Numerical study of polar effects in shear zones

Numerical studies on polar effects in an infinite plane layer of a granular material under shearing with a constant vertical pressure are presented. A micro-polar approach is formulated within the framework of hypoplasticity to describe the mechanical behavior of a dry and cohessionless granular material like sand. The constitutive equations are based on incremental nonlinear tensor-valued functions which take into account Cosserat rotations and couple stresses using the mean grain diameter as a characteristic length. Furthermore the model captures the influence of the stress and density on the incremental stiffness for both contractant or dilatant deformations using one set of constitutive constants. The numerical results show that for large shearing the deformations are localized within a narrow zone which is strongly influenced by the boundary conditions, the stress level, the initial density and the mean grain diameter.