A powerful and general concept, the DSC concept, that can capture a wide spectrum of behavior of geologic materials is developed in this dissertation. Factors such as nonassociativeness, induced anisotropy and damage are included in the concept as disturbances with respect to two reference states. One reference state is the intact state where the material is assumed to be associative initially isotropic and hardening isotropically. It is modelled by the basic hierarchical model δₒ. Its hardening parameters are modified to include the influence of relative density Dᵣ and confinements, σₒ. The other reference state is the fully disturbed state which is assumed to be the critical state. In this state the material is assumed to experience no change in void ratio under further shearing. The average response is expressed in terms of the responses corresponding to the reference states through a disturbance function D. The disturbance function parameters have been found to be dependent on Dᵣ and σₒ. Comprehensive laboratory tests have been performed on Leighton Buzzard sand covering a wide range of relative densities and confinements. Some of these tests were used in the formulation of the DSC concept to incorporate the effect of Dᵣ and σₒ into the model parameters. Verification of the new model is performed with respect to the observed behavior of loose and dense sand. Verification was done with respect to laboratory tests that were used and the ones that were not used in the development of the model. The proposed model provides overall highly satisfactory predictions of the observed behavior for the entire range of loose to dense sand. It is concluded that the DSC concept along with the new contributions of this research which allow incorporation of the entire range of loose to dense behavior can provide a powerful and general approach for constitutive modelling of geomaterials.
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