PSI - Issue 64

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Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1666 © 2024 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 SMAR 2024 Organizers Keywords: Distributed fiber optic sensing; tunnel lining segments; structural integrity monitoring; deformation behavior Christoph M. Monsberger et al. / Procedia Structural Integrity 64 (2024) 1665–1672

1. The Brenner Base Tunnel: An Introduction The Brenner Base Tunnel (BBT), a flat rail link with high transport capacity, will connect the Tulfes portal (near Innsbruck, Austria) with the Franzensfeste portal (Italy) over a total length of about 64 km in the future. The cross alpine rail link is a key project of the 9,121 km long TEN-T Scan-Med (Scandinavian-Mediterranean) corridor (cf. Fig. 1, left) and cuts the alpine crest in the base, with high overburdens of up to 1740 m. It consists of two single-track railroad tunnels with a diameter of 8.1 m, accompanied by a continuous exploratory tunnel running 12 m below in between (Fig. 1, right). The exploratory tunnel improves the geological forecast for the rail tunnels, which are being advanced by tunnel boring machines afterwards.

Fig. 1. The Brenner Base Tunnel project (BBT SE 2024): Location within the Scandinavian – Mediterranean corridor (left) and schematic representation of the typical tunnel cross-sections (right)

Railway tunnels, especially in alpine regions, are bottlenecks, where the time of any interruption of the operation must be reduced to a minimum. This aspect of reliability is crucial for the overall infrastructure system due to the lack of redundancy. The optimization of the future availability of the BBT has therefore played a crucial role during tunnel planning as safety limits are increased to 200-year service life and maintenance work must be carried out without interruption of operation as far as technically feasible. Tunnel equipment has been shifted to accessible areas or high maintenance installation areas became accessible by horizontal shafts from the accompanying exploration tunnel. Additionally, the BBT-SE planned a structural health monitoring system for the construction and operation phase based on a distributed fiber optic sensing network among others, which is currently being implemented. Distributed Fiber Optic Sensors (DFOS) are advantageous compared to conventional techniques as the sensing cable can be directly embedded inside the structure. This enables distributed strain (and temperature) measurements of hundreds of sensing points without blind spots and therefore, an overall assessment of the structural utilization. The sensing unit itself may be placed even kilometers away from the measurement location and monitoring is possible