Temperature-Dependent Shear Strength in Clay Slopes: Experimental Insights and Implications for Stability Assessment

Temperature fluctuations within landslide shear zones can arise from interactions with deeper subsurface layers and the atmosphere crossing the landslide body. Shallow landslides, particularly those with depths less than 10 m, are notably susceptible to seasonal temperature variations and swift climatic shifts. The hydro-mechanical properties of clayey soils exhibit sensitivity to temperature alterations. Some investigations have proposed significant variations in residual shear strength, even within temperature ranges typical of shallow layers in temperate and warm regions. This study examines the response of two pure clays (Ca-bentonite and kaolin) to shearing at temperatures up to approximately 55 °C, considering various normal stresses (50–150 kPa) and shear rates (0.018–44.5 mm/min). A temperature-control system integrated into a ring-shear device facilitated the experimentation. Subsequently, we conducted experiments on an ideal slope to quantify the impact of ground temperature on the stability of clay slopes across seasons and prolonged warming. By accounting for the most substantial effects determined experimentally (residual shear strength changing by ±1.5 %/°C), we identified variations in the global factor of safety of approximately 20% for rotational slides at depths of approximately 6 m, solely due to seasonal heating-cooling cycles. A warming of 5 °C over decades would introduce an additional ±7% change in the stability condition. While acknowledging the simplified geometry and boundary conditions in these results, and the exclusion of triggers, preconditions, and effects of other thermo-hydro-mechanical couplings, they establish an upper limit for the influence of temperature-dependent residual shear strength on the factor of safety. We emphasize that this influence should not be disregarded in slope stability and landslide hazard assessments for clay-rich soils, necessitating thorough experimental analyses and advanced modelling.