Methodological development of special inspection protocols for landslide-bridge interaction

Landslide risk assessment for bridges and viaducts is often challenging, as standard inventory and hazard maps do not always provide a sufficiently detailed understanding of potential slope–structure interaction. Field inspections may be hindered by dense vegetation or by the absence of clear indicators of slope movement. The Italian Guidelines for the Risk Assessment of Existing Bridges (LLGG) propose a progressively detailed knowledge acquisition process, in which special inspections (SIs) represent an intermediate assessment level aimed at determining whether detailed investigations and safety verifications are required, or whether risk can be managed through targeted monitoring and surveillance strategies. This study presents a set of representative case studies from the Italian motorway network, selected as representative scenarios within a broader application dataset, encompassing different forms of landslide–bridge interaction. For each case, the role of SIs is discussed in relation to the available level of knowledge, the landslide mechanism, and the interaction modality, with the objective of identifying proportionate and operational investigation and monitoring strategies. The outcomes support the development of the Guidelines for Special Inspections for Landslide Risk Assessment (LLGGIS), providing a structured methodology to optimize resource allocation while ensuring adequate safety levels in the large-scale management of bridge infrastructure.