基于点稳定系数法的非饱和河岸边坡稳定性分析

Stability of Unsaturated Bank Slope Based on Local Factor of Safety

河岸边坡的整体稳定性计算,无法定量反映水位变化对边坡各部位局部稳定性的影响。基于点稳定系数法与非饱和土力学理论,运用非饱和流固耦合模型进行河岸边坡的稳定性数值分析。以某大型模型试验为例,通过绘制边坡在水位升降作用下各时段所对应的点稳定系数分布云图,揭示边坡的破坏原因与内部稳定性变化过程,并与实际观测结果进行对比。研究表明:点稳定系数法能合理地描述河岸边坡各位置的稳定性及其动态变化,与实际吻合良好;边坡临空面稳定性较低,水位缓慢上升将导致有效应力降低及非饱和区基质吸力丧失,易诱发浅层失稳;水位下降形成的动水压力,是导致边坡稳定性下降的主因,坡脚处最易失稳,致使边坡发生牵引破坏;边坡内部点稳定系数随水力梯度的增大而降低,非稳定区分布面积随水力梯度的增大而增大,并主要分布于浸润线以下、坡脚以上。研究成果为此类边坡的稳定性评价及治理提供了一定的科学依据。

Overall stability calculation for river bank slopes could not reflect the impact of water level fluctuation on various parts of the slope stability quantitatively.On the basis of the theory of unsaturated soil mechanics and local factor of safety method（ LFS）,we conducted numerical analysis on the stability of river bank slope by the model of unsaturated liquid-solid coupling.Taking a large-scale model test for example,we plotted the contours of LFS at different instances under water level fluctuation to reveal the causes of destruction and the processes of internal stability.Compared with actual observations,the analysis result demonstrates that 1） the LFS method could describe the river bank slope stability and its dynamic changes at various slope positions reasonably; 2） the free face of slope is of low stability,and water level rise would reduce the effective stress and lead to the loss of matrix suction in the unsaturated zone of slope,which is easy to induce shallow slide; 3） the hydrodynamic pressure formed by rapid drawdown is the main cause of the decline of slope stability and the most vulnerable zone is the toe of slope where retrogressive failures often emerges; 4） along with the increase of hydraulic gradient,the internal local stability coefficient decreases and the instability zone,which distributes mainly between the saturation line and the toe of slope,expands.