The Bundner schist (Bundnerschiefer) discussed in this paper is found widely in the canton of Grisons (Graubunden). Its properties as a highly tectonic, metamorphic rock, found in different states of weathering, present an interesting geological-geotechnical problem, which also has far reaching effects on the economy and the communications system. The schist breaks up into plate-like fragments and, in addition, is subject to weathering so that with time the strength of the material is progressively reduced. Due to movements in a slope the rock fragments can be structrually rearranged, leading to a further reduction in strength. Creep movements may be initiated or accelerated simply by natural means, like erosion, but also as the result of artificial disturbance of slopes. This behaviour of the rock is the cause of extensive creep slopes in the Grisons, with the consequence that day to day life in villages and whole valleys is inconvenienced. The creep behaviour of Bundner schist is illustrated in this paper mainly by means of the results of tests on the rock in a broken but unweathered condition. The main test employed in the investigation was the triaxial test, the results being supplemented by test results obtained using the direct and ring shear apparatus. Normally, the material exhibits no plasticity. It was tested at degrees of saturation of 100% and approx. 80% and at different unit weights. The influence of the maximum fragment size on the shear strength was also investigated. It was found that the strength of the material tested was dependent only on the unit weight of the material and was independent of the fregment size. The effect, whereby the material is shattered was shown at all round pressures of 50 kg/cm2, while the influence of structural readjustment was investigated in the ring shear apparatus. The influence of weathering on the fragment size distribution and thus on the shear strength is shown for a naturally occurring weathered schist. Practical examples with measurements of deformation demonstrate the importance of the structural behaviour of Bundner schist.

  • Supplemental Notes:
    • This article was reprinted from Lauritis Bjerrum Memorial Volume, Oslo, 1976.
  • Corporate Authors:

    Institut fur Grundbau und Bodenmechanik

    Gloriastrasse 37-39
    CH-8006 Zurich,   Switzerland 
  • Authors:
    • HUDER, J
  • Publication Date: 1976


  • German

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  • Accession Number: 00151994
  • Record Type: Publication
  • Report/Paper Numbers: Report Number 107
  • Files: TRIS
  • Created Date: Apr 13 1977 12:00AM