A fully coupled thermo-hydro-mechanical model for freeze-thaw damage in fractured rock

The damage evolution of fractured rocks under freeze-thaw cycles involves complex multi-physical field coupling, posing a significant challenge for engineering stability in cold regions. This study develops a fully coupled thermo-hydro-mechanical model to simulate fracture displacement, damage propagation, and property degradation induced by freeze-thaw cycles. A discrete fracture network is adopted to represent the natural fracture system, while fracture initiation and propagation are described using elastic damage theory. Fracture normal displacement and shear slip are modeled using a nonlinear constitutive model. Key coupling mechanisms are considered, including ice-water phase change, thermo-poro-elastic response, and the evolution of material properties with freezing and damage. The model is validated against laboratory experiments and successfully reproduces nonlinear frost-heave deformation, the secondary peak of frost-heave pressure, and the coupled matrix-fracture interaction. Using the validated model, the degradation mechanism and the influence of fracture network geometry on damage evolution are investigated. Results indicate that initial fracture-induced damage irreversibly enhances rock storage and transport capacity, leading to intensified frost heave and progressive damage in subsequent cycles. A denser fracture network results in more severe and interconnected damage, while the intersection angle of fracture sets controls whether damage is highly localized or diffusely distributed.