Thermo-Hydro-Mechanical Behavior of Unsaturated Loess Considering the Effect of Porosity and Temperature on Water Retention Properties

Loess is featured by a metastable structure, which results in its significant volumetric decrease under self-weight pressure when subjected to the increase in moisture. The prerequisite for analyzing such a unique deformation characteristic is to understand both water retention and thermo-hydro-mechanical (THM) behaviors of the loess. It has been well recognized that the water retention behavior of loess is related to its porosity and temperature. However, the influence of porosity and temperature-dependent water retention curve on the THM behavior of loess is still unclear and worthy of investigation. In this study, a coupled theoretical model for the THM behavior of loess was developed and then numerically solved using the finite-element method, in which the effects of changes in porosity and temperature on loess hydraulic properties are incorporated. Suction-controlled oedometer tests and pressure plate tests on loess specimens were conducted in the laboratory to calibrate the corresponding model parameters and validate the coupled model. The model was then adopted to investigate the coupled THM or deformation behavior of loess by simulating both the column tests and the field immersion tests. It was found that the predicted water saturation and void ratio increase with an increase in temperature. The results based on the van Genuchten model overestimated the water saturation and the void ratio, compared with that predicted using the Gallipoli model. The larger temperature during the field immersion test caused a larger volumetric strain rate and a larger surface settlement rate. The results of this study would contribute to the understanding of the coupled THM process for unsaturated loess and also enhance the importance of the effect of void ratio and temperature change on loess behavior.