The marine deposits in the South China Sea are characterized by an abundance of calcareous sand. The dynamic characteristics and properties of this sand are important for potential engineering seismic analysis and infrastructure development in this oil-and gas-rich region. The present study aims to investigate the dynamic shear modulus and damping ratio of typical calcareous sand in the South China Sea. A series of dynamic triaxial tests under the strain control condition of cyclic loading were conducted, with a specific focus on the effects of relative density and confining pressure. The normalized dynamic shear modulus increases with the increase in confining pressure, and the shear modulus-shear strain relationship can be adequately described with the well-known Hardin-Drnevich model. However, the influence of confining pressure tends to decline in the sand samples of high initial relative density. Overall, the variations in the damping ratio as affected by confining pressure or relative density are not very significant. The experimental results were assessed and found to be reasonably consistent with some of the previously reported results in the literature.
Earthquake ground motion records often show that soil sites typically exhibit nonlinear amplification characteristics during strong seismic motions. The surface ground motion amplification effects are typically affected by site conditions and topographic features; however, the ground motion and site response of sea-based soil sites have not been extensively investigated due in part to the scarcity of available strong seismic records from few geotechnical observation arrays in the sea areas. In the present study physical centrifuge models are explored to simulate the ground motion response of land-based and sea-based soil sites and site response analysis is conducted to assess the free-field response of both deposits to earthquake motion. Both sites exhibit multiple modes of vibration; the first-order mode dominates in both the land-based and 1 the sea-based soil sites with strongest amplification effect. The secondorder mode occurs in both sites and the amplification effect is far more modest than the first-order mode. The amplification effects in the seabased site are somewhat weaker than those in the land-based site. The third-order mode is found only in the response of sea-based site and the distribution of the amplification factor across the depth appears more complex without a clear pattern than in the lower order modes.
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