Fines-controlled drainage in just-saturated, inertial column collapses

Abstract

The wide particle size distributions, over several orders of magnitude, observed in debris flows leads to a diverse range of rheological behaviours controlling flow outcomes. This study explores the influence of different scale grains by conducting subaerial, fully saturated granular column collapse experiments with extreme, bimodal particle size distributions. The primary particles were of a size where their behaviour was controlled by their inertia while a suspension of kaolin clay particles within the fluid phase acts at spatial scales smaller than the pore space between the primary particles. The use of a geotechnical centrifuge allowed for the systematic variation of gravitational acceleration, inertial particle size and the degree of kaolin fines. Characteristic velocity- and time-scales of the acceleration phase of the collapse were quantified using high-speed cameras. Comparing tests containing fines to equivalent collapses with a glycerol solution mimicking the enhanced viscosity but not the particle behaviour of the fines, it was found that all characteristic dynamic quantities were dependent on the degree of fines, the system size, the grain fluid-density ratio and the column– and grain-scale Bond and Capillary numbers. We introduce a fine-scale Capillary number showing that, although surface tension effects at the column scale are negligible, fines do control the movement of fluid through the pore spaces.

DEM-LBM insights into unsteady grain-fluid collapses on a geotechnical centrifuge

“…g = 9.81 m s −2 ) [e.g. [24][25][26][27][28], recent investigations [15,23] have also examined its dynamics within a geotechnical centrifuge. However, theses studies primarily focused on grain-fluid interaction and did not thoroughly investigate the contributions of varying centrifugal and Coriolis accelerations to the collapse dynamics.…”

“…The initial configuration of the granular-fluid column is characterised by two parameters: the initial column height h 0 and radius r 0 . As was the case for the two previous studies [15,23], we set h 0 = 50 mm and r 0 = 54 mm for each phase, resulting in a column aspect ratio of a = h 0 /r 0 = 0.93. The granular phase comprises monodispersed particles with a mean diameter D = 8 × 10 −3 m (±10% to prevent crystallisation within the initial configuration [21]) and a particle density ρ p = 2650 kg m −3 .…”

“…The study aims to enhance our understanding by employing numerical modelling to examine a just-saturated granular column collapse configuration within a geotechnical centrifuge. Two recent experimental studies [15,23] have provided valuable insights into the system, with a strong focus on grain-fluid interaction and its…”