Study on crack propagation law of overlying strata in the process of small coal pillar mining in inclined extra-thick coal seam

Aiming at the problem of unclear crack propagation law of overburden rock in the process of small coal pillar mining in inclined extra-thick coal seam, this paper takes the 11,002 working face of Tengda Coal Mine in Heze, Xinjiang as the background. Through physical similarity simulation and 3DEC numerical simulation, the mining-related laws of small coal pillar working face in inclined extra-thick coal seam are clarified, and the height of caving zone and fracture zone are determined by combining multi-method weights. The results show that: (1) when mining in strike (dip), the fractal dimension of overburden fracture decreases rapidly in the range of 3-25 m (3-22 m) from the roof, the height of caving zone is 25 m, the height of fracture zone is 66.5 m (81.7 m), and the stress concentration coefficient is 1.17 in both cases; (2) The caving form of the whole overlying strata in the goaf is asymmetrically distributed, and a stable area is formed on the upper side of the small coal pillar, and the overlying strata do not collapse; (3) The subsidence and fracture rate of overlying strata show a vertical gradient decreasing law; (4) Using the weighted average method based on weight, the height of the caving zone is determined to be 24.98 m, and the height of the fracture zone is 81.67 m. The research results provide a theoretical basis for mining overburden control and gas control in small coal pillar working face of inclined coal seam.