Study on the mechanism of top coal cavability and the optimization of layered mining schemes in the extra-thick coal seams of Huating Coal Mine

Aiming at the problem of safe and efficient mining of extra-thick coal seam with an average thickness of 42 m in Huating Coal Mine, a reasonable top coal caving layered mining scheme for extra-thick coal seam was studied. Based on theoretical analysis, field measurement and numerical simulation, the influence mechanism of coal seam strength, occurrence depth, joint fissure, gangue characteristics, roof condition and mining height on top coal cavability in extra-thick coal seam is studied. The Griffith strength criterion and critical buried depth model of top coal failure are established, and the comprehensive evaluation method of caving multi-factor membership degree is proposed and verified by engineering. The research results show that the weak compressive strength (7.8 MPa), large buried depth (>500 m), fracture development and medium stability of direct roof of No.5 extra-thick coal seam in Huating Coal Mine are conducive to caving factors, which create favorable conditions for fully mechanized caving mining of extra-thick coal seam with large mining height and large mining ratio. Through the comparative analysis of top coal cavability in different layered mining schemes, it is considered that the two-layer fully mechanized caving mining scheme is feasible for the extra-thick coal seam with an average thickness of 42 m, and the non-equal height layered mining scheme is designed. The first layer thickness is 23 m, the lower layer thickness is 19 m, and the high resistance support (>18000 kN) and comprehensive fire prevention and extinguishing measures are matched.