Comparison of Symmetrical and Unsymmetrical Rectangular Collars on Reduction of Local Scour at Bridge Abutment

Already many studies have been done on the mechanism of scour around hydraulic structure especially bridges and methods for control or reduction of scour around them have been investigated and evaluated. In the field of scour around bridges, researches are more focus on scour of piers in compare with abutment. While the review of available information on the bridge required cost, the major problems are related to abutment. There fore most costs has spent in this part. One of the methods used to reduction of scour is collar. Collar is the flat plate with small thickness that can be installed around the piers or abutment. In this research 93 set of experiments are performed to find the effect of different dimensions of symmetrical and unsymmetrical collars on reduction of scour around bridge abutment. Results show that increasing dimensions of both collars will increase the efficiency of performance. Comparing of both collars indicated, when the upstream width of collar was larger than its downstream width, its performance will be better than the symmetrical collar with uniform area. The influences of installing elevation of symmetrical collars were also investigated. The results show that the collars installed bellow the bed level have less scour in compare with the one installed on the bed or above the bed.