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Title
Abstract
Overview
Review of Previous Work
Background
Introduction
Testing and Test Data
Recommendations and Conclusions
References
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Engineering
Mechanics of Materials

Snow Mechanics: Review of the state of knowledge and applications

Profile image of Jerome JohnsonJerome Johnson

US Army CRREL Report

Abstract

: A review of snow mechanics indicates that, with the exception of avalanche studies, it is seldom used. In this report we give our interpretation of why this is the case, and suggest ways to help expand the range of problems to which snow mechanics can be ...

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A review of finite-element modelling in snow mechanics
Mohamed Naaim

Journal of Glaciology, 2013

The finite-element method (FEM) is one of the main numerical analysis methods in continuum mechanics and mechanics of solids (Huebner and others, 2001). Through mesh discretization of a given continuous domain into a finite number of sub-domains, or elements, the method finds approximate solutions to sets of simultaneous partial differential equations, which express the behavior of the elements and the entire system. For decades this methodology has played an accelerated role in mechanical engineering, structural analysis and, in particular, snow mechanics. To the best of our knowledge, the application of finite-element analysis in snow mechanics has never been summarized. Therefore, in this correspondence we provide a table with a detailed review of the main FEM studies on snow mechanics performed from 1971 to 2012 (40 papers), for facilitating comparison between different mechanical approaches, outlining numerical recipes and for future reference. We believe that this kind of comp...

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Mechanical property measurements on various snow surfaces
Sally Shoop

2020

The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR.

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Snow stability measurements
Bruce Jamieson

Field measurements of snow stability provide the only direct evidence of snow stability except avalanche observation. In-situ snow stability measurements are reviewed. Field data on shear strength of weak layers and tensile strength of slabs are described, as well as the appropriate techniques to collect the data. An overview of presently applied snow stability tests (rutschblock, compression test etc.) is given. New possibilities to measure the mechanical properties (e.g. SnowMicroPen) relevant for assessing avalanche danger are discussed.

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Measurement of mechanical properties of snow for simulation of skiing
Gerhard Innerhofer

Journal of Glaciology, 2013

In the simulation of skiing the force between ski and snow is a decisive factor. We decompose the reaction force into a penetration force normal to the snow surface, a shear force and friction. Two portable measurement devices were developed to study the penetration and shear forces for compacted snow on groomed ski slopes. The penetration force was assessed by measuring the penetration depth of a ski-tool loaded normal to the snow surface. For the shear force the tangential load was measured when the snow began to fail. Overall 236 penetration and 108 shear experiments were conducted on different types of snow. The penetration force was proportional to the volume of snow displaced by the ski-tool. The failure shear force was proportional to the penetration depth multiplied by the length of the tool. The constants of proportionality, H V and S f , are material parameters of snow. The snow hardness, H V , varied between 0.04 and 90 N mm-3 and the failure shear stress, S f , between 0.04 and 0.40 N mm-2. In another investigation, skiing turns were simulated using the presented snow reaction forces. Maximum deviations between computed and real trajectories were <1% of the overall length of the runs.

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Advanced Micromechanical Description of Snow Behaviour --- PART II --- Model Validation
Dr. Mark Michael

The advanced micro-scale approach proposed in the companion paper (Part I- Mechanical and Numerical Modelling) is employed to predict the mechanical response of snow under compression in dependence of different strain rates, initial densities and temperatures applied. The objective of this study is the validation of the micro-mechanical approach on the micro- and macro-scale by the prediction of the material behaviour of dry snow throughout ductile and brittle loading regimes. On its micro-scale, snow consists of an assembly of ice grains joined by ice bonds. The macroscopic response of a specimen to loading depends strongly on the deformation and failure of the bonds and the inter-granular collisions during grain rearrangement. Inter-granular bond and collision model deployed in this study use a discrete element method to describe the interaction on the grain-scale. The micro-structure of a snow sample is represented by an ensemble of explicit geometrical shapes of spherical snow grains and cylindrical bonds. Within here the approach is first validated on the micro-scale deformation behaviour of snow grains at different loading rates and temperatures. Thereafter, macro-scale simulations of confined and unconfined, deformation-controlled compression tests have been conducted and successfully compared to similar experimental predictions reported in the literature.

