Creep characteristics and constitutive model construction of offshore soft soils

The main objective of this study was to investigate creep characteristics and construct a suitable constitutive model for soft soils in offshore areas. Soft soil samples were obtained to evaluate the physical and mechanical properties. Additionally, a triaxial creep test was conducted by applying different axial deviator stresses under three confining pressures to analyze the creep characteristics and establish a creep constitutive model suitable. It was found that the physical and mechanical properties of soft soils at different depths are significantly different, and the physical properties have a significant correlation with compression modulus and compression coefficient. The soft soils creep mainly present linear viscoelasticity under low axial stress, while it shows nonlinear viscoplasticity characteristics when the axial deviator stress is greater than the yield stress. The correlation coefficient R² of Merchant model fitting curves are significantly larger than that of Burgers model. The Burgers model fitting curves have a large deviation from the actual creep characteristics under smaller axial deviator stress and the parameters are also inconsistent with the internal creep mechanism. The Kelvin body in Merchant model can better simulate attenuation creep characteristics of soft soils, but it cannot exhibit nonlinear viscoplasticity creep characteristics. Furthermore, a combination of Merchant model and power function empirical model can dramatically characterize the linear viscoelasticity and nonlinear viscoplasticity creep behaviors of offshore soft soils, with a correlation coefficient above 0.94. Verification of the combined constitutive model indicates that it has excellent credibility and applicability in offshore areas.