Microseismic Monitoring of a Room and Pillar Retreat Coal Mine in Southwest Virginia

Abstract

Ground control, one of the key elements in mine safety, is an issue that warrants continuous improvement in the underground coal industry. The United States experienced over 3,300 injuries and 42 deaths between 2006 and 2012 from the fall of a roof or rib (MSHA, 2015). Out of the underground coal mining methods, room and pillar retreat mining lacks significant research to adequately understand the rockmass behavior associated with the process. A microseismic monitoring system was installed in a retreat mine in Southwest Virginia to provide more information about the changing stress conditions created by retreating and ultimately reduce risk to miners. Microseismicity has been proven to be an acceptable method of monitoring stress redistribution in underground coal mines and assist in explaining rockmass behavior (Luxbacher, et al, 2007). An array of geophones was placed underground along a single retreat panel to record failures due to stress redistribution throughout one panel of retreat. These microseismic events were located, and their moment magnitudes were found. An analysis was completed to observe the redistribution of stress and related gob formation throughout the panel's retreat. Expectations for the gob formation were consistent with the distribution of microseismic events. Over 13,000 microseismic events were found in 1.5 months of monitoring. Approximately 2,800 of these events were well enough located to provide analysis of the changing underground stress conditions from the retreat process. On average, recorded microseismic events during retreat produced a moment magnitude of -0.9, with no events higher than a magnitude of 2.0.