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

Based on the hard and thick overlying strata of the protected coal seam in Yushutian Coal Mine.Physical experiments, numerical simulation and field application were adopted to study on the stress characteristics 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, stress-concentrated area and the pressure relief area.The scheme of protective layer mining was therefore designed.The high directional long borehole was selected for gas drainage.The results showed 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 intensity 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, antireflection and gas extraction can be achieved by employing the upper protective layer mining and directional long borehole methods.