Experimental study on accelerated destabilisation of creeping coal body under medium impact dynamic loading

Deep coal-rock masses exhibit pronounced creep characteristics. Under moderate dynamic impact loads (impact energy levels ranging from 103 J to 104 J), creep-affected coal-rock masses undergo time-delayed instability failure. This presents certain difficulties for the assessment and early warning of engineering hazards. To address this issue, a self-developed creep-impact testing system was employed to investigate the mechanical response characteristics of creep-prone coal under moderate dynamic impact loading. The study analyzed the influence of moderate dynamic impact loading on the creep failure of coal bodies and discussed the mechanism by which such loading accelerates the failure of creep-prone coal. Test results indicate: (1) Increasing the magnitude and frequency of moderate dynamic impact loads accelerates the transition of coal mass from isochronous creep deformation to accelerated creep deformation, while simultaneously reducing both the time required for coal mass to enter the accelerated creep stage and the corresponding stress threshold. (2) At low stress levels, coal exhibits only a hardening effect under creep conditions. However, under moderate dynamic impact loading, the coal demonstrates a hardening-damage effect, ultimately inducing a macroscopic failure mode dominated by tensile fracture. (3) The concept of “impact damage stress” in creep coal bodies was proposed, indicating that moderate impact dynamic loads accelerate damage and failure in creep coal bodies when stress levels reach a minimum of 0.4σc. This stress state may be regarded as the “impact damage resistance strength” of creep coal bodies. The research findings provide theoretical support for the early warning and prevention of rockburst disasters in deep mines.