Three-Dimensional Discrete Element Simulation of Ballast Direct Shear Testing in Vibration Field

To reveal the mechanical properties of ballast particles under the disturbance of dynamic loading, a 3D DEM model for ballast direct shear test was established in a horizontal vibration field. Based on 3D scanning technology, the morphological characteristics of ballast particles were rebuilt in the numerical model by Voronoi tessellation. By calibrating with experimental results of ballast static direct experiments, meso-mechanical parameters for ballast particles were also obtained. On this basis, ballast sample’s shear strength and volume changing under dynamic condition were studied. Numerical results showed that the ballast shear strength in vibration field were smaller than that under static shear condition. Vibration amplitude was the main factor affecting the dynamic shear strength of ballast, as vibration amplitude increased from 0.1 to 0.48 mm, the peak shear stress of the ballast sample decreased from 185 to 102 kPa; while as the vibration frequency increased from 10 to 60 Hz, the dynamic shear strength of ballast didn’t change obviously. Dilatancy feature of ballast was confirmed by volume change before and after shearing process. For the static and low frequency dynamic shear condition, the volume of the ballast sample increased monotonously; while as the vibration frequency exceeded a critical value, the volume of the ballast sample increased first and then decreased during the shearing process. Moreover, increasing the amplitude could effectively reduce this critical frequency. For the dynamic condition that the shear direction was not coincident with the vibration direction, as the angle between these two directions changed from 90° (perpendicular to each other) to 0° (same direction), the smaller the angle was, the more the shear strength decreased.