Abstract: Coral sand is a type of soil with special engineering properties. It is of great significance to study the bearing capacity of coral sand for construction of islands and reefs in the South China Sea. The influence of density and gradation of coral sand, shape and size of load plate on the bearing capacity of coral sand foundation were quantitatively studied by self-made indoor model device of plate load, and bearing capacities of coral sand and quartz sand were compared. Test results show that, compared with quartz sand with the same density, coral sand has prominent flat features and sharp edges and corners, which leads to an increase of internal friction angle and further leads to an increase of its bearing capacity. Settlement under the same load is much smaller than that of the former, and size effect of foundation on bearing capacity is obviously greater than that of quartz sand. However, dependence coefficient of stress level of coral sand foundation soil is linearly related to its relative density, and internal friction angle is significantly affected by gradation. Relationship between bearing capacity coefficient of foundation Nγ and internal friction angle ? is established. At the same time, the bearing capacity of coral sand foundation increases with the increase of load plate size, and the bearing capacity of coral sand foundation under square foundation is obviously higher than that of circular foundation with the same area, and size effect is more obvious, which shows that the foundation type has practical significance on improving the bearing capacity in practical engineering. Based on the Meyerhof formula, a modified formula of foundation bearing capacity for coral sand is also proposed, which improves the accuracy of calculation results of bearing capacity of coral sand.

Key words: coral sand, foundation bearing capacity, indoor model test of plate load, foundation size effect, modified formula