PSI - Issue 84

Antonio Fiorentino et al. / Procedia Structural Integrity 84 (2026) 749–756

750

1. Introduction 2. The Italian territory is characterized by an intrinsic fragility due to youthful morphologies and active tectonics, making the country particularly susceptible to natural hazards (Doglioni et Al. 2015), exposing existing infrastructure to significant risks. The studies developed by Consorzio Fabre (Salciarini et AL., 2024; Gabrieli et Al. 2025, Simeone et Al., 2024, Fiorentino et Al. 2026; Di Taranto et al., 2026) during the last years have shown that several existing bridges face significant problems in relation to interaction with landslides. This highlights an alarming scenario for the safety of Italy’s infrastructure system. Several recent events underscore the vulnerability of infrastructures to slope instabilities: the collapses of the Himera viaduct Palermo, 2015, the bridge on the A6 Turin–Savona motorway, the Albiano bridge over the River Magra, and the viaduct on SS117 near Longobucco can all be linked, directly or indirectly, to landslides or poor geotechnical conditions. This study focuses on the effects of the interaction of the “earthflow” with the viaduct “Fortunato” of the Italian National Road 653. Earthflows are one of the most common and complex forms of mass movement often triggered by rainfall, and capable of compromising both slope stability and the integrity of infrastructure. These phenomena can severely impact on the functional performance of civil works, potentially reaching or exceeding ultimate limit states and posing significant risks to public safety and local economies. Earthflows can reactivate over multi-year periods, significantly influencing the long-term morphological evolution especially at the toe zone (Sdao & Simeone, 1997, Doglioni et al., 2013). The phenomenon was identified and analyzed using an integrated approach that combines systematic in situ surveys with GIS-based geospatial analyses. The morphological reconstruction was supported by a high-resolution LiDAR model (1 m), used for detailed landslide mapping and capable of capturing the most distinctive morphological features. These data were integrated with multi-temporal satellite imagery (Google Earth and Google Maps), allowing reconstruction of the temporal evolution of the phenomenon. Finally, an analysis of the rainfall preceding the last reactivations was developed to show the effect of precipitation as a possible triggering factor. In addition, the examination of road maintenance records provided further evidence useful for defining precursory conditions, early deformation indicators, and the progression of the earthflow. The results contribute to improving the understanding of earthflow–infrastructure interactions and provide operational insights for monitoring strategies and risk mitigation in tectonically active and natural hazard fragile settings 3. Geological and geomorphological setting 4. Basilicata Region is part of the Southern Apennines orogenic system, its present configuration results from major tectonic deformation and eastward migration of thrust sheets towards the Apulian Foreland, producing overall shortening and structural complexity (Patacca & Scandone, 2007). The study area is located along the left bank of River Sinni, immediately downstream of Monte Cotugno dam. It is characterized by the juxtaposition of allochthonous units overlying and locally interbedded with Pliocene–Pleistocene sediments, as well as by synorogenic flysch tectonically superposed over older flysch, reflecting a Middle Pliocene deformation phase affecting the Apennine front. Based on geological reconstructions from Sheet 523 “Rotondella” (1:50,000) (https://www.isprambiente.gov.it/Media/carg/523_ROTONDELLA/Foglio.html) of the Geological Map of Italy and field surveys (Fig. 1a), the zone of the slope affected by the earthflow is characterized by earthflow detrital made by the degraded part of Varicoloured scaly clay of Red Flysch (Auct.) a thick turbiditic sequence marked by alternations of clay-rich and sandstone beds, commonly affected by intense tectonization. These are mainly bordered by underlain Pliocene silty–clayey marly lithotypes. The marly silty–clayey deposits are locally deformed and partially interbedded within thrust-related structures associated with the flysch units, which contribute to the steep slope morphology. The slow-moving earthflow affecting Fortunato viaduct develops within highly tectonized flysch deposits pinched between Plio-Pleistocene sands and clay; their fabric and pervasive discontinuities promote repeated reactivations and direct interaction with the roadway infrastructure. To support the interpretation of the mobilization processes and provide input parameters for the modelling of the geotechnical aspects a basic geotechnical characterization was performed on samples collected along the earthflow. Laboratory tests included grain-size analysis, Atterberg limits, and residual strength the material shows high plasticity (WL = 62, PI = 39) and low residual shear strength, with average values of φ′≈ 13 ° and c ′≈ 5 kPa, consistent with clay-rich turbiditic deposits. The use of the digital terrain model provided important insights into the morphology of the earthflow. This allowed to analyse in detail the topographic