SCOUR PROTECTION AT BRIDGE PIERS USING COLLAR AND RIP

Abstract

When an alluvial stream is partially obstructed by a bridge pier, the flow pattern in the channel around the pier is significantly changed. The pier produces an adverse pressure gradient just upstream from the pier. The boundary layer that develops upstream of the pier undergoes a three — dimensional separation resulting in the formation of horseshoe vortex. The shear stress distribution around the pier is drastically changed due the to formation of the horseshoe vortex and it causes formation of a scour hole around the pier, which in turn, changes the flow pattern and shear. Several investigators have studied control of bridge pier scour around bridge piers by using various devices as collar, rip-rap, piles etc. In the present thesis an experimental investigation is made to study the effectiveness in scour reduction of the combined use of a collar and the rip-rap. The experiments were restricted to the case of clear-water flows only. Use of a collar alone was found to reduce scour depth upto a maximum of about 60 percent. A thin rip-rap was found to reduce scour depth by about 40 percent while a thick rip-rap was found to reduce the same by about 70 percent. Use of a collar alongwith the thin rip-rap also was found to reduce the scour depths by about 70 percent