Evaluation of particle shape on direct shear mechanical behavior of ballast assembly using discrete element method (DEM)

Ballast layer is a part of railway foundation that its behavior is affected by the properties of constituent particles. The shape of the particles, which affects ballast behavior, is an important characteristic that is represented by angularity and sphericity indexes. In this study, the macro- and micro-mechanical shear behaviors of railway ballast are investigated by using Discrete Element Method (DEM). For this purpose, a three-dimensional (3D) program based on DEM has been modified and verified with the experimental results to simulate different real particle shapes for the direct shear test. Eight assemblies with different particle shape indexes were prepared. The results showed that the shear strength of ballast layer increased significantly with an increase in the angularity index; however, the strength initially increased with increasing sphericity and then dropped in as the sphericity decreased in the assembly of particles. Also, micro-mechanical responses showed that particle shape affected the formation of shear band.