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.