Railway ballast layer is an indispensable component of railway transport. Ballast morphology plays an important effect in ballast-sleeper interaction and the durability of ballast layer. In this study, four types of ballast with different morphological parameters were generated and discrete element method was adopted to investigate the direct shear behaviors. The initial packing states were studied by analyzing the porosities and the normal contact force distributions. The shear results were verified by the reported testing results. On the other hand, one-way ANOVA tests were performed to explore the impact of ballast shape on the initial packing behaviors and the direct shear performance. Results indicated that for all four parameters, aspect ratio (AR), sphericity (Φ), roundness (RD) and convexity (CON), the initial porosities decreased first and increased subsequently along with the increase of the parameters. The four parameters could significantly affect the internal friction inside the assemblies. For each parameter, the larger the parameter, the insignificant the internal friction effect. One-way ANOVA tests revealed that all the four parameters were significant in affecting the initial porosities and the internal friction. Moreover, during the direct shear process, the larger the AR or Φ, the smaller the coordination number, which was mainly ascribed to the ballast shapes.
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