Abstract: During the uplift process of suction caisson foundation, the soil at the bottom of caisson is in an axial unloading state. But there are few studies on the mechanism of the unloading creep of soft clay. Therefore, the axial unloading triaxial creep test on saturated soft clay was carried out to obtain the variation law of axial strain with time and deformation mechanism of soft clay under different confining pressures. At the same time, the long-term uplift test on suction caisson foundation was carried out to analyze the long-term uplift bearing characteristics of suction caisson foundation. The unloading creep test results show that under the condition of the low deviator stress, the unloading creep deformation of soil can be ignored. The unloading deviator stress is higher, the unloading creep deformation is greater and the nonlinear creep characteristics become more obvious. Therefore, by introducing the creep model and considering the influence of the deviator stress, the stress-dependent creep model is proposed to describe the unloading creep of soft clay. Then, the stress-dependent creep 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.

Key words: suction caisson foundation, soft clay, axial unloading, creep model, finite element method