淹没式丁坝回流区二元结构岸滩失稳及其演化机理研究

With the development of the high-grade waterway network, much more attention has been paid to the failure of beach protection structure and riverbank collapse caused by the flow turbulence in the backflow region around spur dikes. Due to the complexity of this problem, until now few research was carried out to study its mechanical properties. The objective of this research is to investigate the essential relationship between the composite riverbank collapse and the turbulence parameters of flow in the backflow region around spur dikes, based on the analysis of observed data, physical model experiment, and numerical simulation. The Han River will be selected as a case study. First, a series of experiments will be conducted in order to identify the main influence factors which control the turbulence intensity in the near-bank zone of backflow region. Second, the influence of unsteady properties of turbulent flow on the river bank collapse will be analyzed. Third, the revulsive mechanism of beach protection structure and riverbank failure will be discussed under the influence of the inflow turbulence. Finally, a new dynamically stable model will be established considering the Reynolds shear stress. On the condition of the flow turbulence, then a quantitative description of the resolving, moving and transporting of the collapsed soil will be determined in the backflow region. This study will not only help us investigate the evolutionary processes of riverbank around spur dikes, but develop the channel evolution theory in the complex flow area. It also provides some technical references for the similar river channel regulation and flood control all over the country.

随着我国高等级航道网建设进程的不断加快，丁坝回流区近岸水流紊动对护滩结构破坏和岸滩崩塌的危害受到了人们的高度重视。但由于问题的复杂性，目前对于其作用机理尚缺少系统的研究。本项目以汉江中游丁坝工程河段为研究对象，针对回流区护滩结构水毁破坏和岸滩崩塌等问题，采用实测资料分析、水槽试验以及数值模拟仿真等相结合的方法，研究具有二元结构的回流区岸滩水毁崩塌破坏机理及其演化过程与水流紊动参量变化间的响应关系；识别控制回流区近岸水流紊动的主要影响因子，分析水流紊动变化的非恒定特性对岸滩崩塌失稳随机过程耦合作用力学机理，揭示水流紊动特性对岸滩防护结构破坏、崩塌的诱导机制；建立包含水流紊动应力的岸滩动态稳定分析模型；确定回流区涡流紊动条件下崩塌体泥沙破碎分解、搬运和快速输移机制的定量描述模式。本研究成果将有助于探明丁坝回流区岸滩演变特性，丰富复杂流区的河道演变理论，且为类似河道治理及防洪安全提供技术参考。

本项目主要以汉江典型河段为研究对象，采用实测来水来沙资料分析、理论分析与模型试验相结合的方法，开展了丁坝工程河段具有二元结构岸滩的崩塌过程与形成机理的模拟研究。首先对典型崩塌河段上游来水来沙变异情况进行了细致分析，得到了岸滩稳定对水沙变异的响应过程。基于实测地形资料与模型试验分析，通过多组次试验揭示了水沙变异、水流紊动、河床与河岸抗冲性等因素对岸滩稳定的影响机制。分析了岸滩崩塌与局部水流紊动作用机理和崩塌土体快速分解、破碎和输送的力学行为过程。建立了基于实测地形的描述丁坝工程河段水流紊动特性的数值模型，对崩塌土体局部水流紊动特性和受力特点进行了详细描述。针对当前丹江口加高蓄水以及三峡水库蓄水后坝下游河道出现的长距离冲刷情况，通过数学模型模拟了典型岸滩崩塌河段在梯级水库调控条件下局部河段的水流紊动特性以及剪切力变化特征，进而为岸滩崩塌以及护岸结构破坏研究提供了理论基础。本项目取得的研究成果不仅有助于掌握丁坝工程河段水流运动特性、岸滩稳定对水沙变化的响应机制，而且能为类似河道治理及防洪安全提供技术参考。