Investigating Experimentally the Effect of Installation of Piers Group on Foundation on Scour Depth Around Bridge Piers

After construction of bridge pier in a river, eddy flow pattern forms around the piers and erosion of bed material and scouring occur, and if foundation depth or piles depth is insufficient, the bridge will be collapsed. In this research, effects of the installation angles of piers group on scour dimensions under different hydraulic conditions and top levels of foundation installation were investigated experimentally. The model of bridge piers group was placed on a rectangular foundation with 3 angles of installation (vertical, degrees of 28, 38 and 45). Experiments were conducted under two different relative velocities (ratio of flow velocity to corresponding inception of motion velocity, 0.8 and 0.95) and three relative levels of foundation (ratio of top level of foundation to width of it, zero, -0.5 and -1). Comparison of the results showed that at zero relative level of foundation, the top level of foundation played as collar and the minimum scour occurred at the vertical installation angle. At the other relative levels of foundation and among the different installation angles of the piers, the angles of 28 and 38 had the maximum and minimum scour depths respectively. Furthermore, variation of the maximum length of scour had a similar trend to the scour depth.