A Thermomechanical Model of Coarse‐Grained Soils With Non‐Orthogonal Flow Rule

ABSTRACT In geo‐energy engineering projects, temperature is an essential environmental variable, and accurately predicting its effect on the thermomechanical properties of geomaterials remains a challenge. Similar to fine‐grained soils, temperature variation is also a crucial factor that affects the stress‐strain response and critical state behavior of coarse‐grained soils. In this study, a thermomechanical model is established for coarse‐grained soils using theories from the critical state and fractional plasticity. The evolution of the critical state line with increasing temperature can be well characterized by introducing a thermal‐dependent parameter, then the state void‐ratio‐pressure parameter that incorporates the effect of temperature can be derived according to the temperature‐dependent critical state. The plastic flow direction and dilatancy function are obtained directly from the fractional derivation of the modified elliptical yield function to describe the nonassociated flow characteristics. Furthermore, the thermal state parameter is introduced into the non‐orthogonal dilatancy function and hardening modulus to reflect the state‐ and temperature‐dependent behaviors. Comparative analysis of experimental data and predictions indicates that the established thermomechanical model can reasonably predict the drained shear characteristics of coarse‐grained soils under different temperatures, including strain‐hardening, strain‐softening, dilatancy, contraction, and thermal softening.