| This dissertation presents the development and implementation of a constitutive model to predict the behavior of unsaturated sands. The model is based on critical state and bounding surface concepts and incorporates parameters to account for sand fabric and suction. The model is implemented into ABAQUS finite element software using UMAT subroutine. Model performance is verified on a wide range of triaxial test data including different drainage conditions, sample preparation method, density, confining stress, and mode of shear. Simulation results show that saturation level significantly affects sand performance, and a modified suction based state parameter is proposed to quantify such effects. A linear relationship between peak stress increment and suction based state parameter for different densities and sample preparation methods was found.;The new sand model is subsequently used to study the effects of sample preparation, saturation level, and density on stress controlled drained triaxial results under repeated loading. It was found that moist tamped specimens have much more resistance to permanent deformation than dry deposited specimens. The model quantified the increased resistance of dense sands as well as reduction in saturation level of all sands to permanent deformation under cyclic loading. The model also quantified the difference in undrained pore pressure response of sands under cyclic loading for the two preparation methods. The dry deposited specimen showed much larger increase in pore pressure response than the moist tamped specimen.;The developed 3D FE model quantified the response of pavement subgrades under differing loading magnitudes, asphalt and base properties, and saturation levels. The moduli of asphalt and base, and saturation level of subgrades, were found to influence the vertical deformation experienced near the top of subgrade, especially at high wheel loads, but their influence gradually reduced with depth. |
