A comprehensive mechanics-based model to describe bedrock river erosion by plucking in a jointed rock mass

Abstract

Plucking is an erosion mechanism usually occurring to sub-meter rock blocks in a bedrock channel subjected to intense water current. The removal of a rock block because of plucking can be either a result of impulsive plucking or accumulative plucking. A plate-like block is more likely to escape owing to impulsive plucking, while a pillar-like block is more likely escape because of accumulative plucking. The potential of impulsive plucking can be evaluated by examining the maximum uplift displacement within the period of the maximum upward impulse load acting on a typical rock block in a rock mass. The size of the rock block, various sources of uplift forces and the frictional resistance of lateral joints play major roles in determining whether accumulative plucking will occur. The present work proposes a mechanics-based model that simulates the kinematics of a rock block subjected to an inclined jet flow. A non-dimensional index APP is derived to assess the potential of accumulative plucking. In addition, a comprehensive approach is proposed to evaluate both the potential depths of the scour hole in a plunge pool and the incision in a downstream channel subjected to a prescribed jet flow passing a spillway or an overflowing weir. Finally, a case study adopting the proposed method is presented to demonstrate and to verify the applicability of the comprehensive approach.