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Direct Simple Shear Tests on Snow and their Relation to Slab Avalanche Formation

  • David M. McClung (a1)

Abstract

Many slab avalanches can be attributed to shear failure in a weak, thin basal layer at the slab base. A reasonable starting point for evaluation of the conditions prior to fracture is, therefore, an investigation of shear failure in thin samples of snow. This paper gives the experimental procedure and data on measurements of shear stress versus displacement for thin samples of snow under plane strain and approximately simple shear conditions. The data are given under varying conditions of strain-rate, normal stress, density and snow type. The results show that the samples exhibited strain-softening provided they were sheared faster than they gained strength by settlement under the chosen conditions. If snow fails at the base of a slab in the way in which it fails in the laboratory, then a mechanism is provided whereby tensile stresses would be produced in the slab and whereby the corresponding maximum principal stresses would be rotated toward a direction parallel to the slope, thereby promoting avalanche release.

Résumé

Tests simples directs de cisaillement dans la neige et leur relations avec la formation des avalanches de plaque. De nombreuses avalanches de plaque de neige semblent étre dues à la rupture au cisaillement d'une couche mince basale, de faible résistance, à la base de la plaque de neige. Un point de depart raisonnable pour l'évaluation des conditions qui précèdent une avalanche est done l'étude de la rupture au cisaillement dans de minces échantillons de neige. Cet article présente la procédure expérimentale et les résultats de mesures de la contrainte de cisaillement en fonction du déplacement dans de minces échantillons de neige pour des conditions de cisaillement simple et de déformation plane. Les résultats sont présentés pour diverses valeurs du taux de déformation, de la contrain te normale, de la densité et du type de neige. Les resultats indiquent que les échantillons exhibent un comportement de ramolissement lorsqu'ils sont cisaillés plus rapidement qu'ils ne gagnent de resistance du a la consolidation. Si la neige se rompt à la base déune plaque de neige comme elle le fait dans le laboratoire, des contraintes detraction sont produites dans la plaque de neige et les contraintes principales maximales correspondantes sont tournées dans la direction parallèle à la pente, favorisant ainsi le déclenchement d'une avalanche.

Zusammenfassung

Unmittelbare, einfache Scherversuche an Schnee und ihre Beziehung zur Bildung von Schneebrett-Lawinen. Viele Schneebrettlawinen sch einen durch ein Sch erversagen in einer schwachen, dünnen Schicht am Grunde des Brettes verursacht zu sein. Ein vernénftiger Ausgangspunkt fér die Untersuchung der Verhältnisse vor dem Bruch ist deshalb das Studium des Scherversagens in dünnen Schneeproben. Die vorliegende Arbeit gibt das Vorgehen und experimentelle Daten für Messungen der Scherspannung gegenüber der Verlagerung an dünnen Schneeproben unter einfacher Scherung und ebener Spannung. Die Daten beziehen sich aufverschiedene Verformungsraten, Normalspannungen, Dichten und Schneearten. Die Ergebnisse zeigen, dass die Proben unter der Spannung nachgeben, sofern sie schneller geschert werden, als ihre Festigkeit durch Setzung unter den gewahlten Verhaltnissen zunimmt. Wenn Schnee am Grunde eines Brettes so nachgibt wie im Laborversuch, ergibt sich ein Mechanismus, durch den Zugspannungen im Brett entstehen und die entsprechenden maximalen Hauptspannungen in eine Richtung parallel zur Hangneigung eingedreht würden, wodurch wiederum die Lawine ausgelöst würde.

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References

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Berre, T., and Bjerrum, L. 1973. Shear strength of normally consolidated clays. Proceedings of the eighth International Conference on Soil Mechanics and Foundation Engineering, Moscow, Vol.1.1, p. 39–49.
Bishop, A. W. 1966. Strength of soils as engineering materials. Geotechnique (London), Vol.16, No. 2, p. 89–130.
Bjerrum, L. 1967. Progressive failure in slopes of over consolidated plastic clay and clay shales. Journal of the Soil Mechanics and Foundations Division, American Society of Civil Engineers, Vol.93, No. SM5, p. 1–49.
Bjerrum, L. 1973. Problems of soil mechanics and construction on soft clays. Proceedings of the eighth International Conference on Soil Mechanics and Foundation Engineering, Moscow, Vol.1·3, p. 11–59.
Bjerrum, L., and Landva, A. 1966. Direct simple-shear tests on a Norwegian quick clay. Geotechnique (London), Vol.16, No. I, p. 1–20.
Canada. National Research Council. 1954. The International Classofication for Snow (with special reference to snow on the ground), issued by Commission on Snow and Ice of the International Association of Hydrology. Canada. National Research Council. Associate Committee on Soil and Snow Mechanics. Technical Memorandum No. 31.
Haefeli, R. 1951. Investigation of the shear strengths of saturated cohesive soils. Geotechnique (London), Vol.2, No. 3, p. 186–208.
Landva, A. 1964. Equipment for cutting and mounting undisturbed specimens of clay in testing devices. Norwegian Geotechnical Institute. Internal Report F.175.
Perla, R. I. [1975.] Stress and fracture of snow slabs. [Union Geodesique et Geophysique Internationale. Association Internationale des Sciences Hydrologiques. Commission des Neiges et Glaces.] Symposium. Mécanique de la Neige. Actes du coUoque de Grindelwald, avril I974, p. 208-21. (IAHS-AISH Publica tion No. 114.)
Perla, R. I. Unpublished. The slab avalanche. [Ph.D. thesis, University of Utah, 1971.]
Roch, A. 1966. Les déclenchements d'avalanches. Union de Géodesie et Géophysique Internationale. Association Internationale d'Hydrologie Scientofique. Commission pour la Neige et la Glace. Division Neige Saisonnière et Avalanches. Symposium international surles aspects scientofiques des avalanches deneige, 5-10 avril 1965, Davos, Suisse, p.182-95. (Publication No. 69 de l'Association Internationale d'Hydrologie Scientofique.)
Schaefer, V..T., and others. [1952.] Entwurfeiner internationalen Schneeklassofikation ausgearbeitet durch das Komitee für Schneeklassofikation, von V. J., Schaefer, G. J., Klein, M. R. de, Quervain. Union Géodésique et Géophysique Internationale. Association Internationale d'Hydrologie Scientofique. Assemblée généra le de Bruxelles, I951. Tom. I, p. 129-41. (Publication No. 32 de l'Association Internationale d'Hydrologie.)
Sommerfeld, R. A., and LaChapelle, E. R. 1970. The classofication of snow metamorphism. Journal of Glaciology, Vol.9, No. 55, p. 3–17.
Sommerfeld, R. A., and others. 1976. A correction factor for Roch's stability index of slab avalanche release, by R. A., Sommerfeld, R. M., King and F., Budding. Journal of Glaciology, Vol.17, No. 75, p. 145–47.

Direct Simple Shear Tests on Snow and their Relation to Slab Avalanche Formation

  • David M. McClung (a1)

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