Pressure relief and permeability enhancement effect and gas extraction scheme of long-distance lower protective layer mining

In view of the difficulty of pressure relief and gas control of overlying protected layer after deep and long-distance lower protective layer mining, based on the engineering conditions of Ⅲ1031 working face in Zhuxianzhuang Coal Mine, the stress evolution law, deformation and failure characteristics and pressure relief and permeability enhancement effect of the overlying strata during long-distance lower protective layer mining were studied by means of similar simulation and numerical simulation.The results show that the protective layer mining produces a longitudinal penetrating fracture extending to the protected layer, and the main roof breaks periodically with an average step of about 15 m.The pressure of the coal seam decreases firstly, and the stress returns to the approximate original rock stress state after recompacting in the middle of the goaf.The stress-concentrated area is formed in the surrounding rock, and when the stress evolves to the middle of the goaf, it develops in an arc-like stress decreasing circle.Because of the coal seam mining, the separated layer fracture development area is formed on both sides of the goaf, which provides a channel for gas flow, and the protected layer is also relieved.The pressure relief rate reaches 0.91, and the antireflection increase rate is 5% to 20%.The protected layer has obvious effect of pressure relief and antireflection.In order to solve the problem of pressure relief and gas extraction protective layer mining, a gas extraction scheme was designed including cross-layer drilling, bedding drilling, high-level drilling with interception drilling and buried pipe in goaf.