The influence of temporal and spatial variations on phase separation in debris flow deposition

Abstract

The phase separation mechanism in a natural debris flow as a solid-liquid mixture is an important aspect in its movement and deposition. In this paper, the relationship between debris flow discharges and densities is studied based on the field observations of the Jiangjia Gully, China. A number of experiments are conducted to study the phase separation mechanism of debris flows, and the characteristics of their depositions over deceleration baffles with varying flow density and bottom slopes. The phase separation mechanism of natural debris flows is analyzed based on the mentioned experimental and field observations. During the decreasing debris flow, the flow density reduces with reduction of the flow discharge, indicating the important role of the flow discharge in changing the flow density as a driving factor. Temporal variations of the debris flow density can have two chronological orders: (a) dilute-viscous-dilute debris flow and (b) viscous-dilute debris flow. The variation order of the flow density has an important influence on the phase separation mechanism and the final deposition morphology. The experimental results show that the bottom slope and the flow density have opposite effects on the phase separation mechanism. Increasing the flow density increases the viscosity of the debris flow, decreasing the phase separation of the solid-liquid mixture. Increasing the bottom slope promotes phase separation by increasing the shear rate inside the debris flow. As a result, the phase separation mechanism of natural debris flow is mostly related to the temporal and spatial variations of the flow pattern and the flow density.