Study On Morphological Characteristics Of Particles Of Coral Reef Calcareous Sand And Their Influence On Shear Behaviors

Researchers are carried out in aspects of the particle morphology,shear behaviors and the influence of particle morphology on the shear behaviors of calcareous sands collected fromreef islands in South China.At the same time,the test results of Ottawa sand,Columbia sand and dry glass sand in the literature are cited to make some comparisons with calcareous sand.The main contents and conclusions are listed as follows:（1）The test on particles’morphology of calcareous sand is carried out,and the statistical rules of three characteristic parameters,such as particles’sphericity,roundness and aspect ratio were studied.The results show that the shape of the largeparticle is close to that ofsphere,and the surface of the particles is smoother,while the small particle is irregular angular its surface is rough and uneven.The void ratio of biogenic particles is significantly higher than that originating from rocks.For calcareous sand particles with different sizes,their surface void area is less than 1000μm².（2）The test results of shear behavior of calcareous sand and three terrestrial sands in the literature are analyzed,and it shows that the initial shear modulus of calcareous sand and the three terrestrial sands increases with the increase of confining pressure and relative density,but the internal friction angle is unchanged with confining pressure,but increases with the increase of relative density.The critical state strength envelope is a straight line passing through the origin,and its slope（i.e.,critical state stress ratio）is constant.Under the same conditions,calcareous sand peak and critical state strength are higher than those of three terrestrial sands.（3）According to test results of sphericity S,roundness R,aspect ratio A of calcareous sand and three terrestrial sands,regression equationfor the initial shear modulus G and internal friction anglesφ_p andφ_cs are obtained by the multiple regression analysis method.It shows that the denser the sample（the greater p₀ and D_r）is,the greater the shear modulus and internal friction angle are.As A increases or S and R decrease,the shear modulus and internal friction angle of the sample also increase.