Implementation of real contact behaviour in the DEM modelling of triaxial tests on railway ballast

Abstract

In the Discrete Element modelling of soils, the micromechanical behaviour at contacts has often been considered to have a minor influence on the macromechanical response, leaving basic theoretical models (e.g., Hertz) to describe the contact response in the normal direction. A realistic description of the contact response may be crucial especially when investigating small strain ranges. Recent experimental inter-particle loading tests on gravel suggest that the classic contact models fail to reproduce certain mechanical features, especially when roughness is significant. Here, some of these experimental observations, including a softer response than the Hertz model under loading in the normal direction, and plasticity on unloading, are implemented in a DEM model for the simulation of small strain tests on railway ballast. The influence of these features on small strain stiffness is highlighted. A micromechanical analysis is carried out to show how each of the contact-level features introduced affects the macroscopic response. • Classic contact models do not work well for rough surfaces. • Accounting for lower normal stiffness due to contact with asperities and plasticity. • True contact behaviour implemented in numerical DEM simulations of ballast. • Contact behaviour can explain small strain stiffness degradation.