Johan Gaume

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Gaume

First Name

Johan

ORCID

0000-0001-8931-752X

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09795 - Gaume, Johan / Gaume, Johan

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Publications1 - 10 of 68

A Depth-Averaged Material Point Method for Shallow Landslides: Applications to Snow Slab Avalanche Release
Guillet, Louis; Blatny, Lars; Trottet, Bertil; et al. (2023)
Journal of Geophysical Research: Earth Surface
Shallow landslides pose a significant threat to people and infrastructure. Despite significant progress in the understanding of such phenomena, the evaluation of the size of the landslide release zone, a crucial input for risk assessment, still remains a challenge. While often modeled based on limit equilibrium analysis, finite or discrete elements, continuum particle-based approaches like the Material Point Method (MPM) have more recently been successful in modeling their full 3D elasto-plastic behavior. In this paper, we develop a depth-averaged Material Point Method (DAMPM) to efficiently simulate shallow landslides over complex topography based on both material properties and terrain characteristics. DAMPM is a rigorous mechanical framework which is an adaptation of MPM with classical shallow water assumptions, thus enabling large-deformation elasto-plastic modeling of landslides in a computationally efficient manner. The model is here demonstrated on the release of snow slab avalanches, a specific type of shallow landslides which release due to crack propagation within a weak layer buried below a cohesive slab. Here, the weak layer is considered as an external shear force acting at the base of an elastic-brittle slab. We verify our model against previous analytical calculations and numerical simulations of the classical snow fracture experiment known as Propagation Saw Test. Furthermore, large scale simulations are conducted to investigate cross-slope crack propagation and the complex interplay between weak layer dynamic failure and slab fracture. In addition, these simulations allow us to evaluate and discuss the shape and size of avalanche release zones over different topographies. Given the low computational cost compared to 3D MPM, we expect our work to have important operational applications in hazard assessment, in particular for the evaluation of release areas, a crucial input for geophysical mass flow models. Our approach can be easily adapted to simulate both the initiation and dynamics of various shallow landslides, debris and lava flows, glacier creep and calving.
Granulation of snow: From tumbler experiments to discrete element simulations
Steinkogler, Walter; Gaume, Johan; Löwe, Henning; et al. (2015)
Journal of Geophysical Research: Earth Surface
It is well known that snow avalanches exhibit granulation phenomena, i.e., the formation oflarge and apparently stable snow granules during the flow. The size distribution of the granules has aninfluence on flow behavior which, in turn, affects runout distances and avalanche velocities. The underlyingmechanisms of granule formation are notoriously difficult to investigate within large-scale fieldexperiments, due to limitations in the scope for measuring temperatures, velocities, and size distributions.To address this issue we present experiments with a concrete tumbler, which provide an appropriate meansto investigate granule formation of snow. In a set of experiments at constant rotation velocity with varyingtemperatures and water content, we demonstrate that temperature has a major impact on the formationof granules. The experiments showed that granulesonly formed when the snow temperature exceeded −1°C. No evolution in the granule size was observed at colder temperatures. Depending on the conditions,different granulation regimes are obtained, which are qualitatively classified according to their persistenceand size distribution. The potential of granulation of snow in a tumbler is further demonstrated by showingthat generic features of the experiments can be reproduced by cohesive discrete element simulations.The proposed discrete element model mimics the competition between cohesive forces, which promoteaggregation, and impact forces, which induce fragmentation, and supports the interpretation of thegranule regime classification obtained from the tumbler experiments. Generalizations, implications for flowdynamics, and experimental and model limitations as well as suggestions for future work are discussed.
A critical state µ(I)-rheology model for cohesive granular flows
Blatny, Lars; Gray, John M.N.T.; Gaume, Johan (2024)
Journal of Fluid Mechanics
