Investigation on Shear Behavior of Calcareous Sand in South China Sea in Undrained Triaxial Tests

To provide reference for design and construction of infrastructures in the hydraulic fill foundation of calcareous sand in the coral reef of South China Sea, the scanning electronic microscope (SEM) and a series of triaxial tests were carried out to investigate the basic physical property and the consolidated-undrained shear behavior of calcareous sand. By means of the nonlinear fitting of test data, the evolution of shear modulus, shear strength and porous ratio in the critical state was quantitatively analyzed, and analysis and test results were compared. The research findings indicate that: ① Calcareous sand in South China Sea is mostly composed of CaCO3, its particle is angular, porous and irregular in shape, and its specific gravity and porous ratio are greater than those of Fujian quartz sand; ② the shear modulus increases with confining pressure and relative density and is a binary power function of them; ③ the shear strength or internal frictional angle in the peak state is more than that in the critical state, it is merely a power or logarithm function of normalized mean principal stress, and the excessive internal frictional angle that is the difference between the peak and critical state internal frictional angle is also a binary power function of confining pressure and relative density; ④ the critical state porous ratio decreases with the normalized mean principal stress and the critical state line (CSL) is characterized by a negative exponential function in the compression plane. © 2022, Editorial Department of China Journal of Highway and Transport. All right reserved.