Experimental investigation of three-dimensional turbulence and scour mechanisms around bridge piers and abutment using acoustic doppler velocimetry (ADV)

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Abstract
Understanding the three-dimensional flow turbulence generated by the combined presence of a bridge abutment and adjacent piers is essential for accurately predicting local scour, a primary cause of hydraulic-structure failure. Although the vortical fields associated with piers and abutments have been studied extensively in isolation, their coupled effect on coherent turbulence and sediment entrainment remains insufficiently clarified. This study evaluates the predictive capability of turbulence diagnostics obtained under rigid-bed conditions, prepared after prior mobile-bed experiments, by organizing all results along four longitudinal transects (Rows 1–4) to ensure direct comparability between hydrodynamic parameters and scour patterns. High-resolution Acoustic Doppler Velocimeter (ADV) measurements collected across multiple depths and cross-sections were used to quantify turbulence intensities, Reynolds shear stress (RSS), quadrant events, and sweep-to-ejection (STE) dynamics around a rectangular abutment and two circular bridge piers. The results demonstrate that the narrow interaction zone between the abutment and the upstream pier constitutes the dominant source of three-dimensional turbulence. Elevated near-bed RSS and strongly dominant sweep (Q4) events in this region represent the principal drivers of sediment entrainment, while the vertical concentration of turbulent energy close to the bed is shown to be more decisive for scour initiation than the magnitude of vertical velocity alone. This critical zone corresponds directly with the deepest scour measured in the mobile-bed tests. Downstream, turbulence progressively weakens, ejection (Q2) events become more prominent, and reductions in RSS and STE coincide with decreasing scour potential toward the second pier and the flow-recovery region. The unified presentation of results along four longitudinal transects confirms that RSS distributions, Q4–Q2 bursting behaviour, and STE profiles obtained under fixed-bed conditions provide robust, physically consistent predictors of scour in compound pier–abutment systems. These findings also strengthen recent hydrodynamic frameworks by confirming that pier–abutment spacing fundamentally governs vortex interaction and near-bed momentum transfer. The insights gained here offer improved guidance for scour prediction and the resilient hydraulic design of bridge foundations in fluvial and coastal environments.

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