An Elasto-Plastic Damage Constitutive Model for the Interface Between Frozen Soil and Ice Incorporating Temperature Effects and Critical-State Theory

The failure of ice-lens-containing frozen soil typically propagates along the interface between frozen soil and ice, and the mechanical behavior of this interface plays a controlling role in the overall stability of frozen soil. In this study, low-temperature direct shear tests were systematically conducted to investigate the shear mechanical characteristics of the interface between frozen soil and ice under various temperature conditions (from −5 °C to −1 °C) and normal stress levels. The results indicate that under the same normal stress, the interfacial shear strength increases significantly with decreasing temperature. At temperatures below −2 °C, the interface exhibits pronounced strain softening and residual strength, whereas at −1 °C, the shear stress versus displacement curve follows a hyperbolic form without a distinct peak. Both the cohesion and internal friction angle of the interface decrease exponentially with increasing temperature, albeit with different patterns of temperature sensitivity. Based on experimental observations, the shear process of the interface is divided into three stages: undamaged, damage evolution, and fully damaged. A damage variable based on the Weibull distribution is introduced, and an elasto-plastic damage constitutive model for the interface between frozen soil and ice is established by incorporating a modified soil mechanics framework and the gradual degradation of ice-cementation strength with increasing plastic strain. The rationality and applicability of the proposed model in capturing peak strength, strain softening, residual strength, and hardening behavior are validated through comparisons between model predictions and experimental results under five temperature conditions and multiple normal stress levels. Within the tested temperature range of −5 °C to −1 °C, the findings provide a theoretical value for understanding the failure mechanism of ice-lens-containing frozen soil and for guiding engineering design in cold regions; extension of the proposed relationships to wider temperature ranges requires further experimental verification.