Y-shaped and T-shaped slots in river bridge piers as scour countermeasures

Slots in river bridge piers have proved effective at reducing foundation scour. This paper reports on 33 experiments carried out under clear-water conditions to assess the performance of Y-shaped and T-shaped slots compared with commonly used straight slots. The variables included three flow discharges, five types of slotted piers and a single pier without a slot, two slots partially embedded in the river bed and non-embedded slots. The scour contours and longitudinal and transverse scour profiles were measured. It was observed that, for the Y-shaped slots, the size of the downstream scour was reduced by decreasing the angle between the downstream slot faces. The results also indicated that the Y-shaped slots were more efficient than the T-shaped slots for scour control, while slot efficiency increased with embedment depth. A maximum efficiency of 59% in scour volume reduction was obtained for the best Y-shaped configuration, compared with a 53% reduction for the straight slot. Regarding the maximum scour depth, the straight slot provided a maximum scour reduction of 38%, compared with 33% maximum reduction for the Y-shaped slot.