Abstract: Calcareous sand is a special medium with high calcium carbonate content or other insoluble carbonates, and has characteristics of irregular shape, porous and rich in inner pores. Capillary rise is a universal phenomenon in soil due to the pores. The tube inside rhizome is like a very fine plant capillary, which can absorb water from the soil. Therefore, the study on height of capillary rise in the calcareous sand has great significance to the ecological construction of the reef island. In this paper, the vertical tube tests are carried out to study the influence of gradation, particle size, dry density and salinity on the capillary rise in calcareous sand. Results show that the finer the particles and better gradation, the higher capillary water rise in the continuous graded calcareous sand. The height of capillary water rise decreases with increasing particle size in the single-sized calcareous sand. The capillary water rise decreases when the particle size is less than 0.075 mm with increasing dry density of the single-sized calcareous sand, while the height gradually increases with the particle size of 0.075-0.250 mm. Compared with fresh water, the NaCl solution inhibits the capillary water rise at low salinity, and the seawater promotes the capillary water rise but only weakly. The relationship between the height of capillary rise and time in calcareous sand fits well with the quadratic polynomial relationship in double logarithmic coordinates, and the physical properties of calcareous sand and the solution type are related to the parameters.

Key words: calcareous sand, height of capillary rise, vertical tube test on capillary rise, influencing factors, fitting analysis