Planar collapse of a submerged granular column

Abstract

Submerged mass flows are commonly considered a natural geohazard that interacts with terrestrial and submarine infrastructure and communities and are linked to the generation of tsunamis. Previous studies have investigated submerged mass flows by means of the benchmark case of a granular column collapse. This study explores the mobility and collapse dynamics of submerged granular columns within a planar configuration as a function of the column aspect ratio a. The use of a planar configuration allows the monitoring of the moving mass and its deformation patterns and provides a novel insight into the particle-fluid interactions at release and during collapse not possible before. Special attention was devoted to the column saturation and release mechanism. The column mobility is observed to be directly controlled by a and is linked to a clear distinction between triangular and trapezoidal deposits. The column collapse is found to be described by two characteristic times, marking transition points through the collapse stages. The associated deformation patterns reflect both at a column scale and at localized particle groups during collapse, reflecting in the velocity scaling of a deformable and moving granular mass and the occasional ejection of particles at its surface. We observed that the area of the released portion decreases during collapse and converge toward an equivalent portion of surface particles with little influence by a. The experimental results provide a novel insight into the study of submerged mass flows and set a reference behavior for future numerical validations.

Wave Generation Across a Continuum of Landslide Conditions From the Collapse of Partially Submerged to Fully Submerged Granular Columns

“…The granular column consists of an assembly of monodisperse ceramic beads of 2 mm diameter and density ρ p = 3,600 kg/m3 (Sigmund‐Lindner GmbH). With this particle size, the gap between the PMMA windows and the column thickness is equivalent to 1.2 particle diameters, and limits the beads packing fraction to ϕ = 0.50, in accordance with a dense configuration of frustrated packings in crystalline systems (Pinzon & Cabrera, 2019). The particles have an angle of repose of 28.15º ± 0.75º, measured inside the experimental setup by releasing the beads in free‐fall under dry conditions and measuring the final repose angle on both sides.…”

“…The granular column has an initial height ( H 0 ) and initial width ( L 0 ), yielding a column aspect ratio of H 0 / L 0 (see Figure 3b). All experiments are performed for a fixed aspect ratio of 1.5, with H 0 = 150 mm and L 0 = 100 mm, resulting in the collapse of a tall column with a wedge spanning across L 0 with equivalent kinematics between repeat tests (Pinzon & Cabrera, 2019; Roche et al., 2008). In this study, we propose the relative depth of submergence ratio H w / H 0 , relating the still water level ( H w ) with H 0 , and explore the transition from partially to fully submerged columns in the range of 0.24 < H w / H 0 < 1.50.…”

“…The planar setup constrains the interactions between particles and fluid, conditioning the effective drag on the particles to a nearly two‐dimensional system. Pinzon and Cabrera (2019) explored these constrains, finding little relevance when comparing with three‐dimensional setups and highlighting the associated advantages of the release mechanism in the planar setup.…”

“…Robbe‐Saule (2019) demonstrated that the release mechanism has strong effects on the generation of waves, and as indicated in Figure 2, the boundary effects due to the opening mechanism are not avoidable. However, for the purposes of studying partially submerged landslides, the horizontal sliding gate only introduces effects across the model width, as the secondary waves do not interfere directly with the landslide runout direction (Pinzon & Cabrera, 2019). The overall effect of release mechanism has been found to have negligible effects on the mobility of the granular material (Robbe‐Saule, 2019), but its interaction with the fluid may affect greatly the generation of waves.…”

“…In this study, we employ a planar granular column with a horizontal sliding gate to investigate landslide‐generated waves, and specifically explore the relationship between wave amplitude and relative depth of submergence for partially to fully submerged scenarios. The planar configuration provides a two‐dimensional simplification of the kinematics of a collapsing granular body, allowing for a detailed visualization of the motions of the granular mass and the water level variations at the free surface and inside the granular body (Lacaze et al., 2008; Pinzon & Cabrera, 2019). Moreover, a narrow horizontal sliding gate allows the granular column to collapse naturally under the force of gravity.…”