Abstract: Experimental research on cyclic behaviors of clay is performed based on undisturbed soil samples from the boreholes of oil field sites in northern region of South China Sea. Combined resonant column test and strain-controlled cyclic direct simple shear test, the dynamic shear modulus and damping ratio of the soils over a range of cyclic shear strain are studied. Additionally, the maximum dynamic shear moduli are compared with the calculation results on the basis of cone penetration test. Stress-controlled cyclic direct simple shear test is developed to capture the threshold value of cyclic strength by symmetric loading method. And then, based on the threshold value, the envelope curves of cyclic strength can be obtained by one-way and two-way loading methods. The test data are compared with Drammen clay and other clays obtained from different locations in the world. The cyclic performance and dynamic parameters of soils in the northern region of South China Sea are studied, which provides the basic data for structure design and evaluation of geological risks. Besides, experimental methods of cyclic tests are mastered, which can provide technical reference for dynamic experimental study and data analysis of geotechnical engineering.

Key words: northern South China Sea, clay, cyclic loading, dynamic shear modulus, damping ratio, cyclic strength