PSI - Issue 62

Giovanna Pappalardo et al. / Procedia Structural Integrity 62 (2024) 460–467 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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al., 2018, Wu et al., 2020). Natural hazards like landslides can critically impact the safe operation of infrastructure, sometimes posing a threat to passenger lives. Masonry arch bridges are integral to this linear infrastructure, traversing valleys and rivers. Their location in geomorphologically complex sites makes them particularly vulnerable. Ensuring their safety requires a multidisciplinary approach that analyses their multi-hazard vulnerability assessment. The scientific community has long recognized the need to estimate potential natural event damages, leading to innovative developments in remote sensing and numerical analysis. (Arias et al., 2007, Macciotta and Hendry, 2021). This study employed advanced methodologies, integrating drone photogrammetry and thermography to create detailed numerical models of the bridge subjected to the actions associated to landslide. These models, based on a original discrete macro element method (DMEM), allow an in-depth analysis of the current conditions and understanding of the structural behaviour of the bridge under the different risks to which it is exposed. Namely, a detailed understanding of the bridge's structural responses to landslide action is considered. Additionally, the associated hydraulic risk was evaluated, crucial considering the bridge's location. This assessment was particularly important for understanding how extreme hydrological events, potentially worsening landslide conditions, affect the bridge's overall stability. 2. Geology and geomorphology setting The geology of the area consists of Oligocene clay formations of the Varicolored Clays, which overlie the Numidian Flysch Clays (Ogniben 1960, Lentini and Vezzani 1978). These formations have poor physical and mechanical characteristics, being highly tectonized clays and thus prone to landslides. The landslide studied in this work is located south of the town of Maletto. It has a maximum length of about 140 meters and a width of about 40 meters (Figure 1 a and b). This landslide involved a masonry bridge of the historic Circumetnea line, particularly affecting two of the four arches of the bridge by 2021, reaching an elevation just below the extrados. In 2022, the landslide foot was artificially cut to reduce the thrust against the bridge. However, this intervention lacked proper containment and surface water drainage design, leading to water stagnation near the bridge (Figure 2). This slow-moving landslide shows a gradual retreat of the scarp towards the east and has been active for over twenty years, as observed in satellite images. The landslide is bordered by deep-cutting gullies in the clayey soils, which during rainy periods cause greater erosion of one side of the bridge. The causes of this phenomenon can be attributed to the saturation of the exposed clays due to an increase in water content, which reduces cohesion and increases the pressure of interstitial water, leading to a reduction in shear resistance.

Fig. 1. (a) 3D model of the landslide slope, (b) frontal view of the landslide body.

3. Methodology Through the integration of multi-sensor photogrammetric techniques, three-dimensional models of the landslide and the bridge were successfully created. The acquisition of multi-sensor aerial images involved two distinct flight plans, characterized by an average altitude of approximately 80 meters above the ground with 70% lateral and 80% longitudinal overlaps, and a ground sampling distance (GSD) of about 5 cm. This methodology was complemented with infrared thermal imaging, allowing the identification of moisture zones and morphological escarpments within