Abstract: To obtain the static undrained shear strength of the saturated marine soft clay in the Pearl River Estuary in Guangdong, a series of tests are conducted, i.e. the unconsolidated undrained (UU) shear tests, the consolidated undrained (CU) shear tests, the unconfined compression tests, the static T-bar penetration tests in the centrifuge model foundation of normally consolidated soft clay, the field vane shear tests, and the cone penetration tests (CPTs); empirical formulations of soil mechanics are also employed. Based on these tests and calculations by the formulations, the distribution patterns of the undrained shear strength of the marine soft along with the depth clay are determined and the validity of different methods mentioned before are evaluated comprehensively. In order to acquire the cyclic degradation behaviors of the marine soft clay in this area, cyclic triaxial tests, cyclic T-bar penetration tests in the centrifuge model foundation of normally consolidated soft clay, and cyclically horizontal loading tests on a single pile in the field are carried out respectively. It is found that there is a double logarithm linear relationship between the cyclic secant modulus ratios of the soft clay and the number of cycles, from which three types of degradation factors for three testing condtions are achieved. The results can provide a guide for the offshore structure design in this area, and can also be used for reference in other engineering projects.

Key words: marine soft clay, undrained shear strength, cyclic degradation