Thermo-hydro-mechanical coupling analysis of dynamic responses of green sandstone subjected to high-strain rates: Experimental study and damage-based modeling

Deep rock engineering is affected by coupled thermo-hydro-mechanical (THM)-dynamic fields, necessitating the elucidation of the dynamic mechanical behavior and failure mechanisms. This study utilized a Multi-field Coupled Controlled Split Hopkinson Pressure Bar (MCC-SHPB) system to elucidate the cross-scale dynamic responses of rocks and the boundaries of failure modes under THM coupling. Impact tests were conducted on green sandstone under coupled conditions of temperature (25 °C-80 °C), confining pressure (0–15 MPa), and seepage water pressure (0–15 MPa). Scanning electron microscopy (SEM) microstructural characterization and COMSOL Multiphysics numerical simulations were conducted, and a dynamic constitutive theoretical framework and failure-prediction methodology were established. We investigated the impact toughness index ( I t ), dynamic modulus ( E d ), dynamic triaxial compressive strength (TCS d ), fragmentation degree ( W ), and failure modes of green sandstone under thermo-confining pressure-seepage-impact loading conditions. The key findings reveal that the I t reflects different energy regulation mechanisms across different confining pressure regimes. Thermal-microcrack interactions dominate at low pressure, and energy absorption prevails at high pressure. A triphasic dynamic modulus model captures stiffness evolution under energy-driven conditions, revealing cross-scale crack nucleation-propagation and fragment reorganization. The TCS d inflection point signifies energy dissipation shifts, causing nonlinear skeleton bearing-capacity degradation. A critical criterion based on the W was established to distinguish between the two failure modes and predict the unstable failure initiation. Numerical simulations were used to elucidate the effects of inertia-dominated crack propagation and stress wave interference, validating the critical criterion and the predictive accuracy of the theoretical model during cross-scale failure. This study provides a theoretical foundation for assessing the dynamic stability of rock masses subjected to multi-field coupling during deep resource exploitation.