EFFECT OF SKIRTING ON THE DEPTH OF SCOUR AROUND BRIDGE PIERS

Abstract

When an alluvial stream is partially obstructed by bridge piers, the flow pattern in the channel around the bridge piers 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 horse-shoe vortex. The shear stress distribution around the pier is drastically changed due to formation of scour around the pier, which in tern, changes the flow pattern and shear. A vast amount of literature is available on the topic of scour around bridge piers. Several Investigators have studied effectiveness of devices as such as Caissons and Footings, Pier group, Piles and Collar etc. in control of scour around bridge piers. Very little effort has been made so far however to study the tem oral f scour around bridge pier with such devices and no literature is available on Effect of Skirting on the Depth of Scour Around Bridge Piers. In the present thesis experimental investigation is made to study the effectiveness in scour reduction of the combined use of a pier and skirting. Temporal variation of scour around pier and skirt is also studied. From the present study it was observed that there is a reduction in scour depth when the skirt is placed around the bridge pier. The amount of scour depth reduction depends upon the position of skirt with respect to channel bed level. The maximum reduction in scour depth is observed while the top level of the skirt is placed below the channel bed level. The algorithm given by Kothyari et al. (1992 a) for the temporal variation of scour around bridge piers is applied after approximate modification to the case of scour around the bridge pier with skirt around it. The results produced by the modified algorithm compared well with the experimental observations.