From zoned re-crushing visualization to innovative sealing solution: Unveiling the governing mechanisms of air leakage in gas drainage boreholes

Air leakage through the crushed zone surrounding boreholes is a critical bottleneck constraining efficient gas extraction, yet its underlying mechanisms remain unclear. This study employed a CT visual compaction apparatus, enabling, for the first time, the visualization and quantitative investigation of leakage pathways within the crushed zone. The main findings are as follows: (1) Particle re-crushing exhibits significant spatial non-uniformity, with its re-crushing degree descending in the order of upper zone, middle zone, lower zone. (2) As increasing stress, the void network evolves from a mesovoids-dominated system to one dominated by small voids and microvoids, whose combined proportion ultimately reaching 85%, and the voidage decays exponentially with increasing stress. (3) Under the stress, particle morphology evolves toward greater regularity and roughness, evidenced by an average increase of 224.7% in specific surface area, along with increases of 6.6% in flatness and 5.4% in elongation. (4) Based on this non-uniform evolution mechanism, an adaptive sealing strategy is proposed to guide the development of materials with dynamic responsiveness, enabling precise and persistent sealing of evolving leakage channels. The established visual-quantitative framework elucidates the microscopic mechanisms of air leakage and provides a crucial theoretical foundation for the development of adaptive sealing technologies.