Closed-Form Models for Nonisothermal Effective Stress of Unsaturated Soils

Effective stress is a critical factor controlling the mechanical behavior of unsaturated soils. There has been an increasing interest toward fundamental and applied research on emerging applications that involve unsaturated soils subjected to elevated temperatures. However, major gaps remain in the development of a unified model that can properly represent temperature dependency of effective stress in unsaturated soils. The main objective of this study is to develop closed-form equations to describe the effective stress of unsaturated soils under nonisothermal conditions. For this purpose, suction stress-based formulations are developed for representing temperature-dependent suction stress and effective stress of unsaturated soils. The formulations incorporate temperature-dependent moist air pressure and matric suction into a skeleton stress equation originally developed using volume averaging. A nonisothermal soil water retention curve (SWRC) is used to account for thermal effects on the adsorbed water, surface tension, contact angle, and enthalpy of immersion per unit area. The validity of the model is examined by comparing predicted suction stress values against experimental data reported in the literature for various soils ranging from clay to sand. The effective stress equations developed in this study can provide further insight into the behavior of unsaturated soils under nonisothermal conditions. The models can be readily incorporated in numerical and analytical methods, leading to more accurate modeling of unsaturated soils subjected to nonisothermal loading conditions.