Experimental and Numerical Modeling of Overhanging Riverbank Stability

Abstract

AbstractOverhanging riverbank stability is a key feature of bank retreat. Although different mechanisms of bank collapse have been studied by many researchers, prediction of cantilever failure patterns and understanding of three‐dimensional failure surfaces continue to puzzle scientists. To address this problem, we conducted laboratory experiments and numerical simulations to investigate the stability of overhanging riverbank. In the laboratory experiments, we analyzed the characteristics of failure surface using a three‐dimensional laser scanner. Results show that with decreased ratio between bank height and near‐bank water depth, there is a transition from a ‘tensile failures followed by toppling failure’ pattern to a ‘shear failure’ pattern. Flow infiltration in our experiments leads to a sharp decrease in soil shear strength and consequently the occurrence of shear failure. For toppling failure, the observed upper retreat distance is much greater than the lower undermining depth, thus challenging the widely adopted assumption of a constant failure surface along the endpoint of the cantilever. Also, we found that failure surface distance can be characterized by twice the width of the overhanging block. As for the failure surface angle, a negative linear correlation is proposed with respect to bank retreat distance, implying a distinct distribution of bank stability along the arched‐shape bank line induced by bank collapse events. Overall, our study deepens understanding of overhanging stability, providing a new perspective on bank retreat process, critical for the morphodynamics of rivers and estuaries.