Dynamic response and failure mechanisms of laminated soft coal under impact loads: A comprehensive study

To address challenges in soft coal seam excavation, including dynamic coal mass variations, low permeability, frequent dynamic phenomena, and roadway deformation during pre-outburst stages, this study employed a self-developed triaxial loading and impact experimental setup to investigate failure mechanisms of composite specimens with varying ratios. Experimental results demonstrate that external loading induces "cross-shaped" primary fractures, radial secondary fractures, and micro-fractures in coal masses, predominantly formed through shear failure. Numerical simulations reveal significant confining pressure sensitivity in stress field evolution, showing that increased confining pressure elevates stress magnitudes by 15–28 % and expands stress influence zones by 30–45 %. Building on these findings, we propose a high-pressure staged hydraulic fracturing technique targeting key strata to interrupt stress transmission paths. Experimental validation shows progressive pressure relief attenuation ratios of 22.68 %, 39.77 %, and 44.14 % with cavity expansion in critical layers. When combined with roof slotting (7m borehole spacing), this integrated approach enhances coal permeability and structural stability, achieving: 10 % increase in gas extraction volume, 11 % concentration enhancement, 1.22-fold reserve growth, 95 % reduction in dynamic phenomena frequency, and 20 % decrease in return airflow gas concentration. Roadway deformation decreased substantially from initial ranges of 1592-945 mm (height) and 963-715 mm (width) to 162-11 mm and 146-13 mm post-treatment. This methodology provides a novel technical pathway for safe and efficient soft coal seam excavation, demonstrating significant potential for dynamic disaster prevention and risk mitigation.