Non-smooth contact dynamic approach for railway engineering: investigation of ballast behaviour under stabilisation process

Railway maintenance procedures include the stabilisation of ballasted tracks. The procedure of dynamic stabilisation which consists in vibrating laterally the rail while applying a vertical load is analysed using a discrete element code based on non-smooth contact dynamics. The ballast stones are modelled realistically using polyhedrons based on real ballast stones scans. The evolution of the compaction level and contact number between particles is analysed during the dynamic stabilisation process. A model is proposed to predict settlement. The results of simulation show the effectiveness of this maintenance procedure. It also points out the relevance of the model to predict settlement

Modelling realistic ballast shape to study the lateral pull behaviour using GPU computing

The use of the Discrete Element Method to model engineering structures implementing granular materials has proven to be an efficient method to response under various behaviour conditions. However, the computational cost of the simulations increases rapidly, as the number of particles and particle shape complexity increases. An affordable solution to render problems computationally tractable is to use graphical processing units (GPU) for computing. Modern GPUs offer up 10496 compute cores, which allows for a greater parallelisation relative to 32-cores offered by high-end Central Processing Unit (CPU) compute. This study outlines the application of BlazeDEM-GPU, using an RTX 2080Ti GPU (4352 cores), to investigate the influence of the modelling of particle shape on the lateral pull behaviour of granular ballast systems used in railway applications. The idea is to validate the model and show the benefits of simulating non-spherical shapes in future large-scale tests. The algorithm, created to generate the shape of the ballast based on real grain scans, and using polyhedral shape approximations of varying degrees of complexity is shown. The particle size is modelled to scale. A preliminary investigation of the effect of the grain shape is conducted, where a sleeper lateral pull test is carried out in a spherical grains sample, and a cubic grains sample. Preliminary results show that elementary polyhedral shape representations (cubic) recreate some of the characteristic responses in the lateral pull test, such as stick/slip phenomena and force chain distributions, which looks promising for future works on railway simulations. These responses that cannot be recreated with simple spherical grains, unless heuristics are added, which requires additional calibration and approximations. The significant reduction in time when using non-spherical grains also implies that larger granular systems can be investigated

Modelling realistic ballast shape to study the lateral pull behaviour using GPU computing

The use of the Discrete Element Method to model engineering structures implementing granular materials has proven to be an efficient method to response under various behaviour conditions. However, the computational cost of the simulations increases rapidly, as the number of particles and particle shape complexity increases. An affordable solution to render problems computationally tractable is to use graphical processing units (GPU) for computing. Modern GPUs offer up 10496 compute cores, which allows for a greater parallelisation relative to 32-cores offered by high-end Central Processing Unit (CPU) compute. This study outlines the application of BlazeDEM-GPU, using an RTX 2080Ti GPU (4352 cores), to investigate the influence of the modelling of particle shape on the lateral pull behaviour of granular ballast systems used in railway applications. The idea is to validate the model and show the benefits of simulating non-spherical shapes in future large-scale tests. The algorithm, created to generate the shape of the ballast based on real grain scans, and using polyhedral shape approximations of varying degrees of complexity is shown. The particle size is modelled to scale. A preliminary investigation of the effect of the grain shape is conducted, where a sleeper lateral pull test is carried out in a spherical grains sample, and a cubic grains sample. Preliminary results show that elementary polyhedral shape representations (cubic) recreate some of the characteristic responses in the lateral pull test, such as stick/slip phenomena and force chain distributions, which looks promising for future works on railway simulations. These responses that cannot be recreated with simple spherical grains, unless heuristics are added, which requires additional calibration and approximations. The significant reduction in time when using non-spherical grains also implies that larger granular systems can be investigated

Wear of sharp aggregates in a rotating drum

Aggregates constituting ballast layer wear due to the continuous passage of trains and during the necessary maintenance operations of the track. In order to develop efficient solutions for ballasted tracks design and maintenance, a proper knowledge of the degradation laws of ballast grains is needed. In tribology, the amount of wear due to friction when two surfaces are in contact is classically predicted by Archard’s equation. However, due to the continuous evolution of grain angularity and roughness, at the macro-scale wear coefficient cannot be assumed to remain constant, but will depend on the state of degradation of the grain surface. In order to adjust the model to this particular case, the Micro-Deval Attrition test is used. The rotating drum is stopped at intermediate stages and the amount of generated fine particles is measured. Thus the curve of mass loss along time is built. These results are then linked to Archard’s model using the values of contact forces and relative displacements extracted from discrete element simulations. Finally, a morphology analysis is performed tracking shape and roughness parameters at different stages of degradation using X-ray tomography and a laser profilometer

