Investigation into the critical speed of ballastless track

As train speeds are increased, the issue of the critical speed must be faced, especially when tracks run across soft ground. This is the phenomenon describes the amplification of the track deflections due to coincidence of the train speed with the wavespeeds of the underlying ground. Modern high-speed lines are often constructed on ballastless track which has different dynamic behaviour to conventional ballasted track. Therefore, further research is needed to investigate the critical speed of ballastless track. In this paper, a dynamic analysis model comprising track, embankment and ground is presented based on the two-and-half-dimensional (2.5D) finite element method to predict the vibrations generated by train moving loads. The rails and track slab are modeled as Euler-Bernoulli beams resting on the embankment. The concrete base, embankment and ground are modeled by the 2.5D finite elements. The results show that the critical speed of ballastless track is higher than the Rayleigh wave velocity of the underlying soil and quite close to the Rayleigh wave velocity of the subgrade. The existence of the subgrade can highly improve the critical speed of the ballastless track even with a shallow subgrade of 1.25m depth. The underlying soil stiffness is the conclusive factor in determining the track vibration amplitude. It is also found that the embankment plays an essential role in reducing the inhomogeneity of the lateral stress distribution and the amplitude of vertical stress in ballastless track.