Analysis of ballast direct shear tests by discrete element method under different normal stress

• Simulation of the direct shear tests of irregular ballast stones by constructing clump particles.
• Irregular clumped-particles have similar particle size distribution.
• The nonlinear contact force model with Mohr–Coulomb adopted.

The discrete element method (DEM) was applied to simulate the direct shear tests of irregular ballast stones by constructing clump particles, where irregular clumped-particles have similar particle size distribution (PSD) with those of the real ballast stone. With these clumped particles, the interlock of ballast stones in the direct shear test is investigated. The nonlinear contact force model with Mohr–Coulomb is adopted to model the interaction of the clumped particles. With different normal loads, the simulated microscopic characteristics in the direct shear test were linked with that of tests. The results demonstrate that DEM numerical simulations can produce interrelated responses of the ballast behavior, including the critical state response and are in good agreement with experimental observations. The shear resistance value increases with the normal stress application, indicating that the lateral confinement of ballast bed leading to less vertical settlement and more track stability. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes.