Study on the 3D distribution law of overlying rock cracks in fully mechanized mining face of Xinjing coal mine

Understanding the distribution law of overburden cracks in high-gas coal seams is of great significance for rationally arranging high-drainage roadways or directional drilling positions and improving gas drainage effects. Taking the 3213 working face of Xinjing Mine of Yangmei Group as the engineering background, using similar simulation and CDEM three-dimensional discrete element simulation and other methods to study the overburden movement and crack development law after the recovering of the working face, the basic top breaking and periodic breaking of the working face as well as the distance, the development height and evolution of overlying rock fractures were obtained. The results show that the first weighting interval of 3213 working face was 30 m and periodic weighting interval was 10～15m；the straddle overburden was a "trapezoid" structure with a wide bottom and a narrow top; periodic pressure changes, ranging from 55° to 65°; according to similar simulated fracture observations and numerical simulation of the three-dimensional displacement distribution, it is determined that the height of the collapse zone was 8.6 m, which was 3.4 times of the mining height, and the fracture zone height was 25.7m which was 10.3 times of the mining height. The fracture development above the working face has a strong periodicity, and the fracture does not extend upward with the basic top fracture rising in a step shape, and the fracture is no longer extending upward after it reaches a certain height, and the upper cracks were all separated cracks, and the final crack zone was formed. It was distributed in a three-dimensional ring shape with an oblique trapezoid in cross section., the outer ring of the bottom face was 9 m away from the boundary of the gob, the bottom surface was 20 m wide, the top surface was 25 m wide, and the height was 10～20 m above the roof of the coal seam. Determining the three-dimensional position and range of the fracture development ring is of great significance to gas control in the working face and the gob. High drainage or drainage boreholes should be arranged at the top of the fracture ring as much as possible to keep the roadway or borehole intact and able to achieve the best drainage effect.