Mechanics of gravitational spreading of steep-sided ridges («sackung»)

Mécanisme d'affaissement par gravité des crêtes rocheuses à fortes pentes (sackung)

Abstract

Large-scale gravitational spreading of steep-sided ridges characterized by linear fissures, trenches, and uphill-facing scarps high on the sides and tops of ridges are known worldwide. Such spreading, termed sackung, is commonly attributed to pervasive plastic deformation of a rock mass, and is here analyzed as such. Beginning with a previously developed exact elastic solution for gravity-induced stresses in a symmetric ridge, stresses calculated from the exact solution are used in the Coulomb failure criterion to determine the extent of ridge failure under self-weight. Finally, when the regions of failure are established, a plastic flow solution is applied to predict the location of and sense of movement on upward-facing scarps near ridge crests and other features common in sackung.

Résumé

Le phénomène d'affaissement par gravité des crêtes rocheuses à fortes pentes auxquelles sont associés des fissures linéaires, des tranchées et escarpements faisant face au sommet des crêtes est connu dans le monde entier. Cet affaissement, aussi connu sous le nom de «sackung», est communément atribué à un processus de déformation plastique du massif rocheux, et de ce fait, est analysé de cette façon. L'article commence par un rappel sur la solution élastique pour la distribution des contraintes induites par gravité dans une crête symétrique. Ensuite les contraintes calculées à l'aide de la solution élastique sont utilisées pour définir l'extension du domaine de rupture d'une crête rocheuse sous son propre poids avec l'hypothèse du critère de Coulomb. Finalement, après avoir défini les domaines de rupture, une solution d'écoulement plastique est utilisée pour prévoir la position et le sens de mouvement des escarpements faisant face au sommet des crêtes et prévoir d'autres caractéristiques communément associées au phénomène de «sackung».

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Savage, W.Z., Varnes, D.J. Mechanics of gravitational spreading of steep-sided ridges («sackung»). Bulletin of the International Association of Engineering Geology 35, 31–36 (1987). https://doi.org/10.1007/BF02590474

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Keywords

  • Pore Pressure
  • Rupture Surface
  • Coulomb Failure Criterion
  • Ridge Crest
  • Stream Erosion