Snow-Creep Pressure on Masts

Larsen, Jan Otto; Laugesen, Jens; Kristensen, Krister

doi:10.3189/s0260305500007801

Cited by 3 publications

(5 citation statements)

References 3 publications

(3 reference statements)

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“…They have slowly evolved in parallel with new findings and the experience gained from building kilometers of protection barriers. They have been criticized on several occasions because they are based on oversimplified assumptions of the actual rheological behavior of snow [ McClung , ] and because, in some regions, they fail to provide correct approximations of snow forces [ Larsen et al , ; Katakawa et al , ; Shapiro et al , ; Rudolf‐Miklau and Sauermoser , ; Harada et al , ].…”

Section: Force Due To Gliding Snowmentioning

confidence: 99%

Dynamics of glide avalanches and snow gliding

Ancey

Bain²

2015

Reviews of Geophysics

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In recent years, due to warmer snow cover, there has been a significant increase in the number of cases of damage caused by gliding snowpacks and glide avalanches. On most occasions, these have been full-depth, wet-snow avalanches, and this led some people to express their surprise: how could low-speed masses of wet snow exert sufficiently high levels of pressure to severely damage engineered structures designed to carry heavy loads? This paper reviews the current state of knowledge about the formation of glide avalanches and the forces exerted on simple structures by a gliding mass of snow. One particular difficulty in reviewing the existing literature on gliding snow and on force calculations is that much of the theoretical and phenomenological analyses were presented in technical reports that date back to the earliest developments of avalanche science in the 1930s. Returning to these primary sources and attempting to put them into a contemporary perspective are vital. A detailed, modern analysis of them shows that the order of magnitude of the forces exerted by gliding snow can indeed be estimated correctly. The precise physical mechanisms remain elusive, however. We comment on the existing approaches in light of the most recent findings about related topics, including the physics of granular and plastic flows, and from field surveys of snow and avalanches (as well as glaciers and debris flows). Methods of calculating the forces exerted by glide avalanches are compared quantitatively on the basis of two case studies. This paper shows that if snow depth and density are known, then certain approaches can indeed predict the forces exerted on simple obstacles in the event of glide avalanches or gliding snow cover.

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Section: Force Due To Gliding Snowmentioning

confidence: 99%

Dynamics of glide avalanches and snow gliding

Ancey

Bain²

2015

Reviews of Geophysics

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“…Others have adopted a similar distinction, sometimes using gliding rather than sliding to describe basal slip though usually in the context of annual rather than perennial snow (e.g. Haefeli 1953;Schaerer 1981;Larsen et al 1989;McClung et al 1994). As early as 1911, Matthes deduced that such snowslide was occurring from observations of ÔstriationsÕ and associated clasts in the Yosemite Valley.…”

Section: Snowbed Movementmentioning

confidence: 99%

Snow‐push processes in pronival (protalus) rampart formation: geomorphological evidence from smørbotn, romsdalsalpane, southern norway

Shakesby

Matthews

Berrisford

et al. 1999

Geografiska Annaler: Series A, Physical Geography

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M.S., 1999: Snow-push processes in pronival (protalus) rampart formation: geomorphological evidence from Sm¿rbotn, Romsdalsalpane, southern Norway. Geogr. Ann., 81 A (1): 31Ð45.ABSTRACT. It is demonstrated that pronival (protalus) ramparts can be formed by a snow-push mechanism and need not accumulate in the conventional manner as a result of supranival processes. Ridges in pronival positions up to 1.2 m high and of unequivocal snow-push origin are described from two sites in Sm¿rbotn cirque, Romsdalsalpane, southern Norway. The seven lines of evidence are: (1) parallel abrasion tracks on large boulders embedded in the substrate; (2) displaced surface and embedded clasts with proximal furrows; (3) corrugated (flute-like) substrate surfaces; (4) the sickle-shaped plan-form of the ridges; (5) generally asymmetrical ridge cross-profiles (shallow, concave proximal; steep, convex distal); (6) strong preferred orientations and dips of surface-embedded clasts on ridge proximal slopes; and (7) a subnival/pronival ridge comprising loosely packed diamicton forming along the contact zone between the snowbed and substrate. This evidence indicates ridge formation by snow sliding involving bulldozing of the substrate. Factors considered important in favouring snow push producing distinct pronival ramparts at the sites include: a maritime periglacial climate with heavy winter snowfall and rapid snow-firn conversion producing snow densities of up to 900 kg m -3 ; a deformable substrate with relatively small inputs of rockfall or avalanche debris; and a steep headwall susceptible to snow avalanching and hence enhanced snow supply. Consideration is given to the prospect that larger pronival ramparts can form incrementally by a snow-push mechanism.

