  The evolution of wide shear zones (or shear bands) was investigated
experimentally and numerically for quasistatic dry granular flows in split
bottom shear cells. We compare the behavior of materials consisting of beads,
irregular grains (e.g. sand) and elongated particles. Shearing an initially
random sample, the zone width was found to significantly decrease in the first
stage of the process. The characteristic shear strain associated with this
decrease is about unity and it is systematically increasing with shape
anisotropy, i.e. when the grain shape changes from spherical to irregular (e.g.
sand) and becomes elongated (pegs). The strongly decreasing tendency of the
zone width is followed by a slight increase which is more pronounced for rod
like particles than for grains with smaller shape anisotropy (beads or
irregular particles). The evolution of the zone width is connected to shear
induced density change and for nonspherical particles it also involves grain
reorientation effects. The final zone width is significantly smaller for
irregular grains than for spherical beads.
