Pennmadu Multi-axial experiments with local strain measurements will be performed using axial-torsional and true triaxial testing in which he stress-strain relationship of clays will be evaluated for the stress paths associated with the rotation of principal stress directions under undrained conditions. Experiments also include evaluating the relationship between the initial microfabric of clay and the nature of its evolution as a function of the applied loading.
The microfabric will be evaluated quantitatively using digital image analysis of scanning electron micrographs (SEM), and using mercury intrusion porosimetry. The arrangements of solids (clay platelets) is evaluated using digital SEM and the intensity gradient analysis. The microfabric will be described quantitatively using two parameters: fabric index and the inclination of orientation. Repeatable hollow cylinder and cubical kaolinite clay specimens with a controlled and uniform initial fabric will be obtained from a two stage slurry consolidation procedure, and the clays will be subjected to both isotropic and anisotropic consolidation for predetermined stress levels. The two- and three-dimensional void fabric will be uniquely described by a characteristic pore size distribution curve, and analysis will be performed to evaluate yield and failure criteria.
The dependency of yield and failure surfaces on the microfabric, specimen shape, and the differences associated with apparatus type will be evaluated under the generalized three-dimensional stress states. The research plan will provide: a) quantitative procedures for describing the microfabric of cohesive soil, b) a better understanding of mechanical behavior of clay and its relationship with microfabric for a wide variety of loading conditions, and c) a database for the modeling community to develop three-dimensional constitutive model for cohesive soil accounting for microfabric effects. ***
