The behaviour of geomaterials define the strength and volumetric behavioural tendencies of geotechnical structures in terms of their ability to carry load. The expression of these characteristics in a concise constitutive model is necessary to design and implement structures by safe and economical means. Some previous constitutive models of granular materials have attempted to define the interaction between stress and strain without the consideration of inherent properties of the material such as density and pressure dependencies. Other models incorporate pressure and density effects but become complicated when used to describe more complicated behaviour such as strain-softening. This thesis presents a recently developed model which incorporates the influences of these variables into Rowe's classical stress-dilatancy relationship through the use of a ratio of current to critical void ratio. Initially, an experimental program investigates the stress-dilatancy behaviour of a fine Ottawa Sand under conventional triaxial testing at various confining pressures and densities. The results of these are then used to calibrate a new stress-dilatancy relationship through the definition of eleven material parameters, with the model results showing good correlation to the measured responses. An additional laboratory analysis is included which provides an observational study of the pressure and density effects on the behaviour of Ottawa Sand subjected to low frequency, high amplitude cyclic loading.
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