Collapse of granular material is usually accompanied by long run-out granular flows in natural hazards, e.g., rock/debris flow and snow avalanches. This paper presents a novel multi-scale approach for modelling granular column collapse with large deformation. This approach employs the smoothed particle hydrodynamics (SPH) method to solve large deformation boundary value problems while using a micromechanical model to derive the non-linear material response required by the SPH method. After examining the effect of initial cell size, the proposed approach is subsequently applied to simulate the flow of granular column in a rectangular channel at a low water content by varying the initial aspect ratio. The numerical results show good agreement with various experimental observations on both collapse process and final deposit morphology. Furthermore, the mesoscale behavior is also captured owing to the advantages of the micromechanical model. Finally, it was demonstrated that the novel multi-scale approach is helpful in improving the understanding of granular collapse and should be an effective computational tool for the analysis of real-scale granular flow.

The behavior of a natural soil is known to change substantially in presence of water under unsaturated conditions, due to additional capillary forces.Water can be absorbed by hygroscopic soil particles (such as clay), or remains at the surface of solid grains (sand, silt) and forms either a discontinuous (pendular regime) or a continuous phase (funicular regime), depending on the water content of the soil. Capillary bridges exist solely between pairs of grains at small water contents, giving rise to simple capillary force expressions and straightforward subsequent modeling. For larger water contents, these generic capillary bridges

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