PSI - Issue 84

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

1254

If the extension period exceeds five years, a verification of the actual degradation state of the intervention shall be carried out in the fifth year following the verification, in analogy with interventions subject to the VAL4 process. 6. Conclusions This paper presents a detailed procedure for the execution of VAL4, in accordance with the provisions of the Tunnels Guidelines, together with a methodology for extending the nominal service life of interventions installed in tunnels. In the first part of the paper, the procedure for the detailed assessment of lining inspection segments without interventions is described, including the criteria for estimating the acting loads as a function of the available geological and geotechnical information, the evaluation of the level of knowledge, and the execution of structural verifications. Particular emphasis is placed on the estimation of the level of knowledge, assessed for each lining segment and, subsequently, at tunnel level, on the basis of multiple parameters representative of lining verification requirements. In the second part of the paper, a proposed procedure for performing VAL4 on lining inspection segments with existing interventions is analysed. In this case, the objective of VAL4 is the verification of the intervention–lining system, aimed at assessing the residual in-service life of the intervention. The levels of knowledge and the required verifications are defined (load-bearing capacity and durability verification, and robustness verification). Finally, the paper focuses on the development of a procedure for extending the nominal service life of interventions, both in cases where VAL4 is performed and where it is not. When the intervention is subject to VAL4, the nominal service life may be extended up to a maximum of 10 years, depending on the outcomes of the conducted verifications. Otherwise, the assessment includes a survey of the current degradation state, together with pull-out tests performed on at least 2% of the anchors, allowing for an extension of up to a maximum of 10 years based on the obtained results. In all cases, five years after the service life extension, a verification of the actual degradation state of the intervention is required in order to assess the consistency between the degradation assumptions adopted during the verification phase and the observed degradation. Acknowledgements This study was supported by FABRE – “Research consortium for the evaluation and monitoring of bridges, viaducts and other structures” (www.consorziofabre.it/en) through the project “ARCITunLin – Assessment, Risk Classification and Interventions on TUNnel LINings”. Any opinion expressed in the paper does not necessarily reflect the view of the funder. References Italian Ministerial Decree 247/2022, "Guidelines for risk classification, safety assessment, and monitoring of existing tunnels". Italian Ministerial Decree 17/01/2018, Italian Technical code for the design of civil and industrial buildings. ASTM D4729-19, Standard test method for in situ stress and modulus of deformation using the flat jack method Bobet, A., & Einstein, H.H. (2023). Tunnel Design Methods (1st ed.). CRC Press. https://doi.org/10.1201/9781003328940 “Linee guida per la classificazione e gestione del rischio, la valutazione della sicurezza e il monitoraggio delle gallerie esistenti” – Analisi e proposte interpretative, Consorzio FABRE, 2023 Circolare n°7-2019 C.S.LL.PP for the application of the Italian Ministerial Decree 17/01/2018 Highways tunnel inspection manual 2020, Italian Ministry of Infrastructure and Transport