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Li C.,Kunming University of Science and Technology | Zhao Y.-G.,Yunnan Aerospace Non Destructive Evaluation Co. | Liu H.,Yunnan Aerospace Non Destructive Evaluation Co. | Zhang Z.-L.,Yunnan Aerospace Non Destructive Evaluation Co. | And 4 more authors.
Structural Health Monitoring | Year: 2010

Fiber Bragg grating (FBG) makes excellent optical strain gauge with high sensitivity and lead-in fiber insensitivity and Brillouin OTDR offers a distributed sensing method along a sensing fiber. Considering the mismatch in the thermal expansion coefficients between fiber and host structure, the optothermo-mechanical equations of FBG sensor and Brillouin tight buffered fiber are conducted. By using temperature-compensated grating and fiber, FBG, and Brillouin measurement systems provide two independent ways to demodulate strain and temperature. The cross-check of redundancy strain and temperature proves the validity of measurement. According to the exploration of Bai Ni-jing No.3 Tunnel by using seismic CT, 110 gratings are installed on 10 monitoring cross sections; additionally, the four distributed Brillouin fibers are mounted along the three axis directions and 10 transects, and the coils of fiber are placed to independently measure the temperature at intervals of ∼24 m. The long-term measurements indicate that the thermal strain is closely related to the local temperature, but the pressure strain of the wall rock is derived from the deflective pressure of slide slope and rainfall. © The Author(s), 2010. Source

Li C.,Kunming University of Science and Technology | Li C.,Yunnan Aerospace Non Destructive Evaluation Co. | Li M.-J.,Kunming University of Science and Technology | Zhao Y.-G.,Yunnan Aerospace Non Destructive Evaluation Co. | And 6 more authors.
Journal of Applied Geophysics | Year: 2011

Ground penetrating radar (GPR) is a time-dependent geophysical technique for measuring the thickness of second lining, which is one of the most important tunnel quality targets. As the wave transmits from air (or the second lining) to the second lining (or the first lining), the Fresnel reflective coefficient is negative, i.e., the phase of reflective wave is reverse to the incident. In the one dimension time-waveform diagram (A-Scan) of GPR, the lining layers are located on the inflexions which are decided by Fresnel reflection coefficients and the attenuation coefficients of electromagnetic wave in the transmission medium. By towing the antenna over the tunnel surface, two dimension scanning data (B-Scan) is constituted by multiple A-Scan channels, where the grey scale is applied to the amplitude values. In the process of exploration, the lining interfaces are separately plotted by connecting each maximum peak point or second maximum peak point of A-Scan. In the Long Hai Tunnel, the artificial recognition provides 15 sampling values on the exploration line from D9. +. 015.195 to D9. +. 065.195. However, the automatic recognition can provide more information, such as average thicknesses, standard errors of lining thickness and the qualification rates of lining thickness, etc. © 2010 Elsevier B.V. Source

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