往复潮流输沙作用下桩基局部冲淤发展过程与机理

In estuary and offshore areas, wind turbines, sea bridges are increasing. By the influence of tide and reversing sediment transport flow, the course and mechanism of the flow regime and local scour around pile foundation has not yet fully revealed. In this study, it uses idealization model and theoretical analysis to research flow structure and the characteristics in different zones (compression zones, separation zones, recirculation zones, and so on) around pile foundation by reversing flow affecting, and to grasp flow distribution laws and their expression methods. Then, at the cyclical change flow conditions, combining flow distribution around pile foundation, and base on the sediment starting and movement conditions, it researches the scouring development course of different zones around pile foundation, reveals the interaction mechanism between scour parameters (geometric features, spatial scales, and development rate of scour holes) and key factors, and builds mathematical representation of local scour. At the same time, combining the sediment characteristics of Huanghe estuary, it researches suspended sediment distribution laws and deposition characteristics in different zones, fully reveals local sediment transport and deposition mechanism around pile foundation. Finally, based on the above researches, it builds corresponding calculation mode of scour and sediment transport. Coupling existing mathematical model of Huanghe estuary, it systemic tests and comprehensive analyses the computational methods. The study provides theoretical and technical support to optimize the design and maintain of wading pile foundation in estuaries.

河口及近海区域风机、跨海大桥等日渐增多，受海洋潮汐及河道输沙形成的往复输沙流影响，其桩基附近水流流态及冲刷发育过程与机理更为复杂，目前尚未被充分揭示。本研究首先结合概化试验和理论分析，研究往复流作用下桩基附近的水流结构及分区特征（挤压区、分离区、回流区等），精细把握各分区流速分布规律及表征方法；然后，结合桩基附近水流特征，基于床面颗粒的起动与运动条件，研究周期变动水流条件下桩基附近各分区的冲刷发展过程，揭示冲刷坑几何特征、空间规模、发育速度与关键影响因素的相互作用机制，建立往复流作用下局部冲刷的数学表征；同时，结合黄河口区域来沙特征，研究绕流情形下各分区的含沙量分布规律及落淤特征，充分揭示往复流输沙作用下桩基局部输沙与淤积机理；最后，基于上述研究，建立相应的冲淤与输沙计算模式，耦合于已有黄河口数学模型，对计算方法予以系统检验与综合分析。为优化河口涉水桩基设计及维护提供理论支持和技术支撑。

河口及近海区域风机、跨海大桥等日渐增多，受海洋潮汐及河道输沙形成的往复输沙流影 响，其桩基附近水流流态及冲刷发育过程与机理更为复杂。本项目应用河口三维数学模型和概化物理模型，结合理论分析，研究了往复流作用下桩基附近的水流结构，及周期变动水流条件下桩基附近的冲刷发展过程。研究结果表明：（1）水流往复流动时，均在桩基背流侧形成旋涡；旋涡的大小受水流流速的影响，随着水流流速的减小，旋涡逐渐增大，当水流方向发生转变时，旋涡达到最大。（2）当桩基附近水流方向发生变化时，迎流侧底层水流方向先发生变化，背流侧表层水流方向先发生变化。（3）单向水流仅在背流侧冲刷坑外有泥沙堆积，往复水流在桩基两侧的冲刷坑外均有泥沙堆积，背流侧水流强度越大，泥沙堆积厚度越大。（4）水流在桩基背流侧的两侧形成旋涡，挟带泥沙向背流侧的中线位置输移，在桩基背流侧冲刷坑的中线位置向内凸。（5）水流往复运动时，来流量大的一侧冲刷坑的深度及宽度均大于来流量小的一侧。（6）往复水流作用下桩基附近冲刷坑小于单向水流作用下的冲刷坑。（7）单向水流作用下，桩基迎流侧冲刷坑形态为指数型，当反向水流逐渐增强，迎流侧冲刷坑形态逐渐向斜线型发展；单向水流作用下，桩基背流侧冲刷坑形态为斜线型，当反向水流逐渐增强，背流侧冲刷坑形态逐渐向指数型发展。项目的研究成果进一步丰富了局部冲刷机理，具有重要的学术意义和实用价值。