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Damage Detection and Evaluation for an In-Service Shield Tunnel Based on the Monitored Increment of Neutral Axis Depth Using Long-Gauge Fiber Bragg Grating Sensors

1
College of Civil Engineering, Fuzhou University, Fuzhou 350108, China
2
Zhongtian Construction Group Zhejiang Steel Structure Co., Ltd., Hangzhou 310008, China
3
Fujian Provincial Key Laboratory of Advanced Technology and Informatization in Civil Engineering, Fujian University of Technology, Fuzhou 350118, China
*
Author to whom correspondence should be addressed.
Sensors 2019, 19(8), 1840; https://doi.org/10.3390/s19081840
Received: 24 February 2019 / Revised: 8 April 2019 / Accepted: 10 April 2019 / Published: 18 April 2019
(This article belongs to the Special Issue Smart Sensors and Smart Structures)
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Abstract

It is difficult to detect and evaluate the structural damage in a shield tunnel during operation because many traditional techniques based on the observation of vibrations are limited in daily monitoring in tunnels. Thus, the curvature radius of a static longitudinal settlement curve is used to identify the residual health and safety of an in-service shield tunnel. However, there are still two problems. The curvature radius is suitable for a qualitative judgment rather than a quantitative evaluation for longitudinal damage detection. Moreover, the curvature radius, which is calculated from the measured settlements of three neighboring points, gives an average damage degree in a wide scope only and is difficult to use to identify the damage’s precise location. By means of the analysis of three kinds of longitudinal failure modes in a shield tunnel, this paper proposes: (1) a damage detection method based on the monitored increment of the neutral axis depth; and (2) an index to evaluate longitudinal damage. The index is composed of the residual ratios of the equivalent flexural stiffness (HFM1) and the equivalent shear stiffness (HFM3). The neutral axis position and the proposed damage index can be determined using long-gauge Fiber Bragg Grating sensors. Results from numerical simulations show that the deviation between the HFM1 and the true value residual ratio of the equivalent flexural stiffness is no more than 1.7%. The HFM3 is equal to its true value in the entire damage process. A loading experiment for a scaled-down model of a shield tunnel using long-gauge Fiber Bragg Grating sensors indicated that the errors in the HFM1 were no more than 5.0% in the case of early damage development (HFM1 ≥ 0.5). The maximum error did not exceed 9.0% even under severe damage conditions in the model. Meanwhile, the HFM3 also coincided with its true value in the entire testing process. View Full-Text
Keywords: damage detection; damage evaluation; shield tunnel; neutral axis depth; long-gauge Fiber Bragg Grating sensors damage detection; damage evaluation; shield tunnel; neutral axis depth; long-gauge Fiber Bragg Grating sensors
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Shen, S.; Lv, H.; Ma, S.-L. Damage Detection and Evaluation for an In-Service Shield Tunnel Based on the Monitored Increment of Neutral Axis Depth Using Long-Gauge Fiber Bragg Grating Sensors. Sensors 2019, 19, 1840.

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