Large-scale distributed fiber optic sensing network for short and long-term integrity monitoring of tunnel linings

Structural integrity assessment is essential in modern tunneling to ensure safe construction works. State-of-the-art monitoring approaches like displacement readings of geodetic prisms are often limited in the spatial as well as the temporal measurement resolution, which is why potential safety hazards might be overlooked. This paper introduces a large-scale distributed fiber optic sensing (DFOS) network inside the tunnel lining of a highway tunnel currently under construction in Austria. The tunnel construction site faces challenging geological conditions with loose rock excavation near to the surface with minimal covering. Fiber optic sensing cables were installed along both tunnel tubes to autonomously monitor 13 cross-sections of the primary shotcrete lining, about 220 m of the tunnel in longitudinal direction and 10 cross-sections of the secondary inner lining. Measurements are continuously evaluated and autonomously transferred to the geotechnical engineer on-site for further analysis. While the construction works are ongoing, alerts are additionally sent out automatically, if pre-defined thresholds are exceeded. The paper outcomes demonstrate that the innovative DFOS system immediately responds to structural modifications and, indeed, increases safety at the construction site.