Development of shear band in a granular material in biaxial tests

Granular matter is a large assemblage of dense packed particles. A granular skeleton frame is linked by grain-to-grain contacts. An external loading is usually transmitted through selective pathways from the skeleton frame, and heterogeneous force chain architecture is formed. The formation and evolution of shear band have importarit bearing to the stability of a granular assembly. In this work, the mechanical properties of granular matter under biaxial test are studied by using DEM simulations. Evolutions of stress, volumetric strain, coordination number, distribution of particle rotation and solid fractions are analyzed. The results show that within shear zone the solid fraction is smaller and the coordination number fluctuates violently, which indicates that they are unjammed, while beyond the shear band the particles are jammed. Therefore, we could say that the shear band actually corresponds to the complicated jamming transition. Three types of force chain configurations are observed under different axial strains: circle-shaped, column-shaped, both column and vortex-shaped. Such structures would be dominant to the mechanical properties of macro-mechanical properties and granular system, and pending further studies.