Study On Mining Surface Subsidence Law Of Deep-buried Fully Mechanized Caving Face In Wenjiapo Coal Mine

In recent years,geological disasters such as surface movement,deformation and surface cracks caused by mining of fully mechanized top coal caving face in deep coal seam in western loess gully region have damaged the surface buildings,water bodies and roads in the mining area.Therefore,it is of great theoretical and practical significance to study the development law of surface subsidence in fully mechanized top coal caving face of deep coal seam in loess gully region.Taking the 4105 deep buried fully mechanized top coal caving face of Wenjiapo Coal Mine in Binchang mining area of western loess gully region as the main research object,the surface rock movement was observed and analyzed.4105 Deep buried fully mechanized top coal caving face（mining height 9m）the maximum surface subsidence coefficient is 0.25m,the maximum subsidence is-1.82m,the maximum horizontal displacement is 0.77m,and the maximum subsidence speed is-7.3mm/d;the surface subsidence and horizontal movement of 4105 working face are generally inclined to one side of the goaf of 4104 working face,and the maximum subsidence point of the surface is also inclined to one side of the goaf of 4104 working face,and the surface subsidence rate is the highest on the side near the goaf of 4104 working face;the mining of 4105 working face causes the secondary subsidence of the goaf of 4104 working face（mining height 7m）in the east,and the secondary subsidence is 1.50m and 0.16m higher than that of the primary subsidence.The parameters of surface movement in the mining process of 4105 fully mechanized top coal caving face are determined,and the range of surface movement after mining of adjacent working face is predicted by probability integration method.Through field geological mapping and UAV remote sensing,the surface cracks in 4105 deep buried fully mechanized top coal caving face are divided into two types:parallel cut cracks and parallel trench cracks.The parallel cut crack shows the change law of "crack-decreasestability",and the parallel groove crack shows the change law of "crack-increase-stability".Through the on-site tracer mark excavation observation,it is found that the surface crack profile of 4105 fully mechanized top coal caving face shows "wedge" type and "bifurcation" type.The occurrence condition of super-thick loess layer and large depth-thickness ratio coal seam is not conducive to the development of surface cracks in fully mechanized top-coal caving face,and the overlying rock fracture step and strength are closely related to the development of fissures.in the larger area of surface subsidence,there is a positive correlation between the subsidence and the development width of surface cracks.The critical conditions for the development of surface cracks in Wenjiapo deep buried fully mechanized top coal caving face are determined,and the development of surface cracks in adjacent faces after mining is predicted.The results of FLAC^3D numerical simulation show that the plastic failure zone of overlying rock in 4105 working face is "concave",the shear force is "arch" with strong support,and the area of surface movement and deformation can be divided into subsidence edge area and subsidence center area.The mining of 4105 working face causes the overlying rock movement to destroy the coal pillar area between the faces and the goaf of 4104 working face,which increases the failure height of the overlying rock movement in the goaf of 4104 working face,and causes the secondary subsidence of the surface of the goaf.