Experimental study on dynamic shear modulus ratio and damping ratio of marine soils in Qiongzhou Strait with depth less than 100 m

Cyclic triaxial and free vibration column tests on dynamic shear modulus ratio and damping ratio of 70 undisturbed samples of marine soils in Qiongzhou Strait seabed with depth less than100 m are conducted. The reliability of the two tests is mutually verified by investigating the variation rules of the dynamic shear modulus ratio and the damping ratio under the dynamic shear strain ranging from 1×10^-6 to 3×10^-2. It is found that the two test results agree well with each other. Without considering the influence of plasticity index, the maximum dynamic shear modulus has a linear relationship with the effective confining pressure for sand-contained clay, silty clay and sand-contained silty clay. The damping ratio of the marine soils is approximately constant under the dynamic shear strain ranging from 1×10^-6 to 3×10^-5. According to the test results, a damping ratio growth model is proposed. The fitting curves of the dynamic shear modulus ratio and damping ratio changing with the shear strain as well as the recommended parameters in the empirical formula are predicted using the proposed model and the empirical modulus attenuation model proposed by Seed and Martin. The results of this study may be used to make a preliminary estimate of the dynamic properties of marine soils in Qiongzhou Strait and to confirm field and laboratory tests on such soils.