Item: RIDERS AND AVALANCHES FLOATING ON POWDER SNOW: NEW INSIGHTS INTO AIR PORE PRESSURE MECHANISMS FROM HYDRO-MECHANICAL NUMERICAL SIMULATIONS
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Title: RIDERS AND AVALANCHES FLOATING ON POWDER SNOW: NEW INSIGHTS INTO AIR PORE PRESSURE MECHANISMS FROM HYDRO-MECHANICAL NUMERICAL SIMULATIONS
Proceedings: International Snow Science Workshop 2024, Tromsø, Norway
Authors:
- Hervé Vicari [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ] [ Climate Change, Extremes, and Natural Hazards in Alpine Regions Research Center CERC, Davos Dorf, Switzerland ] [ Institute for Geotechnical Engineering, ETH Zürich, Zürich, Switzerland ]
- Camille Huitorel [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ] [ Climate Change, Extremes, and Natural Hazards in Alpine Regions Research Center CERC, Davos Dorf, Switzerland ] [ Institute for Geotechnical Engineering, ETH Zürich, Zürich, Switzerland ]
- Quoc-Anh Tran [ Norwegian University of Science and Technology, Trondheim, Norway ]
- Betty Sovilla [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ]
- Johan Gaume [ WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland ] [ Climate Change, Extremes, and Natural Hazards in Alpine Regions Research Center CERC, Davos Dorf, Switzerland ] [ Institute for Geotechnical Engineering, ETH Zürich, Zürich, Switzerland ]
Date: 2024-09-23
Abstract: Skiing or snowboarding down a mountain covered with fluffy new snow can provide a unique experience, reminiscent of floating above clouds. This sensation is often intuitively attributed to the supporting effect of the interstitial air loaded by the skis or snowboard, creating a feeling of weightlessness. Interestingly, this same principle may also account for the rapid descent and extensive runout distance of much less pleasant phenomena, such as powerful mixed snow avalanches. These avalanches exhibit a complex structure, characterized by a dense basal regime overlaid and preceded by an intermittent layer of coherent snow clusters, along with a lighter suspension layer of fine particles mixed with air. Despite their significance, the processes driving the formation of these structures and the reasons for the remarkable mobility of mixed snow avalanches remain incompletely understood. One prevailing theory proposes that this mobility could result from the fluidization of the porous snow cover, which is transiently weakened by the development of excess pore air pressures upon undrained loading by the avalanche. We test this hypothesis, by means of two-phase simulations. The solid ice grains are simulated using either the Discrete Element Method (DEM) or as a continuum through the Material Point Method (MPM). Compared to previous works, we simulate explicitly the air both within the pores and in the ambient, using CFD (specifically the Finite Volume Method) which is coupled to the conservation equations of the solid phase. Simple preliminary simulations are presented in this work. We simulate a snowboarder dropping over a fresh snow cover. The simulations show that, if the permeability of the snow cover is low enough, the pressurized pore air may lead to fluidization of the snow, favoring its mechanical weakening and suspension as a vertical jet. Instead, if the permeability of the snow is too high, pore air pressure quickly diffuses, which cannot generate significant suspension of the particles. Similar modelling approaches will be applied in future to model mixed snow avalanches interacting with an erodible snow layer. Ultimately, we expect this research to contribute to improved entrainment and fluidization models in depth-averaged numerical methods.
Object ID: ISSW2024_P2.2.pdf
Language of Article: English
Presenter(s): Johan Gaume
Keywords: Powder Snow Avalanche, Powder Skiing, MPM, DEM, CFD, Entrainment, Fluidization
Page Number(s): 321 - 326
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