河床预开挖对围堰上游桩基局部冲刷影响研究

Influence of Riverbed Pre-excavation on Local Scour of Pile Foundation Upstream of Cofferdam

桩基冲刷与水流、泥沙耦合作用密切相关,其局部冲刷深度直接影响结构物的安全稳定性。以某大桥深水基础为研究对象,构建并验证三维泥沙输移数学模型,量化分析河床有无预开挖条件下,围堰及上游桩基水流、泥沙运动规律。结果表明:河床无开挖条件下,围堰迎水面流速较小,直角端流速达到最大,后排桩基受前排桩基尾流及下游围堰阻水形成的反向流影响明显;河床预开挖后,围堰四周流速减小,挖槽有利于前端下降水流形成回流,挟沙能力减弱;上游桩基在预开挖条件下,桩基局部流速及冲刷深度均不同程度地减小,后排桩基最为明显,局部冲刷深度减小程度最大,达82.86%~85.07%。

The scour of pile foundation is closely related to the coupling action of water flow and sediment,and the local scour depth directly affects the safety and stability of the structure.Taking the deep-water foundation of a bridge as the research object,this paper constructs and verifies a three-dimensional numerical sediment transport model to quantitatively analyze the flow and sediment movement rules of cofferdam and upstream pile foundation under the conditions of riverbed with and without pre-excavation.The results show that:the flow velocity at the upstream face of cofferdam is small,and that at the right angle of the cofferdam reaches the maximum.The back-row pile foundation is obviously affected by the wake of the front-row pile foundation and the reverse flow formed by the backwater of the downstream cofferdam.Under the condition of riverbed pre-excavation,the flow velocity around the cofferdam decreases,and the grooving is conducive to the backflow formation of the downward flow,and the weakening of sediment carrying capacity.Under the pre-excavation condition,the local flow velocity and scour depth of the upstream pile foundation decrease to different degrees,especially for the back-row pile foundation,with maximum local scour depth reduction of 82.86%~85.07%.