Journal of Hydraulic Structures

Journal of Hydraulic Structures

Experimental Investigation of Local Scour Around Twin Cylindrical Bridge Piers: Effects of Pier Spacing and Skew Angle

Document Type : Research Paper

Authors
Morteza Shokri
AmirHossein Topal
Majid Fazli
Department of Civil Engineering, Faculty of Engineering, Bu-Ali Sina University, Hamedan, Iran.
10.22055/jhs.2026.51968.1382
Abstract
Local scour around bridge piers is a primary cause of bridge failure worldwide. When multiple piers are placed in proximity, the interference of flow structures between them significantly alters the scouring mechanism compared to a single pier. A series of 42 experiments were conducted in a laboratory flume under clear-water conditions. The sediment bed consisted of uniform sand with a median grain size of d50 = 1.6 mm, and the flow was maintained at a nominal discharge of 28 L/s with a flow depth of 13.5 cm (Froude number Fr≈0.29). Twin cylindrical piers with a diameter of D= 4 cm were tested at six different longitudinal spacings and varying skew angles to the approach flow (0° to 90°). The maximum scour depth, scour hole length, and width, as well as the height of the deposition mound, were measured for both the upstream and downstream piers. The results demonstrate that at close spacings (1D and 2D), increasing the skew angle amplifies the maximum scour depth and the dimensions of the scour holes for both piers. At intermediate spacings (3D and 4D), the upstream scour depth and length increase while the width decreases; conversely, the downstream hole parameters initially increase and then decrease. Furthermore, the height of the sediment deposition mound exhibits an initial increase followed by a decrease across all tested spacings as the skew angle increases. These findings provide critical insights into the optimal spacing and alignment of twin-pier configurations to minimize scour-induced vulnerabilities.
Keywords
Flow interference
Local scour
Pier spacing
Skew angle
Twin bridge piers
Subjects
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