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By Ken Barish

Jane Mine of the Keystone Coal Mining Corporation was started in 1962 and is in the Lower Freeport seas located in Armstrong County, Pennsylvania, approximately 45 miles northeast of Pittsburgh. The mine is a slope/shaft complex with the cover ranging from 100 feet at the slope to 450 feet near the back end of the property. The seam height ranges from 48 to 72 inches. A variety of roof conditions have been en¬countered, and an equal variety of roof control systems have been tried with varying degrees of success. Initially, places could be mined as deep as 100 feet without any permanent roof support. After several problems and the advent of the Health and Safety Act of 1969, roof control became more and more prevalent and predominant at the Jane Mine. It started with 4 foot conventional oolts. As the mine progressed in the northeasterly direction, roof conditions changed from the extremely good roof that was encountered initially, to bad roof; and other types of roof support were required. Sixty pound rails and 6 inch 25 pound to the foot steel I-beams were used for supplemental support in long life headings such as belt and track. Resin bolting was done in many areas for long life support due to the deterioration of the shale roof over time. Several areas had to be abandoned because of uncontrollable top.

Jan 1, 1984

By David C. Johnson

Coal mining in Illinois has resulted in many structures being exposed to subsidence damage. Damage mitigation techniques (DMT) applied in the foundation design/construction have proven successful in minimizing damage in several test cases. To determine the practicality of these techniques, the Costs of their application are investigated. The AMT costs are compared to foundation and total house costs for various classes and sizes of houses. An economical and effective subsidence resistant foundation construction is proposed.

Jan 1, 1993

By David Newman

The latest version of the Surface Deformation Prediction Software (SDPS) package is presented through its application to a number of case studies. The package now exploits all the benefits of the Microsoft Windows platform and has a direct interface to CAD software, thus facilitating input and output. Also, the package features advanced calibration routines to handle predictions over specific regions. The case studies presented highlight the features and capabilities of the new package.

Jan 1, 2001

By M. Zaki Rashad

In this paper, if three slant distances are measured from three given points of known coordinates to an unknown point, the position of this point (X, Y, and Z coordinates) can be determined. A computer program was designed for observing the movement of a point in the roof in Abu-Tartour mine (western desert, Egypt) to measure the convergence. This method, for general using, is very fast and can be applied without any restrictions.

Jan 1, 1990

By Gift Makusha

Total extraction mining of coal is being undertaken on a small scale by Anglo Coal South Africa. Longwall mining has been done in the group at New Denmark colliery since the 80s and recently the company started experimenting with pillar mining at Goedehoop colliery. Total extraction mining methods result in caving of the overburden strata that is often accompanied by displacement of air causing wind blasts. The windblasts can cause injuries to underground mining personnel, damage to mining equipment, and ventilation disruptions. Some incidents of windblast damage and injuries have been recorded at both New Denmark and Goedehoop Colliery that prompted mine management to experiment with the goaf warning device, an instrument developed by CSIR mining technology to give early warning of impending god. The initial version of the Goafwarn was originally developed to operate as a stand-alone unit, with LED lights mounted on the device that would flash if the unit was triggered'. That set up would be effective in small working areas where the flashing lights are visible to all workers. This requirement is more difficult to satisfy in longwall application of the unit where mining activities are spread over large linear distances of up to 250 m and the flashing lights would not be visible to all workers in the longwall face. It was also found that the single unit had limitations in distinguishing between man made vibrations and cracking in rockmass leading to an unacceptably high incidence of false alarms. The case studies describe the experiments that were carried out to ameliorate the two issues mentioned above through networking more than one unit. This was achieved through the development of radio communication from the warning devices to a central control (Trollex Data Acquisition Unit) from which the alarms are issued once the prescribed triggers are satisfied. The operating system was made up of 4 Goafwarn units installed 30 m apart with 2 in the tailgate and other 2 in the main gate. The alarm state was defined where 3 or more units were triggered simultaneously. The concept was applied successfully in real time during longwall mining, and management procedures have been developed to achieve safety through the system including switching off the shearer, and flicking the lights to warn people.

Jan 1, 2005

The properties of coal or rock containing gas are very important both for studying coal and methane outburst mechanism and for controlling underground rock in mining. The theological fracture properties of coal containing gas were studied to obtain its rheological fracture principle both in microscopic scale and in macroscopic scale. The application of this principle is successful in explaining coal and methane outburst mechanism and for putting forward a rheological hypothesis of coal and methane outburst.

