ABSTRACT
During extreme weather events, the risk of underscouring of hydraulic infrastructure such as bridge piers and abutments may significantly increase. Sufficiently energetic flow structures, typically scaling with its cross-sectional lengthscale, may shed downstream bridge piers leading to the removal of coarse bed material and subsequent critical failure of its protective layer against scour (typically a naturally formed armour layer or implemented rip-rap protection, comprising of cobbles and rocks). The goal of this study is to assess the risk of critical failure of the scour protective layer in the vicinity of a bridge pier, by directly monitoring the probability of entrainment of an instrumented particle appropriately positioned on its surface. A set of flume experiments under well-controlled flow conditions is undertaken to assess the change in entrainment frequencies of an instrumented particle, laying downstream a physical model of a bridge pier. Highly resolved time series of the instrumented particle’s entrainment for the tried flow conditions, are acquired with synchronous recordings of a visual assessment method. Flow profiles at different distances downstream the model pier are obtained with acoustic Doppler velocimetry (ADV) in a preliminary attempt to further link the local and dynamic driving mechanisms for particle entrainment to the phenomenologically relevant bulk flow and pier characteristics (such as pier lengthscale, average flow velocity and depth, median size of armor layer particles).
