Multi-phase modelling of loose, unsaturated soil’s continuous motion using a three-phase Eulerian approach

Abstract

This paper develops a numerical model for loose, unsaturated soil to represent its mixing and motion using Computational Fluid Dynamics. It was found that existing models are not suitable for loose, unsaturated soil. The Herschel–Bulkley model is more appropriate for sludge and mud-like materials, and the Kinetic Theory of Granular Flow is inapt because it lacks yield stress. To mitigate these shortcomings, a novel three-phase Eulerian model is proposed, which combines these two models with an air phase. Each phase includes a physical characteristic of loose, unsaturated soil: the Herschel–Bulkley phase includes yield stress, a solid phase includes granular behaviour, and the air fraction adds porosity. To identify the model’s parameters, density is measured, and a slump test is performed. The radial run-out of the slump test is used to determine the required yield stress in the model. Test simulations showed clear improvements over the existing models by combining yield stress and granular, lumpy behaviour successfully. Application of the new model to a 3D screw conveyor simulation showcases its ability to simulate continuous soil motion phenomena, such as avalanching caused by a recirculatory flow, soil spilling over the flight and soil flowing back to the previous pitch.