PSI - Issue 62

Nicola Perilli et al. / Procedia Structural Integrity 62 (2024) 546–552 547 2 Nicola Perilli, Massimiliano Lombardi, Nicola Nenci, Nunziante Squeglia, Stefano Stacul / Structural Integrity Procedia 00 (2019) 000 – 000 1. Introduction Since 2020, the Authors and other FABRE Consortium members are involved in the evaluation of landslide susceptibility, vulnerability, and exposure of existing bridges (Stacul et al., 2024, this volume) according to the new Italian Guidelines (LLG) (MIMS, 2022). These three factors are necessary to assess the Landslide Class of Attention of the bridge under examination. Their evaluation is based on the estimation of primary and secondary parameters and on other cluster of data requested in the Field Sheet Form which is filled out during the Periodic Field Survey. The primary parameters are activity , velocity , and magnitude (i.e., size) of the landslide, while the secondary parameters are the extent of the interference , and the overall reliability of the assessment of the primary parameters (a self-evaluation of the inspector about his/her judgement). During the inspections performed by the Authors and the other FABRE Consortium members is turned out that the selection of the extent of the interference (possible options are Total , Partial , Approach Zone in italian Zona di Approccio) is somehow spoiled by the fact that currently a clear definition of both the parameter and its options is missing in the text of LLG. Thus, the judgement of the inspector is not easy and/or partly arbitrary. In fact, many questions could spontaneously arise in the mind of every inspector: how is it possible to take into account of a landslide (such as a debris flow) which, although not directly interfering with the influence zone of the bridge, can hit it? what is the approach zone? why, in the case of landslides, should a total interference between the unstable mass and the bridge be more penalizing than a partial interference in assessing the Class of Attention?... Furthermore, the evaluation of the overall reliability of the assessment and hence of the susceptibility is also difficult and/or partly arbitrary being spoiled by the limited number of data required by the Field Sheet Form which is often filled out by unskilled technicians with a low background in the application of the new LLG. Aim of this work is to provide a definition of the Approach Zone (totally missing in the LLG), to recognize the existence of direct and indirect types of bridge-landslide interference, and to suggest a procedure for the appropriate identification and characterization of Potential landslides and a better evaluation of the overall reliability of the assessment . According to Perilli et al. (2024, in this volume), to improve the collection of the remote and ground data for the evaluation of primary and secondary parameters, it is helpful to identify three key areas surrounding the bridge under examination, namely: Relevant (RA), Geomorphological Significative (GSA), and Diagnostic Areas (DA). 2. Discussion and suggestions 2.1. Identification of the types and extent of landslide-bridge interference In this work the Authors suggest introducing the definition of two types of landslide-bridge interference, namely direct and indirect . A direct landslide-bridge interference occurs when the unstable mass of a slope interacts with the Influence Zone of the bridge (i.e., according to §6.2.2 in NTC (2018), the soil volume influenced directly by the structure, and which influences the structure itself). An indirect landslide-bridge interference occurs when the unstable mass of a slope will target the Influence Zone or the Approach Zone of the bridge only after its mobilization. With the term Approach Zone the Authors suggest referring to that transitional zone between the Influence Zone of the bridge and the Far-Field Zone (i.e., that zone far enough from the bridge to be considered non-interacting with it). Following the definition of direct and indirect types of landslide-bridge interference, it becomes clear that in the case of a direct interference the extent of the interference can only be Total or Partial as the landslide will totally or partially interacts with the bridge through the Influence Zone . In the case of an indirect interference the extent of the interference can be Total , Partial (Piers or Abutments) or the Approach Zone . To clarify the latter case, consider these two examples: a) an unstable mass (Recognized or Potential) located in the Far-Field Zone upstream the bridge, that may evolve into a debris flow and then hit the structure (totally or partially). In this case the type of interference should be considered indirect while the extent of the interference will be Total or Partial depending on the possible impact mechanism;