Full-scale numerical calculation of ballasted tracks with the Discrete Element Method

Rail transport, both for people and goods, is becoming increasingly significant all over the world, which is reflected in the great growth of conventional and high-speed train lines. Most of these infrastructures are built with railway ballast, a granular material whose main functions are to resist vertical and horizontal loads and to face climatic actions. The growing popularity of these infrastructures has led to the development of numerical models to evaluate their performance. Among a wide range of numerical methods, the Discrete Element Method (DEM) was found to be effective for evaluating the performance of granular materials. This approach considers their discontinuous nature and has proven to be a useful tool to determine the dynamic behaviour of groups of particles. Moreover, the DEM is also used to compute the behaviour of continuum materials. In this work, rails and bearing plates are characterised in the calculations using this methodology, called the bonded DEM. It is a modification of the classical DEM which assumes that bonds exist between particles, resisting their separation. The code used is developed within DEMPack, a specific software tool for modelling physical problems using the DEM. Currently, DEMPack allows the use of two different types of geometry: spheres with rolling friction and clusters of spheres. A previous analysis showed that spheres are more effective for studying the macroscopic behaviour of the ballast layer, while clusters are necessary for small-scale tests involving highly compacted particles since their results are greatly influenced by particles and contacts distribution. After calibrating the code, full-scale tests were performed applying the load of a high-speed train on a railway track section in different situations. Considering the amount of material (about 260,000 particles) and that the aim is to evaluate the deflection of the rails, the calculations are carried out using spheres. The numerical results correctly capture the effect on the deflection of the rails. It can be concluded that the DEM increases the possibilities for analysing innovative solutions since real case-scenarios can be studied with enough accuracy and feasible time