Cross-anisotropic behavior of granular materials under three-dimensional loading conditions

This dissertation presents results of an experimental and theoretical investigation of the cross-anisotropic behavior of gravitationally deposited sands under general three-dimensional loading conditions.; The laboratory study included a series of cubical triaxial tests using a true triaxial apparatus with improved accuracy of measurements and control. The cubical tests were performed on Santa Monica beach sand under general stress conditions allowing for exploration of the entire range of Lode's angles [0°, 180°], necessary for complete description of a cross-anisotropic material. Stress-strain behavior and strength, failure patterns and shear banding, volumetric response and dilative properties were analyzed in view of the inherent material anisotropy.; A series of high-pressure isotropic compression tests were performed on Santa Monica beach and Nevada sands using four different densities and two specimen deposition methods. The evolution of the inclination of the plastic strain increment vector to the hydrostatic axis with pressure was evaluated and analyzed using different elastic models.; A principle of rotation of the principal stress coordinate system to account for the experimentally observed transverse isotropic effects was introduced. A cross-anisotropic constitutive model was derived based on the existing model for isotropic materials. A thorough analysis of response of each component of the modified model was performed. The new model was implemented to predict the results of the cubical triaxial tests producing good fits with the experimental data.