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The role of stress concentration in slab avalanche release: comments on Dr R. A. Sommerfeld's paper

Published online by Cambridge University Press:  30 January 2017

R. Perla
R. Perla*
Affiliation:
US. Forest Service, Alta Avalanche Study Center, Alta, Utah 84070, U.S.A.
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Abstract

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Type
Correspondence
Information
Journal of Glaciology , Volume 9 , Issue 56 , 1970 , pp. 283
Copyright
Copyright © International Glaciological Society 1970

The Editor,

Journal of Glaciology

Sir,

Reference SommerfeildSommerfeld (1969, p. 451) dismisses Haefeli's contributions with the statement “Haefeli (1942, 1963) speaks of the shear fracture of a weak layer”. Actually, Reference Haefeli and KingeryHaefeli (1963) emphasized the importance of tensile failure in his theory of “stress metamorphosis”. Also, recall his discussion in Reference RochRoch (1966):

“We must take into account that the formation of snow slab avalanches is in its first approach not a problem of shear strength in the sliding surface but of the tensile strength within the fracture surface. The latter stays vertical (perpendicular) to the slope. The opening of the crack and the failure process is progressive. The breaking down of the sliding layer and the overcoming of the shear strengths along the sliding surface is no longer a static but a dynamic process, due to the heavy shock produced by the opening of the crack.”

Although Haefeli and Sommerfeld are in agreement on the importance of tensile failure, Sommerfeld advocates a Griffith criterion and Haefeli a Coulomb-Mohr criterion. A Griffith criterion, based on sound first principles, may be preferable: however, the Coulomb-Mohr criterion is still considered a good approximation for the macroscopic failure of granular materials (Reference Paul and LiebowitzPaul, 1968).

It is noteworthy that the Coulomb-Mohr criterion has been modified to account for “tensile cut-offs” (Reference Paul and LiebowitzPaul, 1968), which makes it quite applicable to the “stress metamorphosis” model.

References

Haefeli, R. 1963 Stress transformations, tensile strengths and rupture processes of the snow cover. (In Kingery, W.D. ed. Ice and snow; properties, processes, and applications: proceedings of 0 conference held at the Massachusetts Institute of Technology, February 12–16, 1962 Cambridge. Mass., The M.I.T. Press p. 560–75.) Google Scholar
Paul, B. 1968 Macroscopic criteria for flow and fracture. (In Liebowitz, H. ed. Fracture, on advanced treatise. Vol. 2, Mathematical fundamentals. New York and London. Academic Press p. 313–496.) Google Scholar
Roch, A. 1966 Les déclenchements d'avalanches. Union de Géodésie et Géophysique internationale. Association Internationale d Hydrologie Scientifique. Commission pour la. Neige et la Glace. Division Neige Saisonnière et Avalanches. Symposium international. sur les aspects scientifiques des avalanches de neige, 5–10 avril 1965 Davos, Suisse, p. 182–95. Google Scholar
Sommerfeild, A. 1969 The role of stress concentration in slab avalanche release. Journal of Glacialogy Vol. 8 No. 54, p. 451–62. Google Scholar