Vertical structure of liquid-granular surges over erodible beds: experiments and theory

• Main Authors: Chin-Yang Huang, 黃晉揚
• Other Authors: Hervé Capart
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/9gaawc

碩士 === 國立臺灣大學 === 土木工程學研究所 === 107 === The purpose of the study is to explore the transport mechanism of the debris flow developing in a narrow valley. We conduct small-scale laboratory experiments to simulate the behavior of the flood-induced liquid-granular surge flowing over the loose erodible bed. Via image processing methods, the experimental measurements of velocities and grain concentrations can be simultaneously calculated from the same footage. Grain concentrations are calculated adopting the laser distance-to-wall measurements, based on the relation between the grain concentration and the mean maximum travelling distance of laser beam. Velocities below the free surface are calculated adopting particle tracking velocimetry (PTV). The experimental basal shear stresses are solved via control volume analysis. The results show that when basal shear stresses increase, the wall abrasion behavior can be neglected, which intensifies following a cubic relationship with depth. In theory, we adopt the diffusive flux approach with a diffusivity in terms of the granular pressure to derive the analytical solution for grain concentration profile. The model requires the water level, the bed-load layer thickness, and the initial deposited bed level, as known variables. Besides, the analytical solution can be used to described the relations of stresses with depth earlier found in experiments. The model are compared with experimental measurements to observe the difference between the theory and experiments.