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河岸稳定性动态机理及生态支护方案分析

Dynamic mechanism of river bank stability and analysis of ecological support scheme

  • 摘要: 为研究降雨联合水位波动条件下的河岸稳定性动态机理, 设计合理的生态护坡方案, 采用实地勘察、力学试验、数值模拟相结合的方法揭示嘉陵江北碚段边坡稳定性随水位变动的特点及边坡失效机理, 并对比传统护坡手段探讨"活木桩护坡"措施中的关键技术参数。结果表明: 1)河岸滩涂边坡的稳定性随水位升降而波动, 在水位消落阶段边坡稳定疾速下降, 其原因为边坡外部静水压力随水位消落卸载, 边坡内部指向坡外的渗透压力作用导致中坡位发生浅层破坏。在暴雨多发的夏秋季节, 当江水位下降速率超过3 m/d应激发河岸滩涂的滑坡灾害预警; 2)在活木桩的桩体直径和入桩角度固定的条件下, 适当增加入桩长和减少桩间距有助于限制边坡水平位移, 河岸滩涂缓坡的桩体配置建议为警戒水位和常水位之间的中上部, 桩距2.3 m桩长3.3 m组合, 且只有当桩长接近潜在滑动层时才会影响到表层土的稳定性; 3)在优化参数配置下的活木桩配置初期, 可在水位消落的极端条件下提高稳定系数18.6%, 是传统草灌木固坡效果的3.8倍。木桩根系充分生长后可提高边坡稳定系数22.3%, 较同配置桩体增加3.7%。

     

    Abstract:
    Background In order to study the dynamic mechanism of bank stability under the condition of rainfall combined with water level fluctuation, a reasonable ecological slope protection scheme was designed.
    Methods In this study, the combination of field investigation, mechanical test and numerical simulation was used to reveal the characteristics of the slope stability changing with water level and the failure mechanism of the slope in the Beibei section of the Jialing River, and the key technical parameters of the "living wood pile slope protection" measures were discussed by comparing with traditional plant slope protection methods and engineering pile slope protection methods.
    Results 1) The stability of the river bank beach slope fluctuated with the rise and fall of water level, and the slope stability dropped rapidly during the water level fluctuation stage. The reason is that the external hydrostatic pressure of the slope unloaded with the rise and fall of water level, and the seepage pressure inside the slope pointing outward from the slope caused shallow damage to the middle slope. In summer and autumn, when the water level of the river dropped more than 3 m/d, the early warning of landslide disaster on the river bank and beach should be triggered. 2) When the live wood pile, pile diameter and pile angle were fixed, properly increasing the pile length and reducing the pile spacing will help limit the horizontal displacement of the slope. It was suggested that the pile configuration of the gentle slope of the river bank beach was the middle upper part between the warning water level and the normal water level, with the pile spacing D=2.3 m, pile length L=3.3 m. The stability of topsoil will be affected only when the pile length was closed to the potential sliding layer. 3) At the initial stage of the configuration of live wood piles under the optimized parameter configuration, the stability coefficient increased by 18.6% under the extreme conditions of water level fluctuation, which was 3.8 times of the effect of traditional grass and shrubs on slope consolidation. After the root system of wood piles was fully grown, the slope stability coefficient increased by 22.3%, which was 3.7% more than that of piles configured with the same configuration.
    Conclusions This paper studied the change of pore water pressure of bank slope under the conditions of rainfall and water level fluctuation, and compared the slope stability of different support measures of bank slope in the Jialing River section of the Three Gorges Reservoir. On this basis, the arrangement parameters of movable wooden piles were optimized to provide theoretical basis and technical support for the ecological protection of the riverside in the Three Gorges Reservoir area.

     

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