Thermal and Shear-Rate Effects in Landslides: From the Classics to the Future

The frictional resistance of geomaterials has been shown to depend on the rate of shearing. Both weakening and strengthening have been observed, and various mechanisms that take the mineralogy and stress level into account have been proposed. Evidence also exists that temperature plays an important role in defining the frictional resistance as well as its dependence on the rate of shearing. Temperature and rate-dependent mechanisms can indeed control landslide runouts, causing runaway sliding or prolonged slow creep displacements. We reviewed the literature on the matter and noted that, while studies on shear-rate effects are abundant, systematic classifications useful in predicting landslide fates in a variety of lithologies and environments are lacking. As for the thermal effects, these are well studied with respect to large and fast-runout landslides, where frictional heating plays a major role. Conversely, little is known about changes in slope stability (prior to failure, remobilization, or reactivation) in relation to changes in ground temperature caused by varying boundary conditions, such as changes in groundwater temperature or heat transfer from the surface under seasonal or long-term climatic changes. Results of our preliminary experiments, targeting clay-rich materials, demonstrate an important effect of temperature on the residual shear strength, which is coupled with changes in shear-rate response. Catchment-scale statistical analyses also reveal that surface temperature can be correlated with landslide activity in space and time. We conclude by suggesting that landslide modelling approaches in the future should account for thermal and shear-rate effects. In physically-based modelling, this may be achieved via coupled thermo-hydro-mechanical formulations, in which the constitutive model includes a time-dependent (e.g., thermo-viscous) component.