E-314 土石流の流れに及ぼす砂粒子径の影響

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  • Effect of Sediment Size on Debris Flows

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Results obtained from both of flume tests and theory suggest that an equilibrium bed slope in flow over an erodible bed is determined only by sediment discharge rate when the movements of sediment particles are laminar and thus no suspended transportation take place. This means that the static friction force is dominant in debris flow and that sediment concentration is determined by shear stress balance on the bed surface. i. e., the external shear stress must be equal to the resisting static shear stress of sediment particles, as seen in our previous studies. On the other hand, if part of sediment particles in debris flow body is transported in suspension, sediment concentration will be larger in comparison with that in case of laminar motion of sediment particles and the equilibrium bed slope will decrease. These facts are supported Egashira et al.'s experimental data. The present study discusses an influence of flow scales on an equilibrium bed slope and flow structure expermentally and theoretically. Equilibrium bed slopes and velocity profiles are measured for many flow conditions in flume tests. Those results emphasize that the equilibrium bed slope decreases with increasing of flow scale if part of debris flow body is turbulent. and it is predicted corresponding to increase of mass density of fluid phase.

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