Collapse Dynamics and Runout of Dense Granular Materials in a Fluid

Abstract

We investigate the effect of an ambient fluid on the dynamics of collapse and spread of a granular column simulated by means of the contact dynamics method interfaced with computational fluid dynamics. The runout distance is found to increase as a power law with the aspect ratio of the column, and, surprisingly, for a given aspect ratio and packing fraction, it may be similar in the grain-inertial and fluid-inertial regimes but with considerably longer duration in the latter case. We show that the effect of fluid in viscous and fluid-inertial regimes is to both reduce the kinetic energy during collapse and enhance the flow by lubrication during spread. Hence, the runout distance in a fluid may be below or equal to that in the absence of fluid due to compensation between those effects.

Rockslide and Impulse Wave Modelling in the Vajont Reservoir by DEM-CFD Analyses

“…On the other hand, it can also enhance the granular flow by lubricating the granular mixture. The compensation between these two effects would eventually influence the runout distance of granular materials in a fluid (Topin et al 2012).…”

“…Topin et al (2012) studied the dynamics of dense granular flows in fluid by means of the contact dynamics method coupled with the computational fluid dynamics (CFD). The importance of grain inertia, fluid inertia and viscous effects was analysed by increasing the fluid viscosity in the CFD model.…”

“…Numerical modelling of rockslide dynamics represents a major challenge, as a huge amount of solid materials and complicated solid-solid and solid-fluid interactions would be involved (Boon et al 1963;Topin et al 2012). Topin et al (2012) studied the dynamics of dense granular flows in fluid by means of the contact dynamics method coupled with the computational fluid dynamics (CFD).…”

Tumbling sandpiles in a fluid

“…In the viscous regime, for the same aspect ratio, the kinetic energy available for spreading is still lower and the dissipation due to viscous drag is higher, leading thus to a much shorter runout distance. The scaling of R stop with E max cx at large aspect ratios is consistent with a simple physical picture in which each grain in the spread phase is on average subject to an effective viscous drag force [19].…”

“…The evolution of E cy indicates that the grains do not reach their Stokes velocity in the fluid. Following the mean vertical velocity of the ten highest grains we find that, regardless of the grain/fluid regime, the collapse obeys a power law V y 10 ∝ t β over nearly one decade with β 1 in the grain-inertial regime, corresponding to a ballistic fall, β 0.95 in the fluid-inertial regime and β 0.75 in the viscous regime [19]. Figure 3 shows the total normalized runout distance (R stop − R 0 )/R 0 and runout duration t stop as a function of a.…”