Abstract
The weak parts of shield tunnels are not obvious, so it is urgently necessary to implement distributed monitoring based on an advanced sensing method. As the horizontal loads at both sides of the shield tunnel present a type of symmetric distribution, the deformation parameters under the vertical loads are often selected as the key monitored parameters, such as convergence, settlement, and seam opening. In this paper, the monitoring of the proposed deformation parameters is innovatively implemented with only one sensing technology, namely distributed optical-fiber strain sensing technology. First, the improved distributed optical-fiber sensors are introduced with the sensing performance. Second, a structural health monitoring (SHM) system for operational shield tunnels is proposed, including optical-fiber sensor installation, data logging and saving, key parameter analysis, and structural health assessment. The key monitoring theory and technology are also proposed. The proposed system has been verified by experiments at the Nanjing Yangtze River tunnel. In the experiments, the proposed optical-fiber sensors were installed on the surface of a selected tunnel ring, with a longitudinal span of approximately 90 m long. The experiments were conducted over 55 days to measure the distributed strain and temperature. Then the key parameters were obtained from the measurements, with which the structural health was assessed. The possibility that the shield tunnel SHM system can be constructed with the improved distributed optical-fiber sensors, monitoring theory, and technology is proven.
Highlights
Large-scale infrastructure is being constructed in many cities, such as subways and pathways that cross rivers or seas
The possibility that the shield tunnel structural health monitoring (SHM) system can be constructed with the improved distributed optical-fiber sensors, monitoring theory, and technology is proven
It is not easy to apply the methods from bridge or building SHM to shield tunnels, since there are obvious differences between the two types of structures
Summary
Large-scale infrastructure is being constructed in many cities, such as subways and pathways that cross rivers or seas. Due to its great sensing advantages, some researchers have applied the static load tests, these authors successfully obtained a continuous strain distribution along the to tunnel monitoring. BastianiniYong et al Ding obtained the strain a concrete bridge under system based distributed optical-fiber sensors [15]. The research was implemented basedtheonsensors distributed embedded in the structure, but for the existing shield tunnels, cannot optical-fiber be embeddedsensing inside technology. A new sensor structural was proposed them to monitor the internal forces.to monitor the shield tunnel displacement; the displacement wasthe applied to identify the level ofbased tunnelonhealth status.optical-fiber. The SHM system was proposed for shield tunnels applied during the operation period, and verified by field tests of the Nanjing Yangtze river tunnel
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