Influence of Netted Collar on Scour depth around of Cubic Bridge Pier

Two major factors causing of scour around bridge piers are the down flow occurred in upstream part of the piers and separation of streamlines from piers called horseshoe vortex. Installation of a collar on a pier will reduce the power of the down flow and horseshoe vortex. In this study, the effects of placement of collar and netted collars on scour depth of cubic pier are investigated. The experimental flume was rectangular with the length of 7.3 meters, width of 0.56 m and a depth of 0.6 m. For this propose four collars included, one simple and three netted (with opening parts equal to 15percent, 30percent and 40percent), are tested under clear water condition. The experiments were performed in laboratory flume on Hydraulics Laboratory of Shahid Chamran University. The collars were installed in three levels equal to 0.5B, 0.25B and on the bed. The results were compared with the pier without the collar, and showed that the netted collar reduce the maximum scour depth between 34percent to 97percent in comparison with the case of no collar used. Also in low Froude Numbers, the netted collars showed better protection in comparison with the simple one.