Investigating effect of water level variation and surface tension crack on riverbank stability

During high flow season, the rise and fall of river water level could induce riverbank instability and threaten structural safety of flood-protection facilities on floodplains. Through a flume experiment, this paper investigates the influences of three factors (namely, drawdown rate of river stage, initial water elevation, and riverbank slope angle) on riverbank stability due to the fall of river water level. From the laboratory experiments it was observed that tension crack appeared in all riverbank failure cases and all failure patterns were of planar type. Moreover, this paper presents a riverbank stability analysis model that explicitly incorporates the integral effect of all forces acting upon the failure plane and tension crack. The prediction accuracy of the proposed model is examined by using experimental data obtained in this study and field data of the Hotophia Creek in the USA and the Sieve River in Italy. A comparison of model simulation results with and without considering tension crack clearly indicates the importance and necessity of including tension crack for achieving good accuracy in riverbank stability simulations. For practical application of the improved riverbank stability model, two empirical formulas for estimating tension crack location and failure plane angle were examined and modified to enhance their appropriateness in riverbank stability simulation. Finally, the improved model with the modified empirical formulas was verified to show its good prediction in riverbank stability analysis.