Study on the Influence of Fracture Distribution Characteristics on the Stability of End Face Roof Under Repeated Mining of Close-Distance Coal Seam Group
In order to study the influence of fracture distribution characteristics of overlying rock on the stability of end face roof under repeated mining of close-distance coal seam group,the fracture distribution characteristics under repeated mining of close-distance coal seam group were analyzed by using digital image correlation technology(DIC),triaxial mechanical characteristic test and numerical simulation.The results show that the increase of confining pressure under triaxial stress state will increase the peak strength and elastic modulus of coal samples.With the increase of confining pressure,the failure angle of the sample increases,which easily leads to the spalling of the coal wall,thus inducing the disaster of the end face roof.When mining a single coal seam,the roof breakage is mainly located in the roof position at the coal wall of the working face.Before the mining of the lower coal seam,the number and density of fractures in the rock strata are further increased and the distribution range becomes larger due to the influence of the mining of the upper coal seam.The opening and density of the upper coal seam fractures are significantly higher than those of the lower coal seam.The overlying rock fracture in the working face undergo a dynamic cyclic change process of"generation-development-closure-redevelopment-penetration-reclosure"in turn.The research results can provide theoretical support for the stability control of end face roof in close distance coal seam mining under similar conditions.
Close-distance coal seam groupRepeated miningFracture distributionEnd face roofNumerical simulation