Simulation of collapse of granular columns using the discrete element method

In this study, a three-dimensional (3D) numerical investigation of axisymmetric collapse of granular columns has been conducted using the discrete element method (DEM). The simulated granular columns have a constant initial radius of 5.68 mm and three aspect ratios: 0.55, 1.0, and 2.0. The columns consist of uniform spherical quartz particles with a diameter of 0.32 mm. In the DEM model, rotational velocities of particles are reduced by a factor at every time step to partially account for the additional rolling resistance due to the effect of particle shape and hysteretic contact behavior. The simple linear contact model is used; however, its performance is improved by using different stiffness values calculated by nonlinear Hertz-Mindlin contact model for each aspect ratio. The simulated final deposit heights, runout distances, and energy dissipation values are in good agreement with experimental observations reported in the literature. The effects of initial porosity and rotational resistance on the final deposit profile and energy dissipation at different aspect ratios are investigated through a parametric study. For different aspect ratios, a higher rotational resistance leads to higher final deposit height, shorter runout distance, and less energy dissipation. A lower value of initial porosity leads to higher final deposit height; however, the runout distance and evolution of normalized potential, kinetic, and dissipated energies versus time are insensitive to the initial porosity for the granular columns investigated.