Discrete-Element Method Study of the Effect of Ballast Layer Depth on the Performance of Railway Ballast Bed

In the construction and maintenance of railway track systems, studying the influence of ballast depth on the performance of railway track structures is important to ensure the safety and sustainability of the built environment, and for making informed decisions on how to allocate resources and plan for the future. The present study uses the discrete-element method to study the mechanical behavior of the ballast, the permanent deformation, and the vibration of the railway track system under cyclic loading conditions. Ballast block and linear contact models are proposed to capture the overall behavior of the railway track system. According to the particle size distribution of the French railway ballast, 10 different shapes are created to form the ballast layers. Based on direct shear experiments, our model using a new set of parameters is able to correctly capture the dynamics response based on different depths of the ballast layer and different loading conditions including the rail speed and loads. The obtained bulk density of the ballast layer after being precompacted is equal to 1,280 kg/m(3). The ballast located vertically below the sleepers carries the largest contact force under cyclic loading, while the ballast located on the horizontal plane of the sleepers has the smallest contact force. Based on the stability of the ballast layer performance, a depth of 0.3 m for the ballast layer is recommended for high-speed and heavy-haul railway. The dynamics response at high speed and load suggests that in future experiments, the frequency should be increased to at least 25 Hz to obtain an accurate and realistic response. Our results conclude that the newly built railway track system needs to be precompacted, as then the ballast bed will be stable for future long-term use.