Initial situation, problem statement and motivation: Based on the long tradition of slender plain concrete tunnel lining in Austria and the collected experience with tunnels, it is nowadays usually possible to conclude the cause of typical crack patterns. However, a crack pattern catalogue with defined systematic general assessment criteria has not been drafted yet. Acquisition of crack patterns requires extensive manual effort, especially behind cladding / secondary lining. Existing methods for automated crack pattern acquisition lack reliability and robustness. A reliable measurement technique is needed that is able to capture crack pattern development over the lining area even behind claddings. A large amount of information based on measurement data reduces in principle the risk of unexpected damages, which justifies the application of monitoring techniques as compensation measure. Existing and already in tunnel applied distributed fibre sponsors cannot identify cracks satisfying due to insufficient resolution. However, a methodology for data processing, evaluation of uncertainties, crack propagation prognosis and consecutive condition assessment is still lacking.
Objective and innovation compared to the state of art: The objectives of the project are to harmonize assessment of crack pattern at plain concrete tunnel linings, to establish a basis for automate crack pattern acquisition and to derive a methodology for measurement-based assessment of damage hazard. Criteria for crack pattern evaluation will be formulated, using typical crack patterns that can be assigned to particular hazard levels or condition grades. The criteria will be clearly formulated, so that they can be implemented in software application. A measurement system based on Distributed Fibre Optic Sensing and Rayleigh back-scattering will be developed for tunnel application, which will measure the strain along the whole fibre length without spatial gaps. The measurement fibre technology as well as the crack detection algorithms will be adapted for application in tunnels and appropriate measurement concept will be drafted. Methodology for evaluation of uncertainties of identified crack patterns will be proposed. Algorithms for crack propagation prognosis based on measurement data will be proposed, and possible utilization of monitoring as compensation measure will be evaluated.
Expected results and findings:
- Crack pattern catalogue that typifies tunnel cracks phenomenologically and causally.
- Crack assessment regarding effect on load-bearing capacity, serviceability and durability.
- Fibre measurement techniques that capture strain along the fibre without gaps, calibrated in laboratory and tested in tunnel.
- Algorithms for crack detection based on strain data of measurement fibre.
- Measurement concept and data processing concept.
- Evaluation of uncertainties of crack patterns identified from measurements.
- Data-based crack propagation prognosis and feasibility of compensation measures.