PREDICTION OF DEBRIS FLOW GENERATED BY EROSION OF STEEP WELL-GRADED SEDIMENT MIXTURE BED

In a debris flow which is composed of widely distributed sediment mixture, verysmall fraction and other larger particles behave differently. Namely, the very smallone is suspended in the interstitial fluid among larger particles which are sustainedby the action of mutual encounters. Concentration of such fine particles isimportant, because increased density of the interstitial highly sediment laden fluidworks to increase capacity for transporting larger particles. In this paper, thecriteria to divide fine and coarse particles is given through the discussion on theturbulence and suspended sediment concentration in the interstitial fluid. Largerparticles whose mobility is helped by the buoyancy due to increased density ofsuspending fluid segregate themselves in the manner to concentrate largest particlesagainst the forefront and smaller ones to the rear. A computer simulation methodto predict such phenomena as well as to render possible to predict debris flowhydrograph, solid concentration distribution in the flow, etc. is proposed andvalidated by the laboratory experiments.