RESONANT COLUMN AND BENDER ELEMENT TESTS OF UNSATURATED CORAL SAND ON XISHA ISLANDS IN SOUTH CHINA SEA

Determining the dynamic shear modulus and damping ratio of coral sand is prerequisite for analysing the stability of islands under dynamic loadings. Therefore,this paper presents a study on how the confining pressure,relative compactness and saturation affect the dynamic shear modulus and damping ratio of the coral sand in South China Sea. It uses the resonant column and bender element tests. The results show the follows. (1)The maximum dynamic shear modulus G₀ of saturated coral sand sample is positively correlated to the confining pressure and the relative compactness,and are decreases sensitively to the relative compactness with the increase of the confining pressure. (2)The dynamic shear modulus ratios of the unsaturated coral sand are slightly higher than those of the saturated samples,while its damping ratios are slightly lower than those of the saturated samples. (3)The coral sand samples show the maximum G₀ and the minimum damping ratio at the saturation of about 10%. (4)The predicted G₀ by the empirical functions based on the relative compactness and the void ratio of siliceous sand are higher and lower respectively than the results obtained in the tests. Thus,the empirical formula of G₀ as a function of confining pressure is modified according to the tests. This study contributes sample values of the dynamic shear modulus and damping ratio for the stability analysis of coral sand sites on the reef islands in South China Sea.