A theoretical study on the influence of the track on train-induced ground vibration

An investigation is presented on the nature of train-induced ground vibration propagation. It is based on a theoretical model for the track and a layered ground. Results are given of the responses of the ground and track to a moving harmonic or quasi-static load on the rails. The dispersion characteristics of the propagating modes of vibration in the track and the ground are presented and the excitation of vibration in the ground via the track is discussed in relation to these propagating wavenumbers. An important feature of the coupled system is the coincidence of a propagating wavenumber in the track and the ground that gives rise to the main peak in the vibration spectrum in the frequency range of interest. It has been observed, in some cases, that when the train speed reaches a value close to the speed of propagating waves in the ground, the response to the quasi-static axle loads of the train reaches a peak. The relationship between this critical speed and the wave speeds in the track and ground is considered in order to investigate the effectiveness of controlling this peak response load speed by increasing the bending stiffness of the track/embankment structure or by reducing its mass. It is found that such treatments may, or may not, have a significant effect depending on the ground stiffness and layering. For the multiple quasi-static moving axle loads of a train the loading has strong, closely spaced harmonic components. The effect on the vibration spectrum of the superposition of vibration from multiple axles is shown to lead to the reinforcement or suppression of some frequencies as a function of axle spacing and speed. This is demonstrated with calculated results.