Investigation on scour evolution of bridge groups under tidal currents

Abstract

Local scour threatens closely spaced bridge groups, identifying the evolution mechanism of scour is crucial for proposing targeted protection measures, thereby sustaining the safety of structures in service. This study investigates the scour evolution around a bridge group under tidal reflux peak conditions, using a combination of flume experiments and numerical simulations. Besides, the influence of key hydraulic and sedimentary parameters on scouring dynamics is quantitatively elucidated via a series of parameter analyses. The numerical results demonstrate a strong correlation with the experimental data. The upstream structures, within a certain distance, create a wake-shielding effect that alleviates scour around downstream piers. However, closely spaced bridge groups tend to exacerbate scour, with the deepest scour occurring in wake zones where flow deflection intensifies shear stresses. The study reveals that short pier spacing, multiple piers, and continuous bridge group construction lead to increased scour severity. Among the factors influencing scour, flow velocity had the most significant impact, followed by water depth and sediment grain size. As water depth increases, the reduction in near-bed flow velocity and vortex intensity slows the growth of scour depth. Additionally, scour intensity increases with higher flow velocities, smaller sediment grain sizes, and an optimal water depth.