Research On The Ultimate Pressure Relief Mining Thickness Of Semi-coal Rock Protective Layer Working Fac

As coal mines continue to develop deeper,ground stress,gas pressure and gas content increase significantly,increasing the likelihood of coal mining being threatened by impact pressure and coal and gas protrusion,which has become an urgent problem in deep coal seam group mining.After long-term research and practice,it shows that the protective layer pressure relief mining has obvious effect on the prevention and control of dynamic disasters such as rock burst and coal and gas outburst.For the low permeability coal seam group without conventional protective layer mining conditions,this paper selects the thinner coal seam（coal line）to arrange the half coal rock protective layer working face to achieve the purpose of pressure relief and permeability enhancement.In this paper,theoretical analysis,numerical simulation and similar simulation experiments are used to study the deformation and movement of overlying strata,fracture evolution law and gas migration law after the mining of semi-coal-rock protective layer,taking the mining of semi-coal-rock protective layer working face in a mine in Guizhou as the engineering background.The method of limiting pressure relief mining thickness and the influence of pressure relief effect are determined.The main research results are as follows:（1）Based on the theory of mining-induced overburden failure,the evolution of overburden fracture,the law of movement and deformation and the law of gas migration in protective layer mining are analyzed.The key technology of pressure relief and permeability enhancement in semi-coal-rock protective layer mining is summarized.The basis and main influencing factors of the selection of semi-coal-rock protective layer are summarized.The pressure relief gas extraction technology is summarized,which provides a theoretical basis for pressure relief and permeability enhancement in semi-coal-rock protective layer mining.（2）Based on the engineering site conditions,a numerical analysis model was established by using FLAC^3Dnumerical simulation software under the condition of ideal homogeneous coal seam.The response characteristics of mining thickness to pressure relief and permeability enhancement were studied.According to the variation characteristics of vertical stress and displacement of overlying coal and rock mass in the mining of semi-coal and rock protective layer,the influence of mining thickness of semi-coal and rock protective layer on the pressure relief degree of protected layer was discussed,and the calculation method of ultimate pressure relief mining thickness was proposed.（3）With the help of similar simulation experiment,the failure process of overburden rock,the development law of overburden rock fracture and the pressure relief protection range of overburden rock caused by the mining of semi-coal-rock protective layer working face in a mine in Guizhou are analyzed and studied.Through the self-similar fractal property of mining overburden rock fracture distribution,the distribution characteristics of mining rock fracture network are studied,and the variation law and dynamic evolution process of mining rock fracture network with the advancing distance of working face are analyzed.（4）The UDEC numerical simulation software was used to simulate the development law of overburden fracture under different mining thickness conditions and the distribution pattern of partial mining overburden fracture field when the mining thickness was two meters and different propulsion degrees.The extracted fracture development pattern was imported into the multi-physics field coupling software COMSOL to analyze and study the gas migration law of the overburden fracture field.