Investigations On Physical-Mechanical-Crushing Behaviors Of Calcareous Sand

A floating artificial island is built in Maldives,and the island is affected by wind,wave and current.In order to ensure the stability of floating artificial islands,it is necessary to build a reliable anchorage system.Anchoring system needs to reliably anchor the offshore floating artificial island structure on the seabed.The main material of the seabed is calcareous sand.The calcareous sand can break and the mechanical strength can change under the action of anchoring foundation,and affect the safety of anchorage foundation.Therefore,the study of physical-mechanical-crushing behavior of Maldives calcareous sand has important engineering value for the construction of offshore floating artificial island in planning.In this paper,the physical properties,compression and crushing behavior of Maldives calcareous sand are systematically investigated.The specific research contents and conclusions are summarized as follows:(1)The physical properties of Maldives calcareous sand were examined.The non-uniformity coefficient and the curvature coefficient of Maldives calcareous sand are4.91 and 0.61,and the gradation is poor.The mineral composition of Maldives calcareous sand is predominated by CaCO₃ with a content of 94.69 %.The maximum and minimum void ratio are 1.07 and 0.777,respectively,and the specific gravity is 2.80.(2)One-dimensional compression tests were carried out to investigate the compression and crushing behavior of uniform calcareous sand sample.The results show that the crushing stress decreases with particle size increasing.The crushing stress of sample 0.25?0.5mm is 5.7 MPa,while that of sample 3.35-4.75 mm is 1.9 MPa.In addition,the relative breakage index increases with particle size,where the value of0.25?0.5mm sample is 0.18 and the 3.35-4.75 mm sample is 0.54 when subjected to the vertical stress of 25.6 MPa.(3)The effect of gradation on the compression and crushing behavior of calcareous sand was studied through one-dimensional compression test.The compressibility index increases with mean particle size and decreases with non-uniformity coefficient,ranging from 0.12 to 0.23.The relative breakage index increases with mean particle size and decreases with non-uniformity coefficient.(4)The effect of particle breakage on the shear strength and dilatancy of calcareous sand were studied by preparing raw sand sample,pre-crushed sand sample and broken sand sample prepared from raw sand.Comparison between raw sand sample and precrush sample shows that particle breakage resulted in an increase of shear strength and decreases dilatancy of calcareous sand.It is found that there is little difference in the shear strength between the pre-crushed sand sample and the broken sand sample prepared from raw sand.The shear strength of the pre-crushed sample is slightly larger than that of the broken sand sample prepared from raw sand.