Synergistic Fracturing and Pressure Relief of Residual Coal Pillars and Thick–Hard Interburden Strata in Closely Spaced Coal Seams

To address the high-stress problem in underlying roadways caused by the combined effects of concentrated loads from residual coal pillars and suspended-load-bearing behavior of thick and hard interburden strata during downward mining of closely spaced coal seams, a dual-location synergistic fracturing method for pressure relief was proposed based on the 221001 working face of a coal mine. 3DEC numerical simulations were used to investigate the effects of fracturing location, height, and angle on surrounding-rock stress and coal-pillar deformation, and the optimized scheme was further verified through physical similarity simulation and field tests. The results show that synergistic fracturing provides a better pressure-relief effect than single-location fracturing. The stress in the middle of the interburden strata decreases by 45.54%, and the deformation of the sectional coal pillar decreases by 90.69%. The reasonable fracturing height and angle are 22 m and 70°, respectively. The physical similarity simulation shows that the target strata can progressively fracture along the weakened zone. Field tests show that roof-to-floor and rib-to-rib convergence decrease by 58.82% and 54.39%, respectively; the average support working resistance decreases by 34.58%; and the peak coal stress at a depth of 6 m from the roadway rib decreases by 37.62%. The results indicate that the synergistic fracturing scheme with an interburden fracturing height of 22 m and an inclination angle of 70° can effectively mitigate stress concentration and improve roadway stability, providing a practical reference for pressure-relief control under similar closely spaced coal-seam mining conditions.