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, ν s , 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 ν s values on a rigid barrier. By varying the ν s of sand–water mixtures, the dynamics of different steep creek hazards were modelled. The barrier height was varied to obtain barrier Froude numbers Fr b (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 Fr b < 1, which leads to downward overflow with reduced landing distances. In addition, the landing distance for the watery flows (ν s = 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 Fr b . An existing framework for multiple barriers is modified to provide guidance on the selection of the barrier height using the Fr b .