The dynamic behaviour of granular media can be observed widely in nature and in many industrial processes. Yet, the modelling of such media remains challenging as they may act with solid-like and fluid-like properties depending on the rate of the flow and can display a varying apparent friction, cohesion and compressibility. Over the last two decades, the mu(I)-rheology has become well established for modelling granular liquids in a fluid mechanics framework where the apparent friction mu depends on the inertial number I. In the geo-mechanics community, modelling the deformation of granular solids typically relies on concepts from critical state soil mechanics. Along the lines of recent attempts to combine critical state and the mu(I)-rheology, we develop a continuum model based on modified cam-clay in an elastoplastic framework which recovers the mu(I)-rheology under flow. This model permits a treatment of plastic compressibility in systems with or without cohesion, where the cohesion is assumed to be the result of persistent inter-granular attractive forces. Implemented in a two- and three-dimensional material point method, it allows for the trivial treatment of the free surface. The proposed model approximately reproduces analytical solutions of steady-state cohesionless flow and is further compared with previous cohesive and cohesionless experiments. In particular, satisfactory agreements with several experiments of granular collapse are demonstrated, albeit with shear bands which can affect the smoothness of the surface. Finally, the model is able to qualitatively reproduce the multiple steady-state solutions of granular flow recently observed in experiments of flow over obstacles.
A glacierocean interaction model for tsunami genesis due to iceberg calving
Wolper, Joshuah; Gao, Ming; Lüthi, Martin P.; et al. (2021)
Communications Earth & Environment
Glaciers calving icebergs into the ocean significantly contribute to sea-level rise and can trigger tsunamis, posing severe hazards for coastal regions. Computational modeling of such multiphase processes is a great challenge involving complex solidfluid interactions. Here, a new continuum damage Material Point Method has been developed to model dynamic glacier fracture under the combined effects of gravity and buoyancy, as well as the subsequent propagation of tsunami-like waves induced by released icebergs. We reproduce the main features of tsunamis obtained in laboratory experiments as well as calving characteristics, the iceberg size, tsunami amplitude and wave speed measured at Eqip Sermia, an ocean-terminating outlet glacier of the Greenland ice sheet. Our hybrid approach constitutes important progress towards the modeling of solidfluid interactions, and has the potential to contribute to refining empirical calving laws used in large-scale earth-system models as well as to improve hazard assessments and mitigation measures in coastal regions, which is essential in the context of climate change.
Transient wave activity in snow avalanches is controlled by entrainment and topography
Li, Xingyue; Sovilla, Betty; Gray, John Mark Nicholas Timm; et al. (2024)
Communications Earth & Environment
Waves are omnipresent in avalanches on Earth and other planets. The dynamic nature of waves makes them dangerous in geological hazards such as debris flows, turbidity currents, lava flows, and snow avalanches. Extensive research on granular waves has been carried out by using theoretical and numerical approaches with idealized assumptions. However, the mechanism of waves in realistic complex situations remains intangible, as it is notoriously difficult to capture complex granular waves on real terrain. Here, we leverage a recently developed hybrid Eulerian-Lagrangian numerical scheme and an elastoplastic constitutive model to investigate the processes involved in waves of snow avalanches, including erosion, deposition, and flow instability induced by terrain irregularity. This enables us to naturally simulate roll-waves, erosion-deposition waves, and their transitions in a single large-scale snow avalanche on real terrain. Simulated wave features show satisfactory consistency with field data obtained with different radar technologies. Based on a dimensionless analysis, the wave mechanics is not only controlled by the Froude number and local topography but also by the mass of the wave which governs the entrainment propensity. This study offers new insights into wave mechanisms of snow avalanches and provides a novel and promising pathway for exploring transient waves in granular mass movements.
Decoupling the Role of Inertia, Friction, and Cohesion in Dense Granular Avalanche Pressure Buildup on Obstacles
Kyburz, Michael L.; Sovilla, Betty; Gaume, Johan; et al. (2020)
Journal of Geophysical Research: Earth Surface
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.
Snow fracture in relation to slab avalanche release: critical state for the onset of crack propagation
