Influence of non-linear soil properties on railway critical speed

The design of high-speed railway lines involves geotechnical challenges, one of which is the risk of dynamic track amplification, for example on track sections where the train speed approaches the track-ground critical speed. In these cases, soil strains increase significantly with an increase in train speed, far exceeding the limits of linear elastic behaviour. This can result in a non-linear reduction of soil stiffness. To better understand this relationship, this paper studies the influence of soil non-linearity on the critical speed of concrete slab and ballasted tracks. To perform an in-depth analysis into non-linear critical speed, two models are used: a 3D FEM approach, and a novel dispersion curve technique. Using the models, the effect of soil plasticity on non-linearity is studied, with different ranges of plasticity found to play an important role. Secondly, the influence of soil thickness and loading magnitude are evaluated. It is shown that ballasted tracks are deeply affected by the non-linear soil behaviour, compared to a concrete slab track. Further, it is shown that for the ballasted tracks, the relationship between the critical speed and shallow upper soil layer thickness can be weak.