Understanding the volume change behavior of deep-water sediments is essential for the safety design of deep-water engineering structures. In this study, the volume change behaviors of marine sediments from the South China Sea were studied through oedometer and isotropic compression tests. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests have been conducted to investigate the microstructure evolution of two types of sediments under loads. The experimental results showed that the structural anisotropy of intact specimens is more pronounced in oedometer tests with the increase of stress, however, depolarization occurs in the isotropic consolidation test. The volume change after yield in the oedometer and isotropic consolidation tests comes from inter-aggregate pore variations associated with the adjustment of the soil fabric. The reconstituted specimen presents a more uniform distribution of pores than that of the intact specimen, and the macropores are more easily compressed for the reconstituted specimen than those of the intact specimen. With increasing stress, the oedometer compression and isotropic consolidation curves of intact specimens gradually approach those of the reconstituted specimen. The deformation mechanism under high stresses is that soil particles are reoriented and the variation of micropores.

Loose and uncemented calcareous sand slopes are prone to collapse under rainstorm erosion. In order to improve the erosion resistance stability of slopes, it is crucial to enhance the erosion resistance of calcareous sand. In this study, a new method of cementing calcareous sand with zinc sulfate solution (ZSS) is proposed. The ZSS reinforcement technique can effectively cement calcareous sand, enhance the mechanical properties and help reduce erosion on calcareous sand slopes. A series of laboratory experiments were conducted, including uniaxial compression tests, Brazilian splitting tests, surface penetration tests, microscopic tests, and rainfall scouring tests. The test results show that the uniaxial compressive strength of calcareous sand achieved 8.3 MPa reinforced with ZSS. Microscopic analyses revealed the mechanism of reinforcement, discovering the formation of environmentally friendly compounds such as ZnCO3 and CaSO4 & sdot;2 H2O between calcareous sand particles, which enhanced the soil mechanical properties. The calcareous sand slope reinforced with ZSS forms a hard shell on the slope surface, which effectively improves the erosion resistance of the slope. After being reinforced with a ZSS concentration of 1.0 mol/L, the slope remained stable after 20 min of scouring at a rainfall intensity of 80 mm/h. This method provides a quick solution for reinforcing calcareous sand slopes and holds promising potential for practical engineering applications.

The vast distribution, abundant reserves, and high combustion utilization rate of natural gas hydrate make it an appealing alternative energy source. Nevertheless, the special physical and mechanical properties of the hydrate production test area in the South China Sea have led to frequent geological disasters, requiring monitoring and early warning of potential geohazards. To facilitate this process, a model was established to determine the relationship between sediment resistivity and physical properties in this area. However, there is currently no suitable sediment resistivity inversion model for this region. We obtained an 8 m-long core sediment sample from the hydrate production test area in the South China Sea using a core sediment sampler aboard the research vessel Marine Geology 6. Indoor geotechnical tests were conducted to determine the vertical variation characteristics of the sediment, and indoor resistivity tests were performed to obtain its resistivity vertical variation. Using empirical power function formulae, we established a relationship model between resistivity and physical properties, which we then compared with relevant data from nearby sea areas. This model lays the foundation for using in situ resistivity to invert the dynamic changes of sediment physical properties and promote the development of deep-sea engineering geology.