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Studying the rheological properties of deep-sea shallow sediments can provide basic mechanical characteristics for designing deep-sea mining vehicles driving on the soft seabed, providing anchoring stability of semi-submersible mining platforms, and assessing submarine landslide hazards. Shallow sediment column samples from the Western Pacific mining area were obtained, and their rheological properties were studied. A series of rheological tests was conducted under different conditions using an RST rheometer. In addition, conventional physical property, mineral composition, and microstructure analyses were conducted. The results showed that shallow sediments have a high liquid limit and plasticity, with flocculent and honeycomb-like flaky structures as the main microstructure types. The rheological properties exhibited typical non-Newtonian fluid characteristics with yield stress and shear-thinning phenomena during the shearing process. In contrast to previous studies on deep-sea soft soil sediments, a remarkable long-range shear-softening stage, called the thixotropic fluid stage, was discovered in the overall rheological curve. A four-stage model is proposed for the transition mechanism of deep-sea shallow sediments from the solid to liquid-solid, solid-liquid transition, thixotropic fluid, and stable fluid stages. The mechanism of the newly added thixotropic fluid stage was quantitatively analyzed using a modified Cross rheological model, and this stage was inferred from the perspective of mineralogy and microstructure. The results of this study can be useful for improving the operational safety and work efficiency of submarine operation equipment for deep-sea mining in the Western Pacific Ocean. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

期刊论文 2025-06-01 DOI: 10.1016/j.sandf.2025.101632 ISSN: 0038-0806

The interface resistance during installation is crucial for the stability and safety of suction caisson in offshore geotechnical engineering, which is strongly affected by the penetration rate and soil-structure interface mechanical properties. This research conducts a series of clay-structure interface shear tests using modified direct simple shear device to fully study the mechanical behavior of clay-suction caisson interface. The effect of shear rate, over consolidation ratios (OCRs), interface boundary conditions, stress levels, and interface roughness were considered. Results show that as the OCR increases, the strength of both the clay and interface increase but show distinct patterns under constant volume (CV) and constant normal load (CNL) boundary condition. It was found that the interface strength is positively related to interface roughness and shear rate impact both the clay and corresponding interface strength. Under CNL conditions, the strength of normally consolidated (NC) clay decreases with rising shear rate, while the over consolidated (OC) clay demonstrate a opposite trend. In contrast, the effect of shear rate on interface behavior gets complicated owing to the combination of roughness, stress levels, and OCRs. Under CV conditions, the shear strength of clay and interface exhibits a logarithmic growth relationship with shear rates. The result of this work can provide a basis for interface resistance evaluation for suction caisson installation in clay.

期刊论文 2024-06-01 DOI: 10.1016/j.apor.2024.103998 ISSN: 0141-1187

Based on the modified simple direct shear device which can directly measure the interface pore pressure and interface shear displacement, a series of interface shear tests and corresponding pure clay shear tests were conducted at an undrained state in constant normal load (CNL) boundary conditions or equivalent undrained state in constant volume (CV) boundary conditions. The clay-structure interfaces, consisting of seabed clay and Speswhite kaolin clay with overconsolidation ratios (OCR) of 1 and 3, were tested at three shear rates, respec-tively V1 = 0.0002 mm/s, V2 = 0.001 mm/s, and V3 = 0.01 mm/s. The results demonstrated that the shear strength of the clay-structure interface is lower than that of pure clay, and this difference is more pronounced under CV boundary conditions. In CNL condition, though the pure clay strength decreases with increasing shear rate at OCR = 1 and increases with increasing shear rate at OCR = 3, the shear rate effect on clay-structure interface strength is not obvious. In CV condition, the strength of the interface with the normally consolidated (NC) and over consolidated (OC) clay increases approximately linearly with the shear rate on the semi -logarithmic scale. the shear rate parameter p is used to describe the growth rate of pure clay or clay-structure interface shear strength with a tenfold increase in shear rate. As for normally consolidated clay, in CV condi-tion, the corresponding shear rate parameter satisfies that p (with R1 roughness)> p (pure clay)> p (with R2 roughness). The rate parameter corresponding to NC seabed clay is significantly higher than the rate parameter corresponding to NC Speswhite kaolin clay. For OC clay, the shear rate parameter for interface strength is higher than that for pure clay, meeting with the relationship that p (with R1 roughness)> p (with R2 roughness)> p (pure clay).

期刊论文 2024-02-01 DOI: 10.1016/j.soildyn.2023.108389 ISSN: 0267-7261
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