Water storage mapping and stability analysis of pyroclastic covers through resistivity measurements

The landslides occurred in Campania Region (southern Italy) during last fifteen years have stressed the extreme susceptibility of the ash-fall deposits that cover the mountains surrounding the Mt. Somma-Vesuvius volcano. The resistivity tomography technique is able to give a very detailed image of the subsoil structural pattern on the basis of the high resistivity contrasts characterising the Campanian geological settings susceptible to landslides, i.e. pyroclastic soils overlapping a carbonate and/or lava basement. We describe a new conceptual approach that combines electrical resistivity tomographies and laboratory analyses to study the hazard assessment of pyroclastic covers. We report the results of a high-resolution 2D resistivity survey carried out in a test area (Sarno Mountains, southern Italy), and the results of laboratory analyses performed on undisturbed samples collected from the same area, devoted to the determination of characteristic curves electrical resistivity vs. water content. We use such characteristic curves to evaluate the water content of the investigated slope. Finally, we estimate the local empirical safety factor, recently introduced by the authors, in terms of local resistivities and slope angles and compare the values of this parameter with those of the 1D safety factor commonly used in the slope stability assessment.