Characteristics of the Debris Flow that is Composed of Sediment Mixtures

在由广泛分布的泥沙混合物组成的泥石流中，很小的颗粒和其他较大的颗粒表现出不同的行为。也就是说，非常小的一个悬浮在组织液中的较大颗粒之间，这些颗粒通过相互相遇的作用而维持。这种细颗粒的浓度是重要的，因为间隙高度沉积物负载的流体的密度增加有助于增加输送较大颗粒的能力。本研究首先通过对间隙液中湍流和悬沙浓度的讨论，给出了细颗粒和粗颗粒的划分标准，结果表明，较大的颗粒在分散力的作用下向上运动，并且比留在下部的较小颗粒运动得更快，这是因为在流动的上层中的速度比在下层中的速度快。本文提出了一种计算机模拟方法，它不仅可以预测流量和平均固体浓度的时间变化，而且可以预测从最前面到最后面的平均颗粒直径的时间变化。泥石流在平地上冲出形成的泥石流扇中的颗粒粒度分布，生动地说明了泥石流中颗粒分离的特点，粗粒物质堆积的前沿并不立即停止，而是继续惯性运动，宽度略有扩大，留下一些大颗粒，然后停止形成月牙形堤岸。包含较小尺寸材料的后续流沉积，就好像它将堤后的空洞掩埋，直到溢出发生。本文还提出了一种数值模拟方法，可以预测岩屑堆积区的界限和存款平均粒径的空间分布。两种模拟方法均通过实验室实验进行了验证。

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.