Channel retreat can be responsible for the significant loss of banks, farmland, and wetlands, leading to drastic changes in fluvial sediment and local river regimes. Although current studies focus on the erosion process of natural river channels, the mechanism by which revetments, such as the flexible mattress, influence bank evolution is still unclear. Hence, by conducting a generalized model experiment, this study investigates the point bar failure process under the mattress protection, i.e., the episodic event when the soil reaches the static equilibrium state. Specifically, a scour hole develops at the junction between the soft and hard materials, causing mattress suspension on the bank toe’s side wall and resulting in a reduction coefficient for transverse scouring rate ranging from 0.08 to 0.15. Based on the theories of soil mechanics and river dynamics, the critical conditions for point bar instability were deduced, and a mechanical model describing its erosion process under the mattress protection was established. Furthermore, our model calculated the bank morphology and total erosion volume at different periods in the flume experiment, demonstrating a good agreement with the measured data. Additionally, variations in stability coefficient and forces exerted on soil (including shear strength, gravity, and fluid pressure) of the typical sections during point bar retreat were analyzed. Sensitivity analysis of the bank toe stability emphasized the controlling effect of soil mechanical properties and the negative feedback of mattress weight. The results reveal the interaction mechanism between the mattress protection and point bar failure, theoretically guiding the bank erosion strengthening and river management planning.

中文翻译：

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柔性床垫保护下点杆退缩的侵蚀机理

河道退缩可能导致河岸、农田和湿地的大量损失，导致河流沉积物和当地河流状况的急剧变化。尽管目前的研究重点是天然河道的侵蚀过程，但柔性垫层等护岸影响河岸演化的机制仍不清楚。因此，本研究通过广义模型实验，研究了床垫保护下的点杆破坏过程，即土壤达到静力平衡状态时的偶发事件。具体而言，在软质和硬质材料的交界处形成冲刷孔，导致岸趾侧壁上的床垫悬浮，导致横向冲刷率的折减系数为0.08至0.15。基于土力学和河流动力学理论，推导了点坝失稳的临界条件，并建立了描述点坝在垫层保护下侵蚀过程的力学模型。此外，我们的模型还计算了水槽实验中不同时期的河岸形态和总侵蚀量，与实测数据吻合良好。此外，还分析了点坝退缩过程中典型断面的稳定性系数和土体受力（包括抗剪强度、重力和流体压力）的变化。岸趾稳定性的敏感性分析强调土体力学性质的控制作用和垫层重量的负反馈作用。研究结果揭示了垫层保护与点坝破坏之间的相互作用机制，为河岸侵蚀加固和河流管理规划提供理论指导。