An analytical method to estimate failure plane angle and tension crack depth for use in riverbank stability analyses

Of the many different types of riverbank failure, the planar failure mechanism is perhaps the most common, being associated with steep, relatively low banks composed of cohesive sediments. To reliably analyze the stability of riverbanks against planar failures many parameters (including the failure plane angle and the depth of the tension crack) have to be determined. In this paper we introduce a new analytical method to estimate the failure plane angle. This is achieved by employing a combination of field and laboratory data to first derive a set of empirical curves to estimate the tension crack depth. The estimated tension crack depth is then used in a bank stability analysis, from which the failure plane angle can be evaluated. Based on observations from field and laboratory tests, we found that the new model provides a mean relative error (MRE) of 4%, 23%, and 27% between calculated and observed values of failure plane angle, tension crack depth, and bank-top retreat, respectively. Based on a comparison of these errors with those derived from a range of existing equations, we show that this represents a considerable improvement relative to prior studies. The new model can therefore be used to determine the geometrical parameters of the failed blocks of riverbanks subject to planar failure.