PSI - Issue 84

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

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in active or evolving cases, the model shall also be validated through displacement measurements and monitoring data. A qualifying aspect is that investigation planning shall not follow a standard test “checklist”, but an expert-driven, coordinated, and goal-oriented program guided by the preliminary models, which calibrate investigation depth, spatial distribution, and the number of investigation points according to instability extent, expected slip-surface geometry, and the need to define kinematics and pore-water pressures. Investigations shall enable: (i) an accurate description of the stratigraphic succession and involved geotechnical units; (ii) identification of the geometry and location of slip surfaces (where present); (iii) definition of kinematic characteristics and of the magnitude and distribution of pore water pressures; and (iv) measurement of surface and deep displacements. Investigation depth shall be defined in relation to slope geometry, surface survey results, and the most likely slip-surface position. Where available documentation does not allow a reliable definition of foundation type and geometry, the Knowledge Project shall include specific characterization activities through indirect approaches (non-destructive geophysical investigations) and/or direct methods (e.g., boreholes drilled through foundation elements), in order to reduce uncertainties that significantly affect verification of the soil–foundation system. When assessments under seismic conditions are required, the Knowledge Project shall include dynamic subsoil characterization to support local seismic response analyses (stratigraphy and seismic bedrock definition), integrating surface geophysical surveys, in situ and downhole geotechnical seismic tests, and laboratory tests, as well as checks of predisposing conditions (e.g., liquefaction susceptibility) where relevant. Finally, monitoring shall be conceived as a structural component of the Knowledge Project (not a downstream activity), to be initiated already during the Special Inspection phase and/or at Level 4 and updated according to investigation outcomes, also exploiting boreholes for instrument installation. Monitoring aims to control instability evolution and estimate its main kinematic characteristics (activity state and velocity), as well as volumes and parameters required to correctly define actions on structural components (abutments, piers, foundations) and to support possible updates of the landslide Attention Class. Monitoring techniques may include direct and indirect methods (inclinometers, piezometers, optical fibers (Longoni et al., 2022; Barla et al 2024, Barla et al. 2025), PS InSAR analyses, repeated laser scanning, repeated geophysical surveys), to be selected and dimensioned through explicitly motivated expert judgment according to the instability mechanism and the mode of interaction. 4. Conclusion The adoption of the national Guidelines has introduced a substantial change in the safety management system for existing bridges, providing a multi-level and interdisciplinary methodological framework capable of ensuring uniformity of approach and traceability of decisions at a national scale. However, practical experience has shown that, in contexts involving interaction with landslide phenomena, operational criticalities persist, mainly related to information gaps, the complexity of instability mechanisms, and the difficulty of translating risk classification stages into effective and proportionate knowledge pathways. In this scenario, the Knowledge Project emerges as a central element for overcoming these limitations, being conceived not as a mere data-collection phase, but as a designed and iterative process aimed at constructing reliable models of the bridge–slope system and at correctly setting up Level 4 accurate safety assessments, in compliance with NTC 2018 and CSLLPP Circular No. 7/2019. The definition of preliminary models, the qualifying role of Special Inspections, the targeted planning of investigation campaigns, and the structural integration of monitoring activities represent the cornerstones of this approach. Within this framework, the MARIE project provides a focused scientific and operational contribution to landslide risk management for existing bridges. Through the systematization of case studies, clarification of interaction typologies, and development of strategies for optimizing investigation and monitoring campaigns, MARIE strengthens the link between risk classification and accurate safety verification, reducing decision-making uncertainties and application-related discretion that emerged during the initial implementation of the Guidelines. Project results highlight that an approach based on the integrated understanding of geomorphological, geological, and geotechnical contexts is essential for effectively addressing landslide risk, particularly in cases involving complex, slow-moving, or potentially evolving phenomena, and for ensuring a realistic assessment of structural safety. The integration of investigations, monitoring, and advanced modelling further supports