Protection of bridge piers using a sacrificial sill

Abstract

This experimental study explores the effectiveness of using a sacrificial sill as a pier scour countermeasure. Experiments were conducted under both clear-water and live-bed conditions. Many interdependent parameters affecting the sill performance were systematically examined. The results show that the sill is efficient in reducing the equilibrium clear-water scour depth, reaching a maximum percentage reduction of pier scour depth, %RDP, of approximately 50% under the most favourable condition. The optimum state occurs under the following conditions: (a) the sill is vertical; (b) the sill height is larger than 0·3 times the depth of flow; (c) the clear distance between the pier and sill is 4·4 times the pier width; and (d) the angle of attack is zero. A large angle of attack or flow skewness is detrimental to the performance of the sill. However, this shortcoming may be overcome by installing a sill with a wedge angle of 270°. The efficiency of the sill decreases under live-bed conditions, with the %RDP reducing to approximately 20% at a velocity ratio, U/Uc = 2·6.