PSI - Issue 84

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ScienceDirect

Procedia Structural Integrity 84 (2026) 1334–1338

© 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Abstract Tunnel fires pose a critical threat to infrastructure due to fire-induced explosive spalling. This paper investigates the effectiveness of Hybrid Fibre-Reinforced Concrete (HFRC) in mitigating these risks. By synthesizing experimental data across various scales, the study explores the synergy between steel fibres, which maintain post-cracking ductility, and polypropylene (PP) fibres, which create a sacrificial drainage network to relieve internal vapour pressure. III Fabre Conference: Existing Bridges, Viaducts, and Tunnels: Research, Innovation, and Applications The role played by fibres in limiting the fire-induced explosive spalling in tunnels: critical review of state-of-art Nunzia Gargiulo a, *, Donatella de Silva a , Antonio Cibelli a , Emidio Nigro a a Department of Structures for Engineering and Architecture, University of Naples Federico II 1. Introduction Tunnel fires are among the most severe incidents affecting modern infrastructure, characterised by extreme temperatures and confined conditions that impose significant thermal stresses on structural materials. In contrast to fires in open structures, the rapid heat flux – typical of tunnel environments – frequently induces explosive spalling, a phenomenon that compromises structural integrity and leads to prolonged operational disruptions. The severity of this issue is well-documented by empirical evidence from notable incidents. For instance, the Great Belt Tunnel fore in Denmark resulted in 27 cm degradation of its 40 cm thick lining. Similarly, spalling depths up to 18 cm were recorded in the Pantuoling Tunnel, China, and 12 cm in the A86 Tunnel, France. A particularly severe case occurred in the Channel Tunnel, where the lining thickness was substantially reduced from 45 cm to as little as 10–20 cm. Peer-review under responsibility of the scientific committee of the Conference Keywords: Tunnels; Fire resistance; Spalling ;Fiber-reinforced concrete.

* Corresponding author. E-mail address: nunzia.gargiulo@unina.it

2452-3216 © 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the scientific committee of the Conference 10.1016/j.prostr.2026.06.170