Dynamic responses of coal-rock-bolt composite with axial pre-stress and confining pressure

The stability of coal-rock-bolt composite (CRB) structures is critical in deep coal mining, particularly concerning damage mechanisms under combined static and dynamic loading conditions. This study investigates the dynamic failure mechanism of CRBs subjected to varying axial pre-stress and confining pressures using integrated Split Hopkinson Pressure (SHPB) tests and numerical simulations. Under dynamic loading, the CRBs exhibited a characteristic three stage mechanical response: elastic deformation, yield, and post-peak softening. Axial pre-stress was observed to systematically reduce the effective strain rate achieved during impact, whereas confining pressure increased it. These applied constraints influence energy dissipation by inhibiting lateral deformation and altering failure modes, leading to a significant increase in dissipated energy. Under identical dip angles and strain rates, confining pressure substantially enhanced the dynamic strength of the CRB specimens, while axial pre-stress demonstrated a negligible influence on peak strength under the tested conditions. Furthermore, confining pressure mitigated bolt fracture by restricting shear displacement at the coal-rock interface. Conversely, increasing axial pre-stress was found to exacerbate V-shaped deformation patterns within the specimen, with the severity positively correlating with pre-stress magnitude. Finally, an increase in strain rate resulted in a reduction in specimen section elevation, a decrease in bolt fracture depth, and a greater propensity for localized failure modes under dynamic loading. • Investigated dynamic failure of coal-rock-bolt composites under axial pre-stress and confining pressure. • Confining pressure boosts CRB dynamic strength but axial pre-stress shows negligible effect. • Showed confining pressure mitigates bolt fracture, axial pre-stress exacerbates V-shaped deformation. • Discovered both axial pre-stress and confining pressure enhance energy dissipation by inhibiting lateral deformation in CRB composites. • Higher strain rates reduce bolt fracture depth and promote localized failure modes.