Quasi-static fall of planar granular columns: comparison of 2D and 3D discrete element modelling with laboratory experiments

Abstract

We investigate the fall of planar granular columns in a quasi-static regime using a combination of laboratory experiments and simulations using the discrete element method (DEM). Columns made of alternately coloured sand layers are initially laid out in a box and then released when a retaining wall is set in slow motion with constant speed. The flow of the sand involves failure of the granular material along multiple slip planes at different stages of the deformation, leading to complex flow patterns. DEM simulations, in 2D and 3D, are able to qualitatively and quantitatively reproduce a range of essential elements of this flow, with particle shape being an important contributor to the mobilisation of specific slip planes. We also examine the sensitivity of the DEM predictions to changes in the operating, material and simulation parameters. We find that DEM predictions are invariant to changes of moving wall speed, spring stiffness, particle–particle friction and particle–wall friction. Conversely, they are quite sensitive to the shape of the particles. In particular, the use of 3D blocky particles represented as super-quadrics results in excellent agreement between the DEM predictions and the experiments at the fixed wall and good agreement elsewhere. The particle shape plays a critical role in determining the shear strength of the material and therefore the failure of the particle bed, the formation of shear bands and therefore its flow characteristics.

Keywords:

• quasi-static flow
• planar granular columns
• discrete element method
• particle shape