Influencing Factors of Soil Mechanical Properties in Seasonally Frozen Regions and Thermo-Hydro-Mechanical Coupled Simulation of Embankment Stability

Riverbank stability is critical for flood protection in cold-region rivers, where freeze-thaw processes and river ice-induced water-level fluctuations can accelerate bank degradation and collapse. A typical embankment along the Inner Mongolia section of the Yellow River, subjected to severe freeze-thaw conditions, was investigated in this study. Laboratory tests were performed to quantify the effects of dry density, freeze-thaw cycles, and water content on soil mechanical properties. A thermo-hydro-mechanical (THM) coupling model incorporating freeze-thaw-induced mechanical degradation, water migration, and deformation was developed and applied to simulate the stability evolution of a typical riverbank. The experimental results showed that dry density was the dominant factor affecting soil shear strength, accounting for more than 60% of the explained variance in cohesion. The soil exhibited the highest shear strength at the optimum water content, while increasing freeze-thaw cycles significantly reduced soil cohesion, particularly during the first three cycles due to rapid structural deterioration. In contrast, freeze-thaw cycles had a limited influence on the internal friction angle. By introducing the ratio between ice and unfrozen water volume contents as the key coupling variable, a phase equilibrium relationship was established to link the temperature and moisture fields. The proposed THM model reproduced the coupled evolution of temperature, moisture, stress, and displacement during freeze-thaw processes and identified the critical locations of riverbank instability and the variations in factor of safety under different conditions. The findings improve understanding of freeze-thaw-induced riverbank instability mechanisms and support hazard assessment and mitigation in cold-region rivers.