Abstract
Longwall mining of the adjacent coal seam with the presence of residual coal pillars overlying the seam can result in abnormal strata pressure and severe overburden failure, which poses a significant threat to mining safety. The threat is mainly manifested in the form of intense coal or rock burst and hazardous interconnection between gobs. This study employed the universal distinct element code (UDEC) to investigate the microscopic failure mechanism of the overlying residual coal pillars under the influence of longwall mining of an adjacent underlying coal seam in Yuanbaowan coal mine, China. Using the Voronoi method, we innovatively visualized the evolution of cracks in residual pillars, revealed the mechanism behind the failure of pillars, and explored the evolution and distribution of abutment stress. Also, strata movement characteristics during underlying panel extraction have been surveyed. Based on the modeling results, effective measures are proposed to ensure safe mining under residual coal pillars. This study might provide a certain reference for safe extraction of multiple seams in Datong Coalfield, China, and also in the central and western Appalachian Basin, United States, where many mining activities are carried out under residual pillars.
Highlights
Coal seams in Datong coalfield show distinctive characteristics
Residual coal pillars along with irregular gobs bring a series of difficulties to longwall mining of underlying adjoining coal seams [2,3,4,5,6,7,8]
Three rooms are to be excavated firstly in the #4 seam, leaving two coal pillars in place. e three rooms are excavated simultaneously due to the following two reasons: (1) the #4 seam was mined out about two years ago and (2) this study focuses on the effect of longwall mining of the underlying seam on the stability of the residual coal pillars. en, the #6 seam is to be excavated. e open-off cut of the longwall panel in the #6 seam is located right below the left edge of the Room I. e advance of the panel, from the left side to the right side of the model, is simulated using a stepwise excavation
Summary
Coal seams in Datong coalfield show distinctive characteristics. Most of them occur close to each other and are gently inclined shallow thick coal seams with fewer faults and hard roof. Using physical simulation and 3DEC numerical modeling, both movement characteristics of the overlying strata of shallow coal seams and the hydraulic support jamming mechanism in longwall mining of seams under residual pillars are investigated. A good microunderstanding of the evolution of stress and crack in residual coal pillars and the progressive collapse process during longwall mining of underlying seam is of great importance to make clear the relation among hydraulic supports, roofs, and pillars. Resulting from the extraction of the #6 seam and the failure of the residual coal pillars in the #4 seam, the intense roof weighting could exert dynamic impacts on the coalface in production, leading to rock burst and hydraulic support jamming or damage. Once the mined-out areas are interconnected, hazardous or poisonous gas could enter into the #6 seam coalface, posing a significant threat to personal safety
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