Study on Unloading Creep Characteristics of the Soil and Application of the Stress-Dependent Creep Model in Suction Caisson Foundation

As the anchoring foundation of the tension leg platform (TLP), suction caisson foundation is subjected to the long-term vertical pullout loads. But there are few studies on the mechanism of the unloading creep of soft clay and long-term uplift bearing capacity of suction caisson foundations. To address this problem, unloading creep tests of soft clay were carried out to analyze the strain development with time under different confining pressures. The test results show that the creep curve rapidly develops in the early stage and tends to stabilize in the later stage. The unloading deviator stress is higher, the unloading creep deformation is greater and the soft clay has typical nonlinear creep characteristics. Therefore, by introducing the creep model and considering the influence of the deviator stress, the stress-dependent Merchant model is proposed to describe the unloading creep of soft clay. Then, the stress-dependent Merchant model is extended to a three-dimension constitutive model, and a finite element subroutine is developed to establish a finite element analysis method for analyzing the long-term uplift capacity of suction caisson foundations and validated with the long-term uplift bearing capacity results of caisson model.