PSI - Issue 62

Stefano Stacul et al. / Procedia Structural Integrity 62 (2024) 569–575 Stefano Stacul, Nunziante Squeglia, Nicola Perilli / Structural Integrity Procedia 00 (2019) 000 – 000

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The most important factors for triggering landslides are short and intense rainfall, persistent rainfall, earthquakes, anthropic activities, climate changes and the increasing lack of protection and maintenance of the territory especially due to the abandonment of mountain and hilly areas (Trigila et al., 2021). The IFFI database therefore represents a very important tool for the development of Hydrogeological Planning Plans (PAI), realized by the District Basin Authorities, which in turn contain Landslide Hazard Maps (LHMs). Then ISPRA collects all these data to realize a harmonized Landslide Hazard Map of the entire Italian territory (Figure 1, right side). The ISPRA LHM uses for the entire Italian territory 5 hazard classes: PF1 (moderate), PF2 (medium), PF3 (high), P4 (very high) and AA (Areas of Attention). However, the hydrogeological hazard mapping of the Italian territory is still not sufficiently complete. In fact, the first significative regulation on landslides and floods aspects (Law no. 183 of 18 May 1989), inspired by the results of the De Marchi Commission, saw the light only in 1989. The latter identified the river basin as the territorial reference base for hydrogeological protection and the Basin Authorities as institutions responsible for preparing the PAI. Nevertheless, only the catastrophic event in Sarno on 5 May 1998 triggered the application of Law no. 183/1989. Thus, the subsequent Decree no. 180 of 11 June 1998, converted into Law no. 267/1998, speed up the adoption of preliminary PAI and the Law no. 183/1989 was repealed and integrated into Decree no. 152/2006. Consequently, the actual Landslide Hazard Map is still a “very young tool” and represents the results of the efforts of the last two decades. The PAI maps are dynamic tools which have been subjected to additions and modifications by the former Basin Authorities (now District Basin Authorities), following new studies and investigations. The availability of these data (IFFI and PAI maps) has become extremely important in the application of the new Italian Guidelines for classifying the risk of existing bridges (LLG) (MIMS, 2022). In fact, the first three levels (Level 0, 1 and 2) of the multi-level approach of the LLG consist in three main activities: 1) collection of all the available data (morphological, geological, geotechnical …), regarding the area in which the bridge is located, including the hazard class according to the LHM and the verification of the presence or absence of landslides registered in the IFFI map; 2) a visual inspection of an expert that will check the coherence of the collected data with the “near - field” obse rvations; 3) the assignment of a Class of Attention in reference to the landslide risk based on the information obtained in the previous two steps. In many cases the critical aspects in the application of LLG method are related to a) the lack of the project documentation of the bridge; b) the assessment of the extension of the area to be investigated; c) the accessibility of the area; d) the difficulty of confirming or not what indicated in the consulted maps (IFFI and PAI). This contribution, after describing the main limitation of the Italian LHM, will present a first application of the Italian LHM in the assessment of the Landslide Class of Attention for a representative sample of bridges. 2. The Italian Landslide Hazard Map and its limits Each District Basin Authority uses its own method (qualitative, geomorphological, quantitative or hybrid methods) for the assessment of landslide hazard. All these methodologies are based on the Landslide Inventory (IFFI) and on some parameters collected in IFFI. The qualitative matrix method defines the hazard classes via combining one, two or multiple parameters (i.e., state of activity, type of movement, velocity, depth of the sliding surface…) . For example, the multi-parameter model based on the Swiss method (BUWAL) allows combining, through matrices, the probability of occurrence and magnitude of landslide phenomena, defined on the basis of the velocity of the event and the class of geometric severity. The latter is inferred via the type of movement, which should be known. Two and multi-parameter models have been adopted by the former Marche Regional Basin Authority, the former Upper Adriatic Basin Authority, and the Autonomous Province of Bolzano. This method has the advantage of being replicable and based on simplified schemes, nevertheless, it can only be applied in those areas already affected by landslides that are included in the IFFI Inventory. The geomorphological method consists in the zoning of the slopes on a geomorphological and geological basis (i.e., ongoing landslide phenomena, morphological indications of instability, lithologies prone to landslides). This method was applied by the former Basin Authorities of Magra, Serchio and Liri-Garigliano and Volturno rivers. Compared to the qualitative matrix method the entire territory can be classified, nevertheless, this method is affected by a certain subjectivity in the assessment of the hazard classes.