Author(s): Tamotsu Takahashi; Yoshifumi Satofuka
Linked Author(s):
Keywords: Debris flow; Inertial; Constitutive equations; Velocity; Solids concentration
Abstract: The pore water in a debris flow densely suspending silt and clay can sometimes be so highly viscous that deformation of it may almost balance with the operating shear stress. This is the case of the viscous debris flow. Whereas in the inertial debris flow in which the pore fluid contains little cohesive fine material, deformation of the pore fluid exert only a trivial effect and stresses due to brief inelastic collisions of coarse particles and if particle concentration is very dense stresses due to enduring frictional grain contact may play significant role. Moreover, if comprising particles are small but non-cohesive, much sediment is suspended by the large scale turbulence causing large Reynolds stress. Therefore, all the aspects of the debris flow should be classified on a ternary phase diagram whose three apices represent the roles of visco-plasticity of the material, brief and enduring particle contact, and mixing of material due to turbulence and fluctuating characteristic of particle motion, respectively. In this paper, especially for the inertial debris flow, a unified theory applicable for all the sub-classifications; i. e., the stony, immature, hybrid and muddy debris flows is given. The stony debris flow is defined as the flow whose entire depth is composed of mixture of coarse particles colliding and jostling. In the immature debris flow the coarse particle mixture layer occupies only a lower part of the depth and beyond that virtual y no coarse particles are contained. In contrast to the stony and immature debris flows, the hybrid debris flow appears when the comprising particles are small and it is composed of lower particle colliding and jostling layer and the upper particle suspension layer. Of the hybrid flows that has only a thin particle col iding layer is, herein, cal ed as the muddy debris flow. The unified theory is based on the constitutive equations for an inertial granular flow and the turbulent suspension equation. The experimental data confirm the theory. The theory also revealed that the previous Takahashi’s simplified theory can predict the solids concentrations in the stony and in the immature debris flows equally well.
Year: 1999