Stiffness degradation of marine soft clay under monotonic and cyclic loadings

A series of undrained monotonic and cyclic triaxial tests are conducted on Jiaxing intact marine soft clay by using a testing system combined with triaxial apparatus and bender element to investigate the small strain shear modulus and stiffness degradation of isotropically consolidated soft clay. The results indicate that the small strain shear modulus decreases and then increases under monotonic loading, but it tends to decrease continuously under cyclic loading. At medium to large strains, the normalized equivalent modulus of saturated soft clay decreases gradually with the development of single-amplitude cyclic strain with a larger degradation rate than the monotonic secant modulus. In addition, a fairly unique relationship exists between the cyclic degraded stiffness and small strain shear modulus, which is barely affected by the initial confining pressure and cyclic stress condition. The findings obtained in this study can provide the basis for the design of offshore structures in this area, and can also be used as a reference in other engineering projects.