Abstract Ocean mining activities have been ongoing for nearly 70 years, making great contributions to industrialization. Given the increasing demand for energy, along with the restructuring of the energy supply catalyzed by efforts to achieve a low-carbon economy, deep seabed mining will play an important role in addressing energy- and resource-related problems in the future. However, deep seabed mining remains in the exploratory stage, with many challenges presented by the high-pressure, low-temperature, and complex geologic and hydrodynamic environments in deep-sea mining areas, which are inaccessible to human activities. Thus, considerable efforts are required to ensure sustainable, economic, reliable, and safe deep seabed mining. This study reviews the latest advances in marine engineering geology and the environment related to deep-sea mining activities, presents a bibliometric analysis of the development of ocean mineral resources since the 1950s, summarizes the development, theory, and issues related to techniques for the three stages of ocean mining (i.e., exploration, extraction, and closure), and discusses the engineering geology environment, geological disasters, in-situ monitoring techniques, environmental protection requirements, and environmental effects in detail. Finally, this paper gives some key conclusions and future perspectives to provide insights for subsequent studies and commercial mining operations. 

/pdf/deep-seabed-mining-frontiers-in-engineering-geology-and-77whg8n9.pdf

Deep seabed mining: Frontiers in engineering geology and environment

Deep-sea pipelines play a pivotal role in seabed mineral resource development, global energy and resource supply provision, network communication, and environmental protection. However, the placement of these pipelines on the seabed surface exposes them to potential risks arising from the complex deep-sea hydrodynamic and geological environment, particularly submarine slides. Historical incidents have highlighted the substantial damage to pipelines due to slides. Specifically, deep-sea fluidized slides (in a debris/mud flow or turbidity current physical state), characterized by high speed, pose a significant threat. Accurately assessing the impact forces exerted on pipelines by fluidized submarine slides is crucial for ensuring pipeline safety. This study aimed to provide a comprehensive overview of recent advancements in understanding pipeline impact forces caused by fluidized deep-sea slides, thereby identifying key factors and corresponding mechanisms that influence pipeline impact forces. These factors include the velocity, density, and shear behavior of deep-sea fluidized slides, as well as the geometry, stiffness, self-weight, and mechanical model of pipelines. Additionally, the interface contact conditions and spatial relations were examined within the context of deep-sea slides and their interactions with pipelines. Building upon a thorough review of these achievements, future directions were proposed for assessing and characterizing the key factors affecting slide impact loading on pipelines. A comprehensive understanding of these results is essential for the sustainable development of deep-sea pipeline projects associated with seabed resource development and the implementation of disaster prevention measures. 

Predicting impact forces on pipelines from deep-sea fluidized slides: A comprehensive review of key factors

Improved predictive model for the strength of fluidized seabed sediments with rate effect characteristics by full-scale spherical penetrometer tests

The mechanical behaviour of deep-sea clay is crucial for oil and gas pipeline safety and is traditionally assessed through in situ penetration testing, which is usually conducted in a low-temperature environment (usually at temperatures lower than 4 °C). However, the temperature of deep-sea clay surrounding high-temperature pipelines can reach approximately 20 °C. To date, the influence of temperature variation on the mechanical properties of deep-sea clay, especially strain-softening behaviour, has been largely overlooked, posing a safety risk to practical engineering. Consequently, this study first establishes a temperature-controlled cyclic penetration testing platform. Then, an enhanced mini-spherical penetrometer is employed to investigate the undrained strength and strain-softening behaviour of undisturbed deep-sea clay samples at 4 °C, 10 °C and 20 °C. In particular, an improved framework is proposed to quantitatively characterize the mechanical behaviour. Finally, a strain-softening law considering temperature variations is established and rigorously validated through in situ tests. The findings underscore several significant observations: (a) deep-sea clay in its intact state exhibits a heightened sensitivity to temperature variations compared to that in its remoulded state; (b) temperature variations influence the strain-softening parameters of deep-sea clay, resulting in distinct behaviours; and (c) the proposed strain-softening law considering temperature variations is verified to be more logical. 

