Simulation Study on Energy Release and Weakening Effects of Pre-Fracturing in Hydraulic Fracturing of Thick Hard Roof

In this study, the thick, hard roof group of the 20103 working face in the Dahaize Coal Mine is used as the research object. UDEC discrete element simulations were conducted to examine fracture-induced energy release characteristics under unweakened conditions and single-layer hydraulic fracturing at different burial depths. This study clarifies the evolution of elastic strain energy accumulation and dissipation in thick, hard strata; reveals the post-fracturing energy migration mechanisms of different horizons; and establishes the correspondence between fracturing horizon and energy-weakening effectiveness. The results show the following: (1) Without fracturing, the energy accumulation within 0–30 m ahead of the face differs markedly among key strata. KS1 exhibits stable and relatively uniform elastic strain energy accumulation; KS2 shows a rapid increase at an advance distance of 180–300 m; and KS3, being farther from the coal seam, accumulates less energy than KS2. (2) After individually fracturing KS1, KS2, or KS3, the fractured layer loses its bearing and energy storage capacity, and the adjacent upper key stratum becomes the new load-bearing and energy accumulation layer. The reductions in elastic strain energy accumulation and release vary significantly by fracturing horizon: KS1 decreases by 10.70% and 11.63%, KS2 decreases by 18.73%, and KS3 decreases by 20.83% and 9.10%, respectively. Among the single-layer fracturing schemes, fracturing KS2 provides the most effective weakening of fracture-induced energy release in the mining-disturbed roof strata.