Abstract: According to the features of typical dual soil structure in the Jingjiang River, the calculation formula of transverse erosion was employed to study the influences of flow velocity and sediment concentration on transverse erosion rate of bank slope, as well as the variation law of morphologic changes of bank slope under fluctuation of water level.On the basis of saturated-unsaturated seepage theory, a two-dimensional unsteady seepage model was established by using SEEP/w program and the change process of seepage field of bank slope was simulated. Furthermore, on the basis of calculation of pore-water pressure field, the change law of slope stability in consideration of bank erosion or not was analyzed by using Morgenstern's method.Results show that when bank erosion is not considered, slope stability increases with the raise of water level and declines with the drawdown of water level; but when bank erosion is considered,slope stability decreases both with the raise and the drawdown of water level, and the falling rate of safety factors is obviously larger than that without considering bank erosion. In conclusion, the flood period and the final stage of water level falling are two dangerous periods of slope stability, which should be monitored specially.

Key words: bank slope stability, slope erosion, water level fluctuation, saturated-unsaturated seepage, dual soil structure