The role of fracturing in defining the kinematics of rock slope failure and water circulation on the coastal cliff of Ancona

The conformation of the Italian territory with its geological, morphological and hydrographic features make it strongly predisposed to instability events such as landslide and floods (Triglia & Iadanza, 2015). However, only in the last years, the awareness that the intervention after the occurring of events is not enough, has grown up in Italy together with the consideration that prevention is a fundamental step for the safeguard of the territory.Hydrogeological instability is a form of environmental degradation relating to the soil or the superficial rock layers, produced by the action of waters flowing on the surface and in the rock/soil discontinuities. The most common instability phenomena are landslides and floods, which are concentrated in geologically young territories, or made of not very consistent sedimentary rocks, often bare or covered with insufficient vegetation. These conditions characterize several areas of the Italian territory, located above all along the Apennine ridge and in the pre-Alpine belt. In the Central Apennine ridge, the Umbria-Marche Stratigraphic Succession outcrops extensively. The most external part involves the Ancona coastal cliff (Marche Region), which is composed of sedimentary rocks, of which the public beaches of the Conero Riviera between Ancona and Portonovo are constituted. Intense rainfall and occasional earthquakes characterize this site. Moreover, several large-scale landslide events were experienced, from Portonovo’s 14th-century landslide to Ancona’s more recent 1982 landslide, in addition to more recent rock slope instability events, which caused significant damage to the buildings, but most important to the human health. This thesis aims at defining the main failure mechanisms of the rocky coastal cliff located in the Passetto area (Ancona), especially assessing the role of the secondary permeability on the rock slope instabilities. To this aim, an insight through the infiltration process into the soil and the characteristics of the fracture system present in the site have been performed. Detailed analysis of the fracturing system has been conducted using the scanline method and the Discrete Fracture Network Modelling. The entire study was possible with a multi-level approach in which tracer hydrology, geomechanics and geochemistry are involved. In particular, the cumulative rainfall data have been analysed coupling this information with the rock fall phenomena (documented in the area). The infiltration rate of the topsoil has been evaluated using a double ring infiltrometer test, coupled with tracer test to understand the role of fracturing on water infiltration in the rock mass. Finally, these results were integrated with a conductivity analysis of the water in the area to assess the interaction between the rock matrix and the water. From the obtained results, the importance of carrying out a study with more than one point of view and involving different fields of science has been stressed, even by assessing the role and the benefits that this approach can play both in the prevention of hydrogeological hazard and the environmental monitoring.