岸坡崩塌条件下弯道环流与水流剪切力的变化特征

Characteristics for circulating currents and water-flow shear stress under the condition of bank slope collapse

河岸崩塌(又称为崩岸或塌岸)是水动力作用下岸坡失稳的一种主要形式,属于一种典型的水力与重力的复合侵蚀。本文采用黄河上游宁蒙河段的磴口黏性河岸沙为实验用沙,通过实施8组弯道水槽实验模拟塌岸过程与河道冲淤演变过程,重点观测并分析崩塌近岸水位、流速、颗粒粒径及河床冲淤形态等水力-泥沙-河床三方面因子变化特点,揭示黏性岸坡崩塌过程水流剪切力分布特征及其对河道冲淤形态影响机制,结果显示崩塌体头尾部的剪切力突增,形成较大剪切力区,尾部剪切力大于头部剪切力,尾部形成涡流,流速分布混乱,加快崩塌体的分解和崩塌进程。实验进一步揭示了崩塌过程河床形态对水流剪切力的响应关系,为建立崩塌河段泥沙输移模型提供了基础依据,并可供河道整治工程规划设计参考。

Riverbank collapse is a major form of bank slope instability because of hydrodynamic forces, which is the interaction result of the river water flow and bank slope. Eight series of experiments were car- ried out in a bend flume to simulate the process of bank collapse and river topography in small scale. Co- hesive bank material from Dengkou site of the Ning-Meng river reach of the upper Yellow River was used to make the bank slope model. The experiments pay attention to the features of changes in three aspects of water-sediment-riverbed, such as water level, near-bank flow velocity distribution, particle size and river- bed erosion and sedimentation, and the distribution characteristics of water shear force distribution during the collapse of sticky bank slope are revealed and analyzed. The bed shear stress was calculated and found that the shear stress of the head and tail of the collapse body increased suddenly, which formed a larger shear force zone. The tail shear stress is greater than the head shear stress, and the tail is formed eddy current and the flow velocity is chaotic, which increases the local sediment transport capacity of the river bed to speed up the decomposition of the collapse of the body. The paper analyzes the hydrodynamic change characteristics of the bank slope collapse, which provides not only the basis for cohesive bank sedi- ment transport model, but also the reference for the planning and design of river bank construction.