A study for the requalification and safety against natural hazards of the environmental and building heritage of Sant'Agata de' Goti (Italy)

The progressive transformation from the protection of single monuments to that of the whole fabric of ancient cities, proclaimed by Venice Charter (1964), brings the Geotechnical Engineering to a central role in the conservation of the historical centers for which a strong limit between nature and building heritage does not exist. The town of Sant’Agata de’ Goti, located in Campania region, Italy, was built during the pre-Roman period. It was edified on a tuff cliff between two creeks, Riello and Martorano, in order to give more chance to safeguard populations from barbarian attacks and invasions. However, such strategic location increases the vulnerability towards both landslide and seismic risk, just as occurred in other case-studies of towns located on soft rock slabs or stiff soil ridges in Central-Southern Italy (Fenelli et al., 1998; Costanzo et al., 2007). The high degree of natural hazards follows from both site morphology and subsoil conditions. The cliff is formed by a soft pyroclastic rock slab of 14.000 m2, mostly formed by grey tuff with vertical joints, overlaid by yellow tuff, pyroclastic soils and made ground. The uppermost tuff formation is characterized by the presence of 160 cavities detected insofar, many of which are located close to the ridge edge. The continuous gully erosion affects the slope stability of the valley border down to the Miocene bedrock, constituted by an arenaceous-clayey flysch. Significant seismic amplification phenomena are expected, especially along the ridge edges, due to the topographic irregularity and to the stratigraphic amplification of the seismic waves in the softer shallow subsoil. As a result, the interplay between seismic and landslide hazards might be considered high throughout the whole center, but it might become particularly critical along the ridge rims, where the interaction between buildings and cavities is significantly intense. The need for the safe fruition of the whole site and of the single buildings requires both urban and architectonic plans to account for the multi-hazard complexity. The paper summarizes the subsoil characterization of the cliff of Sant’Agata de’ Goti, as reconstructed from the gathering of existing and new geotechnical investigations, aiming at two urban design proposals which have been recently submitted to the town municipality by a multi-disciplinary research team of the Federico II University of Napoli. The first project proposal is the environmental requalification of the western cliff side, facing to the Martorano creek, by reshaping the creek valley beneath the rock slope. A reinforced soil ramp will allow to create a pedestrian path ascending along the cliff border, partly open and partly hypogeous, integrated by community facilities to be located in the cavities. The second project proposal deals with the ancient seminar and its church, a typical brickwork three-storey building located at the eastern border of the historic centre, and again surrounded by a net of cavities. A site-specific evaluation of seismic response will be addressed to verify the seismic safety of the building, to study interventions for the seismic retrofitting of structure and foundations, and to find a new function compatible with both architectural framework and structural vulnerability. Both themes will be developed as prototype studies highlighting the need of an action strategy which must be a synthesis and not just a compromise between the safe fruition and the conservation of the historical heritage of Sant’Agata de’ Goti.