Dynamic evaluation of vehicle-slab track system under differential subgrade settlement in China?s high-speed railway

Differential settlement is inevitable in soil subgrade which has a direct impact on the service performance of ballastless track systems and the running quality of high-speed trains. In order to estimate the effect of differential subgrade settlement on the dynamic performance of the vehicle-slab track system, a detailed theoretical model considering nonlinear subgrade support and track weight is established. The filtering effect of the layered composite track structure on the subgrade settlement is taken into account. Related dynamic performance indexes are evaluated in terms of running safety and ride comfort of high-speed trains as well as the dynamic performance of the infrastructure, to obtain a control threshold of the differential subgrade settlement for the slab track system of China's high-speed railway. The results show that the uncoordinated deformation between the slab track and the subgrade has significant influence on the dynamic characteristics of the system. Compared with the running safety, the ride comfort of the vehicle and the dynamic performance of the track structure are more susceptible to the differential subgrade settlement. The relative short-wave differential settlement below 20 m has significant impact on the track and subgrade vibration, especially the dynamic rail displacement. The differential settlement with a wavelength above 20 m is more detrimental to the car body acceleration, namely the ride comfort. In particular, a sensitive wavelength of the differential subgrade settlement at 10-20 m poses a high jumping derailment risk to the running safety. Accordingly, the dynamics-based control thresholds of differential subgrade settlement are put forward for different settlement wavelengths.