Abstract: The salinity rich in soil in the sandy coral island and lack of the underground fresh water resources cannot provide a longterm and stable habitat for animals and vegetations. The rain infiltration is the most important conservation of the freshwater resources in these sandy coral islands. Soil conductivity is a parameter that reflecting the salinity,but for various reasons,the grey calcareous sand often mixed with quartz sand,this effects on the conductivity of calcareous sand is of concern to us.The mixed calcareous and quartz sand samples with different particle sizes and different gradations are prepared for the laboratory tests. The threeparameter sensor used in the soil testing was CS655 type and the data were recorded by CR1000 data acquisition system. The results indicate that, the mixed soil conductivityincreased with the increase of quartz sand content and the change trend was first decreased, then increased and then decreased again with the quartz content, in most cases. In the first time the low conductivity appeared at a quartz sand content of approximately 20%. Therefore, this quartz sand content of 20% can effectively reduce the conductivity of calcareous sandy soil.

Key words: Conductivity； Calcareous soil, Quartz sand content