Mechanics of hyperconcentrated sediment laden flow

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Discussions are made on the effect of particle size on the flow structure of sand particle-water mixture in order to investigate the mechanics of debris/mud flows and general sediment laden flows. The experimental results show that a quasi-laminar region is formed on the movable bed even in the flow of fine sediment-water mixture and its depth increases with the increase of sediment concentration as well as of particle size. Generally, the equilibrium bed slope can be predicted in terms of particle to particle friction angle and sediment concentration in the case that sediment particles behave as a laminar motion, which is common in debris flows composed of coarse sediment. But, it is rearized tha the bed slope becomes smaller than that of debris flows. A two-layr model which constitutes the upper and lower layrs is proposed to deseribe such phenomena. The shear stress in the upper layr is governed by turbulent motions. and in the lower layr by the constitutive relations developed by Egashira, etal.