Initial-level reports of landslides involving bridges and viaducts: the case study of Villa Ilii (Central Italy)

In the last decades, the concern for infrastructure damage and collapse due to natural hazards has globally increased. Highways, railways, bridges, and tunnels, worldwide, have faced consistent damage or destruction from landslides and floods, exacerbated by the ongoing climate change and population growth. In Italy, significant examples of these events are the recent failures of the Polcevera and Magra bridges, impacting people and the local economy. Especially, after the Polcevera bridge collapse, the Italian government has considered the need for specific practices of bridge/viaduct risk assessment. In response to this requirement, governmental agencies have developed specific projects oriented to the development of specific guidelines. This work is part of one of these projects, entrusted specifically to the ReLuis consortium, aimed at contributing to the application and optimization of an experimental protocol for bridge/viaduct classification in natural -hazard related risk assessment perspective. In this context, this work describes the results of an initial -level analysis of the interaction condition of a slowmoving landslide with the "Villa Ilii" Viaduct located along the A24 highway at Colledara, in the Teramo Province. The analysis aims to evaluate landslide characteristics, including landslide anatomy and kinematics, and their potential impact, contributing to define and identify viaduct classification in landslide risk perspective. The study area is characterized by the presence of the Laga Formation, mainly represented by sandstones and marls, overlaid by sandy Quaternary deposits. In fact the formation of the Laga (Ricci LucchI, 1975) represents the filling of one of the many foreland basins currently exposed in a wide area between southern Marche and northern Abruzzo, developed at the forefront of the Apennines during its migration eastward and northeastward, as a result of the collision between the European lithospheric plate and the Adriatic plate, a likely protrusion of the African continent.), Methods including existing data collection, field surveys, numerical chartography analysis, geophysical surveys and PS InSAR technique were used to reconstruct the geological setting of the slope affected by the landslide, its anatomy and kinematics. Especially, multiple field surveys and numerical cartography analysis revealed landslide extent over a surface of 78,000 m 2 , geophysical survey indicated a landslide thickness of around 15 m, comparable with the thickness of Quaternary deposits, and SAR-interferometric data, processed by SUBSIDENCE software, indicated persistent slow movement typically accelerating in spring. These data are crucial for understanding the landslide's potential impact on the "Villa Ilii" viaduct's structural conditions, already exhibiting local deformation and cracking, similar to surrounding settlements.