Shear Resistance Of Biotite-Schist: Peak And Post- Peak Behaviour
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Published:2004
L.G. F. S. de Mello, MSc, G.R. Sadowski, MSc, DSc, C. M. Nieble, MSc, 2004. "Shear Resistance Of Biotite-Schist: Peak And Post- Peak Behaviour", Advances in geotechnical engineering: The Skempton conference: Proceedings of a three day conference on advances in geotechnical engineering, organised by the Institution of Civil Engineers and held at the Royal Geographical Society, London, UK, on 29–31 March 2004
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The knowledge of shear behaviour of biotite -schist is of crucial importance for engineering purposes. There is little and sometimes controversial information published about this issue. A special investigative campaign was performed on biotite schist samples.
The samples were extracted from quartz-biotite-schist bands, layered in-between fresh granite-gneiss, in Eastern Brazil.
Shear resistance of this biotite-schist showed to be surprisingly low. After several special tests and investigations, it was concluded that this low shear resistance was related to the following causes: a) a very strong schistosity or textural anisotropy, due to intense quartz grain flattening around at least X/Y >=2:1 and strong laminar orientation of the micas; b) selective dissolution of interstitial quartz grains from the matrix due to differential weathering.
The geomechanical consequence was an extremely low residual friction angle (<15°) during solicitation. This may be explained as associated to an immediately previous negative dilation effect by collapse of the porous structure and local absence of ploughing resistance of the zones where quartz has been selectively removed.
Introduction
Some case histories
Shear strength of lamelar particle aggregates
Laboratory data
Concluding remarks
References
