Dynamic Behaviour of Ballast Under Hanging Sleepers in Railways Track Transition Zones Using Fem-Dem Method

Abstract

Transition zones in railways are the locations with considerable changes in the vertical support due to the sudden stiffness change and differential settlement, which requires higher maintenance costs. Hanging sleepers are one of the most common defects in transition zones, which can cause a significant increase in sleeper velocity and ballast stress, leading to poor elasticity and drainage of tracks and spreading the issue to adjacent sleepers. To accurately study the dynamic behaviour of ballast particles under hanging sleepers in transition zones, a FEM-DEM method is developed, which consists of a FEM model simulating the train-track interaction in a transition zone and a DEM model simulating sleeper-ballast particle interaction of a hanging sleeper. The movement of the hanging sleepers under train passing is simulated in the FEM model and used as the input for the DEM method to calculate the detailed behaviour of ballast particles. The dynamic behaviour of ballast under multiple hanging sleepers in transition zones under good, moderate, and degraded conditions are studied using the FEM-DEM method. The main finding is that most contact forces between ballast particles under the hanging sleeper are small in all cases, which are between 0.1 kN and 0.5 kN. As the sleeper force increases, the contacts in the range of 0.5 kN and 2 kN become more and scattered distributed. It indicates that during the track degradation process, a high sleeper force tends to cause a wide range of small damage to the ballast rather than a small range of larger damage.

Keywords: Track transition zone, Dynamic behaviour of ballast particles, Hanging sleeper, FEM-DEM method