Influence of temperature on the residual shear strength of landslide soil: role of the clay fraction

The occurrence and fate of landslides are, among other factors, controlled by the shear strength of the materials involved and by how this strength changes during the landslide process. Temperature affects the strength of pure clays according to their mineralogy, stress history, and hydro-mechanical boundary conditions. However, natural soils often consist of heterogeneous mixtures of various clay and non-clay minerals. The effect of temperature on the residual shear strength of low-plasticity soils, in particular, remains poorly understood. To address this gap, ring-shear experiments were conducted on remoulded soil samples from a landslide-prone portion of the Melamchi Catchment in Nepal. The tests were performed in water-saturated conditions under representative normal stresses (50, 100, 150 kPa) and a constant rate of shearing (0.1 mm/min). Specimens with clay fractions ranging from 10 to 24% were subjected to heating-cooling cycles (20–50–20 °C) after attaining the residual shear condition. The results were analysed statistically, and a t-test was implemented to discern possible thermal effects from the experimental noise. A decrease in residual friction angle by up to 1° upon heating (thermal weakening) was seen in specimens richer in clay under larger normal stresses. However, the effect was non-significant in many cases, suggesting a minor role of thermo-mechanical coupling in shear zones of slow-moving landslides. Further research encompassing a wider range of soil compositions is warranted to better quantify the influence of temperature on the shear strength of landslide soils.