Nonlinear stress-deformation analyses of Lake Agassiz clays using finite element method

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Valliappan, Palaniappan
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For nonlinear stress-deformation analyses of soils, it is necessary to define the stress-strain behaviour of the soil in quantitative terms, and to develop techniques for incorporating this behaviour in the analyses. The stress-strain behaviour of Lake Agassiz clays was separated into mean normal and deviatoric components and the stresses and strains were interrelated through bulk and shear moduli. Drained isotropic compression tests were used for the evaluation of bulk modulus. A three-parameter stress-strain relationship was used to represent the isotropic stress-strain data. Solutions were obtained for bulk modulus as a function of soil type, void ratio, and imposed stress system. The shear modulus was investigated by drained constant-mean-normal-stress triaxial compression tests. The basic two parameter hyperbolic relationship in a modified form was used to represent the resultant deviatoric stress-strain data and an analytical expression was determined for the shear modulus. The solution for shear modulus was obtained as a function of soil type, previous stress history, failure criterion, void ratio, and imposed stress system. The failure zones and long term uplift capacities predicted for shallow and deep anchors using the finite element method, showed good agreement with those evaluated by using Meyerhof and Adam's theory. The distribution of stresses and displacements along the length of the vertical circular shaft obtained by the finite element analysis were similar to the distributions described by Terzaghi.