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Observations relating to wet snow stability
Howard Conway

Observations relating to wet snow avalanches in a low-elevation, maritime climate are discussed. The effects of crystal structure, water drainage, and lubricated layers on snow stability are considered.

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Snow avalanche formation
Bruce Jamieson

Reviews of Geophysics, 2003

1] Snow avalanches are a major natural hazard, endangering human life and infrastructure in mountainous areas throughout the world. In many countries with seasonally snow-covered mountains, avalanche-forecasting services reliably warn the public by issuing occurrence probabilities for a certain region. However, at present, a single avalanche event cannot be predicted in time and space. Much about the release process remains unknown, mainly because of the highly variable, layered character of the snowpack, a highly porous material that exists close to its melting point. The complex interaction between terrain, snowpack, and meteorological conditions leading to avalanche release is commonly described as avalanche formation. It is relevant to hazard mapping and essential to short-term forecasting, which involves weighting many contributory factors. Alternatively, the release process can be studied and modeled. This approach relies heavily on snow mechanics and snow properties, including texture. While the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner, the knowledge of the quantitative relation between snow texture and mechanical proper-ties is limited, but promising developments are under way. Fracture mechanical models have been applied to explain the fracture propagation, and micromechanical models including the two competing processes (damage and sintering) have been applied to explain snow failure. There are knowledge gaps between the sequence of processes that lead to the release of the snow slab: snow deformation and failure, damage accumulation, fracture initiation, and fracture propagation. Simultaneously, the spatial variability that affects damage, fracture initiation, and fracture propagation has to be considered. This review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale, from the size of a bond between snow grains to the size of a mountain slope, will continue to be very challenging.

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Release temperature, snow-cover entrainment and the thermal flow regime of snow avalanches
Yves Bühler

Journal of Glaciology, 2015

To demonstrate how snowcover release and entrainment temperature influence 7 avalanche runout we develop an avalanche dynamics model that accounts for the thermal 8 heat energy of flowing snow. Temperature defines the mechanical properties of snow and 9 therefore the avalanche flow regime. We show that the avalanche flow regime depends pri-10 marily on the temperature of the snow mass in the starting zone as well as the density and 11 temperature of the entrained snowcover which define the influx of heat energy. Avalanche 12 temperature, however, not only depends on the initial and boundary conditions, but also on 13 the path dependent frictional processes that increase internal heat energy. We account for 14 two processes: (1) frictional shearing in the slope-parallel flow direction and (2) dissipation 15 of random fluctuation energy by inelastic granular interactions. In avalanche flow, non-linear 16 irreversible processes are coupled with variable initial and boundary conditions that lead to 17 transitions in flow regime. Snow avalanches thus exhibit a wide variety of flow behaviour 18 with variations in snowcover temperature. 19 1. INTRODUCTION 20

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Advanced Micromechanical Description of Snow Behaviour --- PART I — Mechanical and Numerical Modelling
Dr. Mark Michael

This study proposes an advanced micro-scale approach able to predict the mechanical behaviour of snow in dependence of the strain rate, density and temperature applied. The mechanical behaviour of snow was long studied to help predict natural hazards, i.e. snow avalanches. For those predictions the behaviour of snow deforming at low rates is of importance. On the other hand, a large group of industrial applications concerning driving safety or winter sport activities also benefit from the understanding of snow physics. These applications requiring an understanding of the high rate behaviour of snow. The mechanical behaviour of snow is fundamentally based on its micro-structure and process on the micro-scale. On the micro-scale, snow consists of ice grains joined by ice bonds which assemble an open-foam like structure. The macroscopic response of a specimen to loading dependents strongly on the deformation and failure of the bonds and the inter-granular collisions during grain rearrangement. This study proposes an inter-granular bond and collision model developed and deployed using the discrete element method to specifically describe the interaction on the grain-scale. The goal is to describe and predict the material behaviour of dry snow with a single micro-mechanical based model throughout all loading rates. The developed algorithm predicts the displacement of each individual grains due to inter-granular forces and torques. Those forces and torques are developing from the bond deformation and grain collision. The micro-structure of a snow sample is represented by an ensemble of explicit geometrical shapes of spherical snow grains and cylindrical bonds. The inter-granular models are based on an elastic viscous-plastic material law which is based on the temperature-dependent material properties and a creep law of poly-crystalline ice Ih.

