Thermo-mechanical modelling for velocity prediction in catastrophic landslides

Thermal pressurisation has been proposed in literature as the key phenomenon to interpret the mechanics of the final collapse of large slope failures. A new thermomechanical model is proposed by improving on an existing one, applicable to large landslides and rockslides consisting of a coherent mass sliding on a thin clayey layer. The considered time window is that of catastrophic acceleration, which starts at incipient failure and ends a few seconds later, when the acquired displacement and velocity are such that the landslide is broken up into pieces. The model takes into account frictional heating, pore pressure build-up and thermoplastic collapse of the soil skeleton, leading to the vanishing of shear resistance and unconstrained acceleration. First, an existing thermo-elasto-plastic constitutive model for clays is discussed, and modified by re-formulating it in a general stress space and taking into account thermal softening. The soil constitutive model is then employed into an existing 1-D landslide model (Vardoulakis 2002), resulting in a set of three equations describing the time evolution of temperature, excess pore pressures within the shearband and slide velocity. The resulting model equations are shown to be well-posed, and then are discretised and integrated numerically to back-analyse the final stage of the case history of Vajont that occurred in Italy in 1963. Finally, a generalisation of this model and its potential applicability to the velocity back-prediction of other well-documented case histories are discussed