Experimental investigation of a breaking size segregation wave in a dry granular flow

The objective of this paper is to provide evidence of the existence of breaking size-segregation waves in dry granular flows down inclined chutes. A flume was initially filled to a constant depth with a bimodal mixture of spherical particles that were retained behind a lock gate at its downstream end. The particles were sharply separated, with the smallest beads confined to a small wedge-shaped space near the flume entrance and the large particles lying above and in front of the fines. The flow was initiated by removing the downstream gate, and an approximately steady uniform flow was obtained by continuing to feed small particles into the chute from a hopper at the top of the flume. As the particles began to flow downstream the velocity shear through the avalanche depth caused the sharp interface to move and steepen until small particles were sheared over the top of the larger ones and it became unstable. Segregation then allowed the small grains to percolate downwards, into slower moving parts of the flow, and squeeze the larger ones up into the faster moving near surface layers. We observed that the interface degenerated into a segregation wave advected by the mean flow, in which particles were recirculated. These observations support the recent segregation model developed by Gray and Thornton.