Effect of Including Sand Component in a Debris Flow on Concentration of Coarser Particles at the Flow Front

Abstract

We conducted flume experiments for a debris flow consisting of coarser particles, finer particles and sand, focusing on the concentration of coarser particles at the flow front. Our experimental results revealed that the concentration of coarser particles at the flow front using sediment mixture with sand was less than that without sand. This may be because including of sand component in the material contributed to be a smaller averaged interstice between particles in the flow layer and a smaller averaged particle size. These may lead to reduce the falling volume of sand or finer particles and dispersion pressure for the rise of coarser particles, respectively, resulting in the inhibition of inverse grading formation. Our experimental results also suggested that the changing trend in the proportion of finer particles depended on the relationship between their particle size and the average particle size of the flow. These are consistent with our previous experimental results using material without sand. This consistency suggested that for the concentration of coarser particles at the flow front, the behavior of the sand component can be considered in the same manner as other coarser-sized components.