Multidisciplinary Study on a Landslide Area Individuated by Using Statistical Methodologies Before and After the Last Reactivation

In this work, a detailed study was conducted to characterize an area selected by applying statistical methodologies for landslide susceptibility modelling of the Imera River basin (Northern Sicily). The area, classified with a very high susceptibility level, was affected by a recent landslide reactivation and it was thoroughly analyzed from the geological and geotechnical points of view. Detailed investigations were performed in the landslide, before and after its last reactivation, in order to evaluate the mechanisms (roto-translational sliding in the upper part and earth-flow in the lower part) which affected a wide and thick body of stiff and highly fissured clays belonging to the Varicolori clay Formation. Remotely sensed datasets, such as orthophotos and digital terrain models, were used for mapping the landslide processes and landforms, as well as to obtain the topographic elements useful to integrate the models into GIS software. The latter was also used for the definition of the moved soil mass after reactivation. The geological and geotechnical models were defined for 2D slope stability analyses. Back-analyses of the two sliding surfaces proved that the mobilized shear strength angle is slightly higher than the upper bound of the residual shear strength angle measured by means of direct shear tests. The obtained results prove that a multidisciplinary study like this represents a promising method for local verification of the reliability of landslide susceptibility analyses conducted at a basin scale with a purely statistical approach.