Direct simple shear (DSS) testing of a very stiff glaciolacustrine clay

G Le Meil

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: SOIL AND TERRAIN CHARACTERIZATION - II Geotechnical Laboratory Testing

ABSTRACT: The purpose of the research presented within this paper has been to investigate the impact of undrained loading conditions and the rate of movement on the strength of a heavily overconsolidated Pleistocene glaciolacustrine clay. Shear planes within this clay are implicated in the movement of many large landslides within the Thompson River valley, near Ashcroft, BC. Peak and residual strengths have previously been evaluated with direct shear tests; strength values similar to the residual strength have been back-calculated from several of the meta-stable landslides. Testing of the isotopes within the pore fluid of this clay has been conducted, along with extensive monitoring of pore pressures and displacements of the most active of the landslides within the valley (the Ripley slide). This has allowed for the characterization of the movement of water through the material over geological time, and the quantification of the current pore pressure distribution and rate of movement. Together, these results have shown that this clay is extremely tight and has raised the prospect that the pore pressures generated at the observed rate of shearing may impact the shear strength that can be mobilized. Direct simple shear (DSS) tests have been conducted on clay specimens retrieved from the Ripley slide in an attempt to mimic the shearing of this clay along the bedding planes under undrained conditions. The use of the conventional NGI-type DSS apparatus for this very stiff clay has been challenging, as it well exceeds the stiffness and strength of soils typically tested with this apparatus. These challenges, the measured strength, and the resulting effective stress paths are presented within this paper.

RÉSUMÉ: présentée sont impliqués dans plusieurs grands Précédemment, les résistances de pic et résiduelle ont été estimées par des essais de cisaillement direct. A partir de certains glissements métastables, des valeurs de résistance proche de la résistance résiduelle ont pu être calculées. Les isotopes du fluide interstitiel ont été analysés et une surveillance approfondie des pressions interstitielles et des déplacements a été effectuée sur le plus actif des glissements de terrain de la vallée (le glissement Ripley). Ainsi, très peu perméable et laissent penser que les pressions interstitielles générées à la vitesse de cisaillement observée peuvent affecter la résistance au cisaillement mobilisable. Des essais de cisaillement simple (direct e de type NGI pour cette argile très raide est difficile difficultés, la mesure de la résistance et les résultats de chemins de contraintes effectives sont présentés ici.

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Cite this article:
G Le Meil (2016) Direct simple shear (DSS) testing of a very stiff glaciolacustrine clay in GEO2016. Ottawa, Ontario: Canadian Geotechnical Society.

@article{3973_0711182716,author = G Le Meil,title = Direct simple shear (DSS) testing of a very stiff glaciolacustrine clay,year = 2016}