Coarse granular flow interaction with slit structures

Abstract

Coarse grains accumulate in geophysical flow fronts and have high solid fractions. Such fronts may arch in slit structures such as baffles and slit dams, leading to the rapid trapping of particles and potentially high-energy overflow. Existing empirical slit-structure design recommendations are limited and inadequate since they only focus on the slit size to particle diameter ratio (s/δ) and neglect the pileup height and pre-impact flow energy. Flume modelling was thus adopted to study coarse flow fronts impacting a slit structure. The characteristic Froude conditions, flow particle diameter and the ratio s/δ were varied. Results have shown the pileup height, and hence the confining stress is dependent on Froude conditions, but is not strongly influenced by s/δ. The flow particle diameter influences collisional and frictional stresses and hence the mean outflow rate, which is correlated with pileup height. Grain-trapping efficiency depends on both s/δ and Froude conditions. In contrast to existing continuum-based theory for slit-structure interaction, frictional contacts should be considered for coarse-grained flow fronts. High-energy supercritical flows lead to low trapping efficiency since stable arches cannot form at high shear rates. This implies that multiple slit structures may be more appropriate for attenuating high-energy supercritical flows.