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By Christopher Mark

A coal burst is defined as the sudden, violent ejection of coal or rock into a mine opening. Coal mines in the North Fork Valley (NFV) of Colorado?s Gunnison River have a long history of coal bursts in a wide variety of settings. These have included longwall and room-and-pillar, development and retreat, and single- and multiple-seam mining. In contrast to other coalfields, where bursts are typically associated with strong, massive sandstone and extremely high stress, many bursts in the NFV have occurred beneath shale roof and some distance from the most highly stressed locations. The goal of this paper is to attempt a systematic study of the entire burst history in the NFV, in order to gain insight into their characteristics and causes. The primary sources of information are the reports of investigations conducted by the Mine Safety and Health Administration (MSHA) Roof Control Division over the past 15 years. This paper provides details on the geologic mapping conducted as part of these investigations, as well as a regional plot of burst locations using a Geographic Information System. The mapping indicates that many of the NFV bursts have been associated with structural features, including low-angled faults and well-defined zones of high-density jointing that exhibit little or no displacement. Some of these features appear to extend for several miles, impacting more than one mine.

Jan 1, 2012

By Theresa M. Bodus

The strength of roof shales is, in part, a function of the preferred orientation of clay minerals within them. Therefore, analysis of clay fabric under both air-dried and hydrated conditions should be helpful in understanding roof shale failure. Core samples were collected from the Energy, Anna, and Lawson shales, which are locally present as roof shales of the Herrin No. 6 coal of southern Illinois. The Clay Fabric Index (CFI) was measured for thirty core samples, using X-ray diffractomtry, to investigate the relationship between clay fabric and roof collapse in coal mines. Greater CFI values indicate a weaker preferred orientation among clay minerals, which generally results in a weaker inter-grain bond. Average CFI values for air-dried samples were: 0.15 for Anna shale; 0.20 for Energy shale; and 0.37 for Lawson shale, .After the introduction of water, average CFI values increased to: 0.28 for Anna shale; 0.22 for Energy shale; and 0.43 for Lawson shale. The laboratory results indicate the following: [l] under air-dried conditions, Anna shale is the most stable, followed by Energy and Lawson shales; and 121 under hydrous (mine) conditions, Energy shale is the most stable, followed by Anna and Lawson shales. In mine environments where roof failures involving Energy shale have occurred, planar trends delineated by a relatively high density of small (0.2-4 cm diameter) iron concretions have been reported along the failure surface. Radial cracks have been observed around unsealed anchor bolt holes in the Anna shale. Instability of the Lawson shale is ubiquitous in coal mines. In the laboratory, similar physical changes were noted in the shale samples after the introduction of water, including [l] increased hydration around the perimeter of iron concretions in Energy shale, [2] radial extension cracks in Anna shale, and 131 extreme slaking of Lawson shale. Measured increases in the CFI reflect the observed physical changes of the samples upon the introduction of water, which probably reflect changes in strength that may result in roof failures in hydrated mine environments.

Jan 1, 1989

By R. Kanniganti

The primary problems of pillar design in seams subject to interaction are due not only to difficulties in predicting loading, but also to the often unsymmetrical nature of the stress fields. The effects of uneven stress fields on failure patterns within a pillar were studied wing a two dimensional finite element method. Lower seams, including ultra- close mining situations were evaluated considering conventional pillars. Pillar case study data for under mining were analyzed to determine if empirical trends in stable pillar sizing could be derived. Recommendations for multi-seam pillar design are made, based on anticipated loading conditions within a pressure bulb. Applications of the research results are demonstrated using case studies

