Local scour around twin bridge piers in open channel flows

Laboratory experiments have been carried out to investigate the local scour with the interaction between twin cylindrical piers in open channel flows. The characteristics of scouring around twin-piers were summarized, which showed differences from that around isolated pier. The experiments conducted for clear-water scour showed that the local scour around the upstream pier at different spacing was almost the same to that around isolated pier. The local scour depth around the downstream pier was bigger than that around the upstream pier in a range of small velocity, after which it entrance the quasi-live-bed scour state as the sediment scoured from the upstream hole landed here. The depth of the downstream scour hole firstly increased to a maximum, then decreased to a minimum, and finally increased as the flow velocity increased to the incipient motion velocity of sediment. The data obtained were used to derive an equation for the maximum depth with the separation of twin-piers to indicate the minimum spacing with no interaction between twin-piers.