A Bounding-surface Plasticity Model For The Two-way Cyclic Behaviors Of Saturated Clay

The embedded offshore structures truly transmit the cyclic loading caused by winds, waves and currents to the surrounding marine soils. The marine soils are subjected to a two-way cyclic loading so that the soils involve both compression and extension states. The destruction of parts of the embedded offshore structures is due to extension deformation produced during the cycle loading. Therefore, it is significance to accurately simulate the dynamic characteristics between the soils and the embedded offshore structures.The current elastoplastic constitutive models always adopt an elliptic yield surface similar to the one in the Cam-Clay model. However, several studies have demonstrated that these kinds of models which adopt an elliptic yield surface are not suitable for predicting the characteristics of the soil under the extension state, due to its over-predicted elastic region. In this paper, combining the transformed stress tensors which are based on the spatially mobilized plane (SMP) yield criterion with the new hardening rule by the authors, a new bounding-surface plasticity model is proposed for the two-way cyclic behaviors of the saturated soils. The predicted results by the model show a good agreement with the experimental data both for the monotonic tests and the two-way cyclic triaxial tests.In order to apply the revised elastoplastic constitutive models proposed by the author the program are developed for the implementation of the models into a language software FORTRAN by using the return mapping algorithm. In the same condition and model parameters, different stress integration are used for the constitutive model to verify the accuracy. The influences of the algorithms to the model are also checked.However, the elasticplastic model is only demonstrated under triaxial condition at present. The stress state of soils is generally in the three-dimensional state . In order to analysis the dynamic responses produced by the embedded ocean offshore structures and the marine soils, the model is extended to the three-dimensional model by the transformed stress method.