Thermo-mechanical coupled constitutive model for saturated clay based on thermodynamic principles

In geotechnical engineering projects related to energy underground structures, nuclear waste disposal and storage, and landfill waste disposal, the thermal exchange between soil and structures can lead to significant changes in the volumetric deformation and shear characteristics of the soil. Establishing a reasonable constitutive model to reflect the thermo-mechanical coupling properties of the soil is of great importance. Firstly based on thermodynamic principles, this paper introduces a new dissipation function and free energy function, deriving a yield surface equation that includes three shape parameters. Further considering the thermo-elastic strain of saturated clay, the pre-consolidation pressure, and the thermal-dependent behavior at the critical state, a thermo-mechanical coupled bounding surface constitutive model for saturated clay is established using a non-associated flow rule. Finally, the predictive capability of the model was validated through heating-cooling cycle tests and temperature-controlled triaxial drained/undrained compression tests. The results indicate that within the temperature range of 0−95 ℃, when the overconsolidation ratio is no greater than 12, the model can reasonably reflect the thermo-mechanical coupling effects in saturated clay, with the strain hardening and volumetric contraction of normally consolidated soil under temperature effects, as well as the strain softening and dilatancy characteristics of over-consolidated soil, being adequately described.