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UBC Theses and Dissertations

Non linear elastic undrained stress-strain model for anisotropicaly consolidated clay Samarasekera, Lal


A nonlinear elastic model for normally consolidated clays which accounts for the influence of initial stress anisotropy and stress system change during shear, is presented herein. The analysis of a number of K₀ normally consolidated stress-strain results(published triaxial compression and extension) of different clay, revealed that, all the stress-strain curves could be adequately represented by hyperbolas, when the deviator stress is measured relative to its initial value. However, the writer believes(although not investigated) that the above finding holds true even for over consolidated clays and therefore, the proposed model is believed to be applicable for over consolidated clays too. The model was incorporated in an incremental linear finite element method of analysis programme. Utilizing the parameters from K₀ consolidated triaxial tests, the programme was used to predict other laboratory stress-strain behaviour such as plane strain and simple shear. The predicted strains were in excellent agreement with the measured values in the working range of strains. In an effort to compare the predictions of the proposed model and widely used isotropic hyperbolic models (Duncan et al., 1970) a load deformation analysis of a strip foundation was performed. Isotropic models always overestimated settlements and in some cases by as much as ten times that of the proposed model predictions. The isotropic model predictions of the ultimate bearing stresses were generally higher than those of its counterpart. The anisotropic model yielded shallower and wider failure zones than those produced by the isotropic model for the same loading conditions. A large number of published data on normally consolidated clays were analysed and correlative trends were found between the model parameters, soil index properties and coefficient of earth pressure at rest, K₀. These correlations can provide valuable tools in judging the reasonableness of the parameters obtained from laboratory tests or they can be used to obtain parameters when such test results are unavailable.

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