Evolution law and influencing factors of borehole pressure relief effect under creep behavior of deep coal

Traditional research on coal seam borehole pressure relief has primarily focused on qualitative static stress transfer, while the continuous dynamic evolution of the pressure relief effect remains under-explored. Given the significant creep characteristics of deep coal, this study employed numerical simulation tests and in-situ electromagnetic wave computed tomography (CT) detection to investigate the dynamic evolution characteristics of stress transfer, energy release, and the rock burst hazard index in the roadway ribs following borehole pressure relief. Furthermore, the influence of parameters such as borehole diameter, spacing, and depth on the evolution of the pressure relief effect was examined. The results indicate that the evolution of the borehole pressure relief effect in deep creeping coal can be categorized into two stages: instantaneous pressure relief and creep-induced pressure relief. After drilling, the creep deformation of the coal mass increases, and fractures around the borehole gradually propagate. Consequently, the stress, stored energy, and the rock burst hazard index in the pressure relief zone continuously decrease, although this attenuation decelerates as the duration of creep increases. As the borehole diameter and depth increase, while spacing decreases, the reduction rates of stress, energy, and the rock burst hazard index during the creep-induced pressure relief stage accelerate significantly, thereby enhancing pressure relief efficiency. Field applications in roadways prone to rock bursts have demonstrated that the anomaly index of the coal mass's absorption coefficient within the electromagnetic wave CT detection area gradually increases, while the rock burst hazard index decreases. In deep mining roadways, it is crucial to accurately determine the advanced pre-relief distance to fully leverage the dual effects of instantaneous and creep-induced pressure relief, thereby enhancing the effectiveness of rock burst prevention.