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A four monthly period was analysed for each retreating longwall face which indicated that output increased from 1140 tonnes/day for Longwall 1, to 1620 tonnes/day for Longwall 2 and to 2090 tonnes/day for Longwall 3. An output of 2500 tonnes/day should be achieved from the new Longwall 4, largely due to the improved tailgate corner design and despite a continuing lump coal problem. The evolutionary trend is a feature of longwall mining; the evolution occurring both with mining and mechanical design at the colliery itself and with the longwall equipment offered by manufacturers. The trend is towards simplicity, increased strength and capacity, simplified maintenance and increase relia- bility.

Jan 1, 1976

By W Farnworth

The Huntly West Mine has undergone significant changes in the last two years, which will affect the remainder of the mine's life. The paper describes the evolvement of plans and an overview of the technical considerations made in planning for and implementing the first New Zealand longwall operation. The technical investigations involve the longwall equipment, exploration, ventilation and strata control. The focus on these areas was to ensure that unacceptable project risks were addressed. Implementation of longwall mining at West Mine is planned in three phases, Development, Panel One extraction trial, and Full Longwall operation.   At present the development phase is complete, longwall installation is in progress and production start-up is planned for the end of August, 1991.

Jan 1, 1991

By T J. Sullivan, H Pinkster, G Swarbrick

From 2002 to 2006, longwall mining was undertaken directly beneath the Cataract Tunnel, which is a 100-year-old, heritage-listed tunnel in Hawkesbury Sandstone responsible for delivering 20 per cent of Sydney’s annual water supply. At one location, undermining resulted in movement of at least 350 mm along a known fault that transects the tunnel. During this movement, the continued operation of the tunnel was ensured through a careful system of planning, monitoring and management.Of key importance to the success of the operation was the use of advanced numerical modelling to guide operations at all levels, including feasibility assessment, pre-mine mitigation works, monitoring design, operation performance and post-mining condition. This allowed many aspects of the potential impacts to be explored, including joint movements, rock mass deformations and changes in permeability. A key challenge was to successfully model near-field influences on adverse geological structure due to very far-field effects. This paper explains the model’s conceptual development, calibration, performance and limitations.Modelling provided the confidence to manage the impacts of large mining-induced movement on key infrastructure and ultimately predicted fault movement accurately. The fault movement remains one of the highest ever recorded due to mine subsidence.CITATION:Swarbrick, G, Sullivan, T J and Pinkster, H, 2014. Longwall mining beneath critical infrastructure – prediction versus performance of the Cataract Tunnel, New South Wales, Australia, in Proceedings AusRock 2014: Third Australasian Ground Control in Mining Conference , pp 157–166 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 5, 2014

Ten years ago, only 3% of Consol's underground coal production resulted from using the longwall mining method. Today, that figure has grown to 45% and has helped the Pittsburgh-based concern fuel an upswing in productivity. The company reported that productivity at its underground mines, excluding labor strike periods, increased 24% between 1978 and 1981. Last year, an additional 8% increase was achieved. Efforts such as improved safety, training, engineering, and maintenance programs as well as the closing of unproductive mines has contributed to these gains, according to Joseph M. Richards, Consol's executive vice president of operations. But, Richards adds, a great part of the credit goes to longwall mining. What is Longwall Mining? To fully appreciate the advantages of longwall, one needs an understanding of how mining is done by other methods. For instance, in both conventional and continuous mining, rooms or tunnels are dug in the coal seam. Pillars of coal are left standing to support the roof as mining moves forward in the seam. In conventional mining, a slot is cut in the base of the seam and holes for blasting are drilled. After blasting, the coal is loaded. A more efficient method - continuous mining - uses a machine that combines cutting and loading. Longwall mining, by contrast, works backwards from the end of a panel. Two parallel sets of tunnels (development panels) are cut into a seam with continuous mining machines, then connected with a set of crosscuts at the far end. Min¬ing then proceeds back toward the entrance. Longwall mining employs some very productive machines. Large drum shearers, for example, run on a track along the length of the coal face for some 150-180 m (500-600 ft). The shearers cut the coal which falls onto a conveyor system or pan that also runs the entire length of the face. The longwall crew works under a roof of heavy steel supports called shields. As the coal is removed, shearers, pans, and shields are moved forward by hydraulic rams. The roof is allowed to collapse behind the shields. In addition to increasing production, longwall mining is considered to be safer because the miners work under strong steel shields. New designs have made them more rugged and maintenance free, as well as more stable on soft mine floors. Early roof supports, called chocks, had gaps in the roof canopies. The new roof shields now cover the entire working area and are better able to prevent roof material from falling into the working area, thereby improving safety and productivity. Longwall mining also results in a cleaner product in many mines. If the first layer of rock over the coal seam is thin, it might have to be removed with the coal in a room-and-pillar operation so a

