Dynamic mechanical response characteristics and damage constitutive model of axially anchored bodies under graded confining pressures

To clarify the dynamic response of a local anchorage bearing unit subjected to coupled impact loading and radial confinement, the axial front-end unit of a roadway bolt support system was idealized as a bolt–resin–rock composite cylinder. Coupled static–dynamic impact tests were conducted at confining pressures of 0, 2, 4, 6, and 8 MPa using a modified Split Hopkinson Pressure Bar (SHPB) system. The incident compressive pulse was applied parallel to the bolt axis to represent compression-dominated disturbances transmitted along the reinforcement direction. At an impact gas pressure of 0.6 MPa, increasing the confining pressure from 0 to 8 MPa increased the dynamic peak stress from 61.27 to 100.79 MPa, decreased the peak strain from 0.01073 to 0.00567, increased the terminal transmitted energy from 40 to 141 J, and decreased the terminal apparent absorbed energy from 71 to 49 J. The dynamic equivalent wave impedance ratio increased from 0.085 to 0.168, indicating progressively improved impedance matching and wave transmission capacity. A confinement-dependent segmented equivalent damage constitutive model was established by combining the strain equivalence principle, Weibull statistical damage theory, and an unloading–rebound branch. The model reproduced the loading stage, peak point, and dominant post-peak response path, with an average R 2 of 0.969 and an average RMSE of 3.102. The proposed model is intended to characterize equivalent responses within the calibrated laboratory range. These results provide a basis for interpreting the confinement-dependent impact response of axially anchored bearing units in deep roadway support systems.