Non-isothermal CSUH model based on micromechanical effects of particle deformation

The mechanical behavior of soils can be significantly influenced by temperature variations. To capture the thermo-mechanical behavior of various types of soils under complex stress paths, a unified constitutive model considering deformation of soil particles is developed for clays and sands. The main novelties achieved in this study include: (1) A basic volumetric strain formulation accounting for the deformation of soil particles is derived, which incorporates the contributions of both the void ratio variation and particle deformation to the overall volumetric strain, and a corresponding formulation for undrained conditions is established. (2) Temperature effects are introduced into the framework of the unified hardening model for clays and sands (CSUH model), and the associated unified yield function, plastic potential function, and hardening equation that account for temperature variations are established. (3) A thermal state variable is proposed to model the thermal cyclic behavior of soils, which enables the model to capture the continuous volumetric strain under thermal cycles without additional parameters. The proposed model provides a fundamental framework for developing constitutive models that incorporate thermal expansion of soil particles. The comparison between test measurement and model prediction demonstrates the significant advantages of the proposed model in modeling the thermo-mechanical behavior of various types of soils under complex stress paths—particularly in capturing the volumetric strain induced by cyclic thermal loading under drained conditions and the effective stress evolution resulting from heating under undrained conditions.