CGRG Bibliography of Canadian Geomorphology
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Author : Brooks, G.R.; and Aylsworth, J.M.
Date : 2011.
Title : Geotechnical characteristics of Champlain Sea deposits.
Publication : Deglacial history of the Champlain Sea basin and implications for urbanization; Joint annual meeting GAC-MAC-SEG-SGA, Ottawa, Ontario, May 25–27, 2011; Fieldtrip guidebook. Russell, H.A.J.; Brooks, G.R.; and Cummings, D.I. (Editors). Geological Survey of Canada Open File
Issue : 6947.
Page(s) : 06-07.
Abstract
The glaciomarine and prodelta silt, clayey silt, silty clay and clay sediments in the Ottawa Valley–St. Lawrence Lowlands region collectively form the Champlain Sea deposits, which are also known informally as ‘Leda Clay’. Typically, the deposits consist of silt- and clay-sized grains that are predominantly composed of quartz, feldspar, amphibole, illite and chlorite minerals, which represent glacial rock flour rather than clay minerals. These fine-grained particles flocculated within the saline-to-brackish water of the Champlain Sea, producing a sediment structure with a porous, loose structural framework that can retain a high natural moisture content. Champlain Sea deposits can be geotechnically ‘sensitive’, a condition whereby the remoulded shear strength is significantly lower than the undisturbed shear strength. In cases where remoulding yields a very low residual strength, the disturbed sediment may liquefy and flow because the collapse of the loose structural framework. The sensitivity of sediment is defined quantitatively by the ratio of undisturbed to remoulded shear strength (at the same moisture content). A sensitivity exceeding a ratio of 30 denotes a ‘sensitive’ clay, while a ‘quick’ clay exceeds 50. In the National Capital Region (NCR), sensitivities commonly range from 20 to 100, but locally values of up to 175 have been recorded. Sensitivity generally relates to the high natural water content in the deposits, flocculated fabric of the fine-grained particles, low electrical attraction between the particles, low overburden pressures during deposition, and post-depositional leaching of salts from the clays. The latter factor is a particularly important factor controlling the development of sensitivity and generally conditions the presence of sediment sensitivity at a given location.
Bibliography of Canadian Geomorphology