Experimental study on the unsteady characteristics of the two-phase debris flow

Lv Liqun, Wang zhaoyin, P. Cui

Friday 3 july 2015

11:30 - 11:45h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 15B. Sediment - Transport

Debris flows are classified into one-phase and two-phase flows according to their movement features and the size distributions of solid particles. The two-phase debris flow is the mixture of the liquid phase composed of water and clay and silt and the solid phase composed of gravel, cobbles and boulders. There is apparent relative movement between the liquid phase and the solid phase in the two-phase debris flow and there is no relative movement between the particles and liquid in one-phase debris flows. The intermittent motion of one-phase debris flow has been reported and studied but few have been done on the intermittency of two-phase debris flows. This paper report the intermittent feature of two-phase debris flows in the nature and physical model experiments in a flume. The surge character in the experiments of the two-phase debris flow was obvious, and the head of the debris flow moved intermittently. In the experiment water flow initiated sediment from bed and side slopes and transported gravel particles to the front, accumulation of the gravel in the front of the flow made the height and front slop of the debris flow increase. Suddenly, the gravel moved forward as the slop reaches the critical value. Then the head height and slope reduced to some value and the flow stag again. The sediment supply from upstream and energy accumulation caused the debris flow moving again. Based on the two-phase debris flow experiments, the article studies the formation and development of intermittent surges process and establishes the mechanical model.