Unification of theories for the debris flow mechanics

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The constitutive equations for the viscous debris flow were given under the hypothesis that the squeezed flow arising from the shearing between the two adjacent layrs of particles in the viscous fluid produces the particle sustaining dispersive pressure as well as the shear stress. Those equations were applied to the flume experiments in the laboratory and the characteristics of flow such as the equilibrium solids concentration, the specific viscosity and velocity distributions were deduced. The particle concentration in an equilibrium viscous flow composed of nearly uniform materials, in which the particles are transported without deposition, is not much different from that of the inertial flow on the same bed slope. This fact brings a kind of paradox that if the material is the well graded mixture, as observed in the actual viscous debris flow, the flow can transport much more dense solids concentration. A hierarchic buoyancy increment effect was suggested for a possibe cause of high competence to transport particles. The viscosity of the highly freighted viscous debris flow becomes very large in comparison to that of the interstitial slurry. The specific viscosity defined as the ratio of that of the entire debris flow material to that of the slurry increases with increase in the concentration of the coarse particles, but the tendency of the change versus concentration seems different depending on the viscosity of the slurry. Such results of investigation were combined with the theory for stony debris flow and an approach to make a unified comprehensive theory of the mechanics of debris flow was proposed.