Abstract: In cold regions, fractured rock masses experience frost heave forces due to the phase change expansion of fracture water, leading to fracture propagation and even rock mass failure. Although existing research has developed models for calculating frost heave pressures, the problem of frost cracking in fractured rocks, which involves the coupled temperature-seepage-stress fields due to moisture migration, phase change heat transfer, and fracture propagation, remains a challenging aspect of current research. Drawing upon the developmental process and mechanism of water-ice phase transition, this study proposes an equivalent water expansion method to simulate phase transition expansion. A finite element model incorporating multi-field coupling is established using COMSOL software to couple the stress field, temperature field and seepage field. Based on experiments on frost heave forces in frozen rock masses, a corresponding multi-field coupled model is established, and the proposed multi-field coupled numerical simulation method is validated from two aspects: frost heave pressure and fracture propagation. The stress, damage and deformation of the fractured rock mass during the freezing process are analyzed. Finally, the evolution patterns of seepage and pore water pressure in the fractured rock are analyzed under varying freezing directions. The simulation results show that the frost heave pressure is mainly composed of the pore water pressure, and the frost heave pressure can be neglected in the region of freezing regions; the range of frost heave pressure action shrinks as the freezing front advances; the fracture propagation starts from the stress concentration area at the fracture tip, with damage extending to the periphery; the freezing direction significantly influences the seepage-hydraulic pressure response: the uniform freezing forms a closed freezing shell to limit the seepage, whereas the unidirectional freezing facilitates the seepage of fracture water out of the fracture, resulting in a reduction of the frost heave pressure. The proposed method offers a theoretical framework for elucidating the freeze-thaw damage mechanism in fractured rock masses and advancing geotechnical engineering research in cold regions.

Key words: frost heave pressure, fractured rock, seepage, multi-field coupling, numerical simulation