Preparatory and triggering factors for slope failure: analyses of two landslides near Bonn, Germany

摘要

This paper investigates landslide susceptibility in the Bonn area, based on analyses of mass movement processes and triggers. Two landslides in different geomorphological and lithological situations were studied to assess their activity patterns and identify triggering factors for the landslide events. Measurements showed that parts of the landslides moved at rates up to several centimetres per year on existing shear surfaces. These movements are related to high groundwater tables in wet seasons (winter/spring). Rising groundwater was identified as potential triggering factor for the landslide events on both field sites. Slope stability modelling showed that landslide history has an important impact on slope instability, with existing shear surfaces being prone to subsequent failure. The present situation of small movements, historical shear surfaces and landslide scars, and the geomorphological situation imply continuous destabilisation and potential increasing future activity for both landslides. The major shear surfaces of both landslides are situated within sensitive Tertiary layers, but the spatial distribution of these sensitive layers differs significantly between the two study areas. Therefore it can be concluded that the areas have considerably different landslide susceptibility.