The silty calcareous soil subgrade in the South China Sea contains fine particle calcareous silt interlayers with a particle size less than 0.075 mm. The permeability of these calcareous silt layers has an important effect on the development of underground fresh water in the islands. This study investigated correlations among the permeability coefficient

dry density and initial water content of calcareous silt through variable-head permeability tests in laboratory. The results demonstrate the reliability of Samarasinghe and Mesri formulas in calculating the permeability coefficient of calcareous silt. The variation of pore size of calcareous silty soil before and after infiltration test was analyzed by static nitrogen adsorption test. The results show that the permeability coefficient of calcareous silt decreases with the increase of the dry density

and increases with the increase of the initial water content. When the dry density is the same

and the permeability coefficient reaches the maximum at saturation. The Samarasinghe and Mesri formulae have high accuracy in calculating the permeability coefficient of calcareous silt. Seepage generates more micropores and transforms mesopores into macropores. The soil mainly shows pores with a uniform cylindrical hole with an opening at one end. This study provides a scientific reference for the calculation and analysis of groundwater seepage field in artificial reclamation island.