Contribution for the modelling of three-dimensional granular matter : study of railway ballast.
Discrete element methods are an alternative to finite element approach to modelise the behaviour of granular materials. This work is devoted to the study of a granular matter submitted to cyclic loadings : the ballast of the railway track submitted to repeated train passing. We choose the NonSmooth Contact Dynamics approach for the resolution method, and we present all technical aspects for the two-dimensional and three-dimensional cases : contact detection algorithm between convex polygons and convex polyhedra, the kinematic parametrization, the resolution of the contact and friction problem. We investigate the best parameters for numerical computation of cyclic loadings. In the following we present some results in order to show the ability of discrete element methods to describe the behaviour of granular matter under cyclic loading. A comparison between experiment and numericals computations underline the special behaviour of this kind of system. We focuse on the thin granular layer behaviour with a specific mechanical reponse due to the creation of special structures. The three-dimensional model has been used as an example to study well known behaviour of masonery structure. We present a numerical study of lateral resistance of railway track based on an experiment with digitised ballast grains.