EFFECT OF STREAM - WISE SPACING OF PIERS ON SCOUR

Abstract

Failure of bridges due to scouring at their supports is a common occurrence. The scouring may occurs at piers, at abutments or at riverbanks. When an alluvial channel is partially obstructed by a bridge pier, the flow pattern around the pier and in the channel is significantly changed. The boundary layer that develops upstream undergoes a three-dimensional separation resulting in the formation of horse shoe vortex, which leads to the formation of scour hole around the structures. The scour depth affects the safe and economic design /Jet-Yr' del 14- depth of bridge piers. Several studies have been carried out in the past for temporal equilibrium scour depth for clear water and live bed condition. All these studies are carried out considering single bridge piers only. Due to increase in traffic volume one has to construct the bridge upstream or downstream of the existing bridge. The present experimental investigation is conducted to study the effect of stream-wise spacing of piers on scour. The experiments were conducted for clear-water and steady flows. The temporal variation of scour depth, equilibrium scour depth, afflux and drag coefficients are measured. In the present study scour depth, afflux and drag coefficient have been measured considering the two types of arrangements of piers,viz; in-line and staggered. In both the arrangements the temporal variation and equilibrium scour depth have been studied for different spacing till non-interference effect attained.