coal. Extensive premining studies, appropriate mine planning, reliable equipment that is designed with ergonomics in mind, adequate roof support, intensive training, and strong face discipline are the ingredients that provided a measure of consistency in production for the last 10 to 16 years, particularly in the Pennsylvania bituminous coalfield where single drum shearers dominate. Plows, which were found to be very productive in suitable strata in Europe, are used in the Pocahontas field. Low seam four- and six-legged shields have been introduced recently. The future holds automation at progressive levels. The first step is batch control with the benefits of quickly applied roof support and reduction of workmen exposure to environmental hazards.

Jan 1, 1981

By David Wilson, T. V. Rao

INTRODUCTION The Alchem trona mine, owned and operated by Allied Chemical Corp., is located approximately 32 km (20 miles) west of the town of Green River, and 8 km (5 miles) north of Interstate 80 in southwest Wyoming. Trona, a naturally occuring sodium sesquicarbonate (NaCO3 • NaHCO3 • 2H2O), is used for the production of sodium carbonate (Na2CO3), commonly known as soda ash. Present annual US consumption of soda ash is approximately 9.07 Mt (10 million st), out of which approximately 7.3 Mt (8 million st) is produced from the Wyoming trona mines. About 44% of soda ash is consumed by the glass industry; 3 % by exports; and the remaining portion by paper, chemical, soap, textile, and nonferrous industries. Allied Chemical operates an underground mine at an average depth of about 488 m (1600 ft). There are three other trona mines in the area operated by FMC Corp., Stauffer Chemical Corp., and Texasgulf Inc. (see Fig. 1). Allied Chemical became interested in southwest Wyoming trona deposits in the early 1940s. Explora¬tion work was begun in 1959 with the acquisition of federal leases. Exploitation of the reserves began in 1968. Two shafts, one 6.1 m (20 ft) and another 3.7 m (12 ft), were completed prior to 1968. The 6.1-m (20-ft) diam service shaft is divided in half by a cur¬tain wall, with one half used for men and material and the other for ventilation as a return air shaft. During the period from 1968 to 1974, the 3.7-m (12-ft) shaft was used as production shaft with two 7.3-t (8-st) skips. Due to the increased demand for soda ash, plant and mine expansions were completed during 1974. Under this expansion, the material handling system capacity was increased by constructing a new 2721-t (3000-st) capacity ore bin, sinking a 6.1-m (20-ft) diam produc¬tion shaft, and installing a friction hoist with two 22.7-t (25-st) skips. The Alchem mine manpower is 484 employees and about 2.3 Mt (2.5 million st) of trona was produced during 1976. Three different mining systems are used at the Alchem mine: conventional, continuous, and longwall. Allied Chemical introduced its first longwall unit in 1973, which was also the first longwall system introduced in the Wyoming trona district. At present, four conventional, seven continuous, and two longwall units are in operation. This equipment is operated in ten production areas. GEOLOGY The bedded trona and trona-halite in the Green River basin of southwestern Wyoming is a major re¬source for the nation. There are 25 beds that exceed 0.9 m (3 ft) in thickness and underlie areas of about 2590 km2 (1000 sq miles). There are other minor beds that range in thickness from 0.3 to 1.2 m (1 to 4 ft). Allied Chemical's Alchem mine is located in bed 17. The trona bed numbering system starts at the lowest elevation and increases upwards. The trona beds are in the Wilkens Peak member of the Green River formation. The Green River formation was deposited in a lake that began in early Eocene as a large body of fresh water, shrank in size and became saline, and then became fresh water again. The sedi¬ment during the saline phase of the lake, which includes the trona beds, is called the Wilkens Peak member. The underlying freshwater lake deposit is called the Tipton member and includes a 25.9-m (85-ft) sand unit which is a high pressure, low permeability aquifer. The over¬lying sediment is called the Laney shale. The Green River formation is underlaid by the Wasatch formation and overlaid by the Bridger formation (see Fig. 2). The structure of the beds in the area of the Allied Chemical mine is mostly postdepositional asymmetrical folds of small amplitude. These folds range in size of 3 to 6.1 m (10 to 20 ft) to as much as 45.7 m (150 ft). The trend of the folds is northwesterly with the north¬east flank of the anticlines having a steep dip and the southwest having gentle dips. Trona bed 17 varies in thickness from 2.4 to 3.4 m (8 to 11 ft) over the 93.2 km2 (36 sq miles) holdings of Allied Chemical and is flat lying except for the rela¬tively minor folding and a negligible regional dip of about 0.017 rad (1°). Trona occurs naturally in several physical forms in the Green River basin, being both massive and crystal¬line. The trona ore in the Alchem mine is a fine-grained massive ore with a compressive strength of approxi-

