Investigations into the Critical Speeds in Ballasted and Ballastless Track

The modern high-speed railway usually consists of track structure, subgrade and soil layers. The existence of track structure and subgrade can both improve the critical speed of railway especially when the railway is built on soft soil layers. However, the role that the track structure played hasn’t been distinguished from subgrade. Therefore, further research is needed to investigate the difference of the critical speeds in ballasted and ballastless track. In this paper, two different types of track structures, ballasted and ballastless track, are built on the same subgrade-soil model using two-and-half-dimensional (2.5 D) finite element method to calculate the vibrations induced by the same high-speed trains. The rails, rail pads and ballast layer in ballasted track and rails, rail pads, slab, CA layer, concrete base in ballastless track are modelled as Euler–Bernoulli beams resting on the subgrade. The subgrade and soil layers are modelled by the 2.5D finite elements. The critical speeds in ballasted track and ballastless track are compared to reveal the consequence of track structure. It reveals that the critical speed in ballastless track is equal or greater than that in ballasted track. When the subgrade has enough stiffness, the critical speeds in both ballasted track and ballastless track can be the same. It can be concluded that the subgrade is more dominant than track structure in deciding the critical speed of railway.