Dynamic shear modulus and damping ratio characteristics of undisturbed marine soils in the Bohai Sea, China

This paper presents results from a series of stress-controlled undrained cyclic triaxial tests on the undisturbed marine silty clay, silt, and fine sand soils obtained from the Bohai Sea, China. Emphasis is placed on the major factors for predominating the dynamic shear modulus (G) and damping ratio (lambda) in the shear strain amplitude (gamma(a)) from 10(-5) to 10(-2), involving depth, sedimentary facies types, and water content of marine soils. The empirical equations of the small-strain shear modulus (G(max)) and damping ratio (lambda(min)) using a single-variable of depth H are established for the three marine soils. A remarkable finding is that the curves of shear modulus reduction (G/G(max)) and the damping ratio (lambda) with increasing gamma(a) of the three marine soils can be simply determined through a set of explicit expressions with the two variables of depth H and water content W. This finding is validated by independent experimental data from the literature. At the similar depths, the G value of the marine soils of terrestrial facies is the largest, followed by the neritic facies, and the G value of the marine soils of abyssal facies is the smallest. The sedimentary facies types of the marine soils have slight effect on the lambda value. Another significant finding is that the shear modulus reduction curves plotted against the gamma(a) of the three marine soils at the similar depths are significantly below those of the corresponding terrigenous soils, while the damping curves plotted against gamma(a) are just the opposite. The results presented in this paper serve as a worthful reference for the evaluation of seabed seismic site effects in the Bohai Sea due to lack of experimental data.