Investigation on the Hydraulic Parameters Affecting Shallow Landslide Triggering in a Pyroclastic Slope

Abstract

Large mountainous areas surrounding the city of Naples (southern Italy) are characterized by the presence of steep slopes covered with few meters of loose pyroclastic materials in unsaturated conditions, lying upon a fractured limestone bedrock, the stability of which is ensured by the contribution to shear strength due to suction. Wetting of the soil cover during rainfall infiltration may cause the triggering of shallow landslides, sometimes developing in form of fast and destructive flows. In this preliminary study, a sensitivity analysis is carried out, aiming at quantifying the effects on the hydrological response of a slope to precipitations, of some factors, related either to the hydraulic properties of the soil cover or to the permeability of the soil-bedrock interface. In particular, the sensitivity analysis refers to the slope of Cervinara, around 40 km northeast of Naples (Italy), covered by a pyroclastic deposit with an average thickness around 2.0 m, and characterized by an average slope angle of 40°. For the sake of simplicity, the analysis is carried out by means of a one-dimensional infiltration model, based on the Richards’ equation written for a single homogeneous soil layer. The obtained results highlight that the equilibrium of the slope during rainfall infiltration is affected not only by the hydraulic characteristics of the soil cover, but a major role is played by the permeability of the soil-bedrock interface.