PSI - Issue 84

Antonio Fiorentino et al. / Procedia Structural Integrity 84 (2026) 757–764

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2. Multi-level and multidisciplinary approach of the national Guidelines The multi-level methodology introduced by the national Guidelines and operationally developed by the FABRE Consortium is the backbone of the current safety management system for existing bridges. It follows a hierarchical, progressive pathway, developed across six levels, in which analytical detail increases with the severity and complexity of the identified criticalities, aiming to ensure coherent, traceable decisions and to reduce application-related discretion. Level 0 focuses on inventory and organization of available data. Level 1 consists of visual inspections to verify the state of conservation and identify potential signs of site instability. Level 2 defines the CoA by combining hazard, vulnerability, and exposure for the main risk types (structural/foundation, seismic, hydraulic, and landslide), thereby guiding priorities for further investigations and interventions. Level 3 provides preliminary site-specific assessments for bridges with medium-high or high CoA, or where inspections highlight uncertainties, to justify escalation to accurate assessment. In the presence of evidence of flood-related, erosional, or landslide phenomena, or in areas classified as high hydrogeological risk with possible structural interference, the Guidelines require Special Inspections, conceived as the technical junction between screening and higher-level assessments; if critical conditions are identified, the process may be anticipated by directly initiating Level 4. Level 4 corresponds to accurate safety verification in compliance with NTC 2018 and CSLLPP Circular No. 7/2019, supported by a dedicated Knowledge Project integrating documentary analyses, in situ and laboratory investigations, detailed geological/geotechnical reconstructions, and, where needed, advanced numerical analyses. For landslide-interacting bridges, Level 4 requires an integrated interpretation of the bridge–slope system, acknowledging the dependence of structural safety on the evolution of surrounding geomorphological and geotechnical conditions. Early implementation by infrastructure managers has nevertheless highlighted critical issues, especially for complex landslide interactions, including difficulties in defining interference conditions, uncertainties in the transition from classification to in-depth stages, and limited standardization of Special Inspections and Level 4 Knowledge Project contents. In response, the MARIE research project aims to strengthen and integrate the existing framework by providing operational criteria, interpretative models, and application-oriented guidance to address these gaps and support implementation in higher-complexity contexts. 2.1. Operational critical issues Although the multi-level framework of the Guidelines is intended to ensure methodological consistency and decision traceability, operational implementation has shown critical issues in landslide–bridge interaction cases. A first limitation is the incompleteness of baseline information (inventory and historical documentation): full reconstruction is often not feasible, especially for bridges built in the 1950s–1980s, and additional investigations are needed to recover essential data (foundations, stabilization works, previous investigations, monitoring). A second issue is the transition from screening (L0–L1–L2) to in-depth stages. For landslide hazard, Special Inspections are required in landslide-affected or high hydrogeological-risk areas (Fig. 1), yet operational criteria and tools are less structured than for other criticalities, leading to heterogeneous applications and uncertainty on activation, minimum contents and to the need to clarify when direct referral to Level 4 is warranted.

Fig. 1. Examples of bridges affected by hydrogeological hazards.

Another critical issue concerns the wide range of landslide phenomena, which differ significantly in terms of mechanisms and velocities (slow-moving landslides, deep-seated gravitational slope deformations—DSGSDs, rockfalls, rotational and translational slides, shallow landslides, debris and earth flows, complex landslides), and may