Gaume, Johan; van Herwijnen, Alec; Chambon, Guillaume; et al. (2017)
The Cryosphere
The failure of a weak snow layer buried below cohesive slab layers is a necessary, but insufficient, condition for the release of a dry-snow slab avalanche. The size of the crack in the weak layer must also exceed a critical length to propagate across a slope. In contrast to pioneering shear-based approaches, recent developments account for weak layer collapse and allow for better explaining typical observations of remote triggering from low-angle terrain. However, these new models predict a critical length for crack propagation that is almost independent of slope angle, a rather surprising and counterintuitive result. Based on discrete element simulations we propose a new analytical expression for the critical crack length. This new model reconciles past approaches by considering for the first time the complex interplay between slab elasticity and the mechanical behavior of the weak layer including its structural collapse. The crack begins to propagate when the stress induced by slab loading and deformation at the crack tip exceeds the limit given by the failure envelope of the weak layer. The model can reproduce crack propagation on low-angle terrain and the decrease in critical length with increasing slope angle as modeled in numerical experiments. The good agreement of our new model with extensive field data and the ease of implementation in the snow cover model SNOWPACK opens a promising prospect for improving avalanche forecasting.
Assessing snow instability in skier-triggered snow slab avalanches by combining failure initiation and crack propagation
Gaume, Johan; Reuter, Benjamin (2017)
Cold Regions Science and Technology
Dry-snow slab avalanches start with a local failure in a weak snowpack layer buried below cohesive snow slab layers. If the size of the failed zone exceeds a critical size, rapid crack propagation occurs possibly followed by slab release if the slope is steep enough. The probability of skier-triggering a slab avalanche is generally characterized by classical stability indices that do not account for crack propagation. In this study, we propose a new model to evaluate the conditions for the onset of crack propagation in skier-triggered slab avalanches. For a given weak layer, the critical crack length characterizing crack propagation propensity was compared to the size of the area where the skier-induced stress exceeds the shear strength of the weak layer. The ratio between both length scales yields a stability criterion combining the processes of failure initiation and crack propagation. The critical crack length was calculated from a recently developed model based on numerical simulations. The skier-induced stress was computed from analytical solutions and finite element simulations to account for slab layering. A detailed sensitivity analysis was performed for simplified snow profiles to characterize the influence of snowpack properties and slab layering on crack propagation propensity. Finally, we applied our approach to manually observed snow profiles and compared our new criterion to Rutschblock scores.
Microstructural Origin of Propagating Compaction Patterns in Porous Media
Blatny, Lars; Berclaz, Paul; Guillard, François; et al. (2022)
Physical Review Letters
Porous rocks, foams, cereals, and snow display a diverse set of common compaction patterns, including propagating or stationary bands. Although this commonality across distinct media has been widely noted, the patterns' origin remains debated-current models employ empirical laws for material-specific processes. Here, using a generic model of inelastic structured porous geometries, we show that the previously observed patterns can be attributed to a universal process of pore collapse. Furthermore, the pattern diversity can be mapped in a phase space of only two dimensionless numbers describing material strength and loading rate.
Continuum modeling of cohesive and compressible granular matter
Blatny, Lars; Gray, Nico; Gaume, Johan (2025)
EPJ Web of Conferences ~ Powders & Grains 2025 – 10th International Conference on Micromechanics on Granular Media
In this contribution, we discuss the ability of elasto-viscoplastic constitutive models in capturing the diverse behavior of granular media as both solids and liquids. In particular, we showcase the recently developed MCC-μ(I)-rheology [1], which combines the Modified Cam-Clay (MCC) model for granular solids with the μ(I)-rheology for granular liquids, creating a best-of-both-worldsa model for describing granular solids and liquids in a single framework. This model is demonstrated on various problems, including granular collapse tests as well as full-scale avalanche modeling.

Publications1 - 10 of 68

Johan Gaume

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