The application of collar on the scour reduction at bridge rectangular abutment in composit channel

The fracturing bridge due to scour of foundation (includes bed and abutment)، reveals the necessity of study for scour predict and the protected methods. Generally،the methods of scour reduction include: placing foundation at the lower level of erosion pit depth، rasing bed resistance and decressing erosion power factors (decreasing downflow and horseshoe vortex). Utilizing a spreadsheat around abutment called collar is one of the methods of power decrease. The collar decreases the power of downflow and horseshoes vortex around the abutment further it decreases the depth of scour decrease. In this research a collar of two times than the abutment width exposed to a discharge of 20 and 25 lit/s. The operation of collar in 3 different depths (on the bed، at 2cm above bed and at 4cm above bed) was studied in the scour conditions of clear water and was compared with abutment without collar. the research indicate that collar decreases scour and it showed better operation above the bed. as a maximum percentage decrease of scour with a discharge of 20 and 25 lit/s is 94% and 93% respectively.