Confinement-induced damage-permeability coupling mechanism in coal seams: Experimental and numerical perspectives

In coal mining and gas utilization, mining-induced disturbances and in situ stress conditions arising from complex geological structures pose significant safety challenges. To investigate the effects of confining pressure on gas-saturated coal, this study developed coupled seepage-damage constitutive models and systematically analyzed the influence of confining and gas pressures on coal permeability, triaxial strength, and damage evolution through integrated experimental and numerical approaches. Results demonstrate that coal permeability exhibits high stress sensitivity. Confining pressure significantly restricts radial deformation, enhances compression and closure of pores and fractures, reduces gas seepage pathways, and consequently decreases permeability. Triaxial compressive strength increases with confining pressure but decreases with gas pressure, revealing antagonistic effects. A robust linear correlation (R2 > 0.97) exists between triaxial strength and confining gas pressures. Furthermore, during triaxial compression, shear-dominated damage propagates preferentially along structural weak planes and defects. Elevated gas pressure increases crack initiation density, while higher confining pressure suppresses microcrack formation, promoting localized macro-fracture propagation until failure. These findings provide critical insights into damage evolution mechanisms in gas-bearing coal under complex stress conditions, supporting enhanced prediction, and mitigation of coal-rock dynamic hazards.