Accounting for granular material dilation during the operation of an annular shear cell

The testing of granular materials for silo design is most commonly carried out using a Jenike shear cell. The alternative instrument is an annular shear cell, which is used less widely. In this paper we draw attention to the many merits of the annular shear cell. During the operation of an annular shear cell a peak shear stress is observed on the consolidation of loosely filled samples of coarse (above 1 mm diameter) granular materials. By the use of a power balance on the vertical displacement of the shear cell lid, we show experimentally that the peak is a consequence of the extra work expended in lifting the lid when the granular material dilates to accommodate shear. If properly accounted for, this peak shear stress could erroneously be attributed to cohesion. This observation has consequences for the Jenike flow function and effective angle of internal friction of coarse granular materials. We further demonstrate that our observations made on an annular shear cell are compatible with similar observations previously made on sand in a simple shear box, at higher stress levels.