DEM analysis of the cyclic behavior of ballast mixed with crumb rubber

[Display omitted] •The box test was conducted for the ballast mixed with different percentages of CR using DEM.•The addition of CR facilitates contact sliding and particle rotation, leading to increase in sleeper settlement.•The effect of CR addition on ballast degradation was studied on the micro-scale. This study presents a numerical investigation of the cyclic behavior of ballast mixed with crumb rubber (CR) using the discrete element method (DEM). To this aim, a series of box tests on ballast mixed with different percentages (0%, 5%, 10% and 20% by volume) of CR were simulated by a three-dimensional DEM code, PFC3D. First, the macroscopic mechanical behavior, i.e., the sleeper displacement, the dissipated energy, and the vertical stiffness of the samples, were compared with previous experimental results to validate the proposed DEM model. Further, the microscopic response, including the coordination number, sliding contact ratio, particle displacement and rotation, contact force ratio, contact force and its distribution, and energy evolution were analyzed to mainly reveal the mechanism underlying the sample deformation and ballast degradation. The results show that the simulation results can well capture the effect of CR on the macro-mechanical behavior of ballast with different CR percentages. On the micro-scale, the sliding contact ratio and particle rotation velocity increase with increasing CR percentage, leading to an increase in sleeper settlement. In addition, as the CR percentage increases, the coordination number for the ballast-ballast contacts decreases while the occurrence of larger contact forces increases. The effect of CR on reducing the coordination number for the ballast-ballast contacts outweighs increasing the occurrence of larger contact forces. At the same time, the contact force distribution for the ballast with a higher CR percentage tends to be more homogeneous. These will reduce the risk of ballast breakage; however, as the CR percentage increases, the frictional energy dissipated by the ballast-ballast contacts increases, indicating an increase in ballast abrasion.