Abstract: Cycles simple shear test are carried out for coral calcareous sand from Xisha Islands and local siliceous sand under multistage normal stress; and the difference of shear properties and particle breaking properties of two kinds of sandy soil under multiple cycles is compared. Under cyclic shear, both sand samples exist relatively weak volume changes and staggered shear dilatation which make the axial displacement curve of the specimen fluctuating. Shear stress peak envelope in cycles simple shear test can be expressed as an ExpAssoc function. Shear stress is divided into synchronous phase and differential phase with the change of cycle period; and the number of cycles corresponding to two phase transition nodes decreases rapidly as the normal stress increases. During the synchronous phase, the shear stress of coral sand and siliceous sand is consistent, while during the differential phase, the shear stress of siliceous sand is significantly higher than that of coral sand. The shear stress difference between the two types of sand varies with the normal stress, with the shear stress of the siliceous sand can be up to 14.7% higher than that of the coral sand in maximum. There are significant differences in the particle breakage between coral sand and siliceous sand. The distribution of particle breakage in the full particle size range of coral sand is more balanced. By contrast, siliceous sand has a violent particle breakage within a certain particle size range with obvious inflection points in the grading curve. The shape of the hysteresis loops and its variation with the number of cycles have significant differences between siliceous sand and coral sand, which reflecting the difference in the shear properties of the two sand samples.

Key words: coral calcareous sand, cycles simple shear test , sand, shear stress, particle crushing