Abstract
Railway track degradation on high-speed lines is a phenomenon which causes high maintenance costs to ensure quality traffic and safety. This geometric degradation is due in part to the vertical strain (settlement) of the ballast layer, which compose the track. The ballast settlement is a difficult phenomenon to estimate and predict because its granular nature and characteristics of this layer induces variability of its mechanical properties. This work is devoted to the study of the mechanical behavior of ballast, to develop a predictive model of track settlement from the initial mechanical characterization of the material (by means a light penetrometer Panda) and the loading on track. By means several test on a full-scale model of railway track, we established and validated a predictive model based on a logarithmic relaxation law. Numerical modeling by discrete element method using the Dynamic Contacts allows to study the mechanical properties of ballast at the grain-scale. Transient deformation analysis shows a clear dependence of the average deformation with respect to the stress and aspect ratio as a result of the frictional feedback at the boundaries. The fluctuations of these deformations are significant and seem to evolve with the average deformation. Finally, the relevance of the ballast characterization using the Panda test has been verified by means a parametric study on mechanisms during the penetration process by the discrete element method.