Permeability distribution characteristics of underlying coal seam disturbed by mining activity

The permeability distribution law for protected coal seam is the core problem linked to protective coal seam mining. Based on the geological conditions of the Zhongxing coal mine, a numerical protective coal seam mining model was constructed in order to investigate the spatial evolution of stress and the damage characteristics of protected coal seams. During the mining of protective coal seam, the coal body of the protected coal seam undergoes loading followed by three-directional stress unloading. The permeability evolution law of the protected coal seam was derived by combining the relationship between the permeability and axial strain of the coal sample from mechanical-seepage experiments and the swelling and relaxation value of the protected coal seam from numerical simulations. We divided the permeability of the protected coal seam into the original permeability zone, the permeability decreasing zone, the permeability increasing zone, the permeability stable zone, and the permeability re-decreasing zone. The gas drainage data of the protected coal seam during the mining of the protective coal seam were measured in situ. The change laws of the gas drainage volume and gas concentration were essentially consistent with the permeability distribution of the protected coal seam.