Recognition of Landslide Risk and Interaction with Arch Bridges: Lessons Learned and Methodological Insights

The interaction between landslides and arch bridges presents complex challenges, demanding a nuanced approach to risk assessment. In Italy, specific guidelines for evaluating and managing risks related to bridges and viaducts-including structural, seismic, hydraulic, and landslide risks-represent a critical step forward. However, their practical implementation often encounters hurdles, particularly when details about landslide characteristics and their interaction with structures are unknown.The expertise of evaluators in identifying precursor signs on the ground and the structure is crucial to prevent critical conditions. Arch bridges, as hyperstatic structures, are particularly vulnerable to longitudinal thrust from slow-moving landslides, even at low velocities. The eventual development of a three-hinge collapse mechanism under such conditions poses significant risks. In fact, the formation of plastic hinges, typically near the supports and the crown of the arch, can transform the bridge into a kinematic mechanism, resulting in sudden, brittle collapse. Such a failure poses severe risks to vehicles and pedestrians, often without warning signs once the mechanism is fully activated. This study consolidates insights from inspections of arch bridges interacting with slow-moving landslides, highlighting precursor signs and lessons learned. Cases of bridges failing to withstand ground thrust, leading to collapse, are also described. Drawing on the authors' experience and literature insights, the article identifies critical signs and aspects to investigate during landslide risk assessments, with emphasis on early indicators of hinge formation, such as cracking, uneven settlements, or arch deformations.Inaccurate risk assessment often leads to insufficient maintenance and safety measures for both the slope and the structure. By integrating observations into a systematic methodology, this approach enables early detection of structural risks and timely interventions to prevent significant deterioration.