Jan 1, 1982

By Philip Lindstrom

Retreat mining, using yielding steel friction props, over a seven-year period has been successful at a uranium mine operated by Hecla Mining Company in southeast Utah. The support system allow good roof control, maximum profit, complete extraction, and good ventilation. Unusual subsidence observations were made in that some of the surface was raised rather than lowered, Longwall mining, commonly practiced in European coal mines, has a potential of broader application because of mechanization possibilities and better roof control and ventilation at greater depths.

Jan 1, 1964

By D. Y. Geng

Longwall mining is a relatively new mining method in the United States. Early trials in the eastern and central coal fields were not successful, mainly because, among others, the face supports did not have sufficient capacity. It was not until in the late 1960's, when the high- capacity self-advancing powered supports became available, that longwall mining was successfully reintroduced. Since then the number of mines employing the longwall method has been steadily increasing. It has reached approximately 7.5% in 1981. Currently longwall mining is used mainly in the Appalachian coal field. The seam depth ranges from 150 to 2500 ft. but mostly between 300 and 1400 ft. The seam thickness ranges from 32 to 144 inches with the majority between 40 and 100 inches. Nearly all longwall mining are in flat or nearly flat seams extracting in single slice, although one inclined and one thick seam longwall mining have been either operated or initiated in Colorado.

Jan 1, 1983

By W. M. Ma, W. L. Zhong, Syd S. Peng

In a longwall section that consisted of 7 longwall panels, there were two high pressure gas transmission pipelines across the panels burying from 3 to 10 ft. below the surface. One pipeline was 20 in. in diameter while the other was 24 in. in diameter. In order to investigate the stress conditions sustained by the pipelines during underground longwall mining, strain gages were mounted on the pipelines above panel #3, #4, and #5. Survey monuments were also installed along but near the pipelines. This paper presents a subsidence prediction method and the preliminary results of the pipelines' stress conditions as affected by underground longwall mining.

Jan 1, 1986

By M. D. Ross

Complex combinations of technical, economical, safety and environmental factors are causing mining engineers everywhere to review their operations. Naturally, some of the traditional methods still have a large role to play because they are, in certain circumstances still adequate and are well understood. But, as circumstances change, a new approach is required. The combination of technical and economical reasons for introducing Long- wall mining in some seams in the United States is associated with strata control. Other reasons include simplifications and improvement of ventilation, reduced coal dust, more output from each unit and crew, increased percentage of recovery from each area of the coal deposit, and reduction of rock dusting. The innovations which transformed Longwall mining from a cyclic to a continuous mining system were the armored conveyor and power loading machines, but the crucial breakthrough for application to high production was the development of the powered roof support, which at once gave the system the advantages of mastery of strata control, increased rate of advance, significant reduction of manpower, and increased safety.

