Evaluation of strength for coral sand and gravel mixed deposits

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Calcareous sediments, which consist of such bioclastics as coral, shell and foraminifera, distribute in shallow tropical and sub-tropical sea-water. In this study the mechanical properties of the calcareous sediments are clarified in order to evaluate the strength of coral sand and gravel mixed deposits for practical use based on the gradation characteristics. Samples used are dredged from sea floor in coral reefs around Ryukyus Island. A series of consolidated drained triaxial compression tests, permeability tests and oedometer tests for K_0 value are carried out on reconstitute samples with head-cut gradation, similar gradation and different content of coral gravel.According to triaxial test results, the peak friction angle of sand and gravel mixed deposits is affected significantly by the coefficient of uniformity and the content of coral gravel. In permeability tests the coefficient of permeability of coral sands is depend on a void ratio, the content of coral gravel and the presence of fine sand less the particle size of 0.25mm. In the determination of K_0 value in the oedometer it is important to take account of the rigidity of an oedometer ring. K_0 value of coral sand measured with relatively rigid oedometer ring is 0.5 irrespective of the void ratio, while this value increases up to 0.8-0.9 under the stress level where a particlebreakageoccurs.