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

Abstract

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.

Controls on the hydraulic geometry of alluvial channels: bank stability to gravitational failure, the critical-flow hypothesis, and conservation of mass and energy

“…Fluvial erosion of the bank toe is still necessary to remove material slumped from the bank into the channel and likely plays an important role in driving bank retreat in channels with cantilevered banks (Pizzuto, 1994). However, if the bank is more than twice the height of the zone of scour, gravitational shear failure nevertheless will be the process by which the majority of material is removed from the bank (Tao et al, 2019). That said, gravitational failure and fluvial shear stresses act in concert in such a way that identifying which process is dominant may be difficult.…”

“…The maximum stable height, h c , of an alluvial channel bank subject to gravitational shear failure is proportional to bankmaterial cohesion, C (Taylor, 1937;Terzaghi and Peck, 1967;Hunter and Schuster, 1968;Chen et al, 1969;ASCE, 1999):…”

Controls on the hydraulic geometry of alluvial channels: bank stability to gravitational failure, the critical-flow hypothesis, and conservation of mass and energy

“…Fluvial erosion of the bank toe is necessary to remove material slumped from the bank into the channel and likely plays an important role in driving bank retreat in channels with cantilevered banks (Pizzuto, 1994). However, if the bank is more than twice the height of the zone of scour, gravitational shear failure nevertheless will be the process by which the majority of material is removed from the bank (Tao et al, 2019).…”