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.
Highlights
Suction caisson foundations can be used as anchoring foundations for tension leg platforms (TLPs)
To determine the soil strength, the triaxial compression and extension tests of soft clay were performed under confining pressures of 50 kPa, 100 kPa, and 150 kPa. e stress-strain curves of saturated soft clay subjected to consolidated undrained (CU) triaxial tests are shown in Figure 2. e Mohr–Coulomb ultimate strength indices of saturated clay were calculated to be c 18.3 kPa and φ 19.6°
The strain softening and strain cumulative deformation of soft clay were characterized through cyclic triaxial tests
Summary
Suction caisson foundations can be used as anchoring foundations for tension leg platforms (TLPs). In terms of strain accumulation, Monismith et al [19] established a relationship between the cyclic cumulative strain of soil elements and the number of cycles through triaxial tests On this basis, Li and Selig [20] introduced the static strength parameter of soil and proposed an empirical relationship for the cyclic cumulative strain. Based on the theory of static creep, Wang et al [25] proposed an empirical model for cumulative cyclic plastic axial strain of saturated soft clay under long-term cyclic loading. Dong [26] studied the creep characteristics of saturated soft clay under long-term cyclic loading, and by applying the empirical model theory of static creep to the study of cyclic creep characteristics, they established an empirical model for cumulative plastic strain with the ability to comprehensively consider the effects of dynamic deviatoric stress and initial static deviatoric stress levels. To determine the soil strength, the triaxial compression and extension tests of soft clay were performed under confining pressures of 50 kPa, 100 kPa, and 150 kPa. e stress-strain curves of saturated soft clay subjected to consolidated undrained (CU) triaxial tests are shown in Figure 2. e Mohr–Coulomb ultimate strength indices of saturated clay were calculated to be c 18.3 kPa and φ 19.6°
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