Evolutionary mechanism of permeability of coal-rock combination considering interface effect: Model development and analysis

The existing permeability model for the coal-rock combinations treats coal and rock as parallel entities, neglecting the interface effect arising from their distinct mechanical responses. In this study, the differential deformation of coal and rock is investigated through triaxial compression-acoustic emission (AE)-seepage synchronous tests. By deriving the additional stress caused by the differential deformation at the interface, a permeability model that accounts for this interface effect is established and validated. The influencing mechanisms of permeability are quantitatively observed using the proposed model. The results show that the permeability of the coal-rock combination increases with the increase of kc0, kr0, ξc, and Lrt, and decreases with the increase of vc and Lct. Comparing kc0 and kr0, Lct and Lrt respectively, kr0 and Lct have a greater impact on the permeability of the coal-rock combination. ξc only affects the plastic section. Finally, for the low-permeability coal seam with poor permeability improvement, permeability improvement measures can be taken on the roof and floor are proposed to enhance the gas flow. This research holds significance for gas extraction and the prevention of compound dynamic disasters.