SCOUR AROUND COMPOUND BRIDGE FOOTINGS

Abstract

A cylindrical bridge pier constructed in a channel with its axis perpendicular to the approach flow creates an adverse pressure gradient in the longitudinal direction and a favorable pressure gradient in the downward direction in the front of the pier resulting in a complex three-dimensional flow system comprising downflow, horseshoe vortex and wake vortices. This results in local scour around the bridge pier. A vast amount of literature is available on the topic of scour around bridge piers. But only a few investigators have made studies related to the bridge footings. Very little effort has been made so far to study the temporal variation of scour around compound bridge footings. Thus there is a need for an investigation regarding the temporal variation of the scour around compound bridge footings. In the present thesis experiments are conducted to study the effect of footing on the local scour around compound bridge footings The algorithm given by Kothyari et al. (1992 a) for the temporal variation of scour depth around the uniform pier is found to be applicable for the case of scour around the compound bridge footing with suitable modifications. From the present study it was observed that there is reduction in scour depth when the top of the foundation is below the bed level in comparison to the scour depth caused by pier alone. However, there is increase in the scour depth, in comparison to the scour depth obtained for pier alone, when the top of the foundation elevation is above the bed level.