Multiphase simulations and experiments of subaqueous granular collapse on an inclined plane in densely packed conditions: Effects of particle size and initial concentration

Subaqueous granular collapse on an inclined plane was investigated by considering the effects of particle size and initial concentration in densely packed conditions. This study adopted the multiphase model developed by Lee [J. Fluid Mech. 907, A31 (2021)], which can capture pore pressure feedback (an important mechanism in subaqueous granular flows). A new set of laboratory experiments were performed to validate the multiphase model with four different particle sizes (from fine sand to very coarse sand). Generally, the multiphase model can reproduce all the experimental collapse processes well. Four particle sizes and four initial concentrations were examined numerically. The simulated results reveal that both the volume of the sliding mass in the early stages (initial sliding volume) and the front speed increase with increasing particle size. In addition, increasing the initial concentration reduces the initial sliding volume and front speed. The simulated results suggest that the front speed can be expressed as a function of the initial sliding volume. A simplified force balance analysis was performed to examine why the particle size and the initial concentration affect the initial sliding volume.

Figure 1

Schematic of experimental setup.

Figure 2

Snapshots of the observed and simulated landslide processes for (a) Case F60, (b) Case M60, (c) Case C60, and (d) Case VC60. The simulated contour lines of $c={10}^{-3}$ (solid red lines), $c=0.09$ (dashed red lines), and $c=0.4$ (dotted red lines) are included for comparison with the observed fluid-sand interface. The blue line in each plot outlines the initial shape of the granular material on the slope. Animations can be found online [44].

Figure 3

Simulated and measured time series of front position for (a) Case F60, (b) Case M60, (c) Case C60, and (d) Case VC60.

Figure 4

Velocity fields of the solid phase and the pressure fields of the fluid phase for (a) Case F55, (b) Case F60, (c) Case C60, and (d) Case VC60. The color maps present the fluid pressure, and the arrows show the solid velocity. The dashed lines are the contour lines of $c={10}^{-3}$, the dashed-dotted lines are $c=0.09$, the solid lines are $c=0.4$, and the dotted lines are the contour lines of $|{\mathbf{u}}^s|$=0.05 m/s.

Figure 5

Flow fields of the solid and fluid phases for (a) and (b) Case F55, (c) and (d) Case F60, and (e) and (f) Case VC60. The color maps represent the solid pressure (a), (c), and (e) and the water pressure (b), (d), and (f). The arrows show the solid velocity (a), (c), and (e) and water velocity (b), (d), and (f). The dashed lines are the contour lines of $c={10}^{-3}$, the dashed-dotted lines are $c=0.09$, the solid lines are $c=0.4$, and the dotted lines are the contour lines of $|{\mathbf{u}}^s|$=0.05 m/s.

Figure 6

Dimensionless volume of the sliding mass at $t$ = 0.1 s.

Figure 7

Front speed versus the particle size and the initial concentration.

Figure 8

The sliding front speed against the initial sliding volume.

Figure 9

Schematic of the initial sliding mass.

Figure 10

$m^{*}$ predicted by the simplified model for different $c_i$ and $d$.