A Bounding-surface Plasticity Model And Its Application For Cyclic Behaviors Of Sand

Anchors that provide the holding capacities for mooring systems are generally fully embedded in the seabed.To develop a numerical model that can be used to assess the cyclic bearing capacity of anchors,two bounding-surface plasticity models are presented.From different theoretical points of view,these two models are developed in the general stress space and the deviatoric stress-ratio space,respectively.Both models succeed in modeling the cyclic behaviors of sand with concise formulations and fewer parameters.By incorporating new features,a combined isotropic-kinematic hardening rule is extended to the deviatoric stress-ratio space.By introducing a maximum prestress surface,an additional mechanism is deployed to avoid the overshooting problem and to promote the simulation of the post-cyclic behavior.The isotropic hardening mechanism is implemented to record the soil fabric changes by integrating the concept that these changes can be memorized in the surface size.A unified hardening function is defined in the model for all loading events.With these new features,the workability of the combined isotropic-kinematic hardening rule in simulating the cyclic shakedown and ratcheting of sand is improved.Both the modified Euler scheme and the explicit Runge-Kutta-Dormand-Prince scheme are exploited to integrate the bounding-surface plasticity models.According to the characteristic of the bounding-surface models and the mechanism of the combined isotropic-kinematic hardening rule,the explicit substepping method with automatic error control is modified.To investigate the accuracy and efficiency of the schemes,triaxial tests are simulated.The bounding-surface plasticity models are implemented into the commercial software via a user subroutine.A finite element model is developed based on the bounding-surface plasticity models to investigate the ultimate and cyclic capacities of anchors.