Volume expansion can occur in overconsolidated clay during shear loading and heating. However, the volume expansion mechanisms driving these two phenomena are different from each other, and it is important to propose a model that can be adopted to describe these two volume expansion phenomena. A new model is proposed to describe the two aforementioned volume expansion phenomena. Specifically, the following three innovative points are made: (1) The thermal-mechanical coupling yield surface is proposed in the p-q-T space, and the overconsolidation stress R can be used to reflect the loss effect of overconsolidation degree during the heating process. The modified unified hardening parameter is used to reflect the shear shrinkage of normal consolidated clay and the shear dilatancy of overconsolidated clay. (2) The nonassociative flow law is used to express the direction of plastic strain increment. The phase transformation stress ratio is expressed as an exponential function of the overconsolidated stress ratio, which can be used to reflect three typical volume deformation modes of overconsolidated clay: full shrinkage deformation, dilatancy deformation after contraction, and full dilatancy deformation. (3) A rotational hardening rule that reflects the anisotropic properties of initial partial consolidation of clay is introduced so that the proposed model can be adapted to reflect the increase of soil stiffness caused by K0 consolidation, as well as the hysteresis loop phenomenon for deviatoric strain and stress relationship curve caused by cyclic loading. The comparison results between prediction and test data show that the proposed new thermal-mechanical coupling model can be easily and conveniently applied to describe the deformation and failure behavior of overconsolidated clay relevant to thermal effects.

Long-term freeze-thaw cycles have a significant impact on the safety and durability of tunnels located in cold regions. In this study, a hydro-thermal-mechanical coupling model and calculation method were developed based on the Guanjiaoshan Tunnel. The model's precision and rationality underwent comprehensive validation. The study aimed to discuss the temporal and spatial distributions of temperature, water, and mechanical fields under long-term freeze-thaw cycles. The findings revealed that the water migration influence zones can be classified into three distinct zones. The ice-water phase change and stress exhibit periodic fluctuations following an annual cycle. Significantly, the lining's stress, or danger level, exhibited two peaks during the autumn and spring seasons. The magnitude of the autumn peak exceeded that of the spring peak. Throughout the initial 12year period, the tunnel's danger level consistently remained below the threshold value of 1.0, affirming its adherence to safety standards during its early service period. Furthermore, the construction of tunnels has the potential to contribute to frozen soils expansion in specific zones due to prolonged freeze-thaw cycles. These study results not only enhance our understanding of hydro-thermal variations but also provide valuable insights for predicting the long-term security performance of tunnels in cold regions.