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“…For three winters, the snow pressures at the poles showed irregularities which previously were difficult to explain. This was first recognized in 1981 with extraordinary high bending moments in the pole construction when the maximum snow depth was 4 m (Larsen and others, 1989). Later, the winters of 1989 and 1990 showed the same tendencies with maximum snow depths of 4.9 and 5.5 m (Table 1).…”

Section: Resultsmentioning

confidence: 99%

“…In a normal winter, the snowpack has an almost linear temperature profile with the lowest values measured close to the surface and an approximate temperature of 0°C at the snow-ground interface. The temperature in the middle depth of the snowpack gives a good indication of the temperature conditions in the snow (Larsen and others, 1989). Roughly, this temperature profile remains the same throughout the winter until mid- or late-April, when the snow reaches the 0°C isothermal in the research field.…”

Section: Resultsmentioning

confidence: 99%

“…Each mast was instrumented with vibrating-wire strain gauges every 0.5 m to obtain the axial stresses and moments at different heights (Larsen and others, 1989). A retaining structure, which is a standard element in avalanche-protection measures, was also erected at the same site in 1975 in order to investigate the snow-creep forces on the wall element.…”

Section: Instrumentationmentioning

confidence: 99%

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Snow-creep forces on masts

Larsen

1998

Ann. Glaciol.

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ABSTRACT. Since 1975, the Nor wegia n Geotechnica l Institute has performed fi eld investigati ons o f snow-creep forces on m asts at t he ]-esea rch site in Grasd a len, Stry n mountain s in No rway. Two poles, with dia meters of 419 a nd 219 m.m , resp ec ti ve ly, we re erected at the site togeth er with a retaining structure. On both poles, stra in gauges were mounted in pai rs ever y 0.5 m to find the ax ia l stresses and the moments in d ifferent sections. In the middle secti on of the reta ining structure, the beams and supporters were instrumented to obtain measurem ents of the strains a nd stresses. Snow glide was controll ed by glide shoes mounted a t the rock surface above the structures.During the winter, snow profil es were made system aticall y; th ese incl uded meas urements of snow depth, density a nd temperature, a nd obse rvations of snow type a nd moisture content. By relating the meas ured stresses a nd moments in th e structures to the snow depth, it was possible to find the snow-press ure distribution. A compa riso n of the snow pressures with the "Body force index" (product of snow depth h, density p a nd accelerati on due to gravity g), show a close relationship for the wa ll element. For th e pole elements, the now temperature during the winter is a n added facto r of high importa nce a nd th e h ighest pressures on these elements occ ur in winters with long peri od s ofO°C isoth erm al snowpack. INTRODUCT IONBecause snow creep causes failure in m as ts almost every winter, the No r wegian Water Resourses a nd Electricity Board (NVE ), which is res ponsibl e [or the electricity transmission lines, was interested in co-opera ting with the Norwegia n Geotechnical Institute (NGI ) to develop a study of snow-creep fo rces on different mas ts. T he goal wa s to find new m ast typ es which could be used in terrain with deep snow a nd to find design cri teri a for different co nstructions.The resea rch site is a 40 m wide a nd 30 m long rock surface til ting at 25° to the ea st, a nd th e m as ts we re located at a n elevati on of 1150 m a .s. 1. in the lower pa rt of th is site. Th e investigati ons we re performed close to NGI's fi el d stati on in th e Sty n mountains, 100 km from the coast in western No rway, where th e coastal climate ha a strong inOuence on the weather and snow conditi ons. The average annual precipitation in thi s area is close to 3 m. At the site, the maximum snow depth, which occurs each winter between late M arch and early M ay, vari es between 2 and 6 m.Different types of mas ts a nd a retaining structure were erected in 1975 (La rsen, 1982). As Nature is unpredictable concerning weather and snow conditions, it took yea rs to discover design load situations. For th e retaining structure, a clear relati onship was di scovered between the snow pressure a nd the "Bod y force index" (product of snow depth h, density p a nd acceleration due to g ravity g) (M c Clu ng and others, 1984; La rsen and others, 1985). In the late 1980s and earl y 1990s, new relationships of int...

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Snow-Creep Pressure on Masts

Cited by 3 publications

References 3 publications

Dynamics of glide avalanches and snow gliding

Dynamics of glide avalanches and snow gliding

Snow‐push processes in pronival (protalus) rampart formation: geomorphological evidence from smørbotn, romsdalsalpane, southern norway

Snow-creep forces on masts

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