Macro- and micro-characteristics and mechanical properties of deep-sea sediment from South China Sea

The research on deep-sea sediment is meaningful for the exploitation and utilization of resources in the South China sea. Because of the difficulties in getting the natural deep-sea sediment, there are scarce researches on it. Besides, the mechanical properties and microstructures of the deep-sea sediment are different from the ordinary soft soil due to the unique geological environment. In this study, the basic material tests, ESEM tests, oedometer tests, 1D creep tests and conventional triaxial tests are conducted to investigate the material properties, microstructures, compression and creep characteristics and shear strengths of the deep-sea sediment. As shown in the results, the deep-sea sediment is a kind of silt with a high liquid limit, high water content, low bulk density, large void ratio and high saturation. The analysis of mineral composition shows calcite and illite are abundant. The micro-pictures show a lamellar layered stacked structure with loose skeleton and large pores, which attributes to the large void ratio and high water content, and there are some biological remains. In the oedometer and 1D creep tests, the deep-sea sediment shows high compressibility and large secondary consolidation deformation. The consolidation coefficient decreases with the vertical pressure, while the secondary consolidation coefficient ascends with the vertical pressure and then decreases after reaching the peak value. In the conventional triaxial tests, the deep-sea sediment shows strain hardening. The stress path from the consolidated undrained shear tests shows both loading and unloading processes, while only the loading process is found in the consolidated drained shear tests.