Laboratory experiments on local scour around cylinder for clay and clay–sand mixed beds

New data on scouring around cylinders embedded in clay–sand mixed beds are reported and the mechanism of the scouring process is described. The effects of clay-content, water content, bed shear strength and pier Froude number on maximum equilibrium scour depth, equilibrium scour hole geometry, scouring process, and time variation of scour were investigated. Existing literature on scouring around cylinders in cohesive sediment beds suggested that the maximum equilibrium scour depth in clay beds was similar to that of sand, while increase in the clay fraction for clay–sand mixed beds reduced maximum equilibrium scour depth. The present study attempted to fill this gap between observations made by different investigators in cylindrical pier scour in clay–sand mixed sediment beds. Further, equations for estimation of non-dimensional maximum scour depth for cylinders embedded in clay–sand mixtures were proposed as functions of pier Froude number, clay content, water content, and bed shear strength, while the clay–sand mixtures had clay content in the range of 20–100% and water content in the range of 20%–45.92%.