A Study on the Evolution of Coal Seam Stress and Permeability During Coal Mining and Its Application Effects: A Case Study of T Coal Mine

Background: The pressure reduction range in traditional protective coal mining is often set conservatively, resulting in diminished actual pressure reduction effects near the mining boundary. Therefore, analyzing the stress and permeability evolution patterns at the mining boundary is particularly essential. Method: A three-dimensional numerical model was established according to the mining conditions of the 864 working face in T Mine to study the stress evolution, fissure development, and permeability evolution of the coal and rock mass overlying the protective seam mining, especially those near the mining boundary. Results: The overlying coal and surrounding rock mass near the mining boundary are in the state of increasing vertical stress and decreasing horizontal stress, and under this mechanical path of “increasing axial pressure and decreasing peripheral pressure”, the coal mass is damaged and destroyed, fissures are developed, and the permeability is increased; as a result, the coal and surrounding rock mass near the mining boundary mainly produce vertical longitudinal fissures, and the permeability can be increased 900 times compared with that of the overlying coal and surrounding rock mass in the mining boundary. After ground drilling and enhanced depressurization, the measured maximum gas content of the coal mass at the strike boundary is 3.25 m3/t, and the measured maximum gas content of the coal mass at the inclination boundary is 2.63 m3/t. Conclusions: After mining the protective layer, the permeability enhancement effect diminishes from the center toward the sides, yet remains sufficient to eliminate the risk of gas outbursts. This validates the importance of verifying permeability enhancement effects at coal seam boundaries.