重庆云阳旧县坪滑坡成因特征与变形机制分析

三峡水库蓄水后大量涉水老滑坡产生复活变形,其中旧县坪滑坡是三峡库区典型滑坡之一,自水库蓄水以来一直持续变形,变形位移呈现出典型的阶跃型特征。根据地质调查及专业监测资料,深入分析了滑坡变形特征,得到了滑坡变形的影响因素及其变形机制。结果表明:砂泥岩互层的靠椅形软弱地层为滑坡的形成提供了地质条件,滑坡复活变形的最主要影响因素则是库水位波动,受库水位下降时的饱水加载效应和动水压力效应影响,增加了滑坡下滑力,因此导致坡体稳定性急剧下降,从而产生显著变形。运用SEEP/W程序的计算结果表明,旧县坪滑坡在库水位快速消落期水位下降速率增大或叠加50年一遇的暴雨条件下,稳定性系数位于1.055~1.069范围内,在最危险工况下仍处于基本稳定状态。滑坡整体处于等速蠕滑变形阶段,在持续暴雨情况下有发生局部变形破坏的可能,在汛期须对变形破坏严重处采取局部防护治理措施。研究结果为滑坡监测预警与防治以及实际库水位调度提供了参考和依据。

Analysis on genetic characteristics and deformation mechanism of Jiuxianping landslide in Yunyang County of Chongqing

A large amount of water related old landslides are revived and deformed after the impoundment of the Three Gorges Reservoir，among which Jiuxianping Landslide is one of the typical landslides within the reservoir area，which is continuously deformed since the impoundment and the deformation displacement presents a typical stepped feature. In accordance with the geological investigation and the professional monitoring data concerned，the deformation characteristics of the land slide is deeply analyzed，and then the impacting factors and the deformation mechanism of the landslide deformation are obtained. The result shows that the chair shaped weak stratum of sand shale interbed provides the geological condition for the formation of the landslide，while the main impacting factor for the deformation and revival of the landslide is the fluctuation of the reservoir water level； i.e. under the impacts from both the water saturated loading effect and the hydrodynamic pressure effect during the lowering of the reservoir water level，the downward sliding force is increased，which causes the stability of the slope rapidly lowered，thus induces significant deformation. The result from the calculation made with SEEP/W shows that under the condition of the increase of the lowering of the water level or superimposition of the rainstorm with the recurrence interval of 50 years during the rapid drawdown period of the reservoir water level，the coefficient of stability of Jiuxianping Landslide is in a range of 1.055～1.069，even under the most dangerous operation condition，the lanslide is still to be within a basic stable status. The whole body of the landslide is now in a phase of creep deformation with constant speed，which is possible to be locally damaged under the condition of a continuous rainstorm，thus the local prevention measures must be adopted on those locations with serious deformation damages. The study result provides reference and basis for both the monitoring and early warning of thelandslide and the actual scheduling of the reservoir water level.