Jan 1, 1995

By S. S. Rowland

Good afternoon, ladies and gentlemen. It is a pleasure, for several reasons, to be here at this 13th International Conference on Ground Control in Mining. Of course it's always a pleasure to be able to see and reacquaint myself with many long-time friends; but it's also a pleasure, or 1 should say worthwhile, because I take something back with me, some knowledge about mining that lets me do my job better and more safely. if I can do that, I've accomplished my purpose in being at a conference such as this. This conference is a little different, though. I have to earn my stay. I have to earn it by telling you a story; a story about mining through a mile of rock to get from one coal seam to the same seam on the other side of an ancient river channel; a story about mine personnel taking over the job from a contractor; a story about having to mine through two faults after the hard part was supposed to be over, but, most importantly, it's a story about how it was accomplished successfully and safely by a group of ordinary coal miners possessed with determination, belief in themselves, and a "can do" attitude. If you can take any part of my story and use it to do your job better and more safely, then I will have accomplished my purpose in being here today. Kerr-McGee Coal Corporation's Galatia Mine is located in Southern Illinois near the town of Harrisburg in Saline County, about 350 miles south of Chicago and 120 miles southeast of St. Louis. Construction of the mine began in 1982, and the first coal was shipped in 1984 from the Harrisburg No. 5 Seam, 550' below the surface. Mining began in the Herrin No. 6 Seam, 100' above the No. 5 Seam, on April 1, 1985. Mining in both seams began by using the room-and-pillar method. In 1989, the No. 6 Seam was converted to longwall mining, as was the No. 5 Seam in 1992. Today, all mining is done by the longwall method except for the required development work, which is performed by continuous miners. A heavy-media preparation plant with a 4.2 million-ton annual clean-coal capacity processes the coal. By the end of 1994, with annual production now exceeding 4 million tons, we will have shipped over 30 million tons of steam and metallurgical coal throughout the United States and the world. Most of the coal has been used as the primary source of fuel to generate electricity for the city of St. Louis. The No. 5 Seam coal can be used as a semi-soft coking coal or as a high-Btu, relatively low-sulfur steam coal. Its use allows utilities to comply with Phase I of the Clean Air Act Amendments of 1990 without installing flue gas desulfurization units or blending with other coals. The Herrin No. 6 Seam is a high-Btu, medium-sulfur steam coal that requires blending to meet Phase I requirements. Because the No, 6 Seam coal does not meet the Clean Air Act Amendments' Phase I compliance standards, we were forced to cease mining operations in the No. 6 Seam, leaving 170,000,000 tons of minable coal in the ground. Last month the Galatia Mine became a single-seam operation mining the Harrisburg No. 5 Seam only. The Clean Air Act Amendments of 1990 and the resultant S02 emission limitations on electrical power generation plants effectively eliminate, beginning in 1995, the near-term potential for profitable mining of the Galatia Mine's high sulfur Herrin No. 6 Seam coal. Because of the Clean Air Act Amendments, it is virtually impossible to market high-sulfur coals like the No. 6 coal unless the mine location and mining conditions enable greatly depressed sales prices to cover costs. We, along with the majority of

Jan 1, 1994

By D. S. Choi

This paper describes an improved source location technique for microseismic events related to coal mining. A system of non- linear distance equations is solved with the use of the Newton-Raphson method. This computational method is- advantageous when the number of geophones is limited. In addition, this paper includes the results of the analysis of data from several instruments which characterize both mine seismicity and environmental noise such as vehicle traffic. Analysis of the mine seismicity has contributed to a better understanding of caving above a longwall gob and of what constitutes stable ground conditions.

Jan 1, 1990

By J. Nielen van der Merwe

Rock engineering research and technology development in South Africa only received serious attention in reaction to the Coalbrook disaster in 1960. At the time, a number of gaps in knowledge of rock related matters were identified and in the ensuing years, these were progressively attended to. The paper describes the events that led up to the Coalbrook disaster and reviews the developments that took place afterwards. The effectiveness of the research outcomes are tested by referring back to the disaster. It is concluded that tremendous advances were made but that not all the unknowns were attended to at the same level. The strength of nominally square internal pillars is the one issue that received the most attention, but the strength of barrier pillars, overburden behaviour and loading systems are still largely unknown. Due to the complexity of the remaining unknowns, they can and should be addressed by the application of back calibrated numerical models. There are no readily available simple analytical solutions. The state of mining rock engineering research in South Africa borders on an emergency. More than a 1000 years of aggregate research experience has been lost in the last three years and funding is under severe pressure. There are disturbing parallels between the current positioning of the industry as a whole and the Coalbrook mine in the years preceding the disaster.

