Mohammad Vaghefi

This research examines the influence of abutments placement near the inner and outer walls, alongside the deployment of convergent-vertical and divergent-vertical bridge pier groups. Three positions 60, 90, and 120 degrees out of a 180-degree bend were selected and tested. Additionally, the impact of varying flow conditions in three states: clear water, incipient motion, and live bed, on bed changes and scour rate was examined. The findings revealed that, under incipient motion conditions, when piers were positioned at 60 degrees, the deepest scour of the main hole occurred near the piers; however, when placed at 120 degrees, this deepest scour shifted to the area around the outer abutment. The greatest scour depth under incipient motion conditions was observed in the convergent pier groups positioned at 90, reaching about 1.3 times the flow depth. At this position, the maximum depth of the second scour hole and the sediment ridge height were higher compared to the 60 and 120 positions. When piers and abutments were positioned at 90, the deepest scour of the second hole and the sediment deposit height increased as the ratio of average flow velocity to the critical velocity for bed particles rose from 0.87 to 0.98 and 1.03.