库水位升降下三峡库区滑坡堆积体渗流滞后性研究

Study on seepage hysteresis of landslide mass in Three Gorges Reservoir Area under fluctuation of reservoir water level

三峡水库库区涉水滑坡较多,滑坡渗流特征及滞后性对水库滑坡稳定性分析评价具有非常重要的意义。为此,采用数值模拟方法对三峡库区涉水滑坡体在库水位升降作用下的渗流滞后性特征进行了研究,提出将滑体饱和渗透系数与库水位升降速率的比值定义为滞后系数作为评价滞后性的重要指标,从而得出滞后系数与水位变动带坡度为影响滑坡渗流滞后性的主要因素,并给出了计算其渗流滞后时间的简便方法。研究结果表明:饱和-非饱和界面的基质吸力是渗流滞后性产生的主要原因,可将滞后系数35近似作为渗流滞后型与同步型的界限值,滞后系数1.67与2.5作为区分滑坡滞后性强、中、弱等级的划分值;当库水位下降速率保持0.6 m/d时,库区45.7%的滑坡渗流为强滞后型,当增大库水位下降速率为1.2 m/d时,强滞后型滑坡数量达到64.4%。

The seepage hysteresis characteristics of the water-related landslide mass occurred in the Three Gorges Reservoir Area under the fluctuation of reservoir water level is studied herein with the numerical simulation method. It is proposed to define the ratio of the saturation permeability coefficient of the landslide mass to the rate of reservoir water level fluctuation as an important index to evaluate the hysteresis, and then it is obtained that the hysteresis coefficient and the slope gradient of the water level fluctuation zone are to be the main factors affecting the seepage hysteresis of landslide mass, while a simple method for calculating the hysteretic time is given out as well. It is revealed that the matric suction at saturation-unsaturated interface is the main cause of seepage hysteresis, and then the hysteresis coefficient of 35 can be approximately taken as the boundary value between the hysteretic seepage and the synchronous seepage and the hysteresis coefficients of 1.67 and 2.5 can be taken as the dividing values of the hysteresis level. When the drawdown rate of the reservoir water level remains at 0.6 m/d, 45.7% of the landslide seepages in the reservoir area are the strong hysteretic ones, while the number of the strong hysteretic seepage are to reach to 64.4% when the drawdown rate of the reservoir water level increases to 1.2 m/d.