Characteristics of the Debris Flow that is Composed of Sediment Mixtures

点击翻译按钮获取中文摘要

In a debris flow which is composed of widely distributed sodiment mixture, very small fraction and other larger particles behave differently. Namely, the very small one is suspended in the interstitial fluid among larger particles which are sustained by the action of mutual encounters. Concentration of such fine particles is important, because increased density of the interstitial highly sediment laden fluid works to increase capacity for transporting larger particles. In this investigation, at first, the criteria to divide fine and coarse particles is given through the discussion on the turbulence and suspended sediment concentration in the interstitial fluid.Next, it is shown that the larger particles go upward by the effect of dispersive force and transported faster than the smaller particles which are remaining in the lower part because of the faster velocity in the upper layer of the flow than in the lower layer.A computer simulation method which renders it possible to predict the temporal tauariations in not only the discharge and the mean solid concentration but also in the mean particle diameter from the forefront to the rear is presented. The distribution of the particle size in a debris fan that is formed by runout of the debris flow on a flat area gives a vivid account of the characteristics of particle segregation in the debris flow.The forefront where the coarsest materials accumulate does not immediately stop but a while continues its inertial motion with a small expansion in its width thereby leaving some large particles aside and then stops making a crescent bank. The succeeding flow that contains smaller size materials deposits as if it buries the hollow behind the bank until overflow occurs. A numerical simulation method that predicts the limit of the debris depositing area and the spatial distributions of the mean diameter of the sediment in the deposit, is also proposed. Both of the two simulation methods are verified by laboratory experiments.