Clear‐Water Scour around Bridge Pier Group

Abstract

Recent attempts have been made to reduce scour around solid circular piers. Such attempts use riprap, a circular collar around, a rectangular slot through, and a delta wing‐like fin ahead of piers. Providing another scour reduction device, the present paper replaces the solid pier by a group of three smaller piers. A pier group starting from its foundation and extending fully into the flow depth is termed a “full pier group” and one extending partially into flow depth a “partial pier group.” The scour due to a pier group in its best orientation is compared with that due to a solid pier of diameter equal to the circumscribing circle diameter of the pier group. It was observed that the scour reduction due to a full pier group is about 40%, and 75% of this reduction can be realized by a partial pier group extending into half the flow depth only. Also, the full pier group is seen to be more effective than a solid cylinder with a full slot of width equal to half its diameter and as effective as a solid cylinder with a collar 3.5 times its diameter. A collar on a pier group is much more effective than on a solid pier.