Avalanching granular flows down curved and twisted channels: Theoretical and experimental results

Abstract

Depth evolution and final deposits play a crucial role in the description of the dynamics of granular avalanches. This paper presents new and important results on the geometric deformation and measurements of avalanche depositions in laboratory granular flows and their comparisons with theoretical predictions through some benchmark problems for flows down curved and twisted channels merging into a horizontal plane. XY-table and analoglaser sensor are applied to measure geometries of deposited masses in the fanlike open transition and runout zones for different granular materials, different channel lengths, and different channel mouths in the runout zone. The model equations proposed by Pudasaini and Hutter ͓"Rapid shear flows of dry granular masses down curved and twisted channels," J. Fluid Mech. 495, 193 ͑2003͔͒ are used for theoretical prediction. We show that geometric parameters such as curvature, twist and local details of the channel play a crucial role in the description of avalanching debris and their deposits in the standstill. Asymmetric depositions and surface contours about the central line of the channel could not be produced and predicted by any other classical theories and available experiments in the literature as done in this paper. Such a role played by the geometrical parameters of the channel over physical parameters for the flow of granular materials down a general channel was not investigated before. It is demonstrated that the numerical simulations of the model equations and experimental observations are generally in good agreement.

DebrisInterMixing-2.3: a finite volume solver for three-dimensional debris-flow simulations with two calibration parameters – Part 2: Model validation with experiments

“…The experimental setup focused on surface superelevation (lateral difference in flow surface elevation in a channel bend), and we consider it suitable for verifying the modeled rheology of the mixture in channel bends. We mention that effects of curvature were analytically modeled and validated for dry granular flows and flows of mixtures by Pudasaini et al (2005Pudasaini et al ( , 2008) with a depth-averaged approach.…”

“…Based on the forced vortex approach with the assumption of a constant radius of the channel bend, Scheidl et al (2015) investigated the effect of flow velocity and super-elevation for several debrisflow mixtures. However, for a mathematical derivation of the slope induced super-elevation, we refer to Pudasaini et al (2005).…”

“…Because we expect the enhanced superelevation of debris flows in curved channels to be connected to a change of viscosity due to the pressure increase caused by deflection within the curve, the second group of experiments focuses on the pressure-dependent rheology. Enhanced super-elevation of debris flows was first modeled by Pudasaini et al (2005) where the pressure (as normal load) increased as explicit functions of slope curvature and twist. Such a model has further been extended in Fischer et al (2012) where this aspect has further been explored by implicitly connecting the surface-geometry-induced curvature, and possibly also twist, to viscosity via its pressure dependence (Domnik et al, 2013).…”

Modelling rapid mass movements using the shallow water equations in Cartesian coordinates

“…A formulation for granular flow in general curved and twisted channels was provided by Pudasaini and Hutter (2003) and later extended and applied to data (Pudasaini et al, 2005(Pudasaini et al, , 2008. Recently, an implementation of this concept called r.avalanche in the open-source GIS software suite GRASS was presented by Mergili et al (2012).…”

Enhanced mobility of polydisperse granular flows in a small flume

“…Denlinger and Iverson, 2004;Iverson and Denlinger, 2001;Pudasaini and Hutter, 2003) and experimental flows (e.g. Pudasaini et al, 2008;Yang et al, 2014). Parameters used in the numerical simulations are usually obtained by back analyses of occurred events or by calibration, as a result of the extreme complexity of such phenomena and the still incomplete knowledge of the governing laws controlling the behavior of these materials (Crosta et al, 2009).…”