Numerical study of railway track ballast behaviour

Details

Supervisors

Docquier, Nicolas ; Fisette, Paul

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil des constructions

Abstract

The railway companies use faster and faster trains and can carry more and more people and goods, increasing maintenance requirements needs due to the increased loads induced by the train. This is due to two main reasons: the rails are welded together and the longitudinal expansion is prevented, causing a buckling that pushes the ballast outwards. In addition, the trainloads apply forces on the sleeper causing it to settle and deform the ballast. With this thesis, a numerical study of the behaviour of the track ballast is developed so that it can be effectively compared with the results obtained through laboratory tests. For this to happen, it was decided to use the LMGC90 software developed by the Université de Montpellier, which is dedicated to the modelling of granular material, such as the railway ballast. Although over the years there have been numerous improvements in the elements that make up the track, the ballast has not undergone particular changes. This was modelled using the granular model, the one that best describes the behaviour of the ballast and the resistance to lateral forces and its settlement caused by the application of sinusoidal forces on the sleeper. In the first part, as for the lateral resistance, simulations have been carried out which have shown the validity of the modelling, according to the different profiles of the ballast bed, its compactness, and the friction coefficients. Moreover, the graph of the lateral resistance as a function of the movements of the sleeper was found to have a consistent behaviour with the tests carried out in the laboratory. In the second part, graphs were obtained showing the settlement of the sleeper as a function of the stiffness and the number of elastic layers, as well as of the type of force applied to the sleeper. These were compared with curves in the literature, demonstrating the constant presence of three phases in the graphs. Furthermore, the field of accelerations, velocities, and frequencies in the ballast has been studied. Finally, this thesis mentions possible improvements for future developments.