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Multiple-seam mining in the United States: design based on case histories.

Mark-C; Chase-FE; Pappas-DM
Proceedings: New Technology for Ground Control in Multiple-Seam Mining. Mark C; Tuchman RJ, eds., Pittsburgh, PA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 2007 May; :15-27
To conduct this study, NIOSH collected the largest database of multiple-seam case histories ever assembled. These data were analyzed with the multivariate statistical technique of logistic regression. The study also employed LaM2D to estimate the multiple-seam stress, ALPS and ARMPS to determine pillar SFs, and the CMRR to measure roof quality. Several of the study's findings confirm the conventional wisdom about multiple-seam interactions. Overmining was found to be much more difficult than undermining, and isolated remnant pillars caused more problems than gob-solid boundaries. For the first time, however, it was possible to quantify these effects in terms of the equivalent thickness of interburden needed to compensate for them. The study also found that pillar design is a critical component of multiple-seam mine planning. Many of the failed cases involved pillars whose SF seemed inadequate once the multiple-seam stresses were accounted for. Weaker roof was also found to significantly increase the risk of multiple-seam interactions. Some factors that were not found to be statistically significant included the interburden competence, the time lag between mining the two seams, the lower coalbed-to-interburden thickness ratio, and the angle between the active mining and the remnant structure. The most important result of the study is an equation that predicts the critical thickness of the interburden required to minimize the likelihood of a multiple-seam interaction. This equation has been incorporated into a step-by-step methodology that allows mine planners to evaluate each potential interaction and take steps to reduce the risk of ground control failure. Such measures could include installing cable bolts or other supplemental support, increasing the pillar size, or avoiding the remnant structure entirely.
Mining-industry; Underground-mining; Coal-mining; Computer-models; Computer-software; Models; Mathematical-models; Ground-control; Ground-stability; Rock-mechanics; Rock-bursts; Rock-falls
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Proceedings: New Technology for Ground Control in Multiple-Seam Mining
Page last reviewed: March 11, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division