Abstract: Calcareous sand is often used as filling material in construction of artificial islands in South China Sea. The permeability of calcareous sand has significant influence on the consolidation and settlement of soil mass. The drag force coefficient, which expresses the fluid drag force on particle surface, likewise an important parameter that characterizes the permeability of calcareous sand, is not extensively studied by researchers so far. In this study, a modified three-dimensional shape coefficient is introduced to quantitatively evaluate the shape of calcareous sand. A series of single calcareous sand particle settling tests is carried out in which a high-speed camera is employed to record the settling course and imaging technique is used to obtain the terminal equilibrium settling velocity of the sand particle. By doing so, the drag force coefficient-CD and Reynolds number-Re can be determined. The experimental results show that for the same Reynolds number, the drag force coefficient increases as the shape coefficient increases. Through a comparison with other test results, it is found that the richness of particle surface pores of calcareous sand can reduce the drag force coefficient. Finally, a semi-empirical model of the drag force coefficient for calcareous sand including CD, Re and , is obtained. This model will improve the prediction of permeability of soil mass especially with particles of irregular shapes. This improvement of drag force coefficient model has the significance on the analysis of the consolidation and settlement of foundations or artificial islands filled with calcareous sand in South China Sea.

Key words: calcareous sand, particle shape coefficient, drag force coefficient, Reynolds number, settling tests