  Usually, the degree of stability of a slope is quantified by the Factor of
Safety whose values depend on physical and mechanical soil properties analyzed
on samples of much reduced sizes or referring to very small soil volumes around
porous probes. To overcome the limit of punctual information, we propose a
semi-empirical approach based on the use of geophysical methods and the
employment of a geophysical Factor of Safety recently introduced by the authors
in terms of local resistivities and slope angles. In this paper, we show an
application of our proposal on a test area of about 2000 m2 on Sarno Mountains
(Campania Region - Southern Italy), where shallow landslides involving
pyroclastic soils periodically occur triggered by critical rainfall events.
Starting from two resistivity tomography surveys performed on the test area in
autumn and spring, we obtained maps of the geophysical Factor of Safety at
different depths for the two seasons. We also estimated the values of the
Factor of Safety by using the infinite slope model in the dry and saturated
scenario. A comparison between the values of the geophysical and geotechnical
Factor of Safety shows advantages and disadvantages of our approach.
