Study on Cyclic Cumulative Deformation Characteristics and the Equivalent Cyclic Creep Model of Soft Clay

Abstract

Suction caisson foundations can be used to anchor tension leg platforms. The soil at the bottom of the caisson undergoes both unloading and cyclic loading under wind and wave loads. However, the problem of cyclic cumulative deformation of soft clay under unloading has rarely been addressed. So, the strain cumulative deformation and strain softening characteristics of soft clay are studied by cyclic triaxial tests. The test results show that under low static deviator stress ratios and dynamic deviator stress ratios, the soil has a low level of strain accumulation and softening. As the dynamic deviator stress ratios increase, the cumulative cyclic deformation gradually increases, which rapidly develops in the early stage and tends to stabilize in the later stage. Moreover, the softening index gradually increases and is linearly related to the logarithm of the number of cycles. The cyclic cumulative deformation of the soil increases with increases in unloading stress and dynamic deviator stress, showing a creep characteristic of attenuation and then stabilization. Based on the tests, an equivalent cyclic creep model is established to describe the strain accumulation and softening of soil and verified through comparison with the test results. Then, the model is extended to a three-dimension model, and a finite element subroutine is developed for studying the strain cumulative deformation and strain softening characteristics of soft clay.

Analysis of Re-Tensioning Time of Anchor Cable Based on New Prestress Loss Model

“…The long-term prestress loss of anchor cable is mainly determined by the material properties of anchor cable itself and the mechanical properties of rock mass, therefore, the calculation model of prestress loss of anchor cable is generally established by reasonably combining the calculation model of anchor cable and rock mass [22][23][24][25], as we all know, the premise of establishing the coupled creep model is to assume that the rock mass is uniformly stressed [19,26], from the previous analysis, it can be seen that the frame beam is the guarantee of the uniform stress of the rock mass, and the actual stress of the rock mass under the action of the frame beam can be closer to the assumed condition, Therefore, the role of frame beam should not be ignored in the establishment of prestress loss model of anchor cable.…”

Vertical Monotonic and Cyclic Responses of a Bucket in Over-Consolidated Clay

“…The stiffness was lower at higher V c under purely compressive loading with ζ c = 0 and a logarithmic function was used to describe the relationship between stiffness and the number of cycles [29]. For the bucket in clay subjected to cyclic loading, most existing studies were focused on the responses under horizontal cyclic loading [34][35][36][37]. The bucket under cyclic vertical loading was concerned in a limited number of recent studies only, such as by [29,33], however, their model tests were conducted at 1 g. Since the stress levels of soil are much lower than those in practical applications, the centrifuge test is preferred to provide more reliable data, especially for the loading with larger V c .…”

A Simplified Calculation Method for Cyclic Response of Laterally Loaded Piles Based on Strain Wedge Model in Soft Clay

“…Yang et al [18] established an improved strain wedge method by considering the nonlinear deformation of a pile. Peng et al [19] proposed an upper soil wedge and a modified lower strain wedge for the analysis of laterally loaded piles on sloping ground, and Zhu et al [20] proposed a simplified calculation method for analyzing the long-term deformation of the suction caisson foundation in the soft clay under cyclic lateral loading.…”