Three-Dimensional Stability Analysis of Unsaturated Soil Slopes under Nonisothermal Conditions

Recently, the thermodynamic behavior of unsaturated soils has received increasing attention because of the requirements of energy geotechnical structures and climate evolution. Nonisothermal conditions have rarely been considered in previous slope analyses. To fill this gap, this paper further investigates an analytical solution for the vertical distribution of matrix suction under nonisothermal conditions based on steady unsaturated flow. The profile distribution equations for capillary cohesion and effective unit weight are obtained in conjunction with the van Genuchten (V-G) model, and the temperature-dependent saturated hydraulic conductivity equation is extended using normalized flow rates. Within the framework of kinematic limit analysis, a nonisothermal three-dimensional (3D) slope analysis method that accounts for variation in the effective unit weight of unsaturated soils is proposed. Specific expressions for the factor of safety (Fs) were derived using the gravity-increase method and the energy-balance equation. The method’s validity is confirmed through comparison with published results. Parametric studies were conducted on three typical soil slopes to analyze the effects of temperature, normalized flow rate, and 3D effects on slope stability. The results indicate that under nonisothermal conditions, the response of Fs on slopes is complex. When infiltration occurs, Fs of silty and clayey slopes increases, but the rate of increase decreases with increasing normalized flow rate, whereas Fs for sandy slopes fluctuates. During evaporation, Fs for sandy and silty slopes remains essentially unchanged, whereas Fs for clayey slopes continues to decline (by 9.45%). In addition, ignoring the 3D effects of slopes will overestimate the influence of temperature—the decline in Fs for clayey slopes can be overestimated by 30 percent.