Simulation of quasi-static axisymmetric collapse of granular columns using smoothed particle hydrodynamics and discrete element methods

Flow of granular materials under different conditions poses significant challenges to engineers as their behavior can vary from solid-like to fluid-like. The quasi-static axisymmetric collapse of granular columns is an interesting case of granular flow relevant to the active deformation of retaining structures. This study aims to shed light on this type of collapse using numerical simulations including the smoothed particle hydrodynamics (SPH) method in the continuum framework and the discrete element method (DEM) in the discrete framework. Three-dimensional SPH and DEM models are developed to investigate the quasi-static axisymmetric collapse of granular columns, which is initiated by slowly expanding the cylindrical wall of the column. The Drucker-Prager constitutive model with non-associated flow rule is implemented into SPH formulations to model elastoplastic behavior of granular material. The linear contact model is used in DEM simulations with calibrated contact stiffness parameters. The effects of particle shape and hysteretic contact behavior in the DEM model are indirectly considered through reducing particle rotational velocities by a calibrated constant factor at every time step. Using the developed models, the final deposit profile (e.g., height, runout distance, repose angle), non-deformed region, collapse pattern and energy dissipation for different initial aspect ratios are investigated. In addition, final height, runout distance and energy dissipation are theoretically derived and are found to be in good agreement with SPH and DEM simulations. Results show that the quasi-static axisymmetric collapse can be modeled using both the continuum and discrete frameworks as long as appropriate constitutive models or contact behaviors are implemented. However, DEM simulations are more capable of capturing particle-level behaviors, such as the sharp edges of the free surface and flow front. Results demonstrate that quasi-static granular collapse is qualitatively similar to the dynamic collapse, but results in smaller runout distances for all aspect ratios.