The «Viadotto Chiusa», constructed around 1976 for the realization of the variant to the SS18 “Tirrena Inferiore,” has been affected by a slow landslide event that involved two intermediate piers, resulting in structural damage. After carrying out temporary safety measures for the bridge, the Province of Salerno decided to act definitively to restore the bridge’s functionality and technology through: the hydrogeological arrangement of the area; the restoration of the existing natural watershed, which had been completely blocked; the demolition of the two piers affected by the damage and the reinforced concrete decks resting on them; the consolidation of the remaining reinforced concrete piers and abutments; the reshaping of the slope area between the road above the viaduct and the punctual structural restoration of the deck slab of the “Viadotto Agropoli”. Based on the needs and critical issues, the project for the partial reconstruction, repair, and consolidation of the “Viadotto Chiusa” was defined in its entirety.
Through a preliminary seismic vulnerability assessment and analysis using the Plaxis software for slope stability data, as well as data from the monitoring carried out over time by the Province of Salerno on the viaduct and the landslide-prone slope, a series of projects and interventions were devised and formulated, aimed at optimizing the intervention from both a functional and economic standpoint. Since alternative solutions that would deeply alter the original design were not feasible, partial demolition and reconstruction of certain spans were planned, along with strengthening and foundation and elevation adjustments for the remaining structures. A particularly complex task was defining the interventions on the slope: several simulations indicated that the presence of underground movement, along with infiltration water from the surface, tended to exacerbate and trigger shallow landslides. Therefore, solutions were adopted, in contrast to the original design, that involved limited containment works and sub-horizontal drains instead of additional sheet piling and barriers.
