NUMERICAL MODEL OF VISCOUS DEBRIS FLOWS WITH DEPTH-DEPENDENT YIELD STRENGTH

Abstract

Non-Newtonian fluids such as Bingham model have been widely used to simulate the motion of viscous debris flow. The materials will flow only if shear stresses exceed its yield strength, and the integrals along the depth can be performed in the shear layer and plug layer, respectively. The pore-water pressure is considered in the rheological model according to the physical properties of viscous debris flow. In addition, the lateral pressure in horizontal direction inner debris flow is different from hydrostatic assumptions due to the presence of particles, the earth pressure coefficient with Savage-Hutter assumption is added into the governing equations. The governing equations of debris flow are solved by using Lagrange difference method, and the effects of material parameters, earth pressure coefficient and inclination angle on the runout characteristics such as velocity distribution, runout distance and deposit shape are analyzed. Numerical results show that the debris flow starts to move due to the gravity, the velocities vary almost linearly, and the rear end of debris flow moves backward because the inclination angle of plane is very small. Finally, it stops due to the basal friction force and the maximum final height locates the start position of horizontal section. Recent studies have suggested that the earth pressure coefficient mainly influences on the depth profile of granular flow, however, these phenomena have not been captured in the numerical results for debris flow perhaps due to the small inclination angle. Further studies are needed to determine the effects of earth pressure coefficient on the natural debris flow with more complex topography.