Andrea Guida

An Instrumented Flume to Investigate the Mechanics of Rainfall-Induced Landslides in Unsaturated Granular Soils

The mechanics of rainfall-induced flowslides in pyroclastic soils have yet to be completely clarified. The complexity of phenomena (rainfall-induced failure in initially unsaturated granular deposits, post-failure transition to flow-like landslide) requires the use of a well-equipped small-scale flume. To this aim, flume experiments at the Second University of Naples were performed to analyze the fundamental aspects of such phenomena. A new experimental program is now being carried out to assess the performance of a time domain reflectometry device and optical fibers as indicators of impending failure. The paper describes the instrumented flume and the procedures adopted for monitoring the major aspects of slope behavior. Our first experimental results are very promising in this respect.

Performance of a Beach Dewatering System—Chiaiolella Beach, Procida Island, Italy

Abstract Chiaiolella Beach is a 1.5-km-long pocket beach located on Procida Island (Italy). The beach is formed by medium sand generated by erosion of vulcanoclastic rocks that form cliffs around the island and at the backshore of the study site. A beach dewatering system was installed in April 2002 to provide a wider beach for users and to prevent cliff undercutting during storms. It has not been operative since December 2004, as local authorities decided to undertake cliff stabilization measures. Surveys carried out immediately before (October 2001) and 1 year after installation (October 2002) showed negligible volumetric change on the drained beach in Ciraccio (−0.52 m3/m), the NNE sector of Chiaiolella Beach, whereas on the undrained control section there was an accumulation of 1.41 m3/m. Since no long-term monitoring of beach profiles was available at the site previous to installation, to obtain an indication of the nearshore hydrodynamics and morphodynamics in absence of the drain, historical shoreline from high-resolution georeferenced aerial photography and numerical model were used. Overall, no evident positive effects of the dewatering system were confirmed, at least for mild wave energy levels. For higher wave energies, e.g., during a storm that occurred in December 2002, part of the beach (SSW sector, Ciracciello) had consistent volume losses and the dewatering system was not able to compensate them, as at some stage it was even damaged. This study points out the inadequacy of the dewatering system as coastal protection under high wave conditions.

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

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.