Numerical Analysis of Static Crushed Behavior of Railway Ballast

In order to reveal the static compressive behavior and breakage mechanism of railway ballast, the discrete element method was applied to simulate its crushed behavior under statically loading between two flat platens. A laser scanner was used to obtain the three dimensional morphology of a ballast. Discrete element models for the ballast with a realistic shape were constructed using hexagonal close packed agglomerates. Contact and bond behaviors between particles were defined in these models. History of load-displacement, distribution evolution of force chain and broken bonds in the ballast during the crush process were analyzed. The numerical results show that the characteristic strength of railway ballast follows a Weibull distribution, being consistent with the existing experimental results. Stress concentration at ballast surface and local crush due to sharp corner and surface irregularity induce the initial rotation of ballast and the change of its contact state, resulting in variation of force chain distribution in the ballast and a short drop of load. During the stable elastic response phase, contact forces between some parts of elements gradually increase with the enlargement of load and then exceed the bond strength, thus broken bonds exist in the ballast. When the number of broken bonds dramatically increases and reaches a certain scale, the ballast is crushed due to the rapid propagation of internal micro cracks.