In 2014, a system composed of fiber Bragg grating (FBG) sensors and a Micron Optics sm125 Optical Sensing Interrogator was installed by Kaisen to monitor the deformation profile of a tunnel during a geotechnical excavation sequence in South Korea. The goal of the installation was to monitor and detect any small dimensional changes to the shape of a tunnel running through a geological structure. These dimensional changes can be calculated from a series of strain measurements along the inner circumference of the tunnel.
For the strain measurements, a series of FBG sensors were embedded in a fiberglass reinforced polymer (FRP) carrier and spliced to a single FBG temperature sensor, which was used for thermal compensation of the strain gages. The sensors were all simultaneously measured using the sm125. Prior to installation, the linearity and repeatability of the FRP-FBG strain monitoring strips were verified through rigorous testing using a Shimadzu tensile strain testing machine.
The system has been in continuous operation and the results of the application will be available in the future. In addition to this project, there have been similar installations that have been completed to date including the Bea-hu-ryung Tunnel, the Song-jung Tunnel, the Map-dunjae Tunnel and the Kim-hye Tunnel.
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