Four-Zone Distribution of Coal Seam Stress in Hard-Roof Working Faces and Its Influence on Gas Flow

To investigate the distribution of coal seam stress ahead of the working face under hard-roof conditions and analyze its impact on gas flow, this study focused on the 16,021 working face in Wu Hua No. 1 Mine. First, we established a mining model using UDEC to analyze stress distribution at different coal seam extraction distances. Second, we used COMSOL Multiphysics 6.3 to simulate the influence of stress on the permeability and gas pressure of coal seams during extraction, thereby exploring how stress distribution affects gas flow. Finally, we deployed gas extraction boreholes to validate the gas flow characteristics associated with the stress zones. The results indicate that the coal seam stress ahead of the working face forms four distinct zones, influenced by the main roof hanging: stress reduction zone I, stress concentration zone, stress reduction zone II, and original stress zone. When extraction days are equal, under high-stress conditions, the extracted coal seam exhibits low permeability and a small decrease in gas pressure, making gas extraction difficult; in contrast, under low-stress conditions, it exhibits high permeability and a large decrease in gas pressure, making gas extraction relatively easier. Field measurements show that the gas extraction flow rate initially increases and then decreases with distance from the coal wall, exhibiting a noticeable rise within the 47–62 m range before stabilizing. This trend aligns well with the characteristics of stress zoning.