Calibration method for discrete element modeling of ballast particles

The discrete element method (DEM) is widely used for the simulation of ballast behavior under static and dynamic loading conditions. Due to the irregular shape of ballast particles, the simultaneous influence of multiple parameters (i.e., static and rolling friction coefficients, Young's modulus, Poisson's ratio, and restitution coefficient) should be considered when calibrating DEM input parameters for ballast particles, which poses a challenge. To reduce the influence of shape factors on the bulk behavior of ballast samples, a series of clumps for describing the shape of particles comprised of 17-24 balls are first created and generated. In the following, an efficient calibration method is proposed with four different tests, including the hollow cylinder test, confined compression test, direct shear test, and ballast box test. The order of the implemented tests is important due to the effect of the variation of friction coefficients on the results of all tests. Since the angle of the repose test is insignificantly influenced by contact and damping parameters due to the lack of external force on the ballast sample, firstly, the calibration of particle friction coefficients is performed by several repose angle tests. Thereafter, the direct shear test is used to calibrate particle Young's modulus and Poisson's ratio. Finally, the restitution coefficient of particles is calibrated by DEM modeling of ballast box tests under cyclic loading. The proposed method would be helpful for the calibration of ballast particle properties which is a necessary stage before the simulation of any experiments.