Research on permeability change of overlying strata affected by mining in working face

In order to optimize the layout parameters of the gas drainage system and improve the effect of gas drainage, this paper studied the gas seepage migration path and the spatial location of the gas enrichment area based on the displacement law of the overlying strata in working face, developed a three-dimensional estimated model of the subsidence of the overlying strata in working face, and analyzed the movement and deformation law of the overlying strata in working face, the concept of "total strain" was introduced to describe the fracture development of overlying strata in working face, then the relationship between "total strain", porosity and permeability was established, the variation law of mining permeability in the final subsidence state of overlying strata and the mining process of working face was analyzed. The results show that the high permeability change area of overlying strata is located in the range from 59 m to 67 m above the coal seam, the gas migration is the most active in this area, under mining conditions, high concentration gas will gather in large quantities and form a high-level annular gas enrichment area. The prediction model developed in this paper provides an important theoretical guidance for the efficient extraction of coal seam gas.