Description
Distributed fibre optic sensing (DFOS) is increasingly being used in civil engineering and geotechnical applications. The key feature, and advantage over conventional point-based measurement methods, is the ability to measure the selected physical quantities continuously over the length of the structure, from a few centimetres to several hundred kilometres. The benefits of this technique are therefore particularly evident when monitoring linear structures such as roads, embankments, bridges, tunnels, pipelines or railway lines. The result of the measurement is not a single value at a selected point on the structure at a given time, but a profile of strains, temperatures, displacements or vibrations, both as a function of time and as a function of length. This allows direct detection of local events such as cracks, stress concentrations, buckling, sinkholes, leaks and others.
The article describes the pioneering application of the DFOS system using composite and monolithic sensors bonded directly to the rail. The monitoring system was launched in early 2023 in central Poland. In total, more than 2,000 metres of sensors have been installed on selected sections, making it the largest system of its kind in the world. Measurements are made on a long-term basis as part of cyclical sessions (with changing external conditions), as well as on a short-term basis (dynamic) during train passes. As the same DFOS sensors can be connected to different optical interrogators (using Rayleigh, Brillouin or Raman scattering), different system outputs can be generated (e.g. strains, displacements or vibrations). The paper summarises the lessons learne
