Multi‑approach for the assessment of rock slope stability using in‑field and UAV investigations

The present study is aimed at analyzing the rockfall phenomena involving a carbonate rock scarp in San Donato di Ninea village (Calabria, south Italy), where some buildings and a portion of a road are exposed to a high hazard condition. The geomechanical investigations of the rock scarp were performed through a multi-approach based on in-field investigations, geophysical surveys, and high resolution of images acquired by a drone. The achieved data allowed to assess the quality of the rock mass and the susceptibility of rock slope to failure through the Rock Mass Rating and the Slope Mass Rating classifications, respectively. The obtained results showed slope conditions ranging between unstable and completely unstable. Geophysical surveys allowed to investigate the subsurface material and showed a high jointing rock mass in the shallower portion. In order to acquire the potential change in geomechanical features on the whole escarpment rock, high-resolution images were acquired by a drone. Thus, a 3D dense point cloud model was reconstructed in a setting of high accuracy based on 55 million of points with a density of 748.85 points for m2. The 3D model was imported into CloudCompare software to extract the geological planes through FACETS plugin, which allowed to recognize the jointing sets on the whole surface of rock escarpment. The digital data were compared with the ones collected by scanline method in order to verify their soundness, and further detailed digital investigations were carried out on human inaccessible areas to examine the corresponding fracturing degree.