Stability analysis of unsaturated slopes under elevated temperatures

Abstract

Several natural and man-made phenomena (e.g., droughts, wildfires, shallow geothermal technologies) can subject unsaturated slopes to elevated temperatures. However, the impact of temperature on the stability of unsaturated slopes is not well understood. This study aims to examine the stability of unsaturated intact slopes under elevated temperatures. An analytical framework is developed to calculate the factor of safety (FOS) of unsaturated slopes under steady fluid flow conditions at various temperatures. The theoretical basis of the framework is built upon the concept that, within the temperatures range investigated, the influence of temperature on the soil's shear strength is primarily attributed to thermal induced changes in apparent cohesion stemming from matric suction. Temperature dependency of apparent cohesion is quantified by employing temperature-dependent soil-water retention curve (SWRC) and effective stress models, which are then integrated into an infinite slope stability analysis of unsaturated soils under steady flow. A saturation-dependent thermal conductivity is used to obtain the temperature profile versus depth. The formulations are used to determine FOS for intact slopes with different hypothetical soils including sand, silt, and clay at surface temperatures of 25, 40, and 55 °C under different steady flow rates. Results show that the effective stress, shear strength, and FOS increase by increasing temperature from 25 °C to 55 °C. Results reveal that the effect of temperature on the stability of clayey and silty slopes can be considerable. The proposed models are validated against two sets of laboratory-measured data from the literature. The presented model provides a simple and effective method for site-specific and regional-scale stability analyses of unsaturated slopes under different thermal and seepage conditions.