Cracks dynamic propagation and permeability jump characteristics of gas-bearing coal–rock combinations under different strain rates

Crack propagation in gas-bearing coal–rock bodies under dynamic disturbance plays a crucial role in coal mine safety. Impact-induced damage can significantly alter the permeability of coal–rock strata, thereby increasing the risk of gas-related hazards. In this article, the dynamic crack propagation and permeability jump characteristics of gas-bearing coal–rock combinations under different strain rate loading conditions were systematically investigated. Triaxial dynamic compression experiments were conducted to obtain the stress–strain responses and permeability evolution patterns of the samples. Further analysis of the failure modes and crack types of the coal–rock combination was conducted using industrial computed tomography scanning equipment, and the three-dimensional crack network was reconstructed. On this basis, a fractal seepage model was developed by integrating the pore network modeling approach. And the intrinsic mechanism underlying the permeability jump in gas-bearing coal–rock combinations is clarified. The results indicate that the dynamic stress–strain curve of coal–rock combinations exhibits dual linear elastic characteristics and elastoplastic instability behavior. The dynamic mechanical response of coal–rock combinations demonstrates pronounced strain-rate dependence. The cracks in the coal–rock combination are induced by compressive-shear failure, tensile-strain failure, and unloading failure, respectively. The crack propagation and failure extent in coal–rock combinations become increasingly severe with rising strain rates. The continuously increasing crack spatial complexity directly leads to a permeability jump. Relative to quasi-static compression failure, the coal–rock combination subjected to dynamic compression failure exhibits gas seepage hysteresis prior to the permeability jump.