Local scour around non-circular piers in clay–sand mixed cohesive sediment beds

Few investigations on local scour around circular piers embedded in clay–sand mixed cohesive sediment beds are available in the literature. However, no study has been reported on the local scour around non-circular piers such as round-nosed, square and rectangular piers embedded in clay–sand mixed cohesive beds. In the present investigation, laboratory flume based experimental data on local scour around round-nosed, square and rectangular pier models embedded in clay–sand mixed beds are reported. The effect of clay-content, water content and bed shear strength of the clay–sand mixed sediment bed on the scouring process, the scour hole geometry, the time variation of scour are described. In general, for circular piers embedded in non-cohesive sediment beds, equations are available in the literature for estimation of maximum equilibrium scour depth as a function of bed sediment and flow characteristics. The maximum equilibrium scour depth for the non-circular piers are obtained by multiplying the maximum equilibrium scour depth for circular piers with the correction factor for each pier shape. The data suggested that for clay and clay–sand mixtures, the shape correction factors are not constant values similar to that for the non-cohesive sediments, rather, these shape factors varied between certain ranges.