As the latest development and benchmark of a gravity installed anchor (GIA), the OMNI-Max anchor stands as a cutting-edge achievement and benchmark, finding increasingly widespread use within mooring systems due to its exceptional operational performance and adaptability. Notably, while investigations into the pullout capacity of OMNI-Max anchors have been conducted extensively in clay, the relevant studies are seldom observed in sand. Actually, the mechanical properties of sand are quite different from those of clay, and sand is also widely distributed in seabed soil. Full knowledge of OMNI-Max anchors not only in clay but also in sand is necessary to a wider application of the anchors. In the present work, the large deformation finite element (LDFE) method is adopted combined with the coupled Eulerian-Lagrangian (CEL) technique to study the end-bearing characteristics of the OMNI-Max anchor in sand seabeds. A bounding-surface plasticity model is taken as the constitutive model to capture the characteristics of sand. Through investigation and analysis, OMNI-Max anchors are closely related to the anchor embedment depth, the soil relative density, the anchor orientation, the loading angle and the bearing area, so the working conditions related to these five factors are designed and calculated. An explicit expression of the end-bearing capacity factor is finally derived to provide a simple and fast tool of evaluating the pullout capacity of the anchor in sand under multiple factors. Validation cases and orthogonal tests have confirmed the effectiveness and applicability of the explicit expression.

The deep-sea ground contains a huge amount of energy and mineral resources, for example, oil, gas, and minerals. Various infrastructures such as floating structures, seabed structures, and foundations have been developed to exploit these resources. The seabed structures and foundations can be mainly classified into three types: subsea production structures, offshore pipelines, and anchors. This study reviewed the development, installation, and operation of these infrastructures, including their structures, design, installation, marine environment loads, and applications. On this basis, the research gaps and further research directions were explored through this literature review. First, different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations. Second, the subsea production structures, including subsea manifolds and their foundations, were reviewed and discussed. Third, the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers, were analyzed and reviewed. Finally, the installation and bearing capacity of deep-sea subsea anchors and seabed trench influence on the anchor were reviewed. Through the review, it was found that marine environment conditions are the key inputs for any offshore structure design. The fabrication, installation, and operation of infrastructures should carefully consider the marine loads and geological conditions. Different structures have their own mechanical problems. The fatigue and stability of pipelines mainly depend on the soil-structure interaction. Anchor selection should consider soil types and possible trench formation. These focuses and research gaps can provide a helpful guide on further research, installation, and operation of deep-sea structures and foundations. This paper reviewed the development, installation, and operation of these infrastructures, including their structures, design, installation, marine environment loads, and applications. The research gaps and further research directions are explored through this literature review. First, different floating structures were briefly analyzed and reviewed. Second, the subsea production structures, including subsea manifolds and their foundations, were reviewed and discussed. Third, the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers, were analyzed and reviewed. Finally, the installation and bearing capacity of deep-sea subsea anchors and seabed trench influence on the anchor capacity were reviewed. image center dot Provide a brief introduction about seabed structures and foundations related to deep-sea resource development. center dot Introduce subsea production structures, including subsea manifolds and their foundations (mudmats, suction piles), from a design perspective. center dot Analyze the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers. center dot Introduce the installation and bearing capacity of anchors in deep-sea, and summarize seabed trench influence on anchor capacity.

Sandy soil in the north of Hebei region of China is widely distributed, the temperature difference between day and night is large, the phenomenon of freezing and thawing is obvious, and the soil body before and after the freezing and thawing cycle of sandy soil slopes is affected by the changes. This paper takes the stability of a sandy soil anchorage interface under a freeze-thaw cycle as the research background and, based on the self-developed anchor-soil interface shear device, analyses the influence of changing sand rate, confining pressure, and the number of freeze-thaw cycles on the shear characteristics of an anchor-soil interface in anchorage specimens. The research findings indicate that, at 50-60% sand contents, the shear strength increases with a higher sand content and is positively correlated with confining pressure within a higher range. A higher sand content stabilises the anchoring body, but an excessively high sand content can lead to failure. Increasing the sand content, confining pressure, and freeze-thaw cycle number all result in a reduction in the shear displacement at the peak strength. After 11 freeze-thaw cycles, the shear strength of the anchoring body stabilises, with a reduction in strength of approximately 32%, and a higher sand content effectively reduces the reduction in strength.

Cyclic loading of deep foundations and soil anchorage elements can lead to failure by accumulation of deformations or loss of strength. Snakeskin-inspired surfaces have been shown to mobilize direction-dependent friction angles and volumetric responses due to their asymmetric profile. This paper presents an investigation on the cyclic interface element behavior of sand-structure interfaces with snakeskin-inspired surfaces with the goal of understanding the potential impact of these surfaces on the cyclic behavior of geotechnical elements. Load- and displacement-controlled cyclic interface shear tests were performed with constant stiffness boundary conditions. Four different snakeskin-inspired surfaces and reference rough and smooth surfaces were tested. The results show that under symmetric shear stress cycles, failure always takes place in the caudal direction (i.e. along the scales) due to the smaller interface friction angles. A shear stress bias can produce a change in the failure direction to the cranial one (i.e., against the scales). An equation is introduced to predict the magnitude of shear stress bias that changes the failure direction. This investigation shows that the snakeskin-inspired surfaces can be used to control the direction of failure of soil-structure interface elements which can help in increasing the cyclic stability and reducing the susceptibility of brittle failure.

Plate anchors have become an attractive technology for anchoring offshore floating facilities such as floating renewable energy devices because they provide high holding capacity relative to their dry weight. This allows for the use of smaller anchors (relative to a driven or suction-installed pile), which provide cost savings on production, transport, and installation. Loads delivered to the anchor via mooring lines may increase pore water pressure in fine-grained soils. This excess pore pressure will dissipate with time, resulting in a local increase in the undrained shear strength of the soil surrounding the anchor, increasing the capacity. There may be opportunities to consider these capacity increases if the consolidation process occurs over time periods that are short relative to the lifetime of the facility. This paper considers the use of drainage channels in a plate to make the anchor permeable and quicken consolidation times. Experimental data generated from model-scale experiments conducted in a geotechnical centrifuge show (for the anchor design tested) that excess pore pressure just above the anchor dissipated almost an order of magnitude faster for a permeable anchor, and that after full consolidation, the permeable anchor capacity was higher. The latter finding was not anticipated and is believed to be due to changes in load distribution resulting from the rapid reduction in negative excess pore pressure underneath the permeable anchor.