Abstract Under ultra-long interlayer spacing, mining-induced fracture zones may not directly intersect the protected seam; therefore, gas connectivity cannot be reliably evaluated from fracture height or pressure-relief angles alone. The 15204 panel of the Fuda Coal Mine, with a 78.52 m spacing between the No. 15 protective seam and No. 8 protected seam, was selected to examine preferential pathway formation under non-penetrating fracture conditions. Borehole observations were used to constrain the heights of the caving and fractured zones. Laboratory testing and Hoek–Brown parameter reduction were conducted to characterize the intermediate strata, and a distinct-element model was used to resolve fracture evolution and goaf compaction. The reconstructed fracture geometry was then introduced into COMSOL Multiphysics for sequential deformation, seepage, and diffusion analysis on a fixed fracture field. The maximum fracture development height was approximately 61 m, indicating that the fractured zone did not geometrically reach the No. 8 seam. Nevertheless, stable permeability zonation was formed in the goaf, with a compacted low-permeability central region and persistent high-permeability belts along both margins. Gas migration was accelerated along the side pathways, whereas transport through the central region remained delayed. Initial cross-seam breakthrough occurred after about 100 d, and complete pathway connectivity was reached by 150 d. The results provide practical guidance for drainage target selection, borehole layout optimization, and control-window determination in high-gas mines with ultra-long interlayer spacing.
Yang et al. (2026) studied this question.