Temperature and shear-rate effects in two pure clays: Possible implications for clay landslides
Marco Loche, Gianvito Scaringi
Abstract
Temperature fluctuations in landslide shear zones can originate from heat exchanges with the atmosphere and the stable substrate. Shallow landslides (depth <10 m) are especially subject to seasonal temperature oscillations and climatic changes. Hydro-mechanical properties of clayey soils are temperature-dependent. Few studies suggested that the residual shear strength varies significantly even in temperature ranges typical of shallow layers in temperate/warm regions. Here, we verified the response of two pure clays (Ca-bentonite, kaolin) to shearing at temperatures up to ∼55 °C under various normal stresses (50–150 kPa) and shear rates (0.018–44.5 mm/min) by equipping a ring-shear device with a temperature-control system. Then, we performed experiments on an ideal slope to quantify the extent to which ground temperature can condition the stability of clay slopes, across the seasons and under prolonged warming. Considering the largest effects evaluated experimentally (change in residual shear strength by ±1.5 %/°C), we determined changes in factor of safety by ∼20 % for rotational slides ∼6 m deep, attributable to seasonal heating-cooling. Warming of 5 °C over decades would change the stability condition by an additional ±7 %. Although these results were obtained under simplified geometry and boundary conditions, without considering changes in triggers, preconditions, and effects of other thermo-hydro-mechanical couplings, they provide an upper bound to the role of the temperature-dependence of the residual shear strength on the factor of safety. We argue that this role should not be neglected in slope stability and landslide hazard assessments in clay-rich soils, thus warranting in-depth experimental analyses and advanced modelling.