laboratory investigation of performance of l-shaped collar on reduction of local scour around bridge abutment

scour around bridge piers is one of the most important fields of hydraulic research. local scour around bridge piers and abutment is one of the main reasons of bridge failures. in the field of scour at the bridges, researches are more focus on scour of piers in compare with abutment. while the available information on the bridge failures required cost, the major problems are related to abutment. therefore, most costs have spent in this part. one of the methods used to reduce of scour around bridge piers and abutment is installing collar. the collars protect the river bed against vortex flow in the vicinity of the piers and abutments . in this research the effect of two types of collar, include complete and l-shaped collar, were investigated on abutment scour reduction and application diagram is proposed. results show that increasing dimensions of collars will increasing the efficiency of performance. comparing of both collars indicated, that if the length of collars is larger than half the length of the abutment, the l-shaped collar is more effective in compare with complete collar. the l-shaped collar doesn’t prevent sediment movement due to lift vortex in downstream of abutment and for this reason it is shown more effective performance than the complete collar. also, using the l-shaped collars with less area is more cost effective.