Modelling including associated testing of cohesive soil using disturbed state concept.

Abstract

A new constitutive model for predicting the undrained stress-deformation and pore water pressure response of saturated cohesive soils subjected to cyclic loading is developed using the Disturbed State Concept (DSC) is presented in this dissertation. The model takes into account inelastic non-virgin behavior. Factors such as non-associativeness, induced anisotropy and degradation are included 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 δ₀. The other reference state is the fully disturbed state which is assumed to be the critical state. The average response is expressed in terms of the responses corresponding to the reference states through a disturbance function D. The inelastic non-virgin loading is modelled by using interpolation functions which are made function of disturbance. Comprehensive laboratory tests have been performed on undisturbed clay samples procured from Sabine Pass, near Houston, Texas. The tests include conventional cylindrical triaxial tests and also cyclic triaxial tests in the multiaxial device with pore water pressure measurements. Some of these tests were used for determination of parameters and verification of the model. The model is verified with respect to the observed behavior of undisturbed clay samples. 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 during virgin and non-virgin loading and cyclic loading. It is concluded that the new model based on the DSC concept can correctly predict the cyclic behavior of cohesive soils and can take into account factors such as non-associativeness, induced anisotropy and degradation. The DSC concept is shown to be a powerful and general approach for constitutive modelling of geomaterials.