Collapse of dry and immersed polydisperse granular columns: A unified runout description

Abstract

The granular column collapse is a simplified version of granular flows such as landslides, avalanches, and other industrial processes mobilized in air or within a fluid. In this configuration, the particles collapse in an accelerating phase, reaching a state of constant spreading velocity until they decelerate and stop. Granular flows commonly involve particles of different sizes, a property termed polydispersity. Understanding the role of polydispersity remains a challenging task that is often analyzed with nearly monodisperse systems and demanding a series of simplifications when coupled with a fluid in a numerical model. Here, we study the effect of particle-size polydispersity in dry and immersed granular columns, using a finite element method-discrete element method model for fluid-particle interactions. We show that the velocity of the column collapse and runout distance decrease with an increase in the level of polydispersity in immersed conditions, and remain nearly independent of the level of polydispersity in dry conditions. Moreover, we find that the runout scales with the spreading front kinetic energy, weighted by the ratio between the particles' density and the density difference between particles and fluid. This scaling helps in identifying the governing processes in polydisperse granular columns, unifying the runout description of both dry and immersed collapses, and indicating that the column initial packing fraction is the governing parameter.

Polydispersity effect on dry and immersed granular collapses: an experimental study

“…The latter result, in the granular column configuration, is in agreement with previous studies that have shown the independence of the shear strength of polydisperse granular materials when they reach a residual stage at large deformation (Nguyen et al 2015;Cantor et al 2018;Cantor, Azéma & Preechawuttipong 2020;Polanía et al 2023). The effect of polydispersity on immersed granular flows has been studied less, but it has been shown with a numerical approach that the collapse of immersed columns is delayed with an increase in the polydispersity level (Polanía et al 2022). Despite these previous works, the effect that polydispersity has on immersed granular columns remains insufficiently investigated, especially experimentally.…”

“…High packing fractions, due to high polydispersity levels, frustrate the rapid percolation of water into the granular structure and produce a retrogressive collapse mechanism. Similar collapse mechanisms have been observed for sand columns (Thompson & Huppert 2007) and polydisperse columns in two-dimensional simulations (Polanía et al 2022). The motion of monodisperse collapses finishes earlier than that of polydisperse collapses, resulting in longer runout distances for systems with λ = 20 than for λ = 1.…”

“…These models work well for flows with monodisperse grains but depend on fitting parameters or flow variables, such as the flow average height, which are difficult to estimate in transitional flows. Polanía et al (2022) proposed a simplified model that links the column mobility to the collapse kinetic energy. This model, which relies entirely on physically based variables, does not need fitting parameters and works for different levels of polydispersity, has not yet been verified experimentally.…”

“…We link the evolution of the pore pressure to the sequence of the column collapse, and reveal how these two are influenced by increasing polydispersity level. Finally, we test whether the link between the collapse kinetic energy and mobility, introduced by Polanía et al (2022), remains true in three-dimensional polydisperse collapses.…”

Numerical investigation of mode failures in submerged granular columns

“…The first part of this section consists of reproducing the granular collapses of Rondon et al (2011). Although, a broad number of works (Izard et al, 2018; Jing, Yang, Kwok, & Sobral, 2019; Meng, Liao, Yu, Li, & An, 2021; Polanía, Cabrera, Renouf, & Azéma, 2022; Riffard & Ris, 2022; Sun, Zhang, Wang, & Liu, 2020; Wang et al, 2017a) have predicted the main features of granular column collapses immersed in a viscous fluid, only a few (Wang, Wang, Peng, & Meng, 2017b; Yang, Jing, Kwok, & Sobral, 2020) have successfully captured the dynamics of Rondon's experiments for both initially loose and dense granular columns, and even fewer have done it with a continuum approach (Baumgarten & Kamrin, 2019; Bouchut et al, 2017; Lee, 2021; Phan, Bui, & Nguyen, 2022; Rauter, 2021; Shi et al, 2021; Si, Shi, & Yu, 2018). The dilatancy model presented herein was able to capture the pore pressure feedback in one-dimensional and 2-D granular avalanches (Montellà et al, 2021) with reasonably good agreement.…”