Jan 11, 1983

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 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 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

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

By Jinsheng Chen

Longwall mining-induced abutment loads on the surrounding coal pillars can be grouped into two categories in terms of the relative position of the coal pillars and the longwall face. They are the front and side abutment loads. Even though a lot of research and efforts have been made to study the nature and behavior of these longwall mining-induced abutment loads, their influence zones and magnitude are still not well defined and fully understood due to the complexity of geological conditions and the longwall muting-induced overburden strata movement. The uncertainty about the mining-induced abutment loads often forces consultants and mining engineers to employ a conservative approach in designing coal pillars and entry roof control plans. The problems with this approach are that: (a) it increases CM development¬longwall retreat footage ratio, (b) it decreases coal recovery, and (c) it increases !Ill' operating costs. However, a more liberal approach may create safety issues and result in loss of production. Therefore, the importance of accurately defining the influence zones and magnitude of the front and side abutment loads induced by longwall mining can never be over emphasized. The authors in this paper attempt to define the influence zones and discuss the magnitude of the longwall mining-induced abutment loads by analyzing the field data measured at RAG American Coal Company's longwall mines. In addition, the relationship between entry stability and the balance among roof/floor conditions, pillar design, and roof control plan is also briefly discussed.

Jan 1, 2002

In recent years, improvements made to the longwall system have accelerated at a faster pace than those made to the gate entry development system. As a consequence, unless planned years ahead of time, extending the panel length is nearly impossible without some innovative approach. At Cyprus Amax Coal's Emerald mine the G panel length was extended by 3,500 ft- by developing three entries across it to facilitate development of its headgate and tailgate entries simultaneously when the adjoining F panel was in operation. After evaluating alternative supporting methods and associated risks, determination was made to backfill these entries and crosscuts using a low strength flyash cement mixture prior to mining thru. Instrumentation was also used to monitor the stress change or front abutment stress in both the coal and the backfilled material ahead of the face. Longwall mining thru these three entries took about four eight-hour shifts and proved to be very successful. The designed flyash cement mixture provided adequate roof stability and caused no difficulty in the shearer's cutting while eliminating an in-panel longwall face move and minimizing the risk of roof or floor failure in the in-panel openings, or in the worst scenario loss of the face during the longwall cutting thru. This approach provided the intended result of extending G panel and recovered about one million tons of coal. This paper summarizes the engineering design of the cutting-thru project and flyash cement mixture, front abutment stress changes within the longwall coal block, backfilled material, and coal pillars ahead of the longwall face, and our underground observations

Jan 1, 1997

By B. C. Lewis

The mining industry has experienced a general trend toward an increasing number of longwall operations, an increasing percentage of underground coal being mined by longwalls, and increasing productivity from the longwalls. Longwall operators have not yet reached a state of mining euphoria. Competitiveness both within the industry and from alternate fuel sources is forcing continued pursuit of higher productivities and lower costs. The following graphics present trends in the industry. Longwall mines, as defined for this presentation, are those reportedly having longwall installations in each of the respective years. Production from both the continuous miner and longwall units is included in the longwall mines. Non-Longwall mines are all other underground mines. Productivity calculations are based on total employee-hours associated with the operation.

Jan 1, 1990

By Vincent A. Scovazzo

During the winter months of late 1985 and early 1986, residents along Dry Fork near Grundy, Virginia (United States) experienced seismic events that they attributed to longwall mining at Island Creek Corporation’s (Island Creek) Virginia Pocahontas Mine No. 3 (VP-3 mine). Island Creek contacted STS D’Appolonia Ltd. (STSDL) on March 7, 1986, to investigate these events. An STSDL representative, Vincent Scovazzo, interviewed residents of Dry Fork on March 10, 1986. It was noted that only people within a residential structure felt the events they described as house shaking, vibrating walls, and ceramics falling from shelves. STSDL representative installed a blast monitor at a residence. Within 2 days, various events were recorded. Some could be attributed to truck and heavy equipment movement. Eight events had no obvious cause but appeared on resident’s written logs as earthquakes caused by mining. STSDL contacted Utah Geophysical, Inc. who had developed a technique to determine the mode of rock failure using the seismic record. Utah Geophysical was engaged to install and monitor a microseismic network, locate the epicenter of the events, and work with STSDL in determining modes of failure. The network was comprised of six geophones located at five stations. Data was recorded for 24 days from May 20 through June 13, 1986. The data was filtered to eliminate events determined to have an origin other than the longwall panels’ overburden and under-burden. The larger events from this filtered data set were selected and analyzed to determine their hypocenter locations, time of occurrence, magnitudes, and failure mode. Processed data was interpreted, tabulated, and plotted by STSDL to provide information relative to the sources of the seismic vibrations and their possible relationship to the mining operation.

