Abstract: The exploitation of deep coal resources constitutes a pivotal component of national energy strategic requirements. Notably, the deformation behavior of coal and rock masses in deep engineering settings is significantly influenced by complex environmental conditions, including elevated ground temperatures, high water pressures, intense stress levels, and strong disturbance loads. To investigate the dynamic strength characteristics and energy dissipation variations of deep sandstone under real-time thermo-hydro-mechanical (THM) coupling, dynamic impact tests were performed utilizing an enhanced THM multi-field coupled split Hopkinson pressure bar apparatus. Furthermore, a dynamic damage constitutive model for deep sandstone was formulated, integrating the viscoelastic-plastic Zhu-Wang-Tang (ZWT) model with the Drucker-Prager strength criterion. The test results reveal the following trends: Under varying water pressures, the plastic yield phase in the dynamic stress-strain curve is markedly prolonged, while the dynamic compressive strength and dynamic elastic modulus demonstrate a progressive increase with rising water pressure. As temperature escalates, these parameters initially rise before declining, with a discernible interval observed between 50 and 75 °C. The time-history curves of dynamic stress rate and dynamic strain rate generally adhere to evolutionary patterns characterized by “increase-decrease-decrease-decrease” and “increase-decrease-level-decrease”, respectively. At a constant water pressure, both incident and reflected energy exhibit a decrease followed by an increase with rising temperature. Conversely, at a constant temperature, transmitted energy displays a gradual increase, whereas dissipated energy initially increases before decreasing with increasing water pressure. The relationship between dissipated energy density and average strain rate transitions from a negative linear correlation to a positive linear correlation. A comparative analysis between the dynamic stress-strain test curves and theoretical curves demonstrates that the established dynamic constitutive model effectively captures the dynamic compressive strength and deformation characteristics of deep sandstone under THM coupling conditions.

Key words: thermal-hydro-mechanical coupling, deep sandstone, dynamic mechanical properties, energy evolution, constitutive model