Thermo-hydro-mechanical coupled model of unsaturated frozen soil considering frost heave and thaw settlement

Frost heave and thaw settlement of subgrade is the most typical engineering disease in permafrost regions, which seriously threatens the safe construction and operation of transportation infrastructure. On the basis of the Modified Cam Clay model, a thermoelastoplastic constitutive model of unsaturated frozen soil is proposed. This model can effectively describe two key issues of the mechanical behavior of frozen soils, that is, soil hardening caused by temperature reduction and volume compression during thawing. The proposed constitutive model is realized in the established thermo-hydro-mechanical (THM) coupled mathematical model, and the reliability of the coupled model is verified by comparing with the experimental results. In addition, the proposed THM framework is applied to describe the long-term freezing and thawing behavior of typical railway subgrade sections in the permafrost region of western China. The results show that water-heat transfer and deformation frequently occur on the subgrade surface as the seasons change. Moreover, the variation of thaw settlement is greater than that of frost heave, which seriously threatens the operation safety of railways in permafrost regions.