The effect of track unevenness correlation on railway induced ground vibration

This paper focuses on quantifying the level of correlation of the track loading at the wheel/rail interface due to rail unevenness and its influence on predictions of ground vibration. The extent to which the unevenness of the two rails is correlated has been estimated from measurements of track geometry obtained with track recording vehicles for six different tracks. It was found that for wavelengths longer than about 3 m the unevenness of the two rails can be considered to be strongly correlated and in phase. To investigate the effect of this on ground vibration, a railway model that works in the wavenumber-frequency domain and includes separate inputs on the two rails has been used. In this model, the track is assumed as an infinite invariant linear structure resting on an elastic stratified half-space. This is excited by the gravitational loading of a passing train and the irregularity of the contact surfaces between the wheels and the rails. The railway model can account or discard the effect of load correlations on the two rails beside the effects of variation of the tractions across the width of the track-ground interface and the vehicle sprung mass, as well as the roll motion of the sleepers and the axle. A comparative analysis is carried out on the influence of these factors on the response predictions using numerical simulations. It is shown that, when determining the vibration in the free field, it is important to include in the model the non-symmetrical loading at the two rails that occurs for unevenness wavelengths shorter than about 3 m