Hydro-mechanically Coupled Processes in Rainfall-induced Landslide Modeling
Special Vardoulakis Lecture
Lyesse Laloui
School of Architecture, Civil, and Environmental Engineering, Ecole Polytechnique Federale de Lausanne
Abstract
Catastrophic landslide events in unsaturated soils causing massif destruction and loss of lives are numerous and recurrent around the world. Rainfall-induced wetting processes in soil slopes can lead to significant contractive deformations associated with changes in stress states. Local stress redistributions within a slope can enable in certain conditions the development of a progressively formed failure mechanism. A physically-based, hydromechanically coupled continuum modelling approach is presented that is suitable for the study of various coupled physical processes and instability phenomena in variably saturated soil slopes subjected to rain infiltration. A transient flow-displacement-stress simulation with a finite element slope model representative for a landslide-prone volcanic ash slope above a pozzolana quarry in Costa Rica is performed to demonstrate the capacity of the modelling approach to deal with the physical processes and instability phenomena due to rain infiltration. An extensive laboratory testing programme was carried out to characterise the behaviour of the volcanic ash and to calibrate the various components of the model. Results of the slope model simulation demonstrate the important role of wetting and drying cycles, slope and bedrock geometry in the time evolution of matric suction and wetting-induced deformation. Instability phenomena are closely related to changes in matric suction. Moreover, it is observed that the pore-collapse upon wetting enhances the development of a localised shear failure mechanism in unsaturated conditions. In combination with analytical considerations, the obtained results contributed to the establishment of a prototype monitoring and an early-warning system.
About the Speaker
Dr. Lyesse Laloui is chaired professor and Director of the Soil Mechanics Laboratory at the Swiss Federal Institute of Technology, EPFL, Lausanne, where he developed a large group in the areas of Soil Mechanics, Geoengineering, and CO2 sequestration. He is also Director of the Civil Engineering Section. His main research interests are in geomechanics (constitutive and numerical modelling of multiphysical coupling processes, laboratory advanced testing), and environmental and energy sustainability (nuclear waste underground storage, petroleum geomechanics, CO2 geological sequestration, geothermal energy). His most know work addresses the effective stress principle for unsaturated soils, thermodynamic mixture modelling for unsaturated soils, experimental and modelling work on thermo-mechanics of clays and investigations of heat exchanger piles.