Jul 1, 2023

By B. Qiu, Y. Luo

The design of the predriven recovery room is not an easy task, because the stress distribution in the barrier pillar, standing supports, fender pillar and the immediate roof is changing as the longwall face approaches the predriven recovery room. An analytical approach is proposed to determine the stress distribution in the barrier pillars, fender pillars, standing supports and immediate roof of the recovery room based on the fracture mechanics approach. Based on the developed mathematical model, a stand-alone computer program has been developed to facilitate the required computations. The parameters such as overburden depth, recovery room width, mining height, shield and standing support capacities are incorporated into this program to access the feasibilities of predriven recovery room designs. Compared to the finite element method previously employed, this analytical approach offers the same, if not better, accuracy without requiring expensive computer hardware and software or specialized expertise.

Jan 1, 2012

By Daniel Su

This paper describes recent ground control challenges encountered at the longwall recovery areas of one of Bailey Mine?s two longwall faces and the proactive measures taken by CONSOL management and engineering to mitigate them. The challenges derived primarily from the following causes: (1) irregular roof coal and draw slate thickness, (2) presence of thick sandstone at the recovery area and extremely weak rocks below the sandstone, (3) close proximity to a regional anticline, (4) low shield set pressure and tip load, and (5) ineffective primary roof support that led to progressive failure of the headgate roof. The presence of the anticline contributed to extensive fracturing of the sandstone. Excessive pot-out in advance of the shields frequently occurred near mid-face due to the presence of thick draw slate and irregular roof coal near the recovery area. This, in turn, resulted in face heights that exceeded the maximum reach of the shields. Subsequently, during longwall meshing, when the advance rate slowed considerably, fractured sandstone would often break loose, causing the shields to yield, thereby reducing the height and inhibiting shearer movement. To improve the headgate and face conditions within the longwall recovery area, several actions were taken, including: (1) assessing site-specific roof geology by conducting in-mine roof coring around the recovery areas and by mapping immediate draw slate and roof coal thicknesses within surrounding entries, (2) increasing pump pressure and thus shield set pressures (3) diligently monitoring shield set pressures and longwall extraction horizon, (4) installing additional cable bolts and roof screening to prevent progressive failure of the immediate headgate roof, (5) fully-grouting supplemental cable bolts to improve headgate support stiffness, and (6) gluing the headgate roof within the recovery areas with polyurethane. As a result of these collective efforts, longwall recovery delays at Bailey Mine were reduced from 21 days in 2006 to nearly zero in 2009.

Jan 1, 2009

Jan 1, 2004

By Ulrich Langosch

In the 1990s the German mining industry introduced a new generation of shield supports. The new design of support has a maximum load capacity of 10,000 kN, making these units as strong as the shields used in Australia and in the USA. DMT took more than 3,100 underground observations in order to verify the roof fall frequency by statistical analysis. The results of this work have led to practical recommendations for roof control and the required shield support system on longwall faces. The underground observations have been correlated to Rock Mass Classification, to stress calculations and to the angle between the direction of the fissures and the direction of longwall mining_ The analysis work yielded the following two sets of results: 1. There is a critical distance between the canopy tip and the coal face (Tip to Face TF,n,). The TF,n, is predictable and relates to: the thickness of the first roof layer and its uniaxial compressive strength. The face support should have a TF that is less than the TFcrtt in every underground longwall situation. Exceeding the TF crit call immediately result in a roof fall. 2. Using the obtained regression equation DMT is able to calculate the probability of the roof fall frequency (FF), which describes the roof fall sensitivity. When TFcr;, is exceeded the predicted roof fall FF relates to: the measured support resistance (MSR) of the shield support the calculated vertical stress (p?) the fissure-direction index (DI = angle between main fissure direction and direction of mining) and the distance by which TFcrit is exceeded (ATF). Armed with these results DMT is now able to predict the critical distance between the tip of the canopy and the coal face (TFcrit), as well as the roof fall frequency, for all shield designs. By applying the new calculation method it is now possible to compare alternative longwall layouts and different shield support types under pre-set geological conditions. Mining engineers on site are therefore in a position to make the necessary roof control preparations required to run the longwall operation to maximum efficiency. The results provide a useful basis for making practical recommendations and for selecting the most effective design of shield support. The paper uses practical examples to demonstrate the R&D results and present the various methods now available for calculation and prediction in longwall roof control.

