Effects of solid fraction of saturated granular flows on overflow and landing mechanisms of rigid barriers

Abstract

Steep creek hazards are characterised according to their solid fraction, νs, which governs the flow dynamics. To arrest these hazards, rigid multiple barriers are installed along a channel. However, existing design guidelines are deficient because the fundamental overflow and landing mechanisms are not well understood. In this study, experiments were conducted using a 5 m long flume to model the impact of flows with different νs values on a rigid barrier. By varying the νs of sand–water mixtures, the dynamics of different steep creek hazards were modelled. The barrier height was varied to obtain barrier Froude numbers Frb (ratio of flow inertia to potential energy related to barrier height) from 0·7 to 3·4. Results show that barriers should be designed so that Frb < 1, which leads to downward overflow with reduced landing distances. In addition, the landing distance for the watery flows (νs = 0 to 0·1) is up to 87% longer than that of dry granular flows. This implies that the design spacing between barriers should cater for different types of steep creek hazards and Frb. An existing framework for multiple barriers is modified to provide guidance on the selection of the barrier height using the Frb.