Jan 1, 2006

By D. N. Bigby

This paper concentrates on ground control innovation in Europe since the first Morgantown conference, mainly from a UK perspective. In particular, it describes the rock engineering and ground control tools developed to address the mine support and design problems associated with coal mining at great depth in areas influenced by previous workings. The differences in approach across the Western European industries are also examined. Perhaps the most significant change in the period has been in the science of coal mine rock mechanics itself, with support design now based firmly on measurement, analysis and understanding. The ground control innovations described here have played their part in increasing the efficiency with which coal is mined and in increasing safety to the extent that fall of ground accidents are now rare.

Jan 1, 2006

By V. D. Jalevsky

A new methodology of an experimental-analytical approach has been developed. It is used in building an information geomechanic monitoring system for the modeling of geomechanic processes during coal seam working. The approach synthesizes experimental (in-situ) measurements of rock pressure manifestation in separate points, methods of numerical modeling of processes on rock boundaries with coal, and a seam analytical calculation of rock mass in a spatial strained state. One of the realizations of this approach is the developed theory and calculation method of adjoining rock surface shift (overhang) formation during underground working of sheet deposits and of rock mass geomechanic state determination. There are description algorithms of cavity configurations with broken lengths of faces during underground working of useful mineral sheet deposits. These algorithms have been used in computer modeling of formations of adjoining rock surface overhangs and abutment pressure upon rock mass in the area of coal faces with irrectilinear longwalls. Peculiarities of surfaces shifts and stress allocation are established for different face schemes. The use of theory and methods alloww working out techniques of automatic control to receive processing algorithms of RPM measurement results and calculate geomechanic situations within panels in the process of planning and development as well as during mining, i.e., to carry out long-term prediction, in-line control, and short-term prediction of rock pressure manifestations.

Jan 1, 1996

By Hideki Shimando

Periodic weighting and windblast which are caused by the dynamic effects of overburden in a longwall panel significantly affect longwall mining This study describes past experience with wind blast at Miike Colliery, proposes a new loosening system using hydraulic fracturing and moistening, and also discusses strength deterioration in hard-to-collapse roof rocks due to water in order to solve the problems caused by the effects of dynamic roof rocks behavior in a longwall face

Jan 1, 1998

By Axel Preusse

For the last 150 years, subsidence damage to the surface has been an unavoidable phenomenon associated with underground coal mining. In particular, the mechanization of mining methods in multiple seam mining and the concentration of mining activities in densely populated European metropolitan areas (e.g., Ruhr, Upper Silesian industrial region) have led to mining having a very strong influence on the earth?s surface. In both these regions, surface subsidence of more than 20m has been reported up to now in comparison to the original state. Underground coal mining in these regions strongly impairs all kinds of surface use, such as urban and industrial development, infrastructure (roads, waterways, and railways) and pipelines?without restricting the functionality of those objects to a greater extent. Demanding and, in some cases, globally unique engineering solutions have been developed and implemented for this purpose. The previously mentioned mining and industrial regions are still very strongly characterized by the (increasingly declining) coal industry and will remain dependent to a large extent and for an indefinite period on artificial drainage measures because subsidence that has already occurred is irreversible. This paper will primarily discuss the prediction of subsidence that is caused by intensive multiple seam mining and its influence on surface objects (e.g., underground pipelines). However, an approach for predicting ground uplifts due to rising mine water as a consequence of mine closures will also be described.

Jan 1, 2012

By Roland C. Walker

Traditional headed rebar has existed in the mining industry as a ground support product for many years. The head of a rebar bolt is most commonly produced by hot upset die forging. Upset die forging produces a rugged, simple head that performs well. Certain elements of the head must comply with regulatory standards, such as ASTM F432-95, which offers a standard test procedure to ensure quality of the product. The head style produced by all major manufacturers has been optimized to reduce manufacturing costs, provide greater miner safety and provide an excellent performing product. Observations were made in some mines of heads failing under in-situ loading. These observations could not be replicated according to the ASTM testing method. This paper highlights the problem and how a solution was developed. The development includes pictures of in-situ failures from the underground operations, laboratory replication tests indicating how this loading occurs, and then the use of this calibrated test method to validate the new design created.

