PSI - Issue 84

I. Vangelisti et al. / Procedia Structural Integrity 84 (2026) 1247–1254

1248

Keywords: tunnels; inspections; detailed safety evaluation; service life of existing interventions.

1. Introduction The Level 4 Detailed Assessment represents the fourth level of the multilevel approach introduced by the Tunnels Guidelines (Ministerial Decree D.M.247/22). The VAL4 follows Levels 1 to 3 and is therefore carried out subsequent to the Level 3 preliminary assessment. A detailed description of the multilevel approach and of the relationships among the different assessment levels, as defined by the Tunnels Guidelines, is provided in Figure 1.

Fig. 1. Multi-level approach introduced by the Tunnels Guidelines.

In accordance with the multilevel framework, VAL4 is required for tunnel lining inspection segments classified as belonging to a high attention class, as confirmed by the outcomes of the VAL3 assessment. The aim of this paper is to present a detailed procedure for the execution of Level 4 assessments and for the extension of the nominal service life of the interventions. The first part of the paper presents the procedure to be applied to the lining inspection segments in the absence of temporary interventions, and it is structured into three main steps: load assessment, evaluation of the level of knowledge, and structural verifications. The second part describes the proposed procedure for tunnel lining inspection segments where temporary interventions are present. Finally, a methodology for assessing the extension of the nominal service life of temporary interventions is presented. The present work was developed by the Fabre Consortium in collaboration with several companies of the ASTM Group. 2. Definition and objectives of the VAL4 According to its definition, the VAL4 assessment (hereinafter referred to as “VAL4”) provides for the execution of “ accurate safety assessments of the tunnel with respect to acting loads and external factors, duly considering the provisions of the current Technical Standards for Construction NTC201818 .” Furthermore, Section 5.1 of the Tunnels Guidelines states that “ the Level 4 accurate assessment is aimed at providing a reliable evaluation of the safety level associated with portions of the tunnel lining or with ancillary structures, including tunnel portals, as well as at determining the need—or conversely, the absence of need—for mitigation measures addressing the specific risk. The reliability of these assessments must be ensured by an adequate level of knowledge; achieving this level will generally require the prior planning and execution of additional investigations and measurements, supplementing the data already available from the preceding levels .”