Research on Gas Seepage Characteristics and Application of Coal Samples in Different Stress Zones under Negative Pressure Influence

To reveal the coupled control mechanism of extraction negative pressure and mining-induced stress zoning on coal gas permeability, taking the 1607 working face of Jiulishan Mine as the engineering background, a combination of physical simulation experiments and field tests was conducted. The permeability evolution of coal samples from the in-situ stress zone, stress concentration zone, and pressure-relief zone under negative pressures ranging from 8 to 30 kPa was systematically investigated. Results show: (1) Negative pressure has a significant zoning effect on permeability. In the in-situ stress zone and stress concentration zone, permeability first increases and then decreases with rising negative pressure, peaking at approximately 25 kPa, which is attributed to the competition between effective stress increase and matrix shrinkage. In the pressure-relief zone, permeability continuously increases, indicating that the well-developed fracture system is more sensitive to negative pressure driving force. (2) Field tests confirmed the laboratory results, but the optimal negative pressure for safety and economy is 15 kPa, at which the pure gas drainage rate reaches a maximum of 0.24 m³/min. Higher negative pressure (30 kPa) reduces extraction efficiency due to intensified air leakage and near-borehole fracture closure. The reasonable negative pressure of 15 kPa is determined for this working face, providing theoretical basis and technical reference for extraction parameter optimization in mines with similar conditions.