local scour around rectangular abutment and their countermeasures by using sacrificial piles

one of the important issues in hydraulic engineering is inspection of local scour depth around bridge pier. using piles is one of the ways for confronting local scour and erosion. in this study, the experiments were conducted in an 8m long, 0.5m deep and 0.25m wide flume. and the effectof using piles and number of them observed on the amount of scour in three different frude numbers. the shape of the pier was a rectangle cube with 5cm long and 2.5cm wide. the diameter of the piles was 6mm, and piles were non-submerged. the results of experiments indicatedthat the use of different number of piles in three different frude number, (0.214, 0.237, 0.297), reduced volume and depth of scour highly. it is observed that 3 and 4 piles in each three fr number, (0.214, 0.237, 0.297), had better results in comparing with 2 and 5 piles. and also the lowest amount of scour and the highest efficiency were related to fr number of 0.214, so the maximum scour depth and volume were reduced by 76% and 92% respectively in comparison with the pierwithout sacrificial piles. while these amounts in the fr number of 0.237 were 88% and 66% respectively and in the fr number of 0.237 were 88% and 52% respectively.