Interaction between dry granular flow and deflectors

Abstract

The application of seawall deflectors for reflecting inviscid waves into the sea have been well established. Recently, rigid barrier deflectors have been proposed prescriptively for mitigating geophysical landslides, but flow characteristics differ fundamentally from waves and merit investigation. In this study, flume tests were used to calibrate a discrete element model to explore the interaction between dry granular flow and rigid barrier deflectors. The deflector angle and length and the effective height (distance between deflector tip and channel base) were studied and compared to barriers without deflectors. Findings reveal that deflectors initially prevent spilling of vertical runup and reduce flow energy underneath the deflector. However, controlling overflow depends heavily on the deflector angle and length, with the effective height as ultimate governing parameter. The additional height provided by the deflector should therefore be considered as part of the design height rather than a prescriptive add-on. Longer deflector lengths shield deadzones from energy losses through grain shearing, thus resulting in higher peak overflow velocities. It is recommended that deflector lengths should be less than 10% of the expected flow depth to suppress peak overflow velocities. Perpendicular deflectors tend to enhance faster energy dissipation through increased deadzone confining stress.