近距离煤层开采上覆采空区岩层二次活化机制研究OA

Mining of close distance double coal seams often causes secondary deformation and subsidence of the ground surface,and the overlying goaf also brings safety production problems to the lower working face being mined.To investigate the characteristics and laws of the secondary activation and fracture of the overlying goaf strata and their impacts on the lower working face during the mining of the lower coal seam,taking the mining of close distance double coal seams in a coal mine in Northwest China as the back-ground,the secondary activation mechanism of the roof strata in the overlying goaf during the mining of the lower coal seam was studied by means of microseismic analysis,numerical simulation and similar simulation tests.The results show that:in the initial mining stage,micro-seismic events were mainly concentrated in the lower strata above the roof of the 317 working face,and in the middle mining stage of the 317 working face,the dense area of micro-seismic events developed to the 221 working face and the coarse-grained sandstone above it,indicating that micro-seismic events tend to develop toward higher strata.Affected by the mining of the 317 working face,the activation and fracture height of the roof in the 221 goaf increased,the bending and subsidence of the upper main roof intensified,and the secondary activation height of the roof increased by about 10 m from the caving stability to the basic stability of the upper goaf,and the overlying strata initially showed a"primary activation-stability-reactivation"mode.Simil-ar simulation tests show that after the mining of the 221 working face,the immediate roof caved,and the weight of strata within the range of the overlying fractured roof acted on the floor of the working face.With the advance of the 317 working face,the roof of the 221 goaf further bent and subsided,the spaces of the upper and lower goafs were connected and overlapped,and the roof of the 221 working face was secondarily fractured and caved.The fractured rock blocks were mutually extruded and hinged,and with the ad-vance of the working face,the main roof and the immediate roof were extruded into an integral body,presenting the"primary activa-tion-stability-reactivation"mode.