Abstract
Coal mine bumps, the violent failures of overstressed coal, present a safety hazard to miners when longwall mining is conducted in deep, bump-prone coal mines. The U.S. Bureau of Mines evaluated two different longwall gate entry systems in a southern Appalachian coal mine located in the Pocahontas No. 3 Coalbed under approximately 610 m (2,000 ft) of overburden that included a massive sandstone member. Both gate entry systems employed a center abutment pillar flanked by yield pillars. The original design used a 24.4-M (80-ft) square abutment pillar, while the new design employed a 36.6- By 54.9-M (120- by 180-ft) abutment pillar. Rock mechanics instrumentation data analysis and in-mine observations indicated that this increase in abutment pillar size significantly decreased bump potential. The new design in worst-case conditions increased effective bearing area 62 pct, with only a 9-pct increase in gate entry system width, and eliminated face bumps that were experienced with the original gate entry design.
