DEM analysis of micro-structural events within granular shear zones under passive earth pressure conditions

Shear zones in initially medium dense cohesionless sand for quasi-static earth pressure problem of a small-scale retaining wall were analysed with a discrete element method (DEM) using spheres with contact moments. The passive sand failure for a very rough retaining wall undergoing horizontal translation was discussed. The DEM calculations were carried out with the different mean grain diameter. Micro-structural events appearing within granular shear zones such as: vortices, force chains, vortex structures and local void ratio fluctuations were investigated. Special attention was laid on a vortex-force chain correlation and frequency of the vortex appearance. The calculated geometry of shear zones was compared with experimental results of laboratory model tests analyzed using the DIC. DEM demonstrated its ability to describe the geometry of shear localization in sand behind the retaining wall and to follow the evolution of micro-structure in granular shear zones.