Discrete-Element Analysis for Compaction-Induced Stiffness Variation of Ballast Aggregate in Large-Scale Triaxial Testing

Large-scale triaxial tests are popular for evaluating the mechanical properties of railroad ballast. The literature shows that different compaction methods have been used to prepare the samples. This research investigates the potential variation caused by different compaction methods, even when the samples are compacted to the same density. A series of triaxial tests are conducted, and the results confirm that the way in which ballast is compacted significantly affects its stiffness, but not its peak strength, as long as the density is consistent. Discrete-element method simulations are performed to explore this phenomenon and discover that stiffness variations are caused by different ways in which particles interlock and arrange themselves during compaction. Based on the findings from this study, it is recommended to consider the influence of compaction methods when conducting large-scale triaxial testing on railroad ballast or when evaluating the test results.