砂粒子を高濃度に含む流れに及ぼす粒子径の影響

Abstract

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 be-have as a laminar motion, which is common in debris flows composed of coarse sediment.But, it is rearized that the bed slope becomes smaller than that of debris flows.A two-layer model which constitutes the upper and lower layers is proposed to describe such phenomena.The shear stress in the upper layer is governed by turbulent motions, and in the lower layer by the constitutive relations developed by Egashira, etal.