Research on the protection range of pressure-relief in the mining of upper protective layer

At present, the research on the protective layer pressure relief range mainly focuses on the analysis of the evolution characteristics of coal seam stress, deformation and plastic failure and the pressure relief range of the lower protective layer mining. There are few investigations on the protective layer protection effect, and more error of experimental results caused by less points taken in the actual measurement process. In order to solve the above problems, taking the 18125 working face of Pan'er Coal Mine of Huainan Mining Group as the research object, the stress distribution of the protected layer, the expansion and deformation rate of the coal seam roof and floor and the change characteristics of coal seam gas pressure after the mining of the protective layer are studied by numerical simulation calculation and field investigation and analysis methods. The results are listed as follows. ① The vertical stress in the direction of the protected layer is symmetrically distributed along the central axis, and the tendency pressure relief zone is elliptical. ② After the mining of the upper protective layer working face, the crustal stress relief zone is formed on its floor, the stress of the floor coal rock layer is reduced, and the coal rock layer in the pressure relief zone moves upwards and deforms. Due to the different spacing between the protective layer and the protected layer, there is a gap between the movement of the protected layer and the amount of deformation. The closer to the mining layer, the greater the expansion and deformation of the protected layer, and the more obvious the pressure relief effect of the protected layer. 30-60 m behind the working face of the protective layer is the best area for pressure relief and gas extraction of the protected layer. ③ According to the relative relationship between the gas pressure observation borehole and the position of the initial cutting hole of the working face of the protective layer and the gas pressure observation results, the maximum effective pressure relief angle of the mining direction of the protective layer is about 69.8°. ④ Through numerical simulation and combining with field investigation and analysis, according to the stress distribution of the protected layer, the expansion and deformation rate of the roof and floor of the coal seam and the change characteristics of the coal seam gas pressure, it is concluded that the pressure relief angle of the protected layer is about 60°, and the pressure relief angles of both the upper and lower tendency are 75°.