Slope Instability in the “Bastardo Basin” (Umbria, Central Italy). The Landslide of Barattano

The Bastardo Basin is one of the classics Apenninic intermontane basins of central Italy. They are enclosed tectonic basins (graben and semigraben) with high anthropization, but with high vulnerability, too (seismic, hydrogeological and geomorphological). The paper concerns some aspects about slope instability in the Bastardo Basin as part of a wider research, which aims to actually define the characteristics of the liability to landslides of the Apenninic intermontane basins. In particular lithological, stratigraphical and hydrogeological conditions are analysed under which a landslide near village of Barattano has developed. This mass movement, at different times, produced partial or total occlusion of the torrent Puglia. Here geognostic investigations together with laboratory tests and subsequent monitoring of landslide area were carried out. A back analysis, based on limit equilibrium solutions for the factor of safety of the slope, provided the residual strenght properties of the soil mass along the sliding surface. The landslide of Barattano is representative of a very frequent situation (in terms of type, factors and causes of the movement, possible development of the movement) not only within Bastardo Basin, but in general within Apenninic intermontane basins, too. The study of landslide and the design of appropriate remedial measures are of great importance in terms of prevention and mitigation of geologic-hydraulic risk in Apenninic intermontane basins.