A unified soil–water retention curve model for unsaturated soils considering freeze–thaw cycle effects

Abstract

Bimodal pore structures are commonly observed in unsaturated soils and play a vital role in controlling soil–water retention behavior, a key factor influencing water migration and soil mechanical performance in seasonally frozen regions. The soil–water retention curve (SWRC), which describes the relationship between soil water content and matric suction, is significantly affected by the evolution of pore structure during freeze–thaw processes. However, existing models seldom consider the coupled influence of freeze–thaw-induced pore structural changes, such as variations in void ratio, on the SWRC. This study proposes a novel bimodal SWRC model for fine-grained soils that accounts for the effects of freeze–thaw cycles, capturing the evolution of pore structure during repeated freeze–thaw cycles through variations in void ratio. Besides, the proposed model can flexibly represent both unimodal and bimodal behaviors within a unified formulation. Validation using experimental data demonstrates that the model accurately simulates the SWRCs of fine-grained soils under various stress states and freeze–thaw conditions. Comparative results further confirm its superior fitting performance and physical interpretability compared with traditional models. Furthermore, the proposed model shows good agreement with experimental data for different soil types, providing a more robust and comprehensive tool for analyzing the hydraulic behavior of unsaturated soils in cold-region engineering.