Room-and-pillar mining with pillar recovery has historically been associated with more than 25% of all ground fall fatalities in underground coal mines in the United States. The risk of ground falls during pillar recovery increases in multiple-seam mining conditions. The hazards associated with pillar recovery in multiple-seam mining include roof cutters, roof falls, rib rolls, coal outbursts, and floor heave. When pillar recovery is planned in multiple seams, it is critical to properly design the mining sequence and panel layout to minimize potential seam interaction. This paper addresses geotechnical considerations for concurrent pillar recovery in two coal seams with 21 m of interburden under about 305 m of depth of cover. The study finds that, for interburden thickness of 21 m, the multiple-seam mining influence zone in the lower seam is directly under the barrier pillar within about 30 m from the gob edge of the upper seam. The peak stress in the interburden transfers down at an angle of approximately 20°away from the gob, and the entries and crosscuts in the influence zone are subjected to elevated stress during development and retreat. The study also suggests that, for full pillar recovery in close-distance multiple-seam scenarios, it is optimal to superimpose the gobs in both seams, but it is not necessary to superimpose the pillars. If the entries and/or crosscuts in the lower seam are developed outside the gob line of the upper seam, additional roof and rib support needs to be considered to account for the elevated stress in the multiple-seam influence zone.
In 2016, room-and-pillar mining provided nearly 40% of underground coal production in the United States. Over the past decade, rib falls have resulted in 12 fatalities, representing 28% of the ground fall fatalities in U.S. underground coal mines. Nine of these 12 fatalities (75%) have occurred in room-and-pillar mines. The objective of this research is to study the geomechanics of bench room-and-pillar mining and the associated response of high pillar ribs at overburden depths greater than 300 m. This paper provides a definition of the bench technique, the pillar response due to loading, observational data for a case history, a calibrated numerical model of the observed rib response, and application of this calibrated model to a second site.
Implementing Energy Release Rate Calculations Into the LaModel Program Morgan M. Sears Mining activity at increasingly greater depths and the tragedy at Crandall Canyon that claimed the lives of nine miners have forced coal bump research to the forefront of mining engineering research. Near the end of the last century, the National Institute for Occupational Safety and Health (NIOSH) and the former U.S. Bureau of Mines investigated the mechanics, conditions, and mitigation of coal bumps. Unfortunately, the exact mechanics of coal bumps is still not fully understood. Following this period, research into coal bumps in the United States has been limited. The Energy Release Rate (ERR) calculation quantifies the dissipation ("release") of the gravitational potential energy of the rock mass as mining progresses. This release of energy can occur passively in the form of heat and sound, or dynamically in the form of coal or rock outbursts. From the initial application of a calculated ERR in the deep hard-rock mines of South Africa, the ERR was found to have a significant correlation with the risk or potential of damaging coal bumps or rock bursts. In the mid 1990s, the ERR was incorporated into the MULSIM/NL displacement-discontinuity computer program and used with limited success. In this research, an ERR calculation is incorporated into the modern LaModel computer program to facilitate an analysis for potential coal bumps. Initially, the ERR calculations in LaModel are verified using a case study of cut sequences originally modeled using the MULSIM/NL computer program. Then, the ERR calculations are applied to a bump-prone mine in Southern Appalachia where a number of different pillar recovery cut sequences were used/analyzed in order to minimize the risk of bumps. Incorporating the ERR calculations into the LaModel program further enhances the most widely used boundary-element model to allow for appropriate bump risk assessment. With this new analysis tool, engineers can adequately perform coal bump risk assessments with an increased margin of confidence. iii Dedication This thesis and its accompanying research are dedicated to the miners and rescuers who lost their lives at the Crandall Canyon mine. Without its mainstream media attention, public outcry, and federal legislation, funding for this project would not have been used for the much needed research in the prediction of coal bumps and rock bursts. I would like to thank everyone who made this project possible. I would especially like to thank Dr. Keith Heasley, my advisor, whose hard work and guidance kept me on track through the countless hours involved in this project. In addition, I wish to acknowledge Dr. Syd Peng and Dr. Yi Luo for being committee members as well as instructors and mentors during both my undergraduate and graduate studies. I would also like to thank Dr. Chris Mark who personally recommended me to be involved with this research. In addition, the ground control groups at the NIOSH Pittsburgh Research Laboratory and Spokane Research Laboratory...
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