A Constitutive Model for Cement‐Fiber‐Improved Loess Considering Constant Load and Freeze–Thaw Conditions

Cement and polypropylene fiber composite improvement technology can effectively enhance the freeze–thaw (F–T) deterioration resistance of soil in seasonal frozen regions. During F–T cycles, overlying pressure alters soil structure and mechanical properties. This research conducted triaxial tests on cement and polypropylene fiber composite‐improved loess (CFIL) under constant load and freeze–thaw (CLFT) conditions, proposed a modified mean stress considering initial vertical stress (IVS) and F–T effects, and established a nonlinear critical strength line equation. Based on composite material theory, CFIL was decomposed into cemented and fiber phases. For the cemented phase, a unified hardening parameter accounting for CLFT damage was proposed, with an elastoplastic constitutive model built using the non‐orthogonal plastic flow rule. For the fiber phase, a fiber slip function considering the modified mean stress was introduced to construct a linear elastic constitutive model. Verification shows the model can effectively simulate stress–strain relationships and reflect CLFT impacts.