A simple anisotropic bounding surface plasticity model for cyclic response of clays

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 complex response. A realistic modeling of clay response under irregular cyclic loading requires an appropriate description of the stress{strain relationship. This thesis extends the formulation of a Simple ANIsotropic CLAY plasticity (SANICLAY) model by incorporation of a 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 sti ness degradation. The proposed projection center is established in the instant of any stress reversal and it realistically re ects the experimentally observed plastic strains. A damage parameter is also adopted to better simulate the continuous sti ness 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 its qualitative and quantitative comparison with experimentally observed clay response. The presented model validation demonstrates the capabilities of the model in capturing a number of important characteristic features of clay response in both monotonic and cyclic loadings. Limitations and recommendations for future work are discussed as well. ii