Influence of Cohesion on River Bed Scour in the Wake Region of Piers

Abstract

Studies on scour in the wake region of piers in cohesive sediments containing gravel were not reported in literature, to the best of our knowledge. Results from the laboratory experiments based study on the process of wake scour are presented here. The sediment used for the experiment were of two types: (1) fine gravel mixed with clay in proportions varying from 20% to 60% by weight, and (2) fine gravel and fine sand in equal proportion by weight mixed with clay in proportions varying from 20% to 60% by weight. The experiments revealed that the process of scour as well as depth, shape, and geometry of scour hole developed in such cohesive sediment were significantly different from that of cohesionless sediments. Proportion of clay fraction and unconfined compressive strength of cohesive sediment mixture were found to be the most significant variables controlling the depth of scour in the wake of piers. On the basis of dimensional considerations, relationships have been proposed for the estimation of the depth of scour in the wake region of piers in clay-gravel and clay-sand-gravel sediment mixtures.