Yilin Yang

Local scour around pile-group foundations is a predominant cause of hydraulic instability in bridge engineering. This study employs a fully coupled three-dimensional computational fluid dynamics model to investigate local scour around a 2 × 2 inline pile group under steady flows. The model is validated against detailed laboratory measurements of flow and scour, demonstrating good agreement in both hydrodynamic and scour results, with scour depth simulations deviating by less than 15% from experimental data. Analysis of the flow fields reveal that scour evolution is accompanied by the descent of the horseshoe vortex, intensification of gap-flow, and acceleration around the side piles, while migration of bed shear stress from the pile flanks to the upstream slope dictates the equilibrium scour morphology. A systematic parametric study was conducted to evaluate the influence of the Froude number (Fr) and pile spacing (G/D) on scour depth. The results indicate that scour depth increases rapidly with Fr up to approximate 0.35, beyond which it plateaus as form-induced drag dissipates the incoming flow energy. Increasing G/D from 1 to 1.5 reduces the scour depth by about 12%, with smaller further reduction beyond G/D = 1.5, suggesting that this spacing offers a pragmatic compromise between structural footprint and scour resistance.

This study presents a high-fidelity CFD-based optimization of a combined sacrificial-pile and collar (SPC) system designed to suppress local scour at circular bridge piers. Following rigorous validation against benchmark flume experiments (scour depth error < 3%), a systematic parametric study was conducted to quantify the influence of pile-to-pier spacing (d_p/D = 4–6) and collar elevation (h_c/D = 0–0.3). The optimal layout is found to be a sacrificial pile at d_p/D = 5 and a collar at h_c/D, which yields a 51.2% scour reduction relative to the unprotected case. Flow field analysis reveals that the pile wake deflects the lower approach flow, while the collar vertically displaces the horseshoe vortex; together, these mechanisms redistribute bed shear stress and prevent secondary undermining. Consequently, the upstream conical pit is virtually eliminated, lateral scour is broadened but markedly shallower, and the downstream dune tail bifurcates into two symmetrical ridges. To the best of the authors’ knowledge, this study presents the first high-fidelity CFD-based optimization of a combined sacrificial-pile and collar (SPC) system with a fully coupled hydrodynamic-morphodynamic model. The optimized layout yields a 51.2% scour reduction relative to the unprotected case and, more importantly, demonstrates a positive non-linear synergy that exceeds the linear sum of individual device efficiencies by 7.5%. The findings offer practical design guidance for enhancing bridge foundation resilience against scour-induced hydraulic failure.

A sea-crossing bridge is typically constructed in a marine environment with complex piers, and is susceptible to severe scour at the foundation. This study presents a numerical investigation on flow and scour around a complex pier, specifically focusing on a real-world sea-crossing bridge in China. A comprehensive CFD model incorporating hydrodynamic, free surface, sediment transport, and morphological models is employed for numerical modeling. Additionally, a wind shear stress model is considered to accurately simulate wind generation. The validation of the CFD model is achieved through comparison with experimental data of scour around a cylinder, demonstrating its capability to accurately replicate scour morphology and the temporal evolution of scour depth. Subsequently, the validated model is utilized for full-scale simulation of scour around the complex bridge pier under different wind, wave, and current conditions. The results indicate that compared to single piers with uniform cross-sectional shapes, flow patterns around complex piers are much more complicated. Scour predominantly occurs around the first row of group piles, while downstream piles experience less scour due to the sheltering effect from upstream piles. Furthermore, it becomes evident that the current exerts greater influence on pier scour than waves and wind, while the latter two factors primarily influence the superstructure of the bridge.

Waves or tsunamis in the onshore area could induce severe scour at the structure foundations, threatening the stability of the structure. This paper presents a numerical study of the solitary wave-induced flow and scour around a square onshore structure. A CFD model coupled with hydrodynamic and sediment transport models is first validated through a large-scale laboratory experiment, which shows that the model can well reproduce the flow and scour characteristics. Subsequently, based on the reliable numerical results, the flow field and scour development during wave inundation of the structure are explored. It is found that the development of the simulated scour depth is faster at the early stage compared to that in the experimental result. The results also show that the scour starts at the front corner of the structure, which is also the position of the maximum scour depth. The scour develops rapidly at the early stage and is almost completed in the first half of the wave period. In addition, the results demonstrate that bed scouring increases the wave force on the structure due to the increase in the flow velocity near the bed, which needs to be considered, especially in the shallow-water scour scenario. Finally, a simplified prediction equation is proposed for the temporal development of the scour depth.