Large landslide system full characterization in central Italy: relevance of geomorphological and geotechnical models to plan monitoring and risk mitigation works.

The geomorphological and geotechnical assessment of a large landslide should be always carried out to plan the best solution for monitoring and risk mitigation works. Too many times monitoring and works were realised following standard procedures without preventively comprehending the morphoevolution of the landslide system. This work aims to offer a full and multidisciplinary analysis in an anthropized area to supply strategic support for civil protection activities, to deepen the local natural hazard and try to reduce them.

We investigate a complex landslide system located in San Vito Romano, Central Italy, 40 km east from Rome. It has a spatial extent of about 1 km². The geological context is characterised by a Tortonian sequence of turbidite deposits, characterised by marls and arenaceous intercalations, forming a monocline with 15-20° dip-direction eastward, parallel to slope inclination. Moreover, a complex hydrogeological system characterises the groundwaters.

A field survey has been carried out to recognize the geomorphological features and elements as crowns, scarps, tension cracks and all other geomorphic evidence. The survey also focused on building damages. A geomorphological-technical model has been realised interpreting boreholes, piezometers, inclinometers, high precision GPS stations and cracks digital metres, geotechnical and geophysical investigations, coupled with detailed digital elevation models analysis through GIS software. In this way the San Vito Romano landslide has been interpreted as a large rock translational slide in the upper part of the slope turning into a rotational slide in its accumulation zone. Data have been used for experimental slope stability analysis to find the main critical areas of the slope and correlate water table changes and landslide movements. Even though data model is still developing and calibrating, preliminary data provide realistic results. The individuation and characterization of most critical areas allow to plan where locate further instrumentations choosing the most appropriate ones for the two different detected portions of the landslide. Based on it, the suggested work consists in a drainage trench system upstream the main scarp to canalize the surface running waters avoiding infiltration in recharging area, and a large drainage borehole, for the purpose of limiting the water table changes downstream in the accumulation zone.