Jan 1, 2009

By Shane McDonald

Australia produces approximately 84 million tonnes of coal per annum from 30 longwalls in New South Wales and Queensland, operating at an average depth of around 300m. Industry trends and expectations place increasing emphasis on the reliability of these operations; for example, the current average face width is 245m and this is expected to increase to approximately 270m by 2010. In recent years, Beltana No.1 Mine has consistently been Australia?s highest longwall producer, with ROM output of 7.2Mt in YEJ2007. Strata management has become a key feature of the operation of Australia?s longwall mines, as a tool to manage variances in the geotechnical environment. This involves an understanding of the impacts of the geotechnical environment on ground behaviour and the implications for mine design, stability and associated support, interaction and horizon selection. The anticipated ground control impacts of these factors form the assumptions that drive the format of plans specifying both triggers and actions, with quantified, monitoring-focussed experience used to refine the plan in a continuous improvement (ie ?plan-do-check-act?) process. This paper summarises the Beltana No.1 Mine strata management methodology and experience to-date.

Jan 1, 2008

By André C. Zingano

The coal pillars in room-and-pillar mining method are subjected to vertical stress due to overburden rock mass and horizontal stress relieve due to entries excavation around them. Some coal mining companies are applying rock bolts and steel straps to improve the pillar strength, consequently to reducing the pillar size and increasing coal recovery. This kind of approach deserves some discussion, whether it is pillar reinforcement or just rib support. The efficiency of pillar reinforcement (or rib support) is directly related to the initial load capacity of coal pillar, the type of excavation, and the width to high ratio of the pillar. The objective of this paper is to understand the mechanism of pillar reinforcement (or rib support) using rock bolts and steel straps on pillar ribs. Numerical simulation taking into account the relations listed above. The results showed that the increase of coal pillar strength is very short, and there is no influence on improvement of load capacity of pillar. However, the rib support avoids block falling, rib failure, and displacement, reducing the pillar failure propagation into the pillar center. Keywords: coal, pillar reinforcement, room and pillar.

Jan 1, 2006

By W. G. Pariseau

A crown pillar cave occurred at the Ropes Mine in December, 1987, that resulted in closure of the mine. Production was resumed soon afterwards with the formulation of a rock mechanics plan designed to address several issues of safety and stability. The plan proved to be successful and shows what can be accomplished in the realm of applied rock mechanics where a cooperative atmosphere exists.

Jan 1, 1989

By Anthony Iannacchione

A Major Hazard Risk Assessment (MHRA) was developed in Australia after a series of mine disasters in the 1990?s. A MHRA is used to help prevent major hazards, i.e. fire, explosion, wind-blast, outbursts, spontaneous combustion, roof instability and chemical and hazardous substances, from injuring miners. A MHRA is a structured process that identifies the characteristics of major hazards, assesses and ranks the risk they present, and evaluates engineering and administrative controls to mitigate them. These controls typically consists of a broad spectrum of prevention, monitoring, first response, and emergency response techniques and helps to move an operation from a reactive to a proactive approach towards safety. This paper documents a MHRA performed at an underground mine where strata instabilities and fire hazards may threaten the condition of its escapeways. The objective of this MHRA is to 1) identify what hazards could affect the egress through the mine?s escapeways, 2) determine what unwanted events pose the greatest threat for the mine, and 3) recommend a plan to prevent or recover from the potential disruption of egress through the escapeway. The plan provides information on the key existing controls that should be monitored and audited, and makes recommendation of new potential controls to further reduce related risks. By documenting the use of MHRA to this specific ground control issue, this paper provides a framework for others to judge the merits of this approach and to help design and perform these activities.

Jan 1, 2007

By Stephen P. Signer

To improve the understanding of the support interaction mechanics between grouted bolts and coal mine roofs and to help lay the foundations for improved design and evaluation techniques, the 0.8. Bureau of Mines has conducted laboratory, field, and analytical studies of the load transfer mechanics of grouted roof bolts. Mechanisms by which load is transferred from a bolt through the grout to the rock mass are analyzed. Strain gauges were installed on over 70 bolts and tested to observe the rate of load transfer when a force was applied at the bolt head. Laboratory and field tests were conducted to determine bolt-grout- rock interaction behavior in both the elastic and postyield phases. Long-term laboratory tests were run to determine the time-dependent properties of both polyester resin- and-gypsum-grouted bolts. Numerical studies using finite- element techniques were compared to the experimental results. Elastic tests showed that 90 pct of the applied load was transferred within 24 in of bolt length. Long-term tests indicated that creep is more significant in gypsum-grouted bolts than in resin- grouted bolts. Plastic studies showed that yielding of steel will translate down the length of the bolt from 6 to 20 in.

