Unified View of the Mechanics of Debris Flows and Sediment Laden Flows

本研究试图统一处理以下主题：流动的水-沙混合物的本构关系，泥沙浓度和流速的剖面，从泥石流到具有两层荷载的水流，以及计算悬浮流参考浓度的“清”水层。在本研究中，Egashira等人提出的本构关系包括一些物理参数：泥沙粒径、粒间摩擦角和泥沙比重等。颗粒间摩擦角对泥石流的影响已经进行了两年的实验和理论研究。结果表明：在刚性床上的泥石流中，颗粒间摩擦角的增大导致流动阻力增大；另一方面，在可蚀层上的泥石流中，出现了相反的趋势。从实验和理论两方面研究了泥沙粒径对泥沙-水混合物流动的影响。实验采用了不同大小的沙粒，在从碎屑流到包括清水流较大的区域。将水槽试验数据与数值模拟的流速和含沙量剖面进行了比较。计算结果与水槽数据吻合较好。无论河床剪应力大小，输沙率随沉积物粒径的增大而减小，随沉积物粒径的减小而增大。利用Egashira等人的本构关系，并考虑雷诺应力的垂直分布，提出了悬浮流参考浓度和参考水平的预测方法。根据该方法，当泥沙粒径较小时，参考浓度较小。计算结果与前人的实验数据吻合较好。

This study has attempted a unified treatment of the following themes : the constitutive relationships of flowing water-sediment mixture, the profiles of sediment concentration and flow velocity from debris flows to flows with both bed-load, and "clear" water lagers to calculate the reference concentration of suspended flows. In this study, the constitutive relationships proposed by Egashira et al. include some physical parameters : the sediment size, the interparticle friction angle and specific weight of sediment etc.The effects of interparticle friction angle on debris flows have been investigated experimentally and theoretically for two years. The following results were obtained : in debris flows over rigid beds, an increase of interparticle friction angle causes flow resistance to increase. On the other hand, in debris flows over erodible beds, the inverse tendency appears.The influence of sediment size on flow of sediment-water mixture were investigated experimentally and theoretically. An experiment was employed with different sizes of sand, in the region from debris flows to the flows including a clear-water larger. The data obtained by flume tests were compared with the numerical simulated profiles of velocity, and sediment concentration. The calculated results agreed well with the flume data. The sediment transport rate became small when the sediment size was large, and became large when the sediment size was small for both large or small bed shear stress.Methods to predict the reference concentration and reference level of suspended flows were proposed using Egashira et al.'s constitutive relationships and taking the vertical distribution of the Reynolds' stress into account According to this method, the reference concentration was small when the sediment size was small. The calculated results were fitted with previous experimental data obtained by many researchers.