Scour around an Erodible Abutment with Riprap Apron over Time

Abstract

Acknowledged as a significant cause of bridge failure is abutment scour around bridge foundations. Because of the complexity of flow structures and scour mechanisms around an abutment, abutment scour remains the focus of extensive research. In this study, to elucidate the complex flow physics and resulting sediment transport around an abutment, time development of abutment scour in three flow types of free, submerged orifice, and overtopping were examined by conducting laboratory experiments in a compound channel. Different lengths of erodible abutment were used to explore the effect of flow contraction on the abutment scour. Detailed bed contours at selected time intervals, as well as velocities, for the initial conditions were measured with acoustic Doppler velocimeters during each experiment. From observations, the scouring process and the resulting scour hole shape and scour depth around an abutment over time were found to be inconsistent depending on the flow type and degree of flow contraction. Tracking the maximum scour location over time explained the complex scouring process around an abutment, which is a simultaneous effect of local turbulence and flow contraction.