凹岸崩塌体对急弯河道水力特性的影响

Study on the effects of failed soil block upon the hydraulic characteristics of sharp bend

二元结构河岸下部非黏性土层持续冲刷侵蚀,上部黏性土体崩塌并堆积于凹岸坡脚,改变弯道水流结构并影响河岸二次侵蚀过程。为探究崩塌体对急弯河道水力特性的影响,以荆江石首河段为背景,建立弯道三维水流数学模型,模拟不同崩塌体尺寸下的弯道水流结构,并对比分析壁面剪切力的变化规律。结果表明:(1)崩塌体堆积于凹岸坡脚驱离水流动力轴线,减小凹岸次环流强度并改变环流方向。(2)崩塌体对弯道不同区域壁面剪切力的影响不同,其中,床面及凸岸坡面的平均壁面剪切力增大;凹岸坡面平均壁面剪切力在崩塌体头部及上游区域减小,在崩塌体尾部区域增大。(3)崩塌体越大,剪切力变化幅度越大,剪切力相对变化幅度为崩塌体截面积变化幅度的2%~10%。研究成果可为河道整治及岸线规划利用提供技术支撑。

For the composite riverbank,the continuous erosion of the lower non-cohesive layer results in the failure of upper cohesive layer.The cohesive soil block deposits at bank toe,which can alter the flow structure and the following erosion process in the bend.To reveal the effect of failed soil block,a three-dimensional numerical model was developed to simulate the flow structure and wall shear stress pattern in the Shishou bend with different failed block.The results indicate that soil block deposit at bank toe shifts the dynamic axis of flow away from the outer bank,decreases the intensity of the secondary flow,and changes the direction of the secondary flow.The effect of failed block on the wall shear stress changes greatly with space.For the riverbed and inner bank,the average wall shear stress tends to increase,while decreases in the head and upstream area of the failed block for the outer bank.The larger the failed block is,the greater the variation of wall shear stress will be.In comparison,The variation of wall shear stress is about 2%—10%of the variation of cross-sectional area of the failed block.The results are expected to provide a basic theoretical and technical support for river regulation and riverbank planning.