Abstract: The geotechnical properties of the coral reef materials widely distributed in all islands in South China Sea have been extensively studied since 1980s in China. However, the majority of these researches are focused on the uncemented calcareous sandy soils and limited studies are available on the engineering properties of the naturally cemented calcareous soils such as calcarenites, which are the prevailing materials at the coral reefs in South China Sea. The state-of-the-art engineering practices in the calcareous soils worldwide indicate that the geotechnical properties of the cemented calcareous sandy soils are significantly different from those of uncemented coral reef soils. Considering the spatial heterogeneity of the naturally cemented calcareous soils, this paper presents factors that affect the strength properties from the microscopic studies. The correlations between the strength of the cemented calcareous sandy soil sample and various parameters, such as unit weight, cementation degree, void ratio, shape of grain as well as grain size, are established from the test results. The results show that good correlations exist between the strength with the unit weight and the degree of cementation of the calcareous sandy soils.

Key words: naturally cemented calcareous soil, microstructure, strength, shape of grains, calcarenite