25. Influence of Pier Shape and Interference Effect on Local Scour

Scour around bridge piers is one of the main reasons for bridge failures. Previous researchers reported that pier shape is an important parameter since it affects the flow field and then scour formation. This study aims (i) to find the effect of pier shape on local scour in comparison with the circular pier shape and (ii) interference effect of different shaped piers placed in tandem arrangement on local scour. Experiments are conducted in a rectangular glass-walled flume with sand of d₅₀ = 0.56 mm, under clear-water, and steady flow conditions. Two modified piers are prepared (P2 and P3) with the area equivalent to the area of the circular pier (P1). P1 is a circular pier with diameter D (=5 cm), P2 is a combination of semi-circle and triangle in which pier is oriented to flow direction in either ways (P2a and P2b), and P3 has a groove with projection on semi-circular face of P2. The results showed that compared to P1 the scour depth reduced by 23.5%, 50%, and 55% for P2a, P2b, and P3, respectively, thereby reducing the need for scour countermeasures. From the results of tandem arrangements, it is observed that P1 as front pier and P2a as a rear pier with a clear spacing of 1.0D and P3 as front pier and P1 as a rear pier with the clear spacing of 1.75D given less scour. These observations can be helpful to construct a new bridge adjacent to an existing bridge.