Characterization of engineering properties of deep-water soils in the South China Sea

The characterization of the geological and geotechnical properties of marine sediments is crucial for the exploration of subsea oil and gas resources. In this study, the engineering properties of deep-water soils recovered from the South China Sea (SCS) were in detail characterized via a series of laboratory tests to explore their physical, mechanical, mineralogical and microstructural behaviors. The results show that the index properties of deep-water soils are characterized by high natural water content, high void ratio, high Atterberg limits, but low density. The sensitivity of these soils is higher than 10, indicating their strong natural structure, which significantly controls the shear behavior and failure model. The intact samples show strain-softening to strain-hardening behavior with an increase in the confining pressure, while reconsolidated samples consistently show strain-hardening phenomenon under any level of confining pressure. The cyclic T-bar penetration tests show a dramatic strength degradation behavior of the intact samples. The compression curves of the intact samples always lie above the remoulded ones, and there is an obvious yielding phenomenon for the intact samples. The deep-water soils exhibit high thixotropy, as proposed by a criterion to evaluate the thixotropic capacity of soils. The mineralogy and microstructure analysis indicate that biogenic silica and an open flocculated structure might be the underlying reasons for the unique physical and mechanical properties of deep-water soils. The findings through this study provide essential parameters for related engineering applications and a deeper insight into understanding the unique properties of deep-water soils.