Influence of ballast heterogeneity on railway induced vibrations and identification of heterogeneous properties of a ballast layer

In the context of railway induced vibration, the excitation induced by a passing train can be separated into a quasi-static and a dynamic component. The quasi-static component is related to the weight of the train transmitted through the wheels to the track. The dynamic component is related to the dynamic train-track excitation resulting from the irregularities of the running surfaces or from the variation of the track stiffness. At sub-Rayleigh speed on a track with longitudinally invariant properties, quasi-static excitation has no significant influence on the far-field vibration. In this paper, a randomly-fluctuating heterogeneous continuum model of the ballast layer is considered. Mechanical properties are represented as 3D random fields. First, the influence of ballast heterogeneity on the vibration field induced by a moving load is studied. The results show that heterogeneity is responsible for the generation of waves propagating away from the track. Then an identification process of the heterogeneous model of the ballast is presented based on experimental measurements of train passages.