PSI - Issue 64

Christoph M. Monsberger et al. / Procedia Structural Integrity 64 (2024) 1665–1672 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1671

7

Fig. 6. Online visualization and analysis dashboard

The provided DFOS data (as exemplary shown in Fig. 6) is used to assess the load on the segmental lining at highly loaded tunnel sections or structural sections of interest, such as the opening sections. In general, the three recorded cross sections in circumferential direction within one segmental lining ring (cf. Fig. 2 and Fig. 4) allow an assessment of the segmental loading and its uniformity in the longitudinal direction of the tunnel. Local overload conditions within the cross-sectional strain profile can be also identified. Furthermore, the strain curve between the inner and outer reinforcement across the segment thickness can be defined by linear inter-/extrapolation of local strain values of both layers. The stresses across the segment thicknesses are derived based on the experimentally determined stress-strain curve of the utilized concrete. Finally, the normal force and the bending moment can be integrated to assess the load state of the segment lining. 5. Conclusion This paper demonstrates that distributed fiber optic sensors have significantly developed within recent years and are definitely capable for large-scale use in civil engineering applications. Known practical limitations can be overcome by suitable monitoring design and appropriate installation techniques, which also represent the DFOS technology path from fundamental research into innovative practice. It should be however highlighted that the quality of the monitoring approach is essentially related to its design and installation. It is therefore strongly recommended to include the monitoring design as early as possible into the project planning process, to use suitable, high-quality fiber optic components (i.e. interrogation unit and sensing cable) and to fit the sensor installation to the construction process and reduce any interruption on-site to a minimum. Machine-driven tunnel construction lots at the BBT project were already being tendered with enhanced fiber optic monitoring solutions, aiming to provide an overall assessment of the structural behavior. This especially beneficial with respect to long-term monitoring since arising changes in the structural performance can be detected at an early stage to plan and design predictive maintenance works in due time during the operational lifetime. The DFOS system is designed to provide measurements without any interference with the regular railway operation from the maintenance cross-passages, which can be accessed from the exploratory tunnel. This fact combined with the fiber optic’s insensitivity against electromagnetic interferences are essential for reliable sensing over decades.