CGRG Bibliography of Canadian Geomorphology
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Author : Bishop, N.F.; Evans, S.G.; and Petley, D.J.
Date : 2008.
Title : The geotechnics of glaciolacustrine sediments and associated landslides in the vicinity of Ashcroft (British Columbia) and the Grand Coulee Dam (Washington).
Publication : 4th Canadian Conference on Geohazards: From Cause to Management. May 20-24, 2008. University Laval, Quebec City, Quebec.
Issue :
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Abstract
Pleistocene valley fills dominated by glaciolacustrine sediments commonly occur in southern British Columbia and northern Washington. The fills contain multiple glaciolacustrine units separated by glacial tills and outwash gravels reflecting multiple episodes of glacial lake formation, glaciation onset and glacial retreat. Typically the sediments consist of silt-dominated varves which contain thin layers of highly-plastic clay. The lower glaciolacustrine units have been overridden by glacial ice and show evidence of glacial-induced deformation and shearing. In addition the sediments have been subject to contemporaneous landsliding during deposition and landsliding during valley-cutting periods between glacial episodes. Thus the glaciolcaustrine materials in present day valley side slopes contain pre-sheared clay-smeared surfaces which may be at residual strength. We review the results of direct shear tests on samples from the Grand Coulee dam area and report results of ring-shear tests on materials from the clay component of the varves in the Ashcroft area. The geotechnics of these sediments is examined with an emphasis on the relationship between geotechnical index properties and residual strength parameters. The controls on residual strength are examined. Empirical relationship between such properties as clay content and plasticity index and residual strength are developed. Finally, the back-analysis of a number of landslides is presented to explore the influence of 1) variation in residual strength and 2) changes in effective stress on slope stability. The precise characterization of residual strength is a key component of landslide hazard assessment of slopes developed in these materials.
Bibliography of Canadian Geomorphology