Objectives  The natural evolution process of bank slope is broken by the impoundment of giant reservoir, showing many different development mechanisms and laws of landslide from those before impoundment. One of them is that there is obvious deep-seated toppling failure in a short period of time for the traditionally believed stable anti-dumping bedrock mountain. The scale, mechanism and failure trend of the landslide are the information needed to be grasped for the geological disaster prevention and control in the reservoir area.

  Methods  After the impoundment of Xiluodu reservoir area in the lower reaches of Jinsha River, the deformation of Yanwan reverse slope occurred. The deformation of the slope was investigated on site twice. The objective is to compare the deformation characteristics of slope before and after impoundment, analyze its deformation mechanism and predict its future deformation and failure trend.Interferometric synthetic aperture radar (InSAR) technology and particle flow code (PFC) method are used.

  Results  The prediction results show that the failure trend of the slope is the collapse of the shallow rock mass and the widening of the cracks on the upper part of the slope under the action of the structural plane, rather than the overall shear sliding.

  Conclusions  The deformation of slope is mainly affected by slope structure, in-situ stress, lithology and reservoir impoundment. The deformation mechanism can be summarized as follows: After impoundment, the rock mass below the water level produces compression deformation; the deformation response of the upper soft rock mass to the front edge produces toppling deformation and interlayer dislocation; the fractured rock mass compresses the front rock mass under the action of gravity, resulting in the shear creep deformation along the fracture surface. After impoundment, the line of sight deformation rate of the slope gradually increases from the outside to the inside. The PFC simulation results are consistent with the deformation characteristics. The formation lithology in the large deformation area monitored by InSAR is argillaceous limestone and shale interbedding, and its mechanical properties are worse than that of the upper and lower strata, and it is easier to deform, corresponding to the deformation characteristics of InSAR.