ABSTRACT
This study investigates the causes of the 2021 landslide in Ollon, Switzerland, an area known for ground instability due to its lithological composition, primarily weathered gypsum and anhydrite. The research integrates historical analysis, geotechnical investigations, and modelling to uncover the mechanisms behind these landslides. The landslide involved silty sand soil and gypsum blocks, driven by an intricate combination of geological and environmental factors. Field investigations and laboratory tests provided essential data for accurate modelling. Geoslope software was used to develop multiple models to assess the key factors triggering the landslide. The study examined various levels of saturation and different thicknesses of the altered gypsum layer. The results identified the primary triggers for the landslide as the saturation and thickness of the altered gypsum layer. A comparison of the boundary conditions derived from the modelling with the recent landslide event in December 2023 has validated the results of the study.
