Investigation of granular batch sedimentation via DEM-CFD coupling

This paper presents three dimensional numerical investigations of batch sedimentation of spherical particles in water, by analyses performed by the discrete element method (DEM) coupled with computational fluid dynamics (CFD). By employing this model, the features of both mechanical and hydraulic behaviour of the fluid-solid mixture system are captured. Firstly, the DEM-CFD model is validated by the simulation of the sedimentation of a single spherical particle, for which an analytical solution is available. The numerical model can replicate accurately the settling behaviour of particles as long as the mesh size ratio and model size ratio are both larger than a given threshold. During granular batch sedimentation, segregation of particles is observed at different locations in the model. Coarse grains continuously accumulate at the bottom, leaving the finer grains deposited in the upper part of the granular assembly. During this process, the excess pore water pressure initially increases rapidly to a peak value, and then dissipates gradually to zero. Meanwhile, the compressibility of the sediments decreases slowly as a soil layer builds up at the bottom. Consolidation of the deposited layer is caused by the self-weight of grains, while the compressibility of the sample decreases progressively.