Deformation analysis of landslides: progressive failure, rate effects and thermal interactions

Abstract

Evaluating landslide risk and its consequences is hardly achieved by “safety factor” concepts, which essentially rely on static equilibrium concepts and forces. Rather, expected displacements, velocities and accelerations are key magnitudes which help to establish the risk of failure and assist in the management of its consequences. The paper focuses on three key aspects for landslide initiation and evolution which are difficult to quantify in practice and are also difficult to analyze by current models: the mechanisms of progressive failure in brittle materials, the thermo-mechanical interactions and the creep deformations. Landslides covered in the Lecture are described by kinematically acceptable mechanisms which are eventually explained by the development of shearing bands or sliding surfaces in clays or claystone materials. Progressive failure will be reviewed and particular attention will be given to a well documented case record (the failure of Aznalcóllar dam) which has received a sustained research effort to explain field behaviour. Thermo-mechanical interactions have been invoked as a plausible mechanism to explain the sudden acceleration of an otherwise “stable” slope if examined from the perspective of conventional static stability conditions. Vajont landslide is examined as an example of the analysis performed. Creep deformations are approached from the concept of rate dependence of shear strength available on shearing bands or discontinuities. Rate effects and thermo-mechanical interactions have been included in a calculation framework which is used to estimate the coupling between slow and fast motions. Attention will also be paid to the search for simple criteria which could be used in practice to estimate landslide risk.