Effects of heterogenous interburden Young's modulus on permeability characteristics of underlying relieved coal seam: Implementation of damage-based permeability model

Mining interaction among adjacent coal seams delivers benefits in realizing coal permeability enhancement and mining safety. Despite large amount of studies on interaction phenomenon from several perspectives of stress redistribution, strata movement and permeability change, few investigations focuses on sensitivity analysis, particularly, impacts of interburden parameters on interaction characteristics. A coupled permeability model was established including coal damage effect for better permeability-estimation accuracy. Meanwhile, a numerical simulation model was developed according to targeted coalmine parameters. Weibull statistical distribution is used for setting model property heterogeneity. Effects of interburden Young's modulus (E) on interaction among adjacent coal seams were investigated, mainly the permeability variations in relieved coal seam corresponding to six Weibull shape parameters of E distribution (4, 8, 12, 16, 20 and No Weibull case) and seven Young's modulus combinations of interburden sublayers (HHH, HHS, HSH, SHH, HSS, SHS and SSS combination). Results indicate that: 1) Caused by first mining activities, permeability in underlying relieved seam rises over 950 times near interburden floor. When being farther away the floor, permeability increase ratio first experiences quick decline, then comparatively slight decrease. 2) Permeability value of relieved seam is negatively related to Weibull shape parameter of E, and average permeability increase ratio (PR_Ave) gets the smallest value when Weibull distribution being not included. 3) For seven interburden-sublayer combinations, permeability increase ratio in relieved seam is positively correlated with soft sublayer's number. Meanwhile, PR_Ave of HSH combination is larger than that of HHS and smaller than that of SHH. Above results could be beneficial in helping mining researchers and engineers recognize intense-interaction coal seam group (i.e. more soft sublayers and small Weibull shape parameter). Thus, they could make use of seam interaction effect for improving relieved seam permeability and achieve efficient drainage practice through first mining an appropriate coal seam.