Dynamic evolution of advanced abutment pressure in downward-mining isolated panels and pressure-relief techniques

Downward-mining isolated longwall faces often experience severe abutment-pressure concentration and roadway instability due to dip-angle-induced disturbance and asymmetric goaf constraints. To address these issues, this study uses theoretical analysis, FLAC3D numerical modelling, and field monitoring to investigate the evolution of advanced abutment pressure and to develop an effective pressure-relief strategy. Results show that the dip angle significantly alters the stress-transfer path, causing a forward shift and amplification of the peak abutment pressure. At a 15° inclination, the stress concentration factor and the plastic-zone width increase by 51.5% and 16.3%, respectively, compared with horizontal extraction. The peak stress exhibits a nonlinear rise with increasing dip angle, and although wider coal pillars can reduce stress concentration, the stress-attenuation effect of the pillar diminishes as its width increases. Asymmetric goaf lengths induce an evident nonuniform stress distribution in the coal pillar during the initial extraction stage, which gradually weakens as the face advances. To mitigate the intensified loading, a collaborative destressing strategy via directional roof-cutting and borehole drilling was proposed to interrupt the high-stress transmission path. Field application demonstrates that within 120 m ahead of the face, rib convergence and roof-floor closure were reduced by approximately 68% and 54%, respectively, ensuring effective roadway stability. The study clarifies the stress-evolution mechanism of downward-inclined isolated longwalls and provides a targeted technical solution for safe and efficient mining under complex stress conditions.