Numerical Study of Local Scour Around a Triangular Group of Circular Bridge Piers

Scour is a critical hydraulic phenomenon that undermines bridge foundations, leading to severe structural failures and significant economic losses. This study investigates the local scour behavior around triangular configurations of circular bridge piers through combined experimental testing in a laboratory flume and three-dimensional computational fluid dynamics (CFD) simulations using FLOW-3D. The experimental program was conducted in a recirculating flume (11.0 m × 0.756 m × 0.55 m) with uniform sediment (D50 = 3.0 mm), varying the center-to-center spacing between the front pier and the two base piers across five non-dimensional spacing ratios (Z/B = 1.0, 3.5, 8.35, 15, 25) 1. Numerical simulations were calibrated against experimental results for a single pier before extending to triangular group configurations under identical hydraulic and sediment conditions. Results shows that smaller Z/B ratios produce severe hydrodynamic interactions between piers, with merged scour holes and increased maximum scour depths (up to 100.5 mm at Z/B = 1.0). Findings from this study provide practical guidance for bridge design engineers, emphasizing the importance of pier spacing in mitigating scour risk in multi-pier arrangements.