/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Geotechnical Journal, 21, 2, pp. 250-258, 1984-05 Measurements of snow creep pressures from the centre section of a 3.4 m high and 15 m long avalanche-defence supporting structure located on a mountain in western Norway are presented. The site has a deep snow cover and an average slope angle of 25". The measurement configuration corresponds to plane-strain conditions and the data, along with measured snowpack parameters, allow comparison with simple theoretical predictions. The analysis shows that the average pressure on the structure I may be calculated fairly accurately using linear, viscous modelling for the snow deformation. The maximum pressures proved to be higher than that provided by a linear model and this is considered characteristic of nonlinear material. The implications of these results for estimates of design loads are discussed. CanadianKeywords: snow pressure, creep, measurements, viscous, plane-strain, finite element. 9L'article prksente des mesures de pression de fluage de la neige sur la section centrale d'une structure de protection contre les avalanches de 3,4 m de haut et 15 m de long, situCe sur une montagne dans l'ouest de la Norvkge. Le site prksente un couvert de neige Cpais et une pente moyenne de 25". La configuration de l'installation de mesure correspond i des conditions de dCformation plane et les dondes, assocites aux paramttres mesures du couvert de neige, permettent une comparaison avec des prkdictions thCoriques simples. L'analyse montre que la pression moyenne sur la structure peut &tre calculCe avec une prkcision acceptable au moyen d'un modtle visqueux linCaire des dCformations de la neige. Les pressions maximum se sont avtrCes plus fortes que celles dCduites d'un modkle linkaire, ce qui est considCrC typique d'un matCriau non-1inCaire. Les implications de ces rksultats sur I'Cvaluation des charges de calcul sont discutCes.Mots-clPs: pression de neige, fluage, mesure, viscositC, dCformation plane, ClCments finis.[Traduit par la revue]Can. Geotech. 1. 21, 250-258 (1984) Introduction compare the field measurements with these models. This An important engineering problem concerning the comparison has two important motivating aspects: (1) design of structures on mountains with deep snow cover by comparing actual measurements with a linear, viscous is the calculation of expected pressures due to intemp-deformation model, those features of the problem that tion of snow creep (internal defo...
/npsi/ctrl?lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?lang=fr Access and use of this website and the material on it are subject to the Terms and Conditions set forth at http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. Geotechnical Journal, 22, 2, pp. 166-71, 1985-05-01 The temporal and spatial variation of snow pressure on structures Measurements of snow creep pressure on an avalanche-defence structure in western Norway are presented. Two different types of measurement methods are described and evaluated. Pressure data from four winters are correlated with the following measured snowpack properties: density, snow depth, snowpack temperature, and snowpack stiffness. The results show that maximum and average pressures are strongly dependent on the product of density and snow depth as well as snowpack stiffness. The highest pressures were observed in spring prior to melting of the snowpack. Canadian
Digitally processed Seasat synthetic aperture radar images from the Beaufort Sea, recorded during August 1978, were analyzed to determine ice-floe displacements and floe-size distributions. Combining data on displacements with those on floe area and thickness yields floe kinetic energies which can then be used as input into design criteria for offshore Arctic structures. Floe-size distributions are needed to determine probablistically the "design" mass of ice for an offshore structure.Vectors of floe movement show the influence of surrounding floes and the compactness of the ice. Floes nearer to more open water showed more movement in the prevailing wind direction while floe movement within the ice pack was primarily affected by floe interaction.Different cutoff criteria in terms of number of resolution cell sizes were applied to the data on floe size. It was found that the numbers of floes dropped by up to 50% of the original count at ten resolution cells (250 m). Exponential and log-normal probability distributions were fitted to the original counts of floe size. The log-normal fit was better but this is based on one dataset at one time of year in one location. More datasets need to be analyzed to investigate this further. If a probability distribution to floe size can be generalized then only a subset of all the floes would need to be analyzed to determine numbers of floes in each size range. This would greatly speed up a tedious task and be beneficial for design and operational purposes. ABSTRACT Thi s study presents estimates of snow creep pressures from the centre section of an avalanche defence structure in western Norway. The structure is 15 m long and is erected on a 25° slope characterized by deep snow covers. Two methods of measurement are described: (1) direct estimates from earth pressure cells, and (2) construction of force, shear and moment diagrams from strains measured using vibrating wire strain gauges mounted on the steel beams of the structure. MEASUREMENT OF SNOW CREEP PRESSURES ON AN AVALANCHE DEFENCE STRUCTUREIn addition to the estimates of pressure, relevant snowpack data were measured, including snow depth, density, temperature and rammsonde hardness profiles as well. as snow crystal stratigraphy. Snow glic1ing was also measured, and was found to be negligible. The snowpack measurements were made at approximately monthly intervals during each of the four winters which yielded useable data for the study.Analysis of the pressure distributions along with the snowpack data yielded the follO\~ing results: (1) the average pressure on the structure is linearly proportional to the product of average density times snow depth, (2) the average pressures are predicted fairly accurately by a linear, viscous creep model, (3) the maximum pressure depends strongly on the snowpack stiffness and decreases rapidly when warming and melt soften the snowpack, and (4) the maximum pressures are of the order of 25% hi gher than predi cted by a linear, viscous creep model. 301
Digitally processed Seasat synthetic aperture radar images from the Beaufort Sea, recorded during August 1978, were analyzed to determine ice-floe displacements and floe-size distributions. Combining data on displacements with those on floe area and thickness yields floe kinetic energies which can then be used as input into design criteria for offshore Arctic structures. Floe-size distributions are needed to determine probablistically the "design" mass of ice for an offshore structure.Vectors of floe movement show the influence of surrounding floes and the compactness of the ice. Floes nearer to more open water showed more movement in the prevailing wind direction while floe movement within the ice pack was primarily affected by floe interaction.Different cutoff criteria in terms of number of resolution cell sizes were applied to the data on floe size. It was found that the numbers of floes dropped by up to 50% of the original count at ten resolution cells (250 m). Exponential and log-normal probability distributions were fitted to the original counts of floe size. The log-normal fit was better but this is based on one dataset at one time of year in one location. More datasets need to be analyzed to investigate this further. If a probability distribution to floe size can be generalized then only a subset of all the floes would need to be analyzed to determine numbers of floes in each size range. This would greatly speed up a tedious task and be beneficial for design and operational purposes. ABSTRACT Thi s study presents estimates of snow creep pressures from the centre section of an avalanche defence structure in western Norway. The structure is 15 m long and is erected on a 25° slope characterized by deep snow covers. Two methods of measurement are described: (1) direct estimates from earth pressure cells, and (2) construction of force, shear and moment diagrams from strains measured using vibrating wire strain gauges mounted on the steel beams of the structure. MEASUREMENT OF SNOW CREEP PRESSURES ON AN AVALANCHE DEFENCE STRUCTUREIn addition to the estimates of pressure, relevant snowpack data were measured, including snow depth, density, temperature and rammsonde hardness profiles as well. as snow crystal stratigraphy. Snow glic1ing was also measured, and was found to be negligible. The snowpack measurements were made at approximately monthly intervals during each of the four winters which yielded useable data for the study.Analysis of the pressure distributions along with the snowpack data yielded the follO\~ing results: (1) the average pressure on the structure is linearly proportional to the product of average density times snow depth, (2) the average pressures are predicted fairly accurately by a linear, viscous creep model, (3) the maximum pressure depends strongly on the snowpack stiffness and decreases rapidly when warming and melt soften the snowpack, and (4) the maximum pressures are of the order of 25% hi gher than predi cted by a linear, viscous creep model. 301
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