A study of the shear modulus of a Lake Agassiz clay

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Liu, Vincent Pong-Hoi
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The shear modulus of a Lake Agassiz Brown clay was investigated. The approach used was to separate the stress system in a soil mass into volumetric and deviatoric stress components. The volumetric stress was related to the volumetric strain by the bulk modulus while the resultant deviatoric stress was related to the resultant deviatoric strain by the shear modulus. The shear modulus was investigated by means of constant mean normal triaxial compression drained tests. The stress-strain data was fitted by a two-parameter rectangular hyperbolic equation. The shear modulus was taken as the first derivative of the rectangular hyperbolic equation. The study was carried out on two block samples of brown clay which were obtained from depths of eight and sixteen feet in the southern part of Winnipeg. The clay is overconsolidated, highly plastic, slightly fissured, highly impermeable and almost fully saturated. The soil was tested in the normally and overconsolidated states... For the soil in an overconsolidated state the shear modulus was dependent on the degree of overconsolidation, the initial void ratio, and the level of deviatoric stress. No simple analytical solution for the shear modulus was established but graphical solutions were developed. The soil at the 8' depth exhibited positive dilatancy for over-consolidation consolidation ratios equal to or greater than 1.67 while the soil at the 16' depth did not exhibit positive dilatancy under deviatoric stresses. The resultant deviatoric stress at failure, Sdf, was found to be linearly related to the effective mean normal stress, om...