Abstract: To investigate the damage evolution of deep tunnel surrounding rock subjected to the coupled influences of temperature, seepage, and stress during excavation, a thermo-hydro-mechanical-damage (THMD) coupling model was developed based on thermoelasticity, Biot’s seepage theory, and continuum damage mechanics. The model was numerically implemented using COMSOL Multiphysics, and a Weibull distribution was introduced to characterize the inherent heterogeneity of the surrounding rock. The spatiotemporal evolution of stress, pore water pressure, temperature, and damage fields following tunnel excavation was systematically analyzed. Numerical results show that excavation induces significant stress redistribution, with stress concentration primarily occurring at the crown and sidewalls and gradually spreading outward. Pore water pressure near the excavation face drops sharply, forming a negative-pressure zone, after which seepage adjusts progressively toward a quasi-steady state. The temperature field develops a pronounced radial gradient due to rapid cooling at the tunnel boundary and subsequently becomes more uniform over time. Damage is mainly concentrated along the tunnel sidewalls and propagates from the excavation boundary into the deeper rock mass, with localized zones approaching failure. These findings elucidate the mechanisms governing damage evolution in deep tunnel surrounding rock under multi-physical coupling and provide a theoretical basis for stability assessment and engineering design of deep tunnels in extreme environments.

Key words: Tunnel Engineering, Rock Mass Instability, Spatiotemporal Evolution, Multi-field Coupling, Numerical Simulation