Effects of Dynamic Excitations Due to Very Fast Trains on the Instability of Railway Rock Ballast

Abstract

It is well known that during the passage of very fast trains (VFT), ballast aggregates can vibrate violently resulting in ballast instability. A simple two dimensional model of the railway track system was proposed, consisting of a sleeper, loose ballast rocks in contact under Coulomb dry friction, compacted rocks and soil foundation. The dynamic behaviour of the system caused by the transient axle load of a single bogie was investigated by explicit finite element method (FEM). It was found that the sleeper exhibits a residual settlement due to irreversible displacement of the ballast rock aggregates. The settlement is maximum at train speed around the Rayleigh wave speed. Similar behaviour was observed for transient force due to two and four closest set of bogies. The simple model shows promising results in investigating this non-linear, irreversible phenomenon and should be extended to more complicated representation of the ballast aggregates under transient forces due to the whole train.