Dynamic Characteristics And Microscopic Experimental Study Of Calcareous Sand

The South China Sea is located in the region of active seismic and volcanic activity in the Pacific Rim,and the calcareous sand is widely distributed.A correct understanding of the engineering mechanical properties of calcareous sand is of vital importance to the development and construction of China’s islands and reefs in the South China Sea.However,different formation modes of calcareous sand cause that particle structure and particle strength are different from those of terrigenous sand,and the construction of islands and reefs is inevitably affected by dynamic loads such as wind,wave and earthquake.However,the current research on the liquefaction of calcareous sand and the influence of microstructure on the dynamic characteristics of calcareous sand is still incomplete.Therefore,the study on the dynamic and microscopic characteristics of calcareous sand in the South China Sea will provide practical guidance for the design and construction of reef projects.The main works are as follows:(1)The effects of gradations,relative density,cyclic stress ratio and confining pressure on dynamic shear modulus and damping ratio of calcined sand and Fujian sand were studied by undrained triaxial test.The experimental results in this paper provide a supplement for the dynamic characteristics of calcareous sand under large strain range.(2)The saturated calcareous sand and Fujian sand were tested under undrained condition by CKC dynamic triaxial apparatus to study the effect of material and gradation on liquefaction resistance.The factors such as different confining pressures,different cyclic stress ratios and different relative density were studied.(3)Calcareous sand is composed of coral debris,shells and other marine materials,so the particle strength is low.The particle breakage of calcareous sand samples after sample preparation,consolidation and cyclic loading were analyzed,and the particle breakage was quantified by surface area and grading index.(4)The calcareous sand samples were scanned by high resolution CT from microscopic perspective.Through the study of the inner pores and intergranular pores of calcareous sand,the influence of the inner pores and intergranular pores on the liquefaction resistance of sample and particle breakage was considered,and the experimental results were explained in a reasonable mechanism.