Study of pore fluid effect on the mobility of granular debris flows

Abstract

Abstract. Granular debris flows in nature are composed of a wide range of solids and viscous pore fluids, moving at high velocities down sloping channels. The pore fluids in a granular debris flow affect the interactions between the solid and fluid phases and thus govern the debris-flow mobility. Study of the pore fluid effect (i.e., excess pore water pressures correlated to solid structures, and the viscous shearing and dragging) is essential for understanding the high flow mobility of granular debris flows. This study critically reviews two dimensionless numbers with clear physical meanings, then demonstrates a new application of field monitoring data for identifying natural debris flows on large scales (i.e., surge and continuous debrisflows, respectively). This study illustrates that, the pore fluid viscous shearing stress dominates solid inertial stress due to solids collision. It is also found that different to continuous debris-flows, the high pore fluid pressures generated in surge debris-flow body dissipate quite slowly and mostly influence particle contact behaviour significantly. A new scientific criterion for identification of continuous and surge debris flow in nature can be given by this study.

Particle Size Segregation in Granular Mass Flows With Different Ambient Fluids

“…This fluid is still Newtonian and has the same density as water. Such a fluid can be likened to the fine particle‐rich slurries found in natural debris flows (Major & Pierson, 1992; Zhou & Sun, 2017) after it has already yielded. The FI and VI regimes will be collectively referred to as the saturated regimes.…”