A 2.5D Coupled FE-BE Methodology for the Prediction of Railway Induced Vibrations

Summary

Ground vibrations induced by railway traffic are often studied by means of two-and-half dimensional (2.5D) models that are based on the longitudinal invariance of the track geometry. In this paper, a 2.5D methodology is used where the finite- element method is combined with a boundary-element method, based on a regularized boundary integral equation. In the formulation of the boundary integral equation, the Green’s functions of a layered elastic half space are used, so that no discretization of the free surface or the layer interfaces is required. The methodology is applied to two cases. In the first case, two alternative models for a ballasted track on an embankment are compared. In the first model, the ballast and the embankment are modeled as a continuum using 2.5D solid elements, whereas a simplified beam representation is adopted in the second model. A very large difference is found for the free field mobility of both models, which demonstrates the need for detailed 2.5D modeling of the embankment. In the second case, the efficiency of a vibration isolating screen is studied. A vibration isolating screen is a soft or stiff wave barrier. Due to the impedance contrast between the isolating screen and the soil, incident waves are reflected. As a result, the vibration levels behind the screen are effectively reduced. Both examples demonstrate that the use of detailed 2.5D models result in a better insight in the mechanical behavior of the coupled soil-track system.