The role of particle shape on the stress distribution in a sandpile

The results of an experimental investigation into the counter-intuitive phenomenon that a local minimum in the normal stress pro. le is sometimes found under the apex of a sandpile are presented. Specifically, the effects of particle shape on the stress distribution are studied and it is shown that anisotropy of the particles significantly enhances the dip. This amplification is attributed to the mechanical stability induced by boundary alignment of the anisotropic particles. Circular, ellipsoidal and pear-shaped cylinders are used and the stress propagates principally towards the sides of the pile through primary stress chains. Secondary chains are also present and we propose that the relationship between the magnitudes of the ratio of primary to secondary chains is correlated with the size of the dip.