Experimental investigation on steady granular flows interacting with an obstacle down an inclined channel: study of the dead zone upstream from the obstacle. Application to interaction between dense snow avalanches and defence structures

Faug, Thierry; Lachamp, P.; Naaïm, Mohamed

doi:10.5194/nhess-2-187-2002

Cited by 41 publications

(15 citation statements)

References 7 publications

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“…Figure 6d shows that for increasing Fr, the standoff distance decreases dramatically from a maximum of ∼2.0 m in the range of Fr < 5, and then levels out at around 1 m for Fr > 5. This result agrees qualitatively with the findings of Cui and Gray (2013) and Faug et al (2002) on the standoff distance of granular bow shocks and size of mobilized domains, respectively. Interestingly, a similar dependency is found experimentally between the drag coefficient of a wall and Fr in a mud flow by Tiberghien et al (2007), as well as for the hydrodynamic impact pressure of debris flows and Fr by Proske et al (2011).…”

Section: Microscale Processes Of Impact Pressure Buildupsupporting

confidence: 91%

Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Build‐up on Obstacles

Kyburz

Sovilla²,

Gaume

et al. 2020

JGR Earth Surface

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Understanding the physical processes involved in snow avalanche‐obstacle interaction is essential to be able to estimate the pressure exerted on structures. Although avalanche impact pressure has been measured in field experiments for decades, the underlying physical principles are still elusive. Previous studies suggest that pressure is increased due to the formation of an influenced flow region around the structure, the mobilized domain, which varies in size depending on snow properties such as snow cohesion. Here, we aim to better understand how cohesion, friction, velocity, and their interplay affect avalanche pressure buildup on structures. This is achieved by simulating the avalanche‐obstacle interaction with a newly developed numerical model based on the discrete element method, using a cohesive bond contact law. The relevance of the model is tested by comparing simulated impact pressures with field measurements from the Vallée de la Sionne experimental site. Our results show that at the macroscale, impact pressure consists of the inertial, frictional, and cohesive contributions. The inertial and frictional contributions arise due to the existence, shape, and dimension of the mobilized domain. The cohesive contribution increases the particle contact forces inside the domain, leading up to a doubling of the pressure. Based on these physical processes, we propose a novel scaling law to reduce the problem of calculating the pressure induced by cohesive flows, to the calculation of cohesionless flows. These findings enhance our understanding of the interaction of cohesive granular flows, such as snow avalanches, and structures at the microscale and macroscale.

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Section: Microscale Processes Of Impact Pressure Buildupsupporting

confidence: 91%

Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Build‐up on Obstacles

Kyburz

Sovilla²,

Gaume

et al. 2020

JGR Earth Surface

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“…At time t = 0•19 s ( Fig. 4(b)), sand begins to deposit, forming a dead zone (Faug et al, 2002;Gray et al, 2003;Ashwood & Hungr, 2016) near the base of the barrier. Subsequent flow impacts the wedge-like dead zone, beginning to run up along the face of the barrier.…”

Section: Interpretation Of Resultsmentioning

confidence: 99%

“…Interaction between dry granular flows and a single obstacle has been investigated, revealing key impact mechanisms, such as dead-zone development (Faug et al, 2002;Gray et al, 2003), runup (Mancarella & Hungr, 2010;Choi et al, 2015) and overflow (Hákonardóttir et al, 2003a(Hákonardóttir et al, , 2003bChoi et al, 2014a). Analytic solutions have also been proposed: for example, Faug (2015a) conducted a series of small-scale experiments using dry sand flow impacting obstacles along an incline.…”

Section: Introductionmentioning

confidence: 99%

Dry granular flow interaction with dual-barrier systems

Choi

Koo³

et al. 2018

Géotechnique

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Multiple barriers are commonly installed along predicted geophysical flow paths to intercept large flow volumes. The main criterion for multiple-barrier design is volume retained. The velocity of the incoming (far-field) undisturbed flow is also sometimes used, although this neglects the influence of other obstacles on the flow characteristics. This study investigates the influence of upstream flowbarrier interaction on downstream runup and impact mechanisms of a dual rigid barrier system. Four physical flume tests were performed using dry sand to investigate flow interaction with dual barriers. Moreover, three-dimensional finite-element simulations were conducted to back-analyse the flume tests and to investigate the effects of upstream barrier height and barrier spacing on downstream impact characteristics. Two key interaction mechanisms that alter downstream flow are identified: (a) flow momentum redirection (i.e. runup) at the upstream barrier, reducing pre-impact momentum at the downstream; and (b) downstream flow-thinning. Runup mechanisms at the upstream barrier and flowthinning between the two successive barriers have profound effects on dynamic impact pressures at the downstream barrier. When the upstream barrier height is taller than twice the maximum flow thickness, flow energy can be dissipated effectively by momentum redirection. The downstream barrier height and design impact pressure can be reduced up to 17% and 35% for dry sand flows, respectively.

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“…up by the tail of the flow, flowing at lower speeds than the bulk of the avalanche. An experimental study of these wedges behind catching dams of varying heights and the so-called 'dead zones' behind the dams for lower Froude number flows (2 < Fr < 6) has been carried out by Faug et al (2002). Numerical calculations of the dead zone behind an obstacle of an infinite height are described by Gray et al (2003).…”

Section: Jet Deflectionmentioning

confidence: 99%

Large-Scale Avalanche Braking Mound and Catching Dam Experiments with Snow: A Study of the Airborne Jet

Hákonardóttir

Hogg

Jøhannesson

et al. 2003

Surveys in Geophysics

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We report a series of ongoing large-scale experiments to study the interaction of a snow avalanche with a dam and a row of mounds which are of a comparable height to the flow depth. The experimental results indicate that the behaviour of the supercritical flow around the obstacles is governed by the large-scale properties of the flowing avalanche rather than micro-scale properties of the granular current. The experiments show that, similarly to smaller-scale experiments with glass particles, the avalanche detaches from the top of the dam or mound and forms a coherent airborne jet, which can be modelled as a two dimensional ballistic projectile with negligible air resistance. We study the two parameters that define the trajectory of the jet, namely the speed at which the jet is launched from the top of the obstacle and the deflection of the jet by the obstacle, and compare the results with a theory for the deflection of a jet of an ideal fluid.

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Experimental investigation on steady granular flows interacting with an obstacle down an inclined channel: study of the dead zone upstream from the obstacle. Application to interaction between dense snow avalanches and defence structures

Cited by 41 publications

References 7 publications

Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Build‐up on Obstacles

Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Build‐up on Obstacles

Dry granular flow interaction with dual-barrier systems

Large-Scale Avalanche Braking Mound and Catching Dam Experiments with Snow: A Study of the Airborne Jet

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