Validation of the rockfall SIF and SAI indexes by a 3D analysis of a rock slope in Valsesia Valley (Italy)

Rockfalls are ubiquitous diffuse hazard in Sesia Valley (Northern Italy). Such instability phenomena often occur along transportation corridors and threaten local communities and tourists. In this paper reference is made to a particular sector of the Sesia Valley, located in the municipality of Varallo (Vercelli), where in the last year a major collapse occurred and involved the road located at the bottom of the slope. After this rockfall event, several mitigation measures were planned and a great number of unstable rock blocks were removed from the slope by expert rock climbers to reduce the hazard of further rock detachments. In this paper a 3D rockfall simulation was carried out in order to back analyze the landslide phenomenon and validate two approaches recently proposed in the literature to characterize the release areas: the Susceptibility Index to Failure (SIF) and the rockfall Source Affecting Index (SAI).