Dynamic mechanical behavior and damage characteristics of marble under combined thermo-hydro-mechanical conditions

Deep rock engineering often involves complex thermo-hydro-mechanical (THM) coupling and dynamic disturbance environments, and the mechanism linking the macroscopic load-bearing response with the microscopic damage evolution remains unclear. To this end, this study conducted dynamic impact tests on marble under different combined THM conditions using a modified split Hopkinson pressure bar (SHPB) apparatus. In combination with coupled PFC 3D /FLAC 3D numerical simulations, a THM‑SHPB model was established to systematically investigate the dynamic impact mechanical properties of marble under combined THM conditions. The results indicate that the dynamic mechanical properties of marble are governed by a nonlinear coupling of temperature and confining pressure, with an optimal temperature-pressure strength gain range. As the temperature increases into the high-temperature range, the results suggest a shift in the dominant mechanical response from stress confinement toward thermal-damage-related effects. Meanwhile, the hydraulic pressure consistently exhibits a monotonic strength degradation effect. The results reveal an asymmetric response pattern between the macroscopic dynamic strength and microscopic fragmentation characteristics of marble: the dynamic strength fluctuates with an initial increase followed by a decrease as the coupling environment changes, while the number of fragments monotonically decreases as the confining pressure increases. Numerical analysis suggests that this asymmetric response may be attributed to the instantaneous bearing capacity of local force chains and the global constraint efficiency of the force-chain network. Furthermore, confining pressure helps maintain the integrity of the strong force chain network by enhancing particle interlocking and lateral confinement, thereby reducing the degree of dynamic fragmentation. This study provides insights into the dynamic response of marble under combined THM conditions and offers a reference for the stability analysis of surrounding rock in deep underground engineering.