Study of ballastless track structure monitoring by distributed optical fiber sensors on a real-scale mockup in laboratory

Ballastless track structure are presently seen as an attractive alternative to conventional ballast. A new model was designed and a real-scale mockup was built and tested in fatigue test at IFSTTAR laboratory. To verify numerical simulations, the railway structure was monitored by conventional strain gages. A distributed fiber-optic strain sensing based on Rayleigh backscatter was also tested in this experiment. Fiber-optic cables were used as long-gage sensors and they were embedded in the concrete slabs of the structure. Firstly, we verified that the sensors were enough mechanical and chemical resistant for withstanding the stresses and the caustic environment experienced during concrete pouring process. Secondly, we validated the strain profiles measurements by comparison with the values obtained by strain gages. A good agreement was found throughout the duration of the fatigue test of 10 million cycles. Moreover, some cracks were observed early during the fatigue test. It is important to be able to monitor them during the service of ballastless track line. We showed that cracks can be detected and localized by fiber-optic distributed strain measurements. Finally, this experiment demonstrates that fiber-optic distributed strain sensing technique based on Rayleigh backscatter is a promising sensing technique to monitor ballastless track structures and more generally, civil engineering structures.