LAUSR

ABSTRACT The characteristics of scour hole around the submerged tandem pier in alluvial bed plays an important role in analyzing the problem of parallel bridge failures. The present study investigates the scour hole properties around single and tandem pier arrangements with spacing 2d (d, diameter of pier) under varying flow conditions. Experiments were carried out on a mobile bed channel having mean sediment size 0.75 mm and geometric standard deviation (σg ) of 1.27. The cylindrical piers of diameter 4.5 cm are vertically embedded in the mobile channel bed having flow depth of 15 cm with a flow range of 0.02–0.035 m3/s in clear water conditions (U0/Uc = 0.45–0.79). The scour depth around the rear pier is 30% less than the front pier in tandem case for all the flow conditions. Further, with increments of 0.005 m3/s discharge, 20–30% more scour depths are observed around the piers (single and front pier of tandem). In all, 40% more sediment erosion is observed around the piers in tandem case vis-à-vis single pier case. The study reveals that parallel bridge piers are more prone to local scour/erosion than single pier in alluvial beds for similar flow conditions.