PSI - Issue 84

Daniela Boldini et al. / Procedia Structural Integrity 84 (2026) 175–182

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shear strain, derived from local seismic response analyses, is adopted, plasticisation becomes more widespread and the mobilisation of the available shear resistance increases markedly; • when a 15 cm inner layer of cracked concrete is introduced in the governing case, to reproduce the degradation observed during field inspections, the crown plastic response becomes more relevant. In this configuration, the SR-based quasi-static analysis leads to the onset of shear failure at the crown, whereas the EC-based demand is not sufficient to activate the same crisis mechanism; • the numerical analysis results indicate that the vulnerability of the reduced-thickness crown cannot be attributed to geometry alone, but to the combined effect of an unfavourable initial stress state, pre-existing cracking, and a site-specific seismic demand higher than that obtained from the simplified Eurocode procedure. Overall, the results show that a quasi-static approach based solely on the Eurocode shear strain may be adequate for preliminary screening, but may underestimate the actual seismic demand in degraded existing tunnels. Conversely, the use of shear strains derived from local seismic response analyses provides a more realistic and still computationally efficient basis for identifying critical conditions and possible shear failure mechanisms in weakened crown sections. Future work should extend the analyses to different tunnel geometries, ground conditions and degradation scenarios, and should adopt more advanced constitutive models capable of reproducing crack propagation and post-peak response more explicitly. Acknowledgements This work was carried out within the framework of the Reserch Project ArciTunLin: “Assessment, Risk Classification and Interventions on TUNnel LINings”, funded by FABRE Consortium (Research consortium for the evaluation and monitoring of bridges, viaducts and other structures). References Alessio, C., Baccolini, L., Di Fiore, D., Conte, M., Cicolani, M., Peila, D., Carigi, A., 2024. The 365 km tunnels assessment along ASPI Motorways Network – Key findings addressing risk analysis procedures and structural conditions evaluation and strategy of interventions. Procedia Structural Integrity 62: 1077-1088. Amorosi, A., Boldini, D., Elia, G. 2011. Analysis of tunnel behaviour under seismic loads using different numerical approaches, International Conference on Earthquake Geotechnical Engineering. Santiago, Chile, 13 pp. Boldini, D., Lusini, E., Spaggiari, C., Carigi, A., Todaro, C., Peila, D., 2026. Seismic performance of existing tunnels affected by lining thickness reduction. Word Tunnel Congress, Montrel, Canada, 8 pages. Bardet, J. P., Ichii, K., Lin, C.H., 2000. EERA. A computer program Nonlinear Earthquake site Response Analyses of layered soil deposits. University of Southern California. Brinkgreve, R.B.J., Kumarswamy, S., Swolfs, W.M., Fonseca, F., Zalamea, N., Ragi Manoj, N., Singh, K., Zampich, L. 2024. PLAXIS 2D 2024.2 Manuals. Carigi, A., Todaro, C., Silvestri, G., 2024. Italian guidelines for the risk classification, safety evaluation and monitoring of existing tunnels: An overview, ITA-AITES World Tunnel Congress 2024 (WTC 2024). Shenzhen, China, 3333-3341. Carigi, A., Todaro, C., Silvestri, G., 2025. Italian legislative scheme for tunnel maintenance up to the guidelines for the risk classification, safety evaluation, and monitoring of existing tunnels. Geomechanics and Tunnelling 18(4), 312-319. EN1992-1-1, 2023. Eurocode 2: Design of concrete structures. Hoek, E., Carranza-Torres, C., Corkum, B., 2002. Hoek-Brown failure criterion – 2002 Edition. 5th North American Rock Mech. Symp. and the 17th Tun. Ass. of Canada Conf. (NARMS-TAC 2002), Toronto, Canada, vol. 1, 267-273. Hoek, E., Diederichs, M.S., 2006. Empirical estimation of rock mass modulus. International Journal of Rock Mechanics & Mining Sciences 43: 203-215. Kontoe, S., Zdravkovic, L., Potts, D.M, Menkiti, C.O., 2008. Case study on seismic tunnel response. Canadian Geotechnical Journal 45(12): 1743 1764. MARTA: a computer program for the site response analysis of a layered soil deposit, developed by L. Callisto, https://luigicallisto.site.uniroma1.it/software, last accessed 2026/01/20. prEN 1998-5:2024, 2024. Eurocode 8: Design of structures for earthquake resistance - Part 5: Geotechnical aspects, foundations, retaining and underground structures – Annex G: Simplified evaluation of peak ground parameters for seismic design of underground structures. Spaggiari, C., Lusini, E., Boldini, D., 2026. A comparative assessment of seismic performance in existing tunnels with lining thickness reduction. Proceedings of the 9th Italian National Conference of the Researchers of Geotechnical Engineering CNRIG 2026, L’Aquila, Italy, 8 pages.