Mapping Relationship between Rail Deflection of Slab Track and Subgrade Settlement

In order to investigate the effect of subgrade settlement on the track geometry of the slab track, a calculation method for the mapping relationship between rail deflection and subgrade settlement was proposed, aiming at both longitudinal connected track and unit slab track of high-speed railways. The method is based on the theory of composite beams on tensionless Winkler foundation, which takes into account the potential voids between the bottom slab and the subgrade. The characteristics of the rail deflections of the aforementioned tracks, induced by different settlement profiles, were investigated and compared. The results show that in terms of the adaptability to the subgrade settlement, the longitudinal connected track is inferior to the unit slab track, while the large-scale unsupported area is more likely to be induced between the longitudinal connected track and subgrade. The difference in rail deflection between the two tracks is significantly aggravated by the amplitude of the subgrade settlement. The rail deflection is also sensitive to the settlement wavelength. When the wavelength is extended to 20 m, the number of voids under the track are significantly reduced and the rail deflection is basically in accordance with the subgrade. The influence of angular-type differential settlement on the deflection is relatively low, while the faulting-type settlement always results in severe rail deflection and voids. For instance, the maximum depth of void reaches approximately 8 mm when the faulting is 10 mm. The induced track irregularity and voids may pose threats to the train's operation quality and the fatigue behaviour of the track structure.