Comparison of Linear and Triangular Arrangements of Submerged Sacrificial Piles on Local Scour Depth around Cylindrical Bridge Piers

The control of local scour around the piers and bridge abutments has been recognized as an issue of considerable importance due to the structural damage of bridges. Many methods have been already proposed by several researchers to tackle this problem, including methods that change the pattern of flow around the piers, such as sacrificial piles (Melville and Hadfield, 1999; Chabert and Engeldinger, 1956), Submerged vanes (Lauchlan, 1999; Grimaldi et al., 2009a), Slot (Chiew, 1992; Grimaldi et al., 2009b), and collars (Zarrati et al., 2006; Alabi, 2006). In addition to the above methods, other methods have been developed to protect the bed against the scour, including the use of riprap around the pier (Parola, 1993; Graziano et al., 1990), sandy bags, gabions, and geotextiles. The sacrificial piles are, indeed, the piers with smaller diameters than the bridge piers, which divert the flow from the bridge pier leading to the reduction of the scour potential. The efficiency of the sacrificial piles in controlling the scour depends on the number and diameter of the piles, the degree of submergence, the arrangement, their relative  placement against the piers, the distance between the piles, the distance between the piles and the piers as well as their angles to the flow (Melville and Hadfield, 1999). According to these methods, many studies have been carried out on the effect of the sacrificial piles in reducing the bridge piers scour. However, the use of submerged piles with different degrees of submergence has been less considered. Since the length of sacrificial piles has an effect on the degree of submergence, the length of the sacrificial piles is effective in scouring, as well. In effect, the present study focuses on the scouring around bridge piers by using 2 different arrangements with and without using the sacrificial pile groups at the upstream of the pier.