EFFECT OF COLLARS AND BARS IN REDUCING THE LOCAL SCOUR AROUND CYLINDRICAL BRIDGE PIERS

In the present work, the efficiency of single and double collar in reducing scour rate and depth around cylindrical bridge piers was studied experimentally. In order to reduce the strength of wake vortices, different numbers of bars were also installed at the downstream face of the pier in combination with a single collar. The best result was achieved for double collar when the collars were installed at the streambed level and one pier diameter below bed level. With this arrangement the lower collar was not undermined after 80 hours of experiment, showing about 56 % reduction in scouring compared with an unprotected pier. It was also shown that by using collars, the rate of scouring decreased considerably. Though installation of bars did not significantly reduce the maximum depth of scour, it postponed the beginning of scouring at the upstream face of the pier.