PSI - Issue 84

Lorenzo Brezzi et al. / Procedia Structural Integrity 84 (2026) 505–512

506

Keywords: Italian Guidelines; Special Inspections; Smart Infrastructure Management; Landslide Risk Assessment.

1. Introduction The safety assessment of bridges and viaducts has become increasingly relevant in Italy, both due to the large extent of the existing infrastructure stock (Santarsiero et al., 2021) and following several recent catastrophic failures (Bazzucchi et al., 2018; Burlando et al., 2020; Scala et al., 2025). In parallel, the combined effects of structural ageing, climate change, and the growing frequency of extreme meteorological events have highlighted new vulnerabilities in infrastructure systems, requiring progressively more integrated and multidisciplinary assessment approaches. Among natural hazards, slope instabilities represent one of the most critical geotechnical threats for bridges and viaducts (Proske, 2019; Scala et al., 2025), with potentially severe consequences in terms of structural performance, serviceability, durability, and user safety. Landslide-related actions often develop over long timescales or occur episodically, making their detection and interpretation particularly challenging during routine inspection activities. The Italian Guidelines for the classification and management of risk and for the safety assessment of existing bridges (MIMS, 2022) adopt a multilevel approach, aimed at progressively increasing the level of knowledge through successive assessment stages. The initial levels, systematically applied to the entire infrastructure stock, rely on inventories, hazard maps, and preliminary inspections to identify potentially critical situations. However, for bridges located in areas affected by hydrogeological hazards, these tools may not always provide sufficient information to reliably characterize the actual interaction between slope instabilities and structural components. In this framework, the Guidelines introduce Special Inspections (SIs) as an intermediate assessment level, intended to bridge the gap between ordinary inspections and detailed Level 4 verifications. SIs are prescribed when preliminary assessments indicate high exposure to landslide hazard and potential signs of structural distress, and their purpose is to determine whether more demanding investigations and safety verifications are required, or whether the structure can be managed through targeted monitoring and surveillance strategies. SIs must therefore be carefully calibrated according to the type of landslide, the direction and mechanism of interaction with the structure, the bridge typology, and its current structural condition. Poorly targeted investigations may lead either to unnecessary costs or to an underestimation of the actual risk, undermining the effectiveness of the overall assessment process. 2. Background and motivation for special inspections The assessment of landslide risk for bridges and viaducts is inherently complex due to the wide variability of landslide mechanisms and their possible modes of interaction with infrastructure (Cruden and Varnes, 1996; Hungr et al., 2014). This complexity is further amplified by the difficulty of directly correlating geomorphological evidence with structural response, particularly in the case of slow-moving or deep-seated instabilities, which may develop over long timescales and may not produce clear or persistent surface indicators. Several recent studies have addressed landslide–bridge interaction through large-scale databases, highlighting the relevance of slow-moving landslides and large-volume failures as critical scenarios (Salciarini et al., 2024; Gabrieli et al., 2025). At a national scale, landslides have been identified as one of the most frequent natural causes of bridge damage in Italy, second only to hydraulic-related processes (Scala et al., 2025), consistently with international findings (Wardhana and Hadipriono, 2003; Proske, 2019; D’Angelo et al., 2025). While these studies provide robust statistical evidence on the relevance of landslide hazard and on the most critical instability scenarios, they offer limited guidance on how to translate inventory-based information and aggregated indicators into operational decisions at the scale of a single bridge. In particular, defining when and how to perform targeted investigations and monitoring activities remains a key challenge within large-scale risk assessment frameworks. In this context, the Italian Guidelines for the classification and management of risk and for the safety assessment of existing bridges (MIMS, 2022) propose, after the census phase, the execution of ordinary inspections. By design, these inspections are rapid and streamlined and may therefore be insufficient to capture the complexity of