Effects of gradation on sandy debris flow behavior

A debris flow, a complex fluid situated between hyperconcentrated flows and granular flows, is recognized as a special natural hazard due to a combination of factors. In addition to parameters such as water content, solid volume concentration, particle shape, and mineral composition, the role of gradation (grain size distribution) on debris flow behavior warrants significant attention, yet it is often underemphasized. In this study, a modified material with discontinuous gradation was prepared by removing the sand (2-0.0625 mm) from Dongyuege debris flow sediments with gradation continuity. The effect of gradation continuity on debris flow behavior was investigated by conducting comparative tests with natural Dongyuege debris flow material. The experimental results indicate that sediments with grading discontinuities are more prone to initiate debris flows. The continuity of the gradation weakens the effect of the solid volume concentration in the slurry on its rheology and mobility. Additionally, debris flow slurries with discontinuous gradations have lower hydraulic conductivity than slurries with continuous gradations, which further inhibits the formation and dissipation of excess water pressure.