LAUSR

Abstract This paper aims at showing that the reversible behavior of track ballast can be reasonably modeled by a homogeneous elastic layer in the computation of the reversible dynamic response of railway structures subjected to moving train loads. To accomplish this, 2D simulations by means of the discrete element method (DEM) and triaxial tests were carried out. Importantly, these two approaches were performed placing a soft support under the granular specimen. A small number of loading cycles has been considered in both approaches since the long-term settlement of the ballast layer is not the focus of this study, unlike most of the existing research on this topic. In the DEM part, the transfer of the mechanical loads applied to the sample through force chains in the granular medium has been illustrated and discussed based on the numerical responses obtained. In addition, the analysis of the overall response of the grain samples using a homogenized constitutive law shows that the reversible behavior of a ballast layer can be modeled by a continuum approach. However, investigating the effect of the subbase stiffness on the mechanical response of the ballast layer indicates that the homogenized behavior is not intrinsic but depends on the sublayer. These results were confirmed by triaxial tests performed in the laboratory on samples of crushed stones resting on an elastomer mat with different values of the stiffness. Finally, the results from the DEM simulations and the triaxial tests attest that the reversible response of railways can be computed using an elastic layer for the ballast bed provided that an appropriate choice for its apparent modulus is made. The approach that consists of deducing a reversible homogenized behavior of track ballast based on DEM simulations and/or triaxial tests taking into account the support layer looks promising. In future research, more realistic DEM simulations could be envisaged to develop more accurate constitutive laws that could integrate nonlinear and/or anisotropic aspects.