A series of cyclic undrained torsional tests on Fujian standard sand is conducted using a newly developed hollow cylinder shear apparatus, aimed at clarifying the influence of complex initial stress states on dynamic shear modulus characteristics of saturated sands. The effect of excess pore water pressure generated during undrained cyclic loading on stress-dependent shear modulus is also properly evaluated. The test results show that dynamic shear modulus of tested sands are strongly affected by complex initial stress states. Nevertheless, the introduction of reference strain to normalizing strain can largely reduce this effect. It is also found that dynamic shear modulus varies linearly with current effective stress on a log-log scale over a wide strain range when the generation of excess pore water pressure is considered. An empirical equation is developed to approximately predict the maximum shear modulus when the inclination of major principal stress is considered.
Dynamic shear modulus (G) of soils is an important parameter in the prediction of site response under cyclic loading induced by earthquake shaking or ocean wave loading. In previous studies, many factors that affect G have been extensively investigated through laboratory experiments using resonant column and cyclic triaxial methods by many researchers (e.g., Seed and Idriss, 1970; Hardin and Drnevich, 1972; Seed et al., 1986; Vucetic and Dobry, 1991). In cohesive soils, such as silts and clays, the effects of mean effective confining stress (pm′), void ratio (e), overconsolidation ratio (OCR), and plasticity index (PI) on G have all been well documented. In sands, the effects of pm′ and e are also well documented. Different from horizontal free site, before subjected to cyclic loading, soil deposits under the foundation of ocean structures are usually in complex consolidation states due to the action of high static shear stress. These complex consolidation stress states can be generally
