Geomechanical modelling of a natural slope affected by a multiple slip surface failure mechanism

This paper presents a geomechanical model that was developed to investigate the behaviour of a natural slope located on the bank of the Rhine between the towns of Stein and Mumpf in Switzerland. The slope, affected by a large landslide, constitutes a relevant case study since three strategic infrastructure assets are located at its toe (a railway, a highway and a cantonal road connecting Zurich and Basel). An intense measurement campaign has been conducted during the last 13 years, collecting information on pore water pressures and displacements within the slope. These measurements made it possible to identify pore water pressure evolution as the main cause for movement accelerations and to detect the presence of a multiple slip surface system. Thanks to advanced finite element hydrogeological and geomechanical modelling, it has been possible to analyse the landslide behaviour. A coupled hydro-mechanical formulation has been used, taking into account the transition of the soil from a partially saturated to a fully saturated state. A modified Cam- Clay constitutive model was adopted for the slip surfaces. Relevant material parameters were obtained by combining the available laboratory tests and the back analysis of the crises in the years 2000 and 2001. After being calibrated and validated, the model was applied to improve the understanding of the physical processes involved, to predict the landslide behaviour under different rainfall patterns and to test a possible stabilization strategy.