Évaluation des apports de géogrilles dans une structure d’assise ferroviaire en conditions opérationnelles

Dans le cadre de la réhabilitation des lignes ferroviaires classiques (vitesse ≤ 220 km/h), SNCF Réseau propose d’intégrer l’utilisation de géogrilles afin d’optimiser et adapter le dimensionnement des structures d’assises à l’évolution du trafic. Ainsi, plusieurs expérimentations ont été mises en place pour étudier le comportement de géogrilles sous conditions opérationnelles et quantifier leurs apports en termes d’amélioration de portance et de limitation de tassements différentiels. Ces expérimentations in situ comprennent la rénovation, l’instrumentation et le suivi de sections de voies. Elles fournissent des données sur le comportement réel des structures d’assises en ce qui concerne des facteurs tels que le chargement dynamique, le confinement latéral, les variations saisonnières, etc. Cet article présente la mise en place et les premiers résultats d’une telle expérimentation. Les premiers résultats indiquent que l’installation de géogrilles a un impact positif net, notamment grâce à une meilleure répartition de la contrainte dans la structure d’assise. Une mobilisation des géogrilles a été observée par des mesures de déformations de leurs brins transversaux, confirmant ainsi que les granulats sont confinés latéralement par l’enchevêtrement des grains dans les ouvertures de la géogrille. Malgré ces résultats encourageants, ce projet de recherche n’en est encore qu’à ses débuts. Les expérimentations sur le terrain nécessiteront encore plusieurs années de suivi avant que l’on puisse se prononcer définitivement sur l’apport quantitatif des géogrilles dans ce cas d’application

X-ray CT analysis of the evolution of ballast grain morphology along a Micro-Deval test: key role of the asperity scale

International audienc

Wear of sharp aggregates in a rotating drum

International audienceAggregates constituting ballast layer wear due to the continuous passage of trains and during the necessary maintenance operations of the track. In order to develop efficient solutions for ballasted tracks design and maintenance, a proper knowledge of the degradation laws of ballast grains is needed. In tribology, the amount of wear due to friction when two surfaces are in contact is classically predicted by Archard’s equation. However, due to the continuous evolution of grain angularity and roughness, at the macro-scale wear coefficient cannot be assumed to remain constant, but will depend on the state of degradation of the grain surface. In order to adjust the model to this particular case, the Micro-Deval Attrition test is used. The rotating drum is stopped at intermediate stages and the amount of generated fine particles is measured. Thus the curve of mass loss along time is built. These results are then linked to Archard’s model using the values of contact forces and relative displacements extracted from discrete element simulations. Finally, a morphology analysis is performed tracking shape and roughness parameters at different stages of degradation using X-ray tomography and a laser profilometer

Sleeper geometry investigations using discrete element modelling and the box test apparatus

This paper evaluates the performance of two types of railway sleeper in a box test apparatus. A laboratory investigation and discrete element modelling (DEM) of the box tests were conducted to ascertain the impact of using a rectangular section and an inverted U-shaped section as railway sleepers on track settlement and ballast-sleeper interaction. Outputs from the modelling and experimental approaches have been found to be comparable and consistent

Non-smooth contact dynamic approach for railway engineering: investigation of ballast behaviour under stabilisation process

Railway maintenance procedures include the stabilisation of ballasted tracks. The procedure of dynamic stabilisation which consists in vibrating laterally the rail while applying a vertical load is analysed using a discrete element code based on non-smooth contact dynamics. The ballast stones are modelled realistically using polyhedrons based on real ballast stones scans. The evolution of the compaction level and contact number between particles is analysed during the dynamic stabilisation process. A model is proposed to predict settlement. The results of simulation show the effectiveness of this maintenance procedure. It also points out the relevance of the model to predict settlement