Monitoring of Railway Deformations using Distributed Fiber Optic Sensors

Natural phenomena like earthquakes, landslides, avalanches or mud flows can cause severe damages of railway tracks. Today’s monitoring concepts either focus on a permanent monitoring of known problematic sites or an epochwise measurement of the railway track with special measurement cars. In this paper we present a new approach for continuous monitoring of railway tracks over long distances. The new concept is based on optical fibers which are attached to the rail and depict occurring strain. The strain development can be measured with distributed fiber optic measurement instruments. Measurement ranges of several tenths of kilometers are possible with state-of-the-art equipment based on Brillouin backscattering. We report about the measurement concept and demonstrate how vertical and horizontal deformations can be derived from strain measurements. We also focus on technologic aspects such as precision, calibration and temperature compensation. Finally, the feasibility is shown in two field experiments. In the first experiment, an existing railway track was equipped with the fiber optic sensing cable and deformed. These deformations were depicted with the distributed fiber optic sensing system and compared to point-wise deformation measurements of a total station. In the second experiment we demonstrate that also small deformations caused for instance by the dead weight of a locomotive or passenger wagon can be measured reliably. As a conclusion distributed fiber optic sensors complement existing railway monitoring solutions and are well suited for the identification of problematic sites which have to be monitored additionally with total stations or GNSS sensors.