Effect of temperature rise on the mechanical behaviour of deep-sea clay surrounding oil and gas pipelines

Simple, precise, and economical evaluation of the undrained shear strength Su of undisturbed marine soil can facilitate the construction of offshore projects. In this study, piezocone penetration tests (CPTu) were conducted at the site of a wind power project, and consolidated undrained triaxial tests were performed on specimens of undisturbed marine fine-grained soil taken from the site. Analysis shows that the Eslami–Fellenius and Chinese soil classification methods based on CPTu data are more applicable for marine soils. The test results indicate that the stress–strain curve exhibits strain softening if the clay content is less than 30 %, otherwise it exhibits either strain hardening or strain stability. Furthermore, the specimens exhibit two deformation failure modes: softening contraction and hardening dilatancy. From the correlation between the consolidated undrained triaxial test data and the CPTu data, Su can be determined simply via an explicit expression involving the measured pore pressure behind the cone (u2), the corrected cone tip resistance (qt), and the soil depth H, and this expression is significantly more precise than the existing empirical formulas. The proposed method offers a sound basis for designing the foundations of marine engineering and infrastructure projects in different sea region. 

A new empirical model for the undrained shear strength of undisturbed marine fine-grained soil based on piezocone penetration tests

Abstract Background As the exploitation of marine resources intensifies, the impact of submarine landslides on underwater structures has become a significant issue. Existing research primarily focuses on the impact on pipelines, often neglecting the actual deformation and mechanical response of underwater structures under impact loads in numerical simulations, thus complicating the evaluation of the reliability of these engineering structures in extreme conditions. Moreover, the dynamic response of bucket foundations, a common form of underwater base, under the effect of submarine landslide impacts remains unclear. Methods To address this knowledge gap, we have developed a fluid-structure coupling system that employs the coupled Smoothed Particle Hydrodynamics (SPH)-Finite Element Method (FEM) to investigate a single impact process and analyze the displacement response of bucket foundations within a water-offshore landslide-bucket foundationsubgrade context. The accuracy of this developed method has been systematically verified through comparisons with previous experimental and numerical results. Results During a submarine landslide impact event, the impact force demonstrates a distinct decrease followed by stabilization, and the displacement response of the bucket foundation exhibits a rebound effect after reaching its maximum value. Furthermore, we conducted an extensive analysis of different impact angles for underwater data centers equipped with multi-bucket foundations. Our study revealed that group-bucket foundations experience a combined translation-turnover failure when subjected to submarine landslide impacts, and the most unfavorable scenario for such impact is identified. The research introduces a novel numerical simulation approach for investigating the impact of submarine landslides on complex underwater structures. 

pdf/investigation-of-offshore-landslides-impact-on-bucket-4e9jmf6a5p.pdf

Investigation of offshore landslides impact on bucket foundations using a coupled SPH–FEM method

An improved evaluation method for the undrained shear strength of uniform soft clay in the nonfull flow state based on ball penetration simulations

The technology for in situ testing of the undrained shear strength of deep-sea clay is underdeveloped. Indoor tests remain necessary, and there is a large temperature difference between in situ and laboratory tests. To analyse the effect of temperature on undrained shear strength, in this study the physical characteristics of marine clay samples from the South China Sea were determined, followed by penetration tests by the mini-ball method under low (4 °C) and room (20 °C) temperatures. The results indicated that the clay strength increased by 14.1–30.0% as the temperature decreased from 20 °C to 4 °C, and the strength of the bound water and the viscosity of the free water in the clay sample increased as the temperature decreased, which was the root cause of the increase in the clay strength. Based on the research, it is possible to correct the undrained shear strength values measured in laboratory tests and provide more reasonable parameters for ocean engineering.

/pdf/effect-of-low-temperature-on-the-undrained-shear-strength-of-2mqbnn5d.pdf

Effect of Low Temperature on the Undrained Shear Strength of Deep-Sea Clay by Mini-Ball Penetration Tests

This study analyzed the biomechanics characteristics for a Chinese subject's 120 kg snatch skills act mainly through photographing measuring. The result showed: the barbell vertical changes were apparent, the barbell's vertical speed reached its maximum of 1.98 m/s when the barbell was 0.72 s away up the ground, and the barbell reached its highest point of 1.05 m when it was 1.0s away up the ground. It was concluded that the subject's skill showed the characteristic of quick breaking pull.

/pdf/biomechanics-analysis-of-snatching-skills-in-women-topnotch-102qp7fnak.pdf

Biomechanics analysis of snatching skills in women topnotch weight lift -a case study

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