Scour Mitigation at Bridge Abutments Using Spur Dikes

Abstract

One of the main reasons for bridge failure is local scour at the bridge abutments. For protection of existing bridge abutment laboratory experiments, under clear water scour condition, were carried out to investigate scour reduction around the vertical bridge abutment by adding one upstream spur dike. Sand with a median and geometric standard deviation of diameter equal to 0.80 mm and 2.27, respectively, formed the bed material. Three different stages of spur dikes with varying sets, i.e., distances from the abutment, orientation angles, and lengths were considered. Each set of the considered spur dike was studied under nine flow conditions, three approach flow depths with three Froude numbers, with 99 experimental runs in total. Empirical equation was developed for each set between the relative scour depth and the Froude number. In addition, four dimensional equations were developed for each stage, to represent different relative dimensions of the scour hole. It is concluded that using spur dikes leads to good reduction on scour depth at the abutment. Maximum reduction in the scour depth, with percentage 81.56%, is observed for spur dike set with touched distance of the flume wall, between abutment and spur dike, of three times the abutment length, orientation angle of 90°, and spur dike length normal to flow direction equals the abutment length. The scour is just shifted from the vicinity of the abutment to the vicinity of the spur dike. Moreover, the scour area is increased at the vicinity of the spur dike in some cases.