Behavioural characteristics and constituitive modelling of Athabasca tar sand at low effective stresses
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AbstractIn this thesis, the behaviour of Athabasca oil sand at low effective stresses is investigated. A series of consolidated drained triaxial tests was performed on undisturbed specimens at a confining pressure range of 30 kPa to 750 kPa. The influence of testing conditions, namely slenderness ratio and end conditions, on the behavioural characteristics of the material is investigated. The results of the shear tests revealed that the use of short specimens with free ends promotes the homogeneity of the sheared specimens. This homogeneity has been attested by the results of magnetic resonance imaging. The results of the shear tests exhibited that at low effective stresses, Athabasca oil sand does not reach to the critical state by the end of the tests. Thus, it is not possible to determine the critical state characteristics from these experimental results. The critical state characteristics of the material were determined from consolidated drained tests on reconstituted oil-free Athabasca sand specimens. A new algorithm is developed to determine the homogenous stress-strain and volume change responses of the material until the critical state is approached. A constitutive model, based on the generalized disturbed state concept, is established to model the response of Athabasca oil sand at low effective stresses. The response of Athabasca oil sand is expressed in terms of the responses of its reference states, namely the virgin and the fully disturbed states, through a disturbance function. A generalized single surface plasticity model is incorporated for modelling the virgin state of the material, whereas the fully disturbed state is assumed to be the critical state. The model parameters required to simulate both the experimental and the homogenous responses of Athabasca oil sand are identified and evaluated. The model is verified against both the experimental and the homogenous responses of the material.
Bibliography: p. 213-224.