A numerical study on the influence of backfill settlements in the train/track interaction at transition zones to railway bridges

Railway track degrades more quickly in the transition zones between embankments and bridges, mostly due to the development of settlements in the backfill. This amplifies the dynamic train/track interaction forces and accelerates the deterioration of the components of both the track and the vehicles. Consequently, it induces additional maintenance costs, reduces passenger comfort and, ultimately, it may affect train safety at transition zones. To address this problem and to obtain more insight into the influence of the settlement profiles of the backfill in the train/track system, nonlinear dynamic analyses were performed using a transition zone model to simulate different settlement profiles of the backfill. In some cases, the results showed significant amplifications of axle accelerations and loads. In general, the greater the number of hanging sleepers and their gap sizes, the higher the vertical accelerations of the sleepers and the larger the vertical contact forces between the sleepers and the ballast layer. Settlement profiles associated with backfills with a wedge shape seem to limit these negative aspects.