A bounding surface non-isothermal hydro-mechanical model for unsaturated fine-grained soils under isotropic stress states

This paper presents a bounding surface model for predicting the influence of temperature on the retention and mechanical behaviour of saturated and unsaturated soils subjected to isotropic stress states. The model couples a non-isothermal, hysteretic and porosity-dependent retention law with a non-isothermal isotropic mechanical law. The retention law is formulated using a non-isothermal scaled suction variable that is function of the temperature-dependent liquid–gas surface tension. The mechanical law employs a non-isothermal scaled stress variable accounting for the effect of temperature on the volumetric behaviour of the soils due to the variation in net attractive Van der Waals forces at edge-to-face inter-particle contacts and the dilation of solid particles. The two retention and mechanical laws are coupled through an iterative procedure, yielding a non-isothermal hydro-mechanical model calibrated and validated against four different experimental datasets from the literature. The results show that the model successfully (i) extrapolates soil retention behaviour at different temperatures without requiring additional parameters relative to reference isothermal conditions, (ii) reproduces thermally induced expansion or contraction of saturated soils depending on the degree of overconsolidation and (iii) captures the coupled non-isothermal hydro-mechanical response of unsaturated soils under isotropic loading.