Dynamic train-track interaction over inhomogeneous foundations

The support conditions of railway tracks usually continuously vary along the longitudinal direction of the track. On the free track, this variation is caused by the varying geotechnical properties of foundation layers, varying embankment heights, cut and fill transitions, passage over culverts, existence of switches and crossings, transition zones to bridges or tunnels, which many times result in differential settlements and hanging sleepers. In view of this, important stiffness variations are not restricted to locations where special technical blocks were built, such as at the entrance to bridges or switches. The existence of local soil deposits or when the railway line needs to cross small valleys are examples of inhomogeneous scenarios corresponding to local changes of the track support with potential impact on the train-track interaction. This paper shows how situations of inhomogeneous track support corresponding to local deposits of soils with different geotechnical properties may influence the train-tracksupport system response. The case-study is defined from the available data from a recently built railway line in Portugal, which included a stiffness evaluation and the track geometry measurements. A numerical model of the selected case-study is then built using a three-dimensional finite element dynamic analysis tool, considering the train-track-ballast-soil interaction and coupling.