Effects of Rectangular Foundation Geometry on Local Pier Scour

Abstract

A method for predicting the effect of rectangular foundation geometry on local scour around bridge piers is presented using existing scour equations and considering the mechanisms of local scour. Normalized scour depths predicted from the method are compared to normalized scour data collected by others and data collected by the writers in a laboratory study. The data and the method show the effect of the rectangular foundations through the entire range of possible pier to foundation width ratios and through the entire range of foundation elevations. The effect of an upstream foundation extension also is examined. The study reveals that considerable reduction in the scour depth may be observed if the foundation is located at or below the streambed. The method can be used to evaluate the potential for scour around existing piers. Problems associated with relying on foundations to reduce scour depths are presented. Recommendations for the use of the method are made and future research is suggested.