Study On Deformation Law Of Coal-rock Mass And Result Investigation Of Upper Protective Layer Mining

Protection layer mining technology is the most effective, safe and economic measures to prevent and control the coal and gas outburst. When the first mining face is mined, the top(bottom) plate of the mining area is destroyed, moved and deformed, and the stress field and the fracture field are re distributed. The top(bottom) plate adjacent to the coal and rock strata in the specific space and time in a certain range of pressure relief area, the expansion of coal seam, fracture development and permeability coefficient of the pressure relief zone are hundreds of times more than that of the coal seam, which has a large amount of desorption gas, which provides favorable conditions for the pressure relief gas drainage in the adjacent coal seams.Based on the geological conditions of the chuanjing mine in this paper, through theoretical research, numerical simulation test and field test, under the condition of high gas pressure in the protective layer, the pressure relief characteristics, displacement deformation and coal seam gas flow law of the underlying rock mass are studied systematically. Through FLAC3 D numerical simulation, we can draw conclusions as below: with the advancing of the working face, the stress value of the same depth is gradually decreased, the pressure relief degree is increasing, and the displacement of the moving deformation is also increased. Along the vertical direction of the mining area, with the increase of the distance between the floor rock layers, the pressure relief degree and the coal and rock mass displacement and the effective pressure relief range slowly decreased. The coal and rock mass at both ends of the mined out area are in the support stress zone, and the concentration factor of the support stress gradually decreases with the increase of the distance between the layers. With the further development of the working face, the roof caving in the goaf is compacted, the stress recovery phenomenon occurs, the displacement and permeability of the coal and rock mass are gradually weakened.According to the characteristics of the fracture zone of the coal and rock in the mining field, the goaf floor is divided into floor crack zone and heave deformation zone, and the coal and rock mass has different fracture development characteristics, gas flow and the law of occurrence in different areas. In the process, we took the regional prevention and control measures of "protective layer mining and pressure relief gas drainage" in the experimental working face.Through the field experiment of the protective layer on the chuanjing mine, residual gas pressure method, residual gas content method and coal seam gas drainage rate method were used to investigate the effect of pressure relief gas drainage, results show: the residual gas pressure is 0.26 MPa, the residual gas content is 4.35m3/t in the full pressure relief area of protected layer, the protected layer is to be road way driving outside the range of 15 m, the maximum residual gas pressure is 0.28 MPa, and the maximum residual gas content is 6.1m3/t. The working surface of the residual gas pressure and residual gas content was less than "the relevant requirements of coal and gas outburst prevention regulations", then the regional outburst prevention measurements effectively.