The shear strength index of alpine snow

Perla, R.; Beck, Tanya M.; Cheng, Ting-Hao

doi:10.1016/0165-232x(82)90040-4

Cited by 44 publications

(37 citation statements)

References 7 publications

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“…The frame index is influenced by the frame mass and loading rate. 11 In particular, the frame index increases with higher frame mass and lower loading rate. The shear index increases for lower temperature.…”

Section: Shear Strengthmentioning

confidence: 99%

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An Apparatus for In Situ Direct Shear Tests on Snow

Barbero¹,

Barpi²,

Brunetto³

et al. 2013

Exp Techniques

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The article presents a prototype of a new device for measuring the shear strength of snow specimens in situ. The resistance to sliding of a snow slab on a mountain slope is a key parameter in snow mechanics. The proposed apparatus acts as a sampler, to obtain a nearly undisturbed specimen, and as a shear box, similar to those used in the laboratory, with complete control of the test procedure. The main components of the device are a pneumatic system, for the application of normal and shear forces to the specimen, a real-time controller for commanding and recording of the data, and a computer. The apparatus can be carried to the place of the experiments and operated by a team of two researchers. Calibration and preliminary tests are also described in the article.

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Section: Shear Strengthmentioning

confidence: 99%

“…To study the scale effects on shear strength of snow, Perla et al 11 performed some tests on alpine snow pack with a rotating shear vane apparatus. A large snow sample is collected in a cylindrical drum, Figure 1 The manual shear frame, hand driven by the operator through a force gauge.…”

Section: Shear Strengthmentioning

confidence: 99%

An Apparatus for In Situ Direct Shear Tests on Snow

Barbero¹,

Barpi²,

Brunetto³

et al. 2013

Exp Techniques

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“…(7) The shear-frame index of alpine snow varies through at least three orders of magnitude (Perla and others, 1982). To sample this range with a 0 .025 m 2 frame it is necessary to use at least three force gauges (e.g.…”

Section: Size Rate and Mass Effectsmentioning

confidence: 99%

Experience with Shear Frames

Perla¹,

Beck²

1983

J. Glaciol.

Self Cite

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ABSTRACT. The shear frame is a simple in situ device for indexing the s hear strength of thin weak layers. The index is sensitive to shear-frame geom etry, rate-of-pull , and shear-frame ma ss. It is time-consuming to carefu ll y align the device on the Gleitschicht (shear failure plane) in a slab avalanche zone. The ratio shea r fra me index/ shear stress of the Gleitschicht has a high va rian ce, a nd may not be a fundamental mea s ure of slab avalanche sta bility. Corrections for th e normal stress on the Gleitschicht reduce th e vari ance only s lightl y. Despite these limitations, the shear frame is a useful tool for gat hering statistica l data on strength distributions and anisotropies of the Gleitschicht until a more fundamental technique is developed . RESUME. Experiences avec ja uges a cisaillemellt. La jauge a cisaillement es t un simple appareil in situ pour indexer la resistance au cisaillement de niveaux faibles et minces. L'indice est sen sible a la geometrie de la jauge, a cisaillement, a I'impulsion qu'on lui donne, et a la masse de la jauge. C'est une manoeuvre tres longue que de pl acer avec soin I'appareil sur le " gleitschicht" (pl a n de rupture au cisaillement) d ans une zone d 'avala nch e de plaque. Le rapport indice de cisaillement/effort de cisaill ement sur le "gleitschicht" a uhe forte va ri abi lite et ne peut constituer une mesure fondamentale de la stabilite des avalanches de pl aq ues. Les correcti o n s pour lenir compte de I'effort normal s'exercrant s ur le " gleitschicht" ne red uit que peu cette variabilite. En depit d e ces limiles. la jauge a cisaillement est un outil utile po ur rassembler des donn ees statistiques s ur la distribution des effort s etles anisotropies du "gleitschicht" jusqu 'a ce qu 'on ait mi s a u point un e methode plus rationnelle.ZUSAMMENFASSUNG. Erfahrungen mil Scher-Rahmen. Der Scher-Rahmen ist eine ei nfac he Vorrichtung zur in silu -Feststellung der Scherfestigkeit diinner und schwacher Schichten . Di e Anzeige reagiert auf die Geometrie des Rahmens, die Zugrate und die Rahmenmasse. Die sorgfalti ge Einpassung des Gerates in die Gleitschicht einer Lawinenzone erfordert viel Zeit. Das Verhaltnis zwisc hen Scherrahmen-Anzeige zur Scherspannung der Gleitschicht ist stark veranderli ch und diirfle kein Grundmass fiir die Stabilitat von Schneebrettern sein . Ko rrektu ren wegen Normalspannung in der Gleitschicht verringern die Schwankungen nur wenig. Trotz dieser Einsc hrankungen ist der Scher-Rahm en ei n brauchbares Mittel zur Gewinnung statistischer O aten iiber die Festigkeitsverteilung und die Anisotropien in der Gleitschicht, bis eine tiefergreife nde Technik entwickelt wird .

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“…For a given time, depth within the snowpack, and location on a slope, snow stability can be described as the balance between snow strength and stress termed stability index (Roch, 1966). This index has been widely used (e.g., Conway and Abrahamson, 1984;Perla et al, 1982) and refined by taking into account triggering by an additional load such as a skier (Föhn, 1987). Whereas, the skier stability index has been shown to be related to the probability of skier triggering (Jamieson, 1995), this critical stress approach does not take into account that slope failure requires crack propagation.…”

Section: Introductionmentioning

confidence: 99%

A process-based approach to estimate point snow instability

Reuter¹,

Schweizer²,

Herwijnen³

2015

The Cryosphere

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Abstract. Snow instability data provide information about the mechanical state of the snow cover and are essential for forecasting snow avalanches. So far, direct observations of instability (recent avalanches, shooting cracks or whumpf sounds) are complemented with field tests such as the rutschblock test, since no measurement method for instability exists. We propose a new approach based on snow mechanical properties derived from the snow micropenetrometer that takes into account the two essential processes during dry-snow avalanche release: failure initiation and crack propagation. To estimate the propensity of failure initiation we define a stress-based failure criterion, whereas the propensity of crack propagation is described by the critical cut length as obtained with a propagation saw test. The input parameters include layer thickness, snow density, effective elastic modulus, strength and specific fracture energy of the weak layer -all derived from the penetration-force signal acquired with the snow micro-penetrometer. Both instability measures were validated with independent field data and correlated well with results from field tests. Comparisons with observed signs of instability clearly indicated that a snowpack is only prone to avalanche if the two separate conditions for failure initiation and crack propagation are fulfilled. To our knowledge, this is the first time that an objective method for estimating snow instability has been proposed. The approach can either be used directly based on field measurements with the snow micro-penetrometer, or be implemented in numerical snow cover models. With an objective measure of instability at hand, the problem of spatial variations of instability and its causes can now be tackled.

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The shear strength index of alpine snow

Cited by 44 publications

References 7 publications

An Apparatus for In Situ Direct Shear Tests on Snow

An Apparatus for In Situ Direct Shear Tests on Snow

Experience with Shear Frames

A process-based approach to estimate point snow instability

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