Spatial distribution law of permeability based on the mining-induced stress relief boundary model of inclined coal seam in overlying strata

To explore the permeability distribution of overlying strata based on the mining-induced stress relief boundary model in inclined coal seams. With surface subsidence and the stress distribution characteristics of coal walls of the goaf as the medium，based on the correspondence between surface subsidence and overlying strata，then combined with the definition of stress relief boundary，the distribution characteristics of overlying strata relief boundary at different dip angles were determined by theoretical derivation. In addition，the permeability spatial distribution law is obtained through 3DEC numerical simulation and Python secondary development. The results show that with the increase of the coal seam dip angle from 0°to 30°，the stress difference between two sides of the coal walls increases from 0 MPa to 13.1 MPa，and the stress relief region increases from the original 38.4 m to 54.5 m in higher side of the goaf. The stress concentration position shifted by 0.4 m in lower side of the goaf，thus，the stress relief boundary of lower side expanded. While the stress recovery position moved to the low side by 28.3 m in the central goaf，thus，stress relief boundary of goaf moved downward，and the maximum permeability increased from 90 mD to 270 mD in overlying strata. The stress relief boundary model can describe the stress relief degree and the corresponding spatial distribution of permeability well in overlying strata，which provides a reference for the accurate dominant gas drainage area identification.