Jan 1, 1992

By C. Srinivasan

Microseismic emissions are generated by deformation and cracking of rock around an opening inside a mine. The rock tends to achieve equilibrium in a new geometry under changing stress conditions was found to provide useful clues to the impending roof falls and ground instability. The typical characteristics of these microseismic event patterns is shown to be of diagnostic value in sensing in advance rook fall that invariably follow such events. In most of the longwall faces, the main problem faced was due to strata behavior in the presence of massive sandstone bed, which is generally difficult to cave. Microseismic monitoring system was used to monitor strata behavior during longwall mining operation at Rajendra underground coal mine of South Eastern Coal Fields limited (SECL). More than 44,000 microseismic events with local magnitude between -3.4 and 0.5 were recorded during the monitoring period from September, 2001 to March 2003. Analysis of these events was correlated with respect to roof falls. The time series of range of source parameters such as Radiated energy, seismic moment, Energy Index, Seismic Schmidt number, time of occurrence and location of fractures before and during roof fall exhibit qualitatively distinct patterns about six hours before roof falls. &ong the several seismic parameters investigated the microseismic event rate as precursor was found to be most significant indicator of an impending roof fall. The results are discussed as case study in this paper.

Jan 1, 2005

By Bruce K. Hebblewhite

Underground pillar extraction continues to be practiced in Australia in various forms, in spite of the dominance of the longwall method, which accounts for over 90% of underground production. Australia has been a leader in various forms of pillar extraction, particularly since mechanisation was introduced to the industry during the middle of the 20th century. Historical developments have included a range of thick seam mining pillar extraction methods; the widely adopted Wongawilli method; early adoption of the use of mechanized breaker line supports; and a number of more recent partial extraction systems including what is known as rib stripping. Current pillar extraction practice varies from total extraction panels to various forms of partial extraction, driven by either surface subsidence constraints or by underground conditions. This paper reviews a number of different pillar extraction methods and mining layouts, and also highlighting a number of fundamental geotechnical principles which have been found to be critical for safe pillar extraction ? often through lessons learned the hard way, as a result of back analysis of different accident scenarios. These principles include the all-important understanding of the location of the goaf (gob) edge at any point in the operation, and the management of that goaf edge; the impact of geological structures on local and regional stability; the critical importance of extraction lifting sequences; the role of stooks (remnant pillars); and a number of other factors. The paper will also briefly reference the educational and training practices adopted in Australia aimed at the continuous improvement of pillar extraction safety.

Jan 1, 2011

By Stanislaw Prusek

The present state of Czech and Polish coal mining industry is presented at the beginning of the article. This paper will inform the reader of the general data concerning hard coal reserves? number of mines, number of miners, output, number of longwalls, productivity, depth of extraction, and extraction methods?in both countries. The main part of the paper describes the methods of gateroad development as well as gateroad support characteristics (support types, gateroad shape and dimensions, distance between support sets, types of reinforcements). The development prospects of gateroad support in the Czech and Polish coal mining industry are also presented.

Jan 1, 2011

By Alexander Kattner

Surface fractures in urbanized areas show the risk potential of near-surface mining. This kind of mining subsidence damage occurs mainly in areas where hard coal was mined near the surface with very little overlying rock strata. In North Rhine-Westphalia (NRW), the mining authorities assess areas that are at risk for caveins by means of envelopes constructed according to Hollmann and Nürenberg (1972). Drafting abandoned underground structures depends on the assessment of historical documents such as mine plans, mine titles, and operation plans of prior mines in this area. A research and development project establishing a comprehensive Geo Information System (GIS) for hazard prevention was undertaken in cooperation with the mining authorities of NRW. It aims to display the areas endangered by abandoned, shallow underground mines for the purpose of hazard prevention. A tool was programmed using ArcGIS as a result of this project. It is used to digitize underground workings from preserved mine plans, calculate outcrop lines of coal seams and display hazardous areas. In the future, a database of shallow mine workings will be established. The tool will be used for a systematical mapping of shallow workings and assessment of endangered areas.

