Control of Scour at Bridge Abutment at River Bend by Riprap

Using riprap is one of the common and economical methods for bridge abutment protection against scouring. Literature review showed that no study could be found for designing riprap size for protection of bed at bridge abutments which are located at the bends of rivers. For this purpose, physical model experiments were conducted with three types of ripraps of specific gravities of 1.51, 2.05 and 2.65, and sizes of 4.75, 9.52, 12.7 and 19.05 millimeters. Tests were conducted under various discharges of 17, 20, 23 and 28 lit/s(corresponding to the Froude number ranging from 0.19 to 0.58). The wing wall abutment was located at 75o of 90o of the river bend. The suitable size of riprap diameter at the bridge abutment located on the river bend was suggested in the form of a formula with error percent of 5.8, and correlation coefficient of 0.97. The formula developed in this research was compared with formulas of earlier studies on riprap around abutments in straight channels, and suitable correction coefficient was suggested for corresponding straight channel relations to be applicable for river bends.