Granular Media and Ballasted Railway Tracks Milieux Granulaires Et Voies Ballastées

Abstract

Since the beginnings of the railway track, ballasted track is widely employed because of its mechanical properties and its exibility for construction and maintenance but also for their capacity to fulfil the mechanical requirements fixed by the transport of heavy loads at a long distance. The study of the track deterioration is one of the principle assignments in railway engineering, specially for SNCF to preserve a good quality of track and to ensure the comfort and the safety of circulation.

In spite of the experience on the railway track structure, the lifespan of a railway remains difficult to estimate and the mechanisms that lead to its deterioration remain insufficiently known. The answers come primarily from experiments or an empirical approach. A SNCF research project is to study the behaviour of the ballast so as to integrate this understanding in a strategy of control of the costs for the design and the maintenance, in particular the renewal of the railway.

In this context, it appears necessary to improve the understanding of the fundamental mechanisms that lead in the medium-to-long term to the appearance of the track defects. The simulation methods resulting from research on the granular medium yielded significant results in Civil Engineering which can be applied to railway problems and make it possible to study the phenomena related to the microstructure of the ballast. The interest of these methods was largely improved by work of Professor J.J. Moreau, in particular on the avalanches and old monuments (Moreau, 2000).

The work performed at SNCF in collaboration with LMGC concerns the development of a two-dimensional and a three-dimensional discrete element software using the platform LMGC90 to study the ballast behaviour (Saussine et al, 2004). The first step is to provide validations through comparisons with some existing experiments or developed for this purpose. It is a prerequisite before an application to the industrial problem. Next, we present some research orientations: on the one hand the behaviour of a granular media subjected to a great number of loading cycles, which is strongly connected to the problems of the ballast settlement and its densification and on the other hand a three-dimensional application of the software to the study of the lateral resistance of the track (Saussine et al, 2004).