Formulation for Critical Shear Stress of Cohesive Sediment Mixture

This article describes results of an experimental study on incipient motion of gravel particles present in the cohesive mixtures, i.e. clay–silt–gravel and clay–silt–sand–gravel, in which the percentage of clay varied from 10% to 50% on weight basis. Incipient motion condition is visually and quantitatively identified which responds to sheet and line erosion type appearance on the top surface of the channel bed for clay up to 30% and mass erosion pattern for 40% and 50% of clay. The clay percentage, weighted geometric standard deviation and bulk density of the cohesive sediment mixture are found to be the main parameters that affect the incipient motion of gravel particles. A functional relationship is proposed to determine critical shear stress of gravel particles present in cohesive sediment mixtures. The regression analyses as well as goodness of fit test were conducted for the proposed relationships which were found to be in good agreement with the present data.