Dense flows of bidisperse assemblies of disks down an inclined plane

Abstract

Using discrete numerical simulations, we have studied the flow down a rough inclined plane of a bidisperse assembly of frictional cohesionless disks. Our study focuses on steady uniform flows, once a stable segregation has developed inside the flowing layer. The material is segregated in three layers: a basal layer (small grains), a superficial layer (large grains), and a mixed layer in the center, so that the average diameter of the grains increases from the bottom to the top. From the measurement of the profiles of velocity, solid fraction, and stress components, we show that the rheological law of such a polydisperse material may be described by a local friction law, which extends the result obtained for quasimonodisperse granular flows. This law states that the effective friction coefficient depends approximately linearly on a generalized inertial number, taking into account the average diameter of the grains.

Debris flows: Experiments and modelling

“…and the overall solids volume fraction is assumed to be constant and uniform throughout the mixture [55,[64][65][66]. A coordinate system O xyz is defined with the x-axis pointing down the chute, the y-axis pointing across the chute and the z-axis being the upward pointing normal as shown in Fig.…”

Visualization of dominant stress-transfer mechanisms in experimental debris flows of different particle-size distribution

“…Large-scale modelling has been found to be very useful in replicating, at near fullscale, the field conditions of debris flows (Major 1997;Iverson et al 2010); however, these types of experiments are costly, and may be limited by the boundary conditions that can be applied. Numerical modelling may be undertaken at the particulate scale using, for example, the discrete element method, to understand granular flow mechanisms, such as frictional and collisional stress transfer, and particle segregation (Campbell and Brennan 1985;Silbert et al 2001;Gray and Chugunov 2006;Rognon et al 2007). However, this numerical modelling can be computationally expensive and such studies suffer from being restricted by one or more of the following: two-dimensional (2D) geometry, use of spherical or round rather than angular particles, limited particle numbers, no interstitial fluid, small range in particle size, restriction to steady flow, and use of periodic boundaries.…”

The behaviour of free-flowing granular intruders

“…A great advantage of the device is the stadium shape which allows for perpetual shear achieved by the gap between the wheels and granular mass allowing for the recirculation of the grains underneath (Figure 1(b)). These tests were all conducted in fixed pressure loading conditions with the same applied pressure and shear rate, which produced an iner- tial number of approximately 0.04 using an area-weighted average inertial number [14]. The grains within the 2D SSD are 10mm high nylon cylinders of three different diameters (12,15 and 20 mm) in order to prevent crystallisation from occurring.…”