Jan 1, 1974

By William Harrison, Robert H. Trent

GENERAL DESCRIPTION History The most striking feature of mining in the United States has been the infrequent use of longwall systems. This system, which accounts for the majority of coal production in Europe, Japan, and other countries, is only recently growing out of its infancy in the mining of normal coal seams and is still untried in the mining of thick coal seams in the US. Its use in the mining of metal and nonmetal ore bodies has been virtually ig¬nored, except for isolated instances in trona, copper, and uranium. Longwall mining is believed to have originated in Shropshire, England, towards the end of the 17th cen¬tury (Laird, 1973). Although the method used would be considered primitive by today's standards, many of the basic concepts have remained unchanged. Longwall mining of coal in the US was first introduced before the turn of the century, but it never gained acceptance as it did in Europe. Historically, longwalling was a cyclic method where a single cut of coal was removed from the face on the producing shift each day, and the work of building stone packs in the gob and manually moving roof support was completed on the off shifts. Due to the amount of dead work, productivity was extremely low. In Europe, however, longwall methods were required despite the high costs involved, because only by this method could coal under heavy depth be mined with any reasonable degree of recovery. Reserves of coal lying under shallow cover, and therefore minable by room¬and-pillar methods, were long ago inadequate to supply most of Europe's coal requirements. In the US coal min¬ing has historically proceeded laterally with the new mines in virgin areas to replace old mines; in Great Britain, Germany, Japan, and many other countries, mining must proceed downward to greater depths. The depth of cover for most coal operations in the US is shallow, i.e., 61 to 305 m (200 to 1000 ft). This, combined with large reserves, has made room-and-pillar methods almost universally applicable. However, longwall systems were tried around the turn of the century. Whenever used, it was frequently noted that the opera¬tion was under the direction of men with foreign ex¬perience and was tried under ideal conditions. Some of the mines that were using longwall or had tried longwall prior to 1910 were the Radiant mine, CO; Vinton Coal Co., PA; Cambria Steel Co., Johnstown, PA; Grundy County and Spring Valley, IL; and unnamed mines in Washington, West Virginia, Kentucky, Iowa, and Kansas. As late as 1961, there was one circular longwall in operation at Centerville, IA. The first modern-day op¬eration to take advantage of European technology and longwall methods was Kaiser Steel Corp. at its Sunnyside mine near Price, UT. Due to deep cover and extremely poor roof conditions, combined with a need for in¬creased production, Kaiser management decided a new method was required and turned to longwall in 1961. The first longwall consisted of an Anderson Mavor shearer loader, British Jeffrey-Diamond conveying equip¬ment, and Dowty roof supports with a capacity made up of two and three 27-t (30-st) capacity props. After nor¬mal start-up problems, this unit averaged over 454 t (500 st) per shift (White and Palacios, 1976). During and after World War II, technology in hy¬draulics and controls had advanced to the point that self-advancing supports and hydraulic props were being developed. In 1960 only I % of West German produc¬tion was from mechanized longwall faces. This in¬creased to 37% in 1970 and 63% in 1973 (Kohlgruber, 1974). In 1976 there were 246 coal mines operating in the United Kingdom. Although this is only 50% of those operating ten years ago, the production has increased 42%, mainly through improvements in longwall equipment and methods (Hunter, 1976). In France and other European countries, the devel¬opment of longwall mechanization has been similar in seams up to 2.44 m (8 ft) thick. In seams that exceed 9.14 m (30 ft), a variety of longwall caving has been developed for coal seams with dips of 0 to 1.6 rad (0 to 90°). Those with the greatest success will be discussed later. As noted, the development of longwall mining to its present state of the art has mainly taken place since World War II with substantial gains in the last ten years. Mechanized longwall has been the result of several re¬lated major innovations (Jackson, 1975) 1) Development of the flexible armored face con¬veyor which can be installed along the face and moved forward without disassembly. 2) Development of face machines such as single and double drum shearer and coal plows which operate in conjunction with the armored conveyors. 3) Development of self-advancing hydraulic roof supports which now include chocks, chock shields, and shields. 4) Reliance of caving of the immediate roof based on proper planning and development. 5) Use of pneumatic slowing to enable extraction below overbuilt areas. The most recent developments in the mining of coal by longwall in the US include the introduction of shield supports at Kaiser's York Canyon mine in New Mexico, single-entry longwall development at Kaiser's Sunnyside mine, and Mid-Continent's advancing longwall system in Colorado. Metal and nonmetal longwall systems in the US have included the mining of copper at White Pine, MI; uranium in Utah and New Mexico, and trona in Wyoming.

Jan 1, 1982

This paper presents the results of a unique study conducted by the National Institute for Occupational Safety and Health (NIOSH) from 2016 to 2019 to evaluate the effects of longwall-induced subsurface deformations on shale gas well casing integrity and underground miner safety and health. At both deep and shallow cover instrumentation sites, surface subsidence measurements, subsurface in-place inclinometer measurements, and underground pillar pressure measurements were conducted as longwall panels were mined. Comparisons of the deep and shallow cover test site results with those from a similar study under medium cover reveal an interesting longwall-induced response scenario. Under shallow and medium covers, measured horizontal displacements within the abutment pillar are one order of magnitude higher than those measured under deep cover. Conversely, measured vertical compressions under deep cover are one order of magnitude higher than those under shallow and medium covers. However, FLAC3D simulations of the casings indicate that, in all three cases, the P-110 production casings remain intact under longwall-induced deformations and compressions, which has serious implications for future mine design in areas where shale gas wells have been drilled ahead of mining.

Jan 7, 2020