PSI - Issue 84

I. Vangelisti et al. / Procedia Structural Integrity 84 (2026) 1239–1246

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with a specific focus on cases involving a presumed downgrading of the attention class as a result ot the VAL3 assessment. Finally, an operational methodology for the prioritization of VAL4 assessments for lining inspection segments that require it as a result of the VAL3 application is presented. 2. Definition, scope of application and objectives of the VAL3 As identified in Section 1.3 of the Tunnels Guidelines, the preliminary assessments involves the execution of preliminary assessments aimed at determining, together with the analysis of the type and extent of defects identified during the inspections carried out at Level 1, the level of safety with respect to potential local failures affecting the lining, as well as failures related to the interaction between the lining and the natural formations crossed. Where required, specific assessments are also developed to address possible interactions with global instabilities of the crossed geological formations. Preliminary assessments are required for lining inspection segments classified within the Medium-High to High attention classes, determined at Level 2; however, they may also be performed for lower attention classes. With reference to the Global Structural and Geotechnical (GSG) and Local Structural (LS) attention classes, it is recommended that VAL3 be carried out for lining inspection segments for which at least one of the two attention classes is Medium-High or higher. Specifically, within VAL3, each attention class that is at least Medium-High is recalculated. At Level 3, it is necessary to verify that the data collected and made available through the inventory of the tunnel and the initial inspection are sufficient to perform the analysis for all risk indicators that led to the assignment of the attention class, thereby confirming the assessments previously carried out at Level 2. It should be noted that the scope of the present document is limited to global structural and geotechnical risk and local structural risk only. Through a critical evaluation of the available information on the tunnel, and, where necessary, the acquisition of additional data concerning geology, the quality class and stress state of the lining concrete, and the extent and consistency of defects identified at Level 1, VAL3 allows the recalculation of the attention class. This process may lead to either a revision or a confirmation of the attention class assigned to the lining inspection segment. Where a High attention class is confirmed, the execution of VAL4 assessments is required, as described in the following sections of the paper. 3. Methodological proposal The approach proposed for the execution of VAL3 is primarily document-based , i.e., founded on a critical analysis and revision of the tunnel available documentation, integrated by additional documents collected after the original assignment of the attention class where available. The execution of the VAL3 is proposed to be based at least on the following steps: 1. Detailed analysis of the outcomes of Levels 0, 1, and 2, and of the as-built documentation: o analysis of outcomes and relevant information derived from Levels 0 and 1; o analysis of Global Structural and Geotechnical (GSG) and Local Structural (LS) attention classes assigned to each lining inspection segment; o analysis of the most important factors on which the hazard, vulnerability, and exposure classes depend; o review of the available documentation (design drawings, as-built documentation, reports from previous investigations, inspection reports, etc.). 2. Analysis of newly available documentation and/or technical reinterpretation of previously analysed documents : o examination of newly collected documents (e.g., intervention projects carried out after the last attention class assessment) and evaluation of their potential impact on hazard, vulnerability, and exposure parameters, and, consequently, on the attention class; o technical re-evaluation of documents previously analysed (to be appropriately justified and documented). 3. New assessment of the GSG and LS attention classes: