Experimental Study of the Effect of Control Structures on the Scour Depth of Bridge Pier Group

Experimental Study of the Effect of Control Structures on the Scour Depth of Bridge Pier Group

Occurrence of conditions beyond the threshold of motion in the alluvial boundaries causes sediment particle movement. Scour about bridge pier foundation follows hazardous consequences which should be controlled. In the present study, scour process around the bridge pier group of diameter D (=9 cm) has been investigated experimentally using the installation of submerged vanes with a quasi-triangular arrangement (of heights 0, 0.44D, and 0.66D), groyne, and sills (of height 0.5D and D) in a horizontal rectangular flume of length 13 m, width 1.2 m, and height 0.8 m. Mean size of sediment particles was 1.8 mm. Using dimensional analysis, Fr, H_v/D and H_s/D were extracted as effective dimensionless terms on scour depth. Results showed the additive effect of the groynes on the scour depth due to flow section contraction and increase in the critical velocity so that an increase of value 89.1% was happened. To decrease sediment particles transportation, submerged vanes and sill were set up. The measurements indicated that the superior performance belongs to the vane of height 4 cm with a maximum reduction of value 79.3%. The effect of the vane on scour depth declination was intensified with installing the sill of height 4.5 cm. Because of the supportive effect of the first pier for two other piers, more scour depth was seen around the first pier than the third one.