Three-dimensional physical simulation of overburden migration in deep thick hard roof fully-mechanized caving mining

In order to analyze the influences of breaking of deep thick hard roofs on the safe mining of thick coal seam, a large three-dimensional physical simulation experiment (3500 mm×3000 mm×2000 mm) is constructed, and the experimental study on the double-working face mining with coal pillar is carried out according to the engineering geology and mining conditions of coal face 402102 of Hujiahe Coal Mine. The grating displacement continuous monitoring device is used to monitor the displacement of overburden in real time, and the fracture migration laws and the dynamic evolution characteristics of "three zones" of overburden in thick coal seam mining under thick hard roofs are obtained. The results show that: when the thick and hard key stratum is deformed and broken, the weak rock stratum will move in coordination, the displacement at the monitoring point will increase sharply, and the displacement curve will be pushed forward in a "stepped" way with the advancing of working face. When one side of the working face is mined out, the first weighting interval of SKS1 (siltstone) of working face 402102 is 43 m, and the periodic weighting interval is 21 m. The first weighting interval of SKS2 (coarse sandstone) is 73 m, and the periodic weighting interval is 51 m. The first weighting interval of SKS3 (medium sandstone) is 171 m. When SKS2 breaks periodically and SKS3 breaks for the first time, the overburden rocks move in a wide range and the ground pressure is intense. Under the influences of mining-induced overburden structure in goaf 402103, the overlying rocks of the return airway on the working face 402102 migrate violently, and the roadway is greatly affected by dynamic pressure. According to the displacement at the monitoring points and the size of overburden deformation and fragmentation expansion factor max (K_i), the development morphology of the "three zones" is identified. Both SKS1 and SKS2 are in the caving zone, and the heights of the caving zone and fracture zone increase in a "stepped" manner with the advancing of the working face.