Dynamic thermo-poro-mechanical analysis of catastrophic landslides

In this paper a dynamic analysis is presented of the early stages of an earth slide, considering two mechanically coupled substructures: (a) the rapidly deforming shear band at the base of the slide, and (b) the accelerating (rotating) rigid body. This is done by exploiting the concepts of frictional rate softening and thermo-poro-mechanical softening of the soil, and by modifying the friction-circle method of Taylor (1948). First the equations are summarised that govern the phenomenon of heat-generated pore pressures inside a rapidly deforming shear band, and then the estimates for the various material parameters that enter the governing equations are critically discussed. In particular an attempt is made to adjust these material parameters to existing experimental data and to the properties of the clay soil responsible for the Vaiont slide of October 1963. The numerical analysis of the governing equations for the two mechanically coupled substructures leads to the following conclusions. The accelerated motion is caused by material strain-softening, which in turn feeds further material strainrate softening inside the shear band. Owing to the speed of the initiated process, heat is trapped inside the shear band, which leads rapidly to a pore-pressure explosion in it owing to thermoplastic collapse of the clayey gouge, leading rapidly to total loss of strength and to uninhibited sliding motion on a frictionless base.