Development rule of ground fissure and mine ground pressure in shallow burial and thin bedrock mining area

With the increase of coal seam mining intensity in the western mining area, which has the typical mining geological characteristics of shallow burial depth, thin bedrock and thick loose layer, the structure of overburden rock has also changed greatly. When there is only one key layer structure in the thick bedrock and it is close to the coal seam, the strata pressure and surface crack development law of the working face are different from those of previous research results. Based on the research background of 52,307 large mining height working face in Daliuta Coal Mine, this paper adopts similar simulation and numerical simulation techniques to systematically study the strata pressure and surface crack development laws of the working face under the roof condition of such main key layer. The results show that: There is only one key layer in the roof overburden of the working face and it is only about 4 m away from the coal seam, and the key layer is broken in layering during the mining process, the lower part of the key layer collapses by itself under the influence of mining and falls into the collapse zone, and the upper part of the key layer forms a "face contact block" structure, which was unstable and broke to form a "surface contact block arch" structure, and caused the periodic pressure of the working face. The fracture and migration of key layers affects the movement of the overlying rock layers. When the key layer is broken and unstable, the overburden rock moves as a whole, forming a tensile effect on the surface and producing surface cracks. When the key layer of the working face is broken by the "fixed support beam" for the first time, ground cracks appear on the surface in a short time, and the surface cracks have a certain hysteresis, but the lag distance is short. In the process of pressure in each cycle, with the fracture and instability of the key layer, the overlying rock layer sinks and deforms, and different forms of surface cracks occur in the surface soil layer due to the increase of tensile stress and horizontal deformation force, and the cracks generally lag behind the working face.