Rate effects and low stress strength of Winnipeg clay

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Au, Vincent C. S.
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The two principal purposes in this thesis are: 1. to investigate the influence of test duration and strain rate on the stress-strain behaviour of Lake Agassiz clay from Winnipeg. 2. to examine the strength of Winnipeg clay at low stress levels. The study also investigated the Undrained Strength of the clay at Large Strains (USALS) and its relationship with the normally consolidated Coulomb-Mohr envelope. Six drained stress-controlled triaxial tests on undisturbed samples were used to study the time-dependent aspects of the YLIGHT model of soil behaviour. Six non-standard and four strain-rate controlled oedometer tests were performed to examine the effects of time and strain rate on the preconsolidation pressure, p'c. The samples were taken from 11.6 m depth, and the sample diameter was 76 mm. The preconsolidation pressure p'c decreased from 249 to 225 kPa as the duration of the load application increased from 0.1 to 100 days... Five 76 mm diameter undisturbed triaxial samples taken from 11.6 m, six 'fully-softened' and five 'freeze-thaw'triaxial samples taken from 8.7 m were tested to study the low stress strengths of Winnipeg clay. Data was obtained on both drained and undrained triaxial behaviour... The Undrained Strength at Large Strains (USALS) obtained for all the undrained tests lay close to the normally consolidated Coulomb-Mohr envelope (o' = 17.5o; c' = 4 kPa).