Jan 1, 1988

By Matt Leeming

Several of the underground mines in the UK require a significant number of cable bolts to be installed, remedially, to control worsening roadway conditions. Often the access is limited and the only power source is compressed air. Machines for this duty are generally designed to perform with 100 psi but regularly only half of this is available. This paper seeks to outline the difficulties this situation causes the Rock Bolting Engineer, highlight the technical requirements for a machine of this type to succeed and detail a solution offered by our engineers.

Jan 1, 2007

By Michael Kelly

Inertial navigation technology has, for the first time, allowed the position of a longwall shearer to be mapped in three dimensions. Following the success of the technology in highwall mining and successful trials on a longwall face, the Australian Coal Association Research Program (ACARP) commissioned a three year "Landmark" project that aimed to advance longwall automation to the level of "on-face observation" by the end of 2004. This project has been completed with the following successful technical outcomes: Automatic face alignment was achieved, using an inertial navigation-based sensor on the shearer, to accurately measure face geometry and feedback signals used to move OEM (Original Equipment Manufacturer) roof supports. Operational on-line measurement of creep with creep information incorporated into face alignment corrections. Inertial Navigation System (INS)-based enhanced horizon control was bench-tested. Operational broadband communications system to shearer using wireless Ethernet on a commercial-product basis. Acquisition of located coal-face features for use in thermal infrared-based horizon control. Automated Longwall Information System (LIS) developed which integrates information from multiple systems and sensors and provides high quality visualisation and control interfaces. Automatic roadway and face convergence monitoring tools successfully tested. Condition monitoring tools developed and demonstrated for improved face reliability. This paper summarises the outcomes of the project and describes the work being undertaken for the 2 year Landmark Extension project approved in April 2005. Consistent with the conference theme, the paper focuses on the ground control aspects of the project.

Jan 1, 2005

By Vedala Sastry

Longwall mining for coal extraction in deeper deposits is gaining momentum in India, due to the increasing stripping ratios and depletion of shallow deposits amenable for surface mining. In longwall mining, presence of multiple seams with varying interburden thickness is a major problem especially while planning for over-mining. An investigation program was taken up to analyze the effect of the presence of goaf and virgin coal blocks in already developed and extracted lower seam by bord and pillar mining, on the stress distribution in the longwall panel in upper seam. Studies revealed marginal increase in horizontal and shear stress as longwall face passes above goaf to the virgin area present in lower seam. Stress distribution over chock shields was considerably affected when the face in upper seam reached 15-25m zone above the galleries in the lower seam. A clear influence of the presence of solid coal, galleries and goaf in lower seam was found in the loading of longwall panel in upper seam.

Jan 1, 2007

By Frank E. Chase

The Harris No. 1 Mine, located in Boone County, WV, has been longwalling the Eagle Coalbed for over 30 years. Harris has experienced numerous interactions associated with the extensive room-and-pillar and longwall mining operations which have been conducted in the overlying No. 2 Gas Coalbed. The problems have included roof falls, excessive rib sloughage, and gateroad and bleeder entry closure. A detailed evaluation of the multiple seam experiences at Harris No. 1 Mine was conducted as part of the National Institute for Occupational Safety and Health (NIOSH) nation-wide multiple seam mining case history data base. One observation from the Harris gateroad case histories was that smaller, critically loaded, upper seam pillars seemed to cause more severe ground conditions than did wider pillars. The LaModel program was used to investigate this supposition, and the results confirmed that "critical" sized pillars do transmit the highest amounts of stress to adjacent seams. In addition, the data suggest that the probability of a major multiple seam mining interaction increases when the depth of cover is 1,000 ft or greater and when the Eagle seam pillars have a Analysis of Longwall Pillar stability factor less than 1.50.

Jan 1, 2005