Abstract
Compared with electrical strain gauges, fiber Bragg grating (FBG) sensing technology is a relatively novel method for tunnel structural health monitoring, which has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In order to study the internal force of the tunnel liner and detect the potential safety hazards, series of strain monitoring tests of a loess tunnel, taking into account the complex stress and strain variation of the loess during tunnelling, were performed by employing the tandem linear FBG sensor arrays controlled by the wavelength division multiplexing (WDM) technology. The concrete strain has obvious linear characteristics over time in the early stage and then gradually tends to a stable value. Moreover, after the necessary temperature compensation, loess tunnel structure safety was assessed through the analysis of real-time strain and internal force of the liner concrete, and the FBG monitoring data and safety assessment results indicate that the safety factors of various liner sections all meet the code requirements, which verify the safety and stability of the tunnel liner structure. The FBG sensors-based in situ monitoring technology can be well applied in the loess tunnel structure safety assessment.
Highlights
Geotechnical structures, such as dam, slope, foundation, and tunnel, are frequently subjected to dynamic loadings for instances seismic and construction loadings, which may result in structure deterioration or failure
Various monitoring instruments had been developed for tunnelling, such as laser displacement sensors (LDS), linear variable differential transformer (LVDT), dial gauges, and vision based systems [4,5,6]
fiber Bragg grating (FBG) sensors are encoded by wavelength, making the signal of FBGs immune to power fluctuations along the optical path, which have been shown to measure local and directional strains with accuracy compared to the conventional strain gauges and extensometers [17, 18]
Summary
Geotechnical structures, such as dam, slope, foundation, and tunnel, are frequently subjected to dynamic loadings for instances seismic and construction loadings, which may result in structure deterioration or failure. Weng et al [29,30,31] developed a FBG-based sensor network to monitor the strain distributions in the pavement structure, axial stress of tunnel anchor, and foundation settlement; the centrifugal model test was performed with an improved packaging and installation method for the quasi-distributed sensor system. In this study, based on a loess tunnel in Northwest China, a series of in situ monitoring of strain and stress in typical cross sections were conducted by employing quasi-distributed FBG sensors; the safety of tunnel liner structure was evaluated. The presented in situ monitoring and safety assessment of tunnel liner structure in loess stratum have the potential to be widely applied to the evaluation of the risk associated with underground excavation
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