Limit state studies in Winnipeg clays

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Noonan, Michael Leonard
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This study investigates the applicability of the limit state concept to the highly plastic, lacustrine clays of the Winnipeg area. The thesis begins with a literature review of the concepts of limit state and critical state, which is followed by discussion of YLIGHT, the most recent qualitative model for the behavior of natural clay. Using the careful sampling and laboratory testing techniques outlined in this thesis, nine three-inch diameter, undisturbed triaxial samples were tested from depths of 8.2 m and 10.0 m in the Lake Agassiz clay from Winnipeg. Data was obtained on both drained and undrained triaxial behavior. Drained stress-controlled triaxial tests were used to establish limit state envelopes for both depths. Strain energy was used as a limit state criterion along various stress paths. The undrained, strain-controlled triaxial tests examined the pore-water water pressure generation characteristics, elastic moduli, and strain rate effects for this clay. Values of Af between 0.45 and 1.34 were found depending on the consolidation stress levels. The relative stiffness, (E50/(o1-o3)/2), varied from 171 to 388. The strain rate parameter, Po.1, was found to lie between 4.5 percent and 10.1 percent. An average effective, normally consolidated, Coulomb-Mohr rupture envelope for the Winnipeg clay at both depths was found using drained and undrained test results The effective strength parameters, c' and o', were 0 and 18*, respectively, in this range of stresses.