Fundamental experiment of the larger]particles concentration at the frontal part of debris flow

Norio HARADA, Takashi WADA, Tomohiko FURUYA, Kana NAKATANI,
Takahisa MIZUYAMA and Yoshifumi SATOFUKA

Generally, larger particles concentrate at the frontal part of debris flow under unsaturated]flow conditions. Many studies have explained the mechanisms of this larger]particles concentration with inverse grading: the upper portion of the sedimentary layers having a larger particle in diameter. The reverse]grading mechanism has been explained in terms of the distributed pressure by particle collisions, dynamic sieving, granular convention and the differences in the velocities of the moving particles. However, further explanation is required. In this study, to understand larger]particles concentrations better, experiments were conducted using a conveyor belt and an experimental flume. Particles of two sizes were sieved on the conveyor belt. The results showed that the concentration rate of larger particles converged at a particular value in response to the various experimental conditions. Finally, our results indicated that the concentration of larger particles on the conveyor belt, in the absence of water, was affected by the moving distance, the flow depth, the particle diameter ratio, the riverbed gradient and the internal frictional angle of the particles.