Experimental Investigation of the Collar and Vanes on Reduction the Scour Depth of Cylindrical Piers

Scouring threaten the stability of hydraulic structures in various forms. One way to indirectly reduce scouring is to put collars and vanes. Collar is a thin plate at a certain height from the base of the bridge which prevents direct contact of down flow in front of the pier with the river bed and undermines the activity of horseshoe whirlpool. Also, in the scouring foundations, the speed of scouring reduces or in other words, the time of scouring is delayed. In this study, using experimental modeling, the researcher investigated the effects of combined collar and vanes on the reduction of scouring depth on cylindrical pier. According to the results of the experiment, the highest scour depth reduction for the Froude number of 0.246 and the pier in the vicinity of the collar of twice the pier diameter and six submerged plates for each tripod occurred respectively (55%, 96%, 98%). Also, the results showed that submerged plates with impact on stream lines and collars with protection of the pier against downstream vortices and Horseshoe vortices are suitable tools for reducing scour depth in Cylindrical bridge pier group.