Mechanics and modelling of shallow landslide in pyroclastic soils
Landslides of the flow type are among the most severe natural hazards, and they often cause catastrophic consequences when involving pyroclastic soils. These soils are widespread all over the world, also in very highly populated regions. Modelling the triggering mechanisms of these landslides is a fundamental step for hazard assessment. Several approaches are available which, however, must be systematically checked through their application to well-documented case histories. In this lecture, a general discussion is provided for these phenomena. Then, a case study is selected from Southern Italy, where huge rainfall-induced landslides of the flow type caused 159 victims in May 1998. Based on geology, engineering geology, geotechnics and geomechanics, a multidisciplinary approach is used for the analysis, at different scales, of the occurred landslides and their triggering mechanisms have been individuated. For some triggering mechanisms, which are observed also in other geoenvironmental contexts and for other geomaterials, the geomechanical modelling is performed through limit equilibrium, uncoupled and hydro-mechanical coupled stress-strain analyses. Those results are achievable starting from standard and advanced laboratory testing of unsaturated volcanic silts and sands susceptible to instabilities and liquefaction upon wetting.