Scour in cohesive soils is a complicated phenomenon that is far from understood. Conventional approaches to cohesive soil scour prediction are applying laboratory experimental results of cohesionless soils to cohesive soils and are usually overly conservative. Previous research focused on the critical shear stress while the effects of vertical pressure fluctuations on scour initiation were not considered. The fact is that although shear stress moves sediments into motion in sliding or rolling modes, the saltation mode of bedload results from the vertical pressure fluctuations or lift. The objective of this study is to understand the soil and fluid characteristics in the bed boundary flow structure, and establish an incipient motion criterion for cohesive soil scour.
The primary objective of this study is to develop design tools for scour in cohesive soils that will be implemented in Hydraulic Engineering Circular No. 18, "Evaluating Scour at Bridges."