Experimental Investigation of the Effect of Sills on the Hole of Local Scour Around the Bridge Pier with Different Geometric Shapes

Abstract Introduction: A physical model was prepared to investigate the effect of the geometric shape of the bridge pier with the abutment attached to it on the reduction of scour depth. This model was made of a laboratory flume with a length of 7.5 meters, a width of 30 cm, a depth of 45 cm with a variable slope and a glass body with bridge pier width of 4 cm were used. For bed sediments, a layer of natural river sand with an average diameter of 0.9 mm and a standard deviation coefficient of 1.1 and a uniformity coefficient of 1.25 were selected and used in a layer with a thickness of approximately 14 cm for experiments. Methods: The geometric shape of the bridge piers, as well as the presence of the footing, prevents direct contact of the descending current, reduces the activity of horseshoe vortices and thus reduces the scouring speed, and delays the scouring start time. Findings: According to the results of the experiments, the greatest decrease in scour depth was related to (0.26 descent and p1 base). The results showed that in the same condition, the relative scour depth at p1 base was less than other bases and reached its maximum in the control base. Also, the relative scour depth increased with increasing the number of landings in the same position. The abutment attached to the bridge base has reduced the scour depth by 29.6%.