An improved analysis model for cantilever failure of composite riverbanks and collapse simulation

The riverbanks in the Lower Jingjiang Reach are mostly composite ones with fine sand overlain by cohesive clay, thus when the sandy layer is undermined due to rapid erosion, the cohesive upper layer generates a cantilever and is prone to beam failure. In this study, the formula of critical width of cantilever failure was improved considering the hydraulic effects. The formula of accumulated width of failed blocks at bank foot was deduced. A collapse analysis model of composite banks was subsequently proposed, and the collapse process of a typical bank slope was simulated using the model. The conclusions include: The cantilever failure of composite riverbanks is more prone to occur during the period of water level decline than that of water level rise. The critical width of cantilever decreases with the dropping of river level, the weakening of the supporting role of river water and the enhancement of the overturning effect of groundwater. The thicker the cohesive layer is, the greater the decrement of its critical overhang width is as river level decline. The protective effect of failed blocks accumulated at bank foot reduces its erosion distance, the more times the bank collapse takes place, the greater the impact is.