Jan 1, 2011

By Anthony T. Iannacchione

Longwall mining produces surface subsidence basins that affect streams by water diminution and contamination. These effects can ultimately impair the biological character of the plants and animal communities living in the streams. The combination of flow, water quality, and ecological effects threaten the environmental sustainability of longwall mining and, ultimately its social acceptability. Pennsylvania has developed new standards, released in 2005 and implemented in 2007, to help protect the commonwealth?s valuable streams from the detrimental effects of subsidence. These standards are aimed at eliminating environmental problems and will therefore help to make underground bituminous coal mining more sustainable. The engineering solutions necessary to comply with these standards are fundamentally affected by the geologic nature of coal-bearing strata, the existing in-situ stress conditions, and the ability of selected species to survive and adapt to changes in their environment caused by longwall coal mining subsidence. Needless to say, geologists, biologists, and engineers are all playing a pivotal role in developing prevention controls and recovery measures necessary to protect streams and sustain underground coal mining. The challenges facing scientists and engineers in sustaining the development of underground coal mining in Pennsylvania are examined through case studies. These challenges all arise from the subsidence effects of longwall mining. The key effects of subsidence, discussed through case studies, are: a) tension cracks, b) springs in headwater stream areas, c) stream gradients and subsidence basins, and d) stream compression ruptures and horizontal stress. All of these potential threats demonstrate the need for high-level scientific knowledge and innovative engineering solutions. One could argue that Pennsylvania?s stringent stream protection standards put the coal mining industry at a competitive disadvantage compared to other coal producing states. It is equally likely that compliance with these standards help to mitigate the effect of subsidence, thereby helping the coal industry achieve a sustainable future.

Jan 1, 2011

By David Bigby

The paper describes research undertaken on an ECSC/K HSE project which investigated several potential physical principles which might be harnessed to provide a non-intrusive means of determining the extent of failure in the near roof of mine roadways and tested the most promising in the laboratory and in the field. It was concluded that the principles which warranted further development were thermal response and laser vibration measurement. In the latter case there is a need to develop an efficient means of imparting energy to the seam to induce sufficient vibration. A new, SIMRAC funded Project will progress work in the field of thermal response.

Jan 1, 2004

By Kent D. Mctyer

Mining commenced at Tasman Mine in late 2006. The current method of mining is bord and pillar using continuous minerbolters and shuttle cars for first workings and secondary extraction using mobile roof supports. The two stage process was chosen to accommodate irregularly shaped coal deposits, allowing adjustments to be made to extraction ratios for better management of subsidence and to maximize the efficiency of the operation. Following the completion of the first three full/partial extraction panels, the mining method was changed due to variable caving. Another partial extraction method, referred to as the Duncan Method was adopted; it involves stripping the developed square pillars on four-sides on retreat to leave a load-bearing remnant coal pillar. The system of partial extraction has been successful in meeting safety, productivity, and subsidence targets.

Jan 1, 2011

By D. W. H. Su

A two-year study was conducted by CONSOL in a northern West Virginia coal mine to evaluate pillar design and support requirements to improve roof control in right-hand longwall headgates subject to high in situ horizontal stresses. Horizontal stress measurements conducted within undisturbed areas of the subject mine revealed a pre-existing regional horizontal stress field with a significant difference in magnitude between the east-west maximum and the north-south minimum stresses. Three¬dimensional stress cells installed to monitor horizontal stress concentration in the headgate roof during mining revealed that a narrow (60-foot center) headgate pillar reduces the east-west horizontal stress concentration in the roof ahead of the face such that the headgate is more stable and requires less support. This 60 foot x 140-foot pillar design, which has been employed in subsequent panels, still provides adequate stress attenuation to protect future tailgates under a maximum cover depth of 1000 feet. Roof geology derived from underground roof reconnaissance and underground bolt load and roof displacement measurements confirmed the effectiveness of 12-foot long cable bolts for controlling the headgate roof subject to high horizontal stresses. With the new headgate pillar design and the supplemental cable bolts, headgate roof conditions in the subsequent panels improved significantly, longwall production delay due to adverse headgate roof condition was totally eliminated, and record coal production was achieved by the subject mine in the subsequent years.

Jan 1, 2003

By Winton J. Gale

The design of the reinforcement systems required to stabilise mine roadways has developed through the application of field measurement techniques. These techniques have allowed the level of security of a given opening to be determined from an assessment of the loading within the reinforcement, the extent of roof deformation and experience. The design systems developed are now used extensively in a wide variety of geological environment. Recent interpretative techniques have been developed to improve the level of confidence when designing roadway reinforcement. The techniques are particularly applicable for roadways subject to either weak materials or extreme stress levels. A second area of application is where roadway advance rates and hence the timing of reinforcement placement are critical. The newly developed techniques include both analytical and computational models. The validated computational techniques allow a more rational approach to investigation of the effect of varying reinforcement type, timing of placement and density on the level of stability achieved.