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Observations and modelling of snow avalanche entrainment
Betty Sovilla

Natural Hazards and Earth System Science, 2002

In this paper full scale avalanche dynamics measurements from the Italian Pizzac and Swiss Vallée de la Sionne test sites are used to develop a snowcover entrainment model. A detailed analysis of three avalanche events shows that snowcover entrainment at the avalanche front appears to dominate over bed erosion at the basal sliding surface. Furthermore, the distribution of mass within the avalanche body is primarily a function of basal friction. We show that the mass distribution in the avalanche changes the flow dynamics significantly. Two different dynamical models, the Swiss Voellmy-fluid model and the Norwegian NIS model, are used to back calculate the events. Various entrainment methods are investigated and compared to measurements. We demonstrate that the Norwegian NIS model is clearly better able to simulate the events once snow entrainment has been included in the simulations.

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Corina Sandu

Journal of Terramechanics, 2022

Snow is a complex material that is difficult to characterize especially due to its high compressibility and temperaturesensitive nonlinear viscoelasticity. Snow mechanics has been intensively investigated by avalanche and army researchers for decades. However, fewer research studies were published for the compacted snow, defined as snow with a density in a range of 370-560 kg/m 3. This review focuses on the various testing methods that are used especially to characterize the behavior of compacted snow under compressive and shear loading. The working principles, inherent assumptions, and advantages/disadvantages of the devices are summarized. In addition, some of the important material properties of snow like density, elastic modulus, etc., and their measurement is highlighted. Lastly, a correlation of the testing methods to commonly used approaches in modeling snow is presented. Overall, we believe that this study can help to better understand the existing test data related to compacted snow and guide future testing in this field.

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Research on snow and ice
Roger Barry

Reviews of Geophysics, 1979

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Studies on the Fluidized Snow Dynamics
Kouichi Nishimura

1991

An inclined chute system and a fluidized snow bed were constructed in a cold laboratory and extensive measurements of mechanical properties of fluidized snow were carried out. In the steady part of the snow flow, where the thickness and velocities are roughly constant, velocity profiles were obtained at various chute inclinations. Assuming that the bulk densities are uniform with depth, a constitutive equation of a Bingham body was applied to simulate the obtained velocity profiles. The apparent viscosity coefficients obtained ranged from 8.3 X 10-2 to 4.5 X 10-1 Ns/m 2 and yield stress 0 to 10 N/m 2 for the bulk densities of 100 to 200 kg/m' and the shear rate of 60 to 70 S-I. On the other hand viscous properties of the fluidized snow which was produced with the fluidized-bed experiment system was investigated with the Brookfield viscometer. All sets of data showed that the relation between the shear stress and shear rate satisfied the constitutive equation of the Bingham body for the shear rate of 1 to 15 S-I. Viscosity coefficients of the fluidized snow obtained ranged from 10-2 to 10-1 Ns/m 2 ; yield stress were 0 to 10-2 N/m 2 • It was also found that the viscosity increased rapidly with the bulk density. The viscosity coefficients obtained in the two different systems were compared in special reference to the shear rate of each experiment; The assumptions made in the former calculations were reexamined. Consequently it was revealed that shear stresses are linearly proportional to the shear rate in a lower shear rate region and shear stresses depend on the square of the shear rate in a higher shear rate region. Furthermore a constitutive equation which expresses the general dynamical properties of fluidized snow was found to be written as the sum of the dry friction, the viscous and the quadratic viscous terms. The dynamical properties of the fluidized snow obtained in the above experiments and analyses were applied to the numerical simulations of the fluidized snow flow motion along the chute and artificial and natural avalanches observed in the Shiai-dani region, showing a reasonable fit of the observed data.

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