Mean Flow Structure and Local Scour around Single and Two-Column Bridge Piers

Bridges constructed across rivers are among the most important structures, especially during and after flood events. Bridge piers are exposed to some hazardous factors such as local and contraction scour hydrodynamics. The lower prediction of maximum scour depth can cause  bridge failure, while over-prediction leads to a very costly project. The appropriate estimation of maximum scour depth around bridge piers is, thus, necessary. In some bridges, more than a single pier is considered during the design phase, and the interaction between the adjacent piers makes the situation very different. The flow structure and scour process around a group of bridge piers are, indeed, very different from a single bridge pier. Many researchers have studied the scour around single and/or multiple-column bridge piers. For instance, studying the scour depth for a group of piers, Mahjub et al. (2014) reported that the maximum scour depth around the second bridge pier was less than that of the upstream pier, while the scour depth around the third pier was lower than that of the first and second piers. Moreover, Daneshfaraz et al. (2014) investigated the effect of pier slots on the maximum scour depth around the two-column bridge piers. The results that the slot reduced the maximum scour depth compared to the piers without a slot. In this paper, the flow and bed topography around a group of piers was studied experimentally.