The riverbanks, subjected to seasonal flooding and tidal variation, are submitted to landslides causing property damage and sometimes human victims. The presented work is conducted to analyze the riverbank stability subjected to the tide variation by considering the influence of external and internal water flows on the bank soil. More particularly, we consider the effect of ground water variation on the soil pore pressure. The Dupuit’s flow model is adopted to find the variation of the ground water table. A method of slices is developed to calculate the safety factor of riverbank slides as a function of tide. Parametric studies of the effect of bank geometry, hydromechanical soil properties and the characteristics of tide variation are then presented. Then the bank surface erosion is simulated by different methods and coupled with the calculation of landslide. Finally, case studies at Mont-Saint-Michel bay and on the lower Mekong riverbank are conducted.The comparison between simulations and field measurements of ground water table during the tide variation let us conclude that the Dupuit’s flow model can be adopted for homogeneous and isotropic soils. However, the mode is less accurate for more complex media, such as multilayered soils. The tide has a significant effect on the pore pressure in the soil, which creates damping and delayed phase phenomena with respect to the tide.Slide safety factors vary as a function of tide and they are minimal during the falling of water level before low tide due to the delay of the ground water table and the slowing down of the speed of the tide. Charts of safety factor have been proposed providing the security domains based on various soil parameters, bank geometry and tide variation. These charts also allow calculation of the safety factor by linear interpolation.When the bank is submerged for a time period long enough, the failure surface is located in the upper part of the bank and occurs at high tide. This failure mode is also observed in the field study (Mont-Saint-Michel). During the falling of tide from the bank surface, the second mode of failure is observed corresponding to deeper slip surfaces associated with high residual pore pressures.In the period of decline after flooding of the bank (Kaoh Chorram site), the bank safety factor decreases with the falling of water level below the top of the bank. At the same water level in the river, the safety factor during decreasing water level is smaller than that during the steady state. Significant different failure surfaces are observed between the two regimes.
Study of riverbank stability subjected to tide variation