Dark Fibre Optic Cables for Shallow Ground Charactrization alongside Railroads
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In order to determine the ‘critical train speed’ phenomenon, it is necessary to determine the surface wave velocity. To do this we used an existing fibre optic telecommunication cable along 5 km of the railway track. We evaluated the feasibility of using this cable as a Distributed Acoustic Sensors (DAS) for shallow ground characterisation along the railway track and using the running trains as a seismic source [1]. The received data were utilized to retrieve coherent and multimodal Rayleigh waves at various soil conditions. After recording several 10 hours of train passages we extracted the energy Rayleigh waves by utilizing seismic interferometry method [2]. The seismic interferometry processing provided virtual broadband shotgathers with coherent and clear surface wave trends. The retrieved dispersion curves allowed us to determine the S-wave velocity profile at a minimum depth of exploration of 2.0 m. The measured Rayleigh waves and computed S-wave velocities are comparable to reference values measured with standard Geophones (MASW) and other technical data available at the test segment.