复杂群桩基础局部冲刷演化机理及冲刷深度预测精细化数值模拟研究

冲刷是造成桥梁破坏的主要原因之一。我国涉水桥梁基础大多采用复杂群桩基础（群桩基础-承台-桥墩结构形式），其局部冲刷机理复杂，冲刷深度预测难度很大。目前，复杂群桩基础局部冲刷研究以水槽试验为主，但存在模型缩尺效应等不足。本项目基于雷诺平均方法建立复杂群桩基础局部冲刷的三维CFD数值模型，并通过发展河床壁面切应力计算的改进模型和自保持来流边界条件，大幅提高数值模型的计算精度。并以该模型为基础，以流场特性、冲刷深度和冲刷坑形态为指标，系统研究结构形式和来流条件等关键因素对复杂群桩基础局部冲刷的影响规律，揭示其冲刷演化机理。然后，基于数值分析结果引入群桩效应和承台尺寸效应系数，建立复杂群桩基础局部冲刷的简化计算公式；建立冲刷前河床壁面切应力和最大冲刷深度的映射关系，发展快速预测冲刷深度的数值方法。最后，基于流动控制理论建立复杂群桩基础冲刷防护方法。研究成果可为复杂群桩基础的抗冲刷设计提供重要参考。

Scour is one of the main causes of bridge damage. Most of the bridge foundation in river in China adopt complex pile group foundation, such as pile-cap-pier. Local scour mechanism around complex bridge foundation is more complex, and the prediction of scour depth is more difficult. At present, the local scour around complex pile group foundation is mainly studied by flume test, but there are some shortcomings such as model scaling effect. This project intends to develop a three-dimensional CFD numerical model for local scour around complex pile group foundation based on Reynolds average method, and improve the computational accuracy of the numerical model by improving the calculation model of riverbed wall shear stress and introducing self-sustaining inlet boundary condition. Based on the above model, the influence law of the key factors such as structure parameters and inflow condition on local scour around complex pile group foundation is systematically studied to reveal the local scour evolution mechanism. Then, based the numerical analysis results, the pile group effect and the cap size effect coefficient are established to simplify the calculation of local scour depth of complex pile group foundation. The numerical method for rapid prediction of scour depth is established through finding the mapping relationship between the wall shear stress under fixed bed and the maximum scour depth. Finally, based on the flow control theory, the scour protection method of complex pile group foundation is established. The research conclusions can provide important reference for the anti-scour design of complex pile group foundation.