Experimental Investigation of Local Scour Around Inclined Bridge Piers on Clay-Sand Mixed Cohesive Sediment Bed in Clear-Water Conditions

A few investigations on clear water local scour around vertical bridge piers on clay-sand mixed (cohesive sediment) beds are found in the literature. However, no research has been reported on local scour around inclined bridge piers for clay-sand mixed cohesive beds. This research work was carried out to investigate the impact of dual inclined bridge piers (convergent-vertical piers) on maximum scour depth installed in flow direction on four beds containing different clay contents from 20–80% with sand. Three different pier shapes of different cross sections were tested (circular, rectangular & diamond) in each case. The effect of inclination (0°, 5°, 10°, 15°, 20°) with the vertical on the same beds was analyzed and discussed. The results revealed a considerable reduction in maximum scour depth with inclined bridge piers in comparison with vertical bridge piers. The least scour depth was observed around 10° inclination for rectangular and circular shaped sections and 5° for diamond bridge pier. On average 53.25%, 57.25%, and 72% reduction in scour depth was observed for inclined rectangular, diamond, and circular bridge piers respectively as compared to the vertical bridge piers. The circular bridge pier proved the most effective inclined pier, exhibiting the least scour depth among the three pier shapes. Furthermore, no equation was found in the literature to predict the maximum scour depth around inclined bridge piers on clay-sand mixed beds, so three non-linear regression-based equations for three different upstream collinear piers as a function of clay content percentage and inclination were predicted which reasonably described the experimental data.