PSI - Issue 62

Vincenzo Simeone et al. / Procedia Structural Integrity 62 (2024) 561–568 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introducion Landslides and more generally slope gravitative deformations are quite common, specially in geologically young regions as those involved by orogenetic uplift (Guerricchio 2022). They may cause damages in the territory as well as significant stresses and deformations for infrastructures, like bridges, that are located in singular points. Understanding the interaction between bridges and landslides or slope gravitative deformations is crucial for implementing effective mitigation strategies. In fact, the integrity of the infrastructure could be compromised by the strain caused by the landslide, until, for extreme cases, the collapse of the bridge (Turner et al., 2018; Croccolo F. et al., 2020; Farneti et al., 2022). Slope gravitative deformations and giant landslides (Doglioni et al. 2015; Galeandro et al. 2013) affecting large areas are characterized by really slow velocities, so slow (Mansour, 2011) that their effects can become evident over several years, sometimes decades. Therefore, it is not easy to understand the real causes of damages affecting bridges and infrastructures, that often are considered the consequences of the age of the structure, and the absence of maintenance activity. This misunderstanding may be dangerous because it can lead to an underestimation of risk, thus making incorrect remediation choices (Schlögel et al., 2015). In the cases where the abutment of bridges are located along slopes subject to slow gravitative movements, the movement may create a compression state of stress in the bridge. Arch bridges may initially tolerate these stresses with deformation that transform the arch of the bridge in a sort of ogival arch with upward deformations, which can be defined as "nutcracker". It is the case of Caracas-La Guaira (Salcedo, 2009) or Serra viaduct in Lagonegro (Southern Italy) (Guerricchio and Melidoro, 1981) or the case of Ginosa bridge (D’Ambrosio et al., 2023). In Italy, these cases are fairly common, therefore the following sections focus on the analysis carried on bridges in South Italy, which show similar deformations, related to a pattern called “ nutcracker ”. 2. Methodology In this section it is going to be discussed the multidisciplinary approach used to detect the terrain-infrastructure interaction. First of all, there are some sign on the bridges, which can be traced back to the interaction between terrain and infrastructure, such as ogival deformations of the arches, compressions on the abutments and lifting or compression of the above barriers, whether they are metal or masonry. Even the crack on the pavement could be interpreted as sign of compression due to landslide. Afterwards the geological and geomorphological context near the bridges are analyzed, by thematic maps and detailed DTM (Digital Elevation Model) acquisitions based on LIDAR survey. The purpose is the reconstruction of the geological structure of the area and discover structural and morphological discontinuities, which may condition landslides and more generally slope gravitational deformations, also deep seated. In this way it is possible to have the frame of the geological and geomorphological conditions of the area where the bridge are located and of the active of potential slope deformations and landslide phenomena that may affect bridges. The next step is collecting the Measurement Points (MP), through the InSAR analysis. This technique allows to measure the displacement of certain points on the ground, due to the periodic passage of the satellite in the same areas, and to derive velocities, expressed in millimeters per year; exactly these make it the ideal tool in the study of very slow landslide and their impact on infrastructure (Crosetto et al., 2022; Constantini et al. 2021). This allows for a quantitative analysis of the deformations affecting slopes and their influence on bridge. This approach proves its effectiveness when the slope-bridge deformations are quite limited and not easy to be measured by traditional approaches. At the same time, it permits a backward monitoring before the installations of specific monitoring instruments, or to back-interpretate failures or severe damages. The obtained velocity could have positive or negative value, depending on the motion detected by the sensor, for which the observed point may respectively be approaching or receding from it. The same operation is carried out both in the ascending and in descending geometry; in the first case if the satellite, moving from the south to the north, detects positive values, the MP could move in uplifting or from east to west, on the contrary for negative value. If the satellite, moving from the north to the south, in descending geometry, detects positive values, the MP could move in uplifting or from west to east, on the contrary for negative value. Just with one geometry acquisition it is possible get