A Binary Medium Model for Unsaturated Silty Clay under Freeze–Thaw Cycles and Repeated Loads

This study proposes a binary medium constitutive model to address critical gaps in predicting the mechanical behavior of unsaturated silty clay under combined freeze–thaw cycles and repeated static loading. Existing frameworks often neglect progressive bond degradation caused by cyclic environmental and mechanical stressors, leading to inaccurate predictions of long-term soil performance. Our framework explicitly integrates a breakage ratio (λ) to quantify transitions between elastic-brittle bonded elements and elastoplastic frictional elements. Laboratory experiments demonstrate the model’s predictive capability, revealing an 18.6% increase in maximum deviatoric stress after the second freeze–thaw cycle at −5°C, which is a critical threshold for irreversible damage. Cumulative degradation reduces the bonded bulk modulus by 48% and increases the plastic strain by 32% after eight loading cycles, aligning with field observations of foundation instability in frost-prone regions. By bridging microstructural transitions (e.g., ice lens growth, pore evolution) to macroscale responses, the model offers a validated tool for designing resilient infrastructure in cold regions, addressing the limitations of existing approaches.