Jan 1, 2003

By Allen McComas, Frank Chase, Phyllip Worley

Longwall mining has gained the reputation as being the safest extraction method in underground coal mines. However, one of the most difficult tasks associated with longwall mining is moving the face once a panel is completed. Based on Mine Safety and Health Administration (MSHA) fatality reports since 1996, longwall face recovery operations have claimed the lives of 5 U.S. miners and have resulted in numerous injuries. Recovery operations can be hazardous because they involve moving large pieces of equipment in very confined spaces. They are also conducted in highly stressed ground conditions due to front abutment loads generated by panel extraction. Shield removal is the most hazardous operation during face recovery because miners are constantly exposed to the unpredictable gob edge. To protect the miners, one or more walking shields, cribbing and/or other supplemental roof and standing supports are typically employed as breaker line supports as each shield is removed. At the Harris No. 1 Mine in southern WV, mobile roof supports (MRS’s) have been used in lieu of traditional walking shields on 17 face moves since 1997. MRS’s are shield-like support units mounted on crawler tracks and are commonly used during room-and-pillar retreat mining operations. For longwall recovery, the two biggest advantages that MRS’s have over traditional walking shields are that they are remotely controlled and are highly maneuverable. MRS’s have contributed to safer shield recovery and shorter move times at the Harris No. 1 Mine. This paper will address both the safety and the operational issues associated with MRS usage during shield recovery. It will also discuss new developments, including the use of the inherently safer battery powered MRS’s, which have been recently certified by the Mine Safety and Health Administration.

By Frank Chase

Longwall mining has gained the reputation as being the safest extraction method in underground coal mines. However, one of the most difficult tasks associated with longwall mining is moving the face once a panel is completed. Based on Mine Safety and Health Administration (MSHA) fatality reports since 1996, longwall face recovery operations have claimed the lives of 5 U.S. miners and have resulted in numerous injuries. Recovery operations can be hazardous because they involve moving large pieces of equipment in very confined spaces. They are also conducted in highly stressed ground conditions due to front abutment loads generated by panel extraction. Shield removal is the most hazardous operation during face recovery because miners are constantly exposed to the unpredictable gob edge. To protect the miners, one or more walking shields, cribbing and/or other supplemental roof and standing supports are typically employed as breaker line supports as each shield is removed. At the Harris No. 1 Mine in southern WV, mobile roof supports (MRS?s) have been used in lieu of traditional walking shields on 17 face moves since 1997. MRS?s are shield-like support units mounted on crawler tracks and are commonly used during room-and-pillar retreat mining operations. For longwall recovery, the two biggest advantages that MRS?s have over traditional walking shields are that they are remotely controlled and are highly maneuverable. MRS?s have contributed to safer shield recovery and shorter move times at the Harris No. 1 Mine. This paper will address both the safety and the operational issues associated with MRS usage during shield recovery. It will also discuss new developments, including the use of the inherently safer battery powered MRS?s, which have been recently certified by the Mine Safety and Health Administration.

Jan 1, 2007

By James D. Pile

Following a methane ignition in the active panel of a longwall coal mine, the affected panel was successfully isolated from the rest of the mine. This allowed for the remainder of the mine to return to regular operation, and the conventional practice of having to seal the portals for a defined period of time was avoided. After the affected panel had remained isolated for a regulatorily mandated period of time, it was reopened in preparation for longwall face recovery. As it was not possible to move the shields from their existing positions to facilitate the installation of recovery mesh prior to shield recovery, alternative methods had to be considered to stabilise the gob and minimise flushing, thereby improving operator safety. The objective of the paper is to show how stabilisation of the gob was achieved during shield recovery, thereby minimising flushing, and improving operator safety. Phenolic foam was chosen and injected from between the shields into the gob behind them. This is a technique that has been used to great effect in Germany, to a lesser extent in Australia, but not knowingly to date in the United States. To ensure nothing was left to chance and thereby guarantee the project?s success, the procedure used in Germany was employed, down to the application of equivalent hardware, which was sourced through the North American supplier.

Jan 1, 2013

By D. W. Park

Longwall Strata Control and Maintenance System (LoSCoMS) is a software and data communication system developed at the University of Alabama. This system integrates real-time shield monitoring, data presentation, analysis and forecasting of forthcoming events. The main objective of this system is to provide stability information on longwall panels including excessive shield load, low setting pressure, leg leakage and poor shield performance, eminent maintenance problems, etc. Analyses of various mining and geological parameters were also performed to determine past and present roof characteristics and to forecast roof loading patterns for the following mining cycles, next periodic weighting, etc. A local coal mine in the Warrior Coal Basin has adopted this system to provide daily evaluation of ground stability and maintenance problems of their longwall panels. Two years of experience with this system is covered in this paper.

Jan 1, 1998