Study on Pressure Relief Effect of Overlying Coal and Rock Mass in Mining Under Protective Layer

In order to explore the pressure relief effect of mining under protective seam on overlying strata in Jincheng Mining Area, the engineering background of mining 9# coal seam as the protective seam of 3# coal seam was studied. The effect of pressure relief of overlying coal and rock mass and the law of swelling deformation of coal mass in protected seam after mining of lower protective seam are studied by numerical simulation, and the effective protection scope is determined. The results show that after the mining of protective seam, the pressure relief effect of overlying coal and rock mass appears in different zones, and the pressure relief effect decreases with the increase of vertical distance from the working face. The inclined pressure relief angle of the protected seam is 63 degrees and the strike pressure relief angle is 60 degrees. The swelling deformation rate of the protected seam in the middle of the goaf is about 4‰, which is a stable pressure relief area. After field test, it was found by borehole television that coal of the protected seam appears separation fissure affected by mining. The coal seam gas parameters shows that the gas content and gas pressure of the protected seam are reduced to 50% and 60% before mining, respectively.