Numerical simulation and application study on pressure relief and antireflection of overlying hard thick roof coal-rock

Based on the fact that the overlying strata of the protected coal seam in Yushutian Coal Mine are hard and thick strata,physical experiments, numerical simulation and field application were adopted to simulate the stress change of the protected area,especially the vertical stress evolution law of the protected coal seam,and the variation law of the original rock stress area,the stress-concentrated area and the pressure relief area. On this basis,the scheme of protective layer mining was designed,and then the high directional long borehole was selected for gas extraction. The results show that the key stratum will be formed in the hard and thick strata when the upper protective stratum is mined,which will directly affect the mining effect of the protective layer. After mining of the upper protective layer,the pressure relief degree of the protected layer is 50%, the swelling deformation is 0. 391%, and the concentration of air gas in the working face of the protected coal seam is reduce to 0. 35%. The field application shows that when the protected coal seam is overlaid with hard and thick rock, the optimal effect of pressure relief and antireflection and gas extraction can be achieved by using the upper protective layer mining and high directional long borehole.