Modelling critical velocities on soft soils using Finite Element Methods

This paper investigates critical velocity effects and predicts the response of high speed rail lines constructed over soft soils. It is of benefit to designers for the prevention of passengers discomfort and the improvement of safety criteria. As train speeds approach the critical velocity of the underlying soil, ground Mach cones can develop. This phenomenon is associated with the generation of surface waves and ground vibrations beneath the track, and can increase the risk of track damage. Critical velocity is lower for a site with soft soil, thus making these the primary areas of concern. To study the problem, a three-dimensional model of Ledsgaard, a high speed rail site with soft soil in Sweden, is developed. The model follows the Finite Element Method and operates in the time domain. The outcomes of the simulations are presented in terms of vertical deflections and the dynamic behaviour of the ground. The critical velocity effects are observed and the relationship between train speed and track vibrations is presented.