三峡库区塔坪H2古滑坡台阶状复活变形的库水–降雨耦合作用机制

三峡水库蓄水以来,出现了大量大规模的老滑坡体复活现象。较多大型复活滑坡体的监测位移–时间曲线呈台阶状阶跃变化。此类滑坡的稳定状态识别难度较大,严重影响治理方案及治理时机的选择。以巫山曲尺塔坪H2滑坡为例,通过地质、位移监测及数值模拟方法,研究了此滑坡在实际降雨与库水涨落条件下渗流场、稳定性以及变形场演化规律。在汛期及库水位变动时期滑坡会发生变形,特别是库水位下降诱发滑坡前缘变形,并对后部坡体产生牵引作用。而降雨主要影响库水位变动带以上部分滑体的变形,并对前缘坡体产生推动作用。在周期性降雨和库水位涨落的循环作用下,滑坡体反复受到"推–拉"作用,导致滑坡的位移–时间曲线呈现台阶状阶跃特征。总体来说,库水位涨落是滑坡变形的主要因素,而降雨促进了滑坡变形进一步发展。

Hybrid effects of rainfall and reservoir level fluctuation on old Taping H2 landslide in Wushan County in Three Gorges Reservoir area

Since the first impoundment of Three Gorges Reservoir, a large number of old landslides have shown signs of reactivation. Usually, the displacements of these large landslides are characterized by a stepped pattern. Besides, the stability identification of the slides is difficult, which severely affects the choice of appropriate measurements and timing of treatment. By taking the H1 sliding mass of Quchi landslide as an example, based on the geological survey, displacement monitoring and numerical modelling, the seepage field, stability and deformation of the landslide under the influence of reservoir level fluctuation and rainfall are fully studied. It is revealed that the changes in reservoir levels have a great influence on the deformation of the landslide, especially, the significant deformations at the toe are induced by reservoir drawdown, which then “drags” the masses in the upper part down. The precipitation affects the deformation of sliding mass above the water fluctuation zone, whose collapse “pushes” the masses at the toe downslope. Under the periodic action of changes in reservoir levels and rainfall, the sliding masses are subjected to “drag-push” influences iteratively and thus exhihit a staged deformation characteristic. On the whole, the fluctuating water level is the main trigger of the deformation while the precipitation facilitates this progress.