In this paper the interface behavior between an infinite strip of a granular mate- rial and a rough boundary under plane shearing is numerically investigated using a micro-polar continuum approach. Particular attention is paid to the influence of a fluctuation of micro-polar boundary conditions along the interface on the evolution of shear strain localization within the granular material. The mechanical behavior of the cohesionless granular material is described with a micro-polar hypoplastic model. The evolution equations for the stress and the couple stress are non-linear tensor valued functions which model inelastic behavior. The investigations show that the micro-polar boundary conditions have a strong influence on the location and thickness of the zone of strain localization when relative displacements within the interface are excluded.