This research project will investigate the stress-strain (constitutive) behavior of soils when subjected to earthquake loading, focusing on the anisotropic response. Although a number of models have already been proposed, verification of such models is difficult. This project involves a combined analytical, computational, and experimental program to determine the constitutive behavior. The analytical component focuses on a hierarchical model that the principal investigator has been developing. The experimental phase of the project will utilize a multiaxial cubical device which is capable of loading the specimen along various loading paths. An ultrasonic method will be used to measure the degree of anisotropy of the soil specimen. The cubical device will be modified so that the degree of anisotropy can be measured during loading, unloading, and reloading. An alternative to the ultrasonic method will also be considered, namely measurement of the electrical properties of the specimen. The above tests will first be done statically, and when verified they will then be extended to the case of dynamic loading. This will be done with a number of soils so as to verify the technique for a wide variety of geological materials. Finally, the constitutive characterization will be utilized to solve typical boundary value problems involving nonlinear soil behavior. For example, the problem of dynamically loaded structure-foundation systems, or of a foundation pile embedded in cohesionless soil will be considered. Then the computed response of the structure-soil system will be compared qualitatively with available closed-form solutions and laboratory or field data. The principal investigator has an international reputation in the formulation of the constitutive behavior of geological materials. He has the expertise and the institutional facilities available to successfully complete the research proposed.
