“Cone method” and 2d simulation for rock fall risk assessment in the Marina Piccola bay (Capri Island Italy)

With the increasing awareness to the geological risks, the study of rocky slopes plays a key role in the earth sciences, especially in areas of high vulnerability due to the presence of infrastructures and human activities. The present paper describes the stability and runout analyses carried out in the Marina Piccola bay (Capri Island - Italy), an urban and touristic area sited at the foot of “Grotta delle Felci cliff” (a rocky slope 200 meters high and 300 meters wide). The integration among various types of survey and analysis methodologies allowed the application of a modern approach for the risk assessment that can be useful in the decision process concerning the choice of the most appropriate mitigation works. Regards to the survey techniques, terrestrial laser scanning and digital close-range photogrammetry were used to produce digital elevation models, oriented stereo-images, orthophotos and accurate positions and volumes of rocky wedges located on the slope overhanging the area. Thanks to this data, the spatial distribution of rock fall density, velocities and kinetic energies was modeled by means of the “cone-method”. Rock falls historical evidences, recognized by the use of aerial photogrammetry and fieldwork activities, confirmed the accuracy of results obtained from the method application and allowed, through a further 2D rock fall runout analysis, the calculation of the dissipation energy that a protection work would need to mitigate the risk in the area.