We show experimental evidence of vortices emanating from collapsed forcechains in shear bands in real sands. Digital image correlation (DIC)-based localdisplacement analyses have been conducted on overlapping particle clusters toprovide grain-scale displacement measurements of sand specimens undergoing planestrain compression. Spatially varying systematic patterns in kinematic data fieldshave been found within shear bands, defining a coordinated collapse event of theforce chains that initially comprise the shear band upon formation. We haveidentified co-rotating vortices or “circulation cells” within the shear band bysubtracting an overlaid linearly varying shear band displacement field from theobserved non-homogeneous shear band displacement field. These vortex structurescorrelate precisely with previously observed kinematic patterns. We discuss the fateof these vortices and note differences in the vortex patterns observed in our sandsfrom those observed by others in simulations on “ideal” granular materials.
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