Rail track support condition monitoring with distributed acoustic sensing (DAS) system

Regular track support condition monitoring is critical for ensuring safe train operations and optimum scheduling of track maintenance activities. Unfortunately, most conventional monitoring systems cannot support continuous monitoring over long-track sections. Distributed Optical Fiber Sensing (DOFS) has recently been proposed as a viable alternative to accomplish this as it can measure mechanical and thermal strains over long distances. DOFS cables have been traditionally buried in the ground adjacent to the track. However, mounting the cable directly on the rail can give better information on wheel and rail defects and track support conditions. This paper presents findings from an ongoing research study aimed at investigating the feasibility of a type of DOFS called Distributed Acoustic Sensing (DAS) system for track support condition monitoring. Field testing was carried out, where a 50-m long track section was monitored using a DAS system. Two types of optical fiber cables were mounted to the rail using two different approaches. The instrumented track segment was loaded using a locomotive moving at speeds ranging from 16 km/h to 97 km/h. Varying track support conditions were simulated through strategic removal of selected crossties. Test results showed that the DAS system could capture variations in the rail strain caused by changes in support conditions under loading at different speeds. This study marks the first successful application of a DAS system for track support condition monitoring through direct mounting on the rail.