Constitutive and numerical modeling of clay subjected to cyclic loading

Natural clays are anisotropic in their in-situ state and have an undisturbed shear strength in excess of the remoulded strength. In addition, most of the structures founded on clay deposits must be designed to withstand cyclic loads such as seismic ground motions or ocean waves. When subjected to earthquake or wind induced cyclic loadings, clay exhibits a complex response. A realistic modeling of clay response under irregular cyclic loading requires an appropriate stress--strain relationship described by a constitutive model. This thesis extends the formulation of an existing constitutive model, namely Simple ANIsotropic CLAY plasticity (SANICLAY) model, by incorporation of a, well-established in geomechanics, bounding surface formulation for successful simulations of clay response under cyclic loading. The most important aspects of the proposed formulation are the position of a projection center and the ability to capture continuous stiffness degradation. The proposed projection center is established in the instant of any stress reversal, and it realistically reflects the experimentally observed plastic strains. A damage parameter is also adopted to better simulate the continuous stiffness reduction during the course of applied cyclic loading. The proposed model is developed with the aim of maintaining the simplicity, and yet including an adequate level of sophistication for successful modeling of the key features of clay response. The model formulation is presented in detail, followed by details of its implementation for applications in boundary value problems. Verification of the model implementation and validation of its performance are also presented. Verification of the model implementation is required in order to build confidence prior to its validation. Followed model validation demonstrates the capabilities of the model in capturing a number of important characteristic features of clay response in cyclic loading. Further exploration of model response in multi-directional cyclic shear is performed demonstrating its extension into more complex multi-directional cyclic shear. Development of the model, its implementation, verification of its implementation, validation of its performance, and exploration of model response in multi-directional cyclic shear provide a tool that can be used in modeling clay response under cyclic loadings. Limitations and recommendations for future work are discussed as well.Applied Science, Faculty ofCivil Engineering, Department ofGraduat