An anisotropic macro element model for bucket-clay interaction under cyclic loading

Each individual bucket of multi-bucket foundations sustains mainly the vertical upward and downward cyclic load during its lifetime. It is evidenced from centrifuge test and engineering experience that the behaviour of individual bucket under upward and downward load is not identical - usually the capacity and stiffness of downward direction is stronger than the upward. This anisotropic behaviour is mainly due to the different failure mechanism and soil strengths mobilized. In this paper, a macro element model is established to reproduce the anisotropic behaviour of individual bucket under vertical cyclic loading, expanded from previous study of the cyclic-softening macro element model. The model is formulated based on multi-surface plasticity and a combined isotropic and kinematic hardening rule. The anisotropy is implemented by establishing the oval yield surfaces and non-symmetrical hysteresis loops. The parameters of the macro element model are calibrated by a small amount of FE analyses, where an anisotropic soil constitutive model and an attached or separated soil plug are adopted to highlight the anisotropy. The performance of the model is demonstrated by a series of numerical cases and is compared to parallel FE analyses. The new macro element model is capable of capturing the anisotropic load-displacement loops real-timely during a cyclic load sequence, with high computational efficiency and reasonable accuracy.