Normalised curvature square ratio for detection of ballast voids and pockets under rail track sleepers

After a railway track experiencing dynamic loading, the track settles and causes ballast to deform, spread and sometime damage. Without appropriate maintenance, void and pocket of ballast underneath railway sleepers can establish overtime and impair the ride quality of train services. In this study, the emphases will be placed on the application of non-destructive vibration-based technology, to investigate and evaluate dynamic characteristics of voided railway concrete sleepers, which are the fundamental element to provide track support to railway systems. The study has developed a curvature-based damage detention method to identify ballast voids under railway track sleepers. This method can be easily deployed in the field by using fibre bragg grating strain sensors to measure strains for curvature analysis. In this study, the assumption is that the time-dependent material degradation negligibly affects the curvature ratios. The dynamic finite element model has been established and validated for railway sleepers in the field. A variety of losses of ballast support have been simulated using the validated model. The dynamic mode shape has been analysed to evaluate curvature ratios under different types of ballast losses. Although the method provides positive outcomes, the advantages, disadvantages and limitation of the method are then identified and discussed.