Jan 1, 1992

By K. Y. Haramy

Strong roof helps minimize roof fall problems in coal mine entries. However, the Inability of strong roof to cave readily may contribute to major ground control problems In Iongwall and retreat mining operations. The concern expressed by mine operators prompted this Bureau of Mines study to analyze the effects of strong roof members on ground stability around Iongwall openings. The problem was approached from three directions: development of a theory to analyze the strain energy conditions In the coal and surrounding strata, modeling the effects of different thicknesses and strengths of Coal and roof strata, and field Instrumentation of powered supports In two Iongwall mines. Results from the theoretical and modeling analysis confirm the accepted belief that a strong roof does, In fact, play a major role in high stress concentration problems In and around the Iongwall panel. Analysis of the effect of different roof overhang dimensions and properties on relative strain energy buildup In the coal and roof Is presented. Shield pressure data Indicate possible methods for detecting noncaving roof behind the shields. Strategies to monitor roof overhang and control dangerous conditions caused by the noncaving roof are also presented.

Jan 1, 1988

By Jiacheng Wang

The current state of thick seam coal mining methods is illustrated in three typical cases of thick seam longwall mining, each pointing out the outstanding achievements in top-coal caving mining and large cutting height mining in China. At the same time, based on current thick seam mining practices in China, some problems urgently need to be solved. These include improving the recovery ratio of coal reserves, determination of overburden strata pressure, shield support selection, supporting methods for large cross-section in-seam roadways, top coal bulk flow theory, and gas flow and control technology. In addition, the rational production capacity should be studied from both economic and technological perspectives in order to optimize coal recovery and efficiency.

Jan 1, 2011

By Kenny D. Basnett

An analysis of the Roof Falls Data Base (RFDB) for underground coal mines in Illinois for the period 2004?2008 indicated that about 80% of the roof falls occur at intersections and are associated with geologic anomalies or a rapidly changing geologic environment. Most falls are associated with anomalies such as clay dikes, differential compaction faults, shear zones, joints and fractures, and geologic structure. Therefore, a better analysis of the geology with emphasis on mapping anomalies such as joints and fractures and their application is necessary to improve ground conditions and safety. Such studies within Illinois Coal Basin are limited. This paper presents a mapping study of the joint orientations with documentation of dip of the several lithological units that lie directly above the Herrin No. 6 Coal seam around southern Illinois. These units include the Energy Shale, Anna Shale, and Brereton Limestone. The mapping was done in three mines and the data were plotted on a stereographic projection to determine the average characteristics of joint planes. The study mines included two deep underground mines and one shallow highwall mine. This study has helped identify favorable mining and support orientations in areas of highly variable geology. These are currently under review by the cooperating coal company for experimental roof control studies.

Jan 1, 2011

By Kent D. Mctyer

Mining commenced at Tasman Mine in late 2006. The current method of mining is bord and pillar using continuous minerbolters and shuttle cars for first workings and secondary extraction using mobile roof supports. The two stage process was chosen to accommodate irregularly shaped coal deposits, allowing adjustments to be made to extraction ratios for better management of subsidence and to maximize the efficiency of the operation. Following the completion of the first three full/partial extraction panels, the mining method was changed due to variable caving. Another partial extraction method, referred to as the Duncan Method was adopted; it involves stripping the developed square pillars on four-sides on retreat to leave a load-bearing remnant coal pillar. The system of partial extraction has been successful in meeting safety, productivity, and subsidence targets.

Jan 1, 2011

By Erdal Unal

In gate roads where supports are subjected to dynamic loading four times due to retreating longwall panels, it is a real challenge to replace the rigid arches with flexible reinforcement systems and yet to provide safety and stability of these openings within better economical limits. The results presented in this paper are based on a three years of research project aimed at developing safe and economical support systems for gate roads in Çayìrhan coal mine. Çayìrhan -Mine Project includes laboratory and field studies, design analysis, pilot scale design applications and performance monitoring. Based on outputs of the design approach developed, four types of bolts, namely, Split Set, Yielding Super Swellex, Sis-Resin, and Fosroc-Resin bolts were installed in a gate road together with widely spaced yielding steel-arches. In order to compare the performance of these flexible support systems and to provide feed back for the design approach, a monitoring program was initiated.

Jan 1, 1993