11. Deformation Detection System for Geotechnical Structures Using Optical Fiber

      To predict phenomena such as disasters on linear structures, including railways, it is necessary to continuously measure and control deformation over the whole structures. For measurement of geotechnical structures such as embankments or ground, sensors require a high level of durability and corrosion resistance.
      Previously developed sensors are intended for measurement at ground level rather than for insertion into the ground. A sensor and a system to measure strain in the ground accurately, easily, and continuously were therefore developed. The system can determine strain from changes in Brillouin light scattering by the deformation of an optical fiber, as well as pinpointing the location of strain by the return time of such scattering. Optical fiber has high signal transmission capacity and can measure strain continuously over long distances, providing linear and planar information. As the optical fiber is relatively resistant to age deterioration, it is highly reliable as a sensor.
      The optical fiber sensor developed is made by attaching optical fiber to the plate substrate forming an ellipse (Fig. 1). Using this formation, linear and planar strain can be sensed with high precision. The sensor is corrosion resistant because FRP and flexible epoxy are used as the substrate. Since it can be rolled, it provides good workability and excellent transportation for long-dimension sensors (Fig. 2). Making use of these features, the sensor can be used for deformation measurement in the ground near excavation work, as well as for measurement management at landslide locations and embankments. The sensor can also easily be linked to optical fiber sensors used in other wooden structures, opening up the possibility of comprehensive measurement.

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