Incipient motion of rocks for bridge local scour protection

The bridge local scour is the largest damage to the bridge safety,and the riprap protection is the widespread method for scour protection.Based on the existing scour mechanism,the bridge local velocity of flow is analyzed,including the bottom velocity in front of and around the bridge pier.The simplified formula is put forward for the incipient motion of rocks for bridge local scour protection.The result shows that the bottom velocity in front of the bridge pier is larger than that around it.When the approach velocity is smaller than 3m/s,the riprap protection can be used,with the rock diameter of 0.2m.When the approach velocity is ranged from 3m/s to 5m/s,the riprap protection is not recommended for local scour protection.