Displacement Evolution of a Large Landslide in a Highly Fissured Clay

The paper presents an analysis and modelling of the reactivation mechanism of a large landslide caused by rainfall, located in Cerda (Sicily, Italy). The study is based on data collected by means of a field investigation, carried out in order to assess the geotechnical properties of the involved material, and a three-year monitoring programme implemented to measure rain and pore water pressures as well as deep and superficial displacements. Three distinct landslides, evolving at variable rates in different directions, were recognized within the overall landslide area. The data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the evolution of displacements on pore water pressure fluctuations. A conceptual and simplified approach is applied to one of the landslides in order to model the time evolution of displacements as a function of pore water pressure on the sliding surface. The model analyses displacement evolution taking into account the viscous forces on the slip surface, assuming infinite slope conditions. The displacements calculated by the model are in good agreement with the measured ones.