PSI - Issue 84

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

511

potential detachment features related to a rotational–translational movement (Fig. 3). At the present stage, no evidence of rapidly evolving instability or of structural distress directly attributable to landslide activity has been identified. Nevertheless, residual uncertainty remains regarding the subsurface conditions and the effective interaction mechanism between the slope and the structure. Accordingly, the special inspection defines a targeted and proportionate investigation and monitoring strategy, aimed at reducing uncertainty while ensuring efficiency in terms of cost and effort. The proposed activities include the installation of a minimum monitoring configuration based on piezometer–inclinometer pairs arranged transversely to the viaduct within the mapped landslide, complemented by basic soil characterization tests, selected geophysical surveys, and topographic targets on the affected piers. This progressive approach is intended to capture potential slow or intermittent movements over multiple seasonal cycles, while allowing the investigation and monitoring framework to be expanded only if monitoring trends or new field evidence indicate an increase in landslide-related risk. In this sense, Case C exemplifies the role of special inspection as a decision-support tool for discriminating between negligible, superficial deformation processes and potentially relevant landslide mechanisms, enabling reliable safety assessment without unnecessary investigations.

Fig. 3. (a) Excerpt from the IFFI Inventory showing the delineation of the rotational/translational slide interfering with the viaduct; (b) aerial view of the structure; (c) detail of the landslide crown highlighting the incisions. 4. Conclusions This paper investigated the role of special inspections within the Italian Guidelines for landslide risk assessment of existing bridges, focusing on their function as an intermediate, decision-oriented assessment level between preliminary screening and detailed Level 4 verifications. The proposed methodological framework is grounded on a broader set of application cases developed within the Italian motorway network; the three case studies presented herein are intentionally selected as representative archetypes, aimed at supporting the definition of operational instructions applicable to large bridge inventories. The results highlight that special inspections should not be interpreted as a predefined or uniform set of investigations, but rather as a flexible process explicitly tailored to the landslide mechanism, the interaction modality, and the level of prior knowledge. In this perspective, the primary objective of SIs is not necessarily to trigger more detailed analyses, but to identify the minimum level of investigation and monitoring required to reliably manage landslide risk, avoiding unnecessary allocation of resources in cases where the interaction is only suspected or evolves slowly over time. In particular, Case C exemplifies a frequent operational condition in large-scale assessments, where a bridge intersects an area mapped as unstable but lacks documented evidence of active deformation or structural distress. In such contexts, SIs provide a rational framework to discriminate between superficial or negligible deformation processes and potentially relevant landslide mechanisms, allowing the definition of minimal and progressive investigation and monitoring strategies. This approach is especially relevant for slow-moving landslides, which typically evolve over long timescales and leave sufficient margins for intervention if adequately monitored. Conversely, Case B illustrates the fundamentally different role of SIs in the presence of rapid