Unified hardening (UH) model for saturated frozen soils

The mechanical behavior of frozen soils is highly sensitive to temperature variations due to their complex micro-mechanisms. In regions with seasonal freeze-thaw cycles, the transition of soils between frozen and unfrozen states is significantly influencing their mechanical properties. This study synthesizes existing theories and data to categorize the effects of subzero temperatures on the properties of frozen soils. By introducing temperature and unfrozen water saturation, the phase change component of void ratio—decoupled from stress—is distinguished from actual voids, enabling the definition of the equivalent void ratio. Nonlinear relationships between temperature and other mechanical properties including elastoplastic deformation, cryogenic cohesion and ice segregation are established. Through the derivation of a loading-temperature yield equation, an elastoplastic constitutive model within a dual stress-variable framework of effective stress and temperature is established. This model captures key aspects of the behavior of frozen soils, including strength weakening due to ice segregation and temperature-induced strength changes. Applicable to conditions at or below the pore water melting point, the model's predictions align well with experimental observations.