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/).

The excellent grounding performance of tracked mining vehicles (TMVs) is a crucial foundation for the normal operation of the entire deep-sea polymetallic nodule mining system. Based on the weak mechanical properties of deep-sea fluidized sediments, this study conducted model tests to deeply analyze the pressure-sinkage relationship curve characteristics and the soil failure process under the vertical action of the TMV track plates. It identified the influence of soil water content on the failure mode and compaction degree and established a new segmented pressure-sinkage model, verifying its accuracy. The test results showed that the width of the track plates and the water content of the sediments had a significant impact on the pressure-sinkage relationship curve, while the sinkage speed had little effect. The bearing capacity of the sediment was an inherent property of the soil, independent of the track plate width and sinkage speed, and decreased with increasing water content. By combining the changes in soil strength and the movement characteristics of soil particles under vertical load, the pressure-sinkage model was divided into the compaction stage, elastic stage, elastoplastic stage, and plastic stage. Based on the experimental results under various conditions, a predictive model for track sinkage depth that considers sediment water content and track plate width was developed. The findings of this study can provide a scientific theoretical basis for the design optimization of parameters such as vehicle weight and track dimensions, promoting the development of deep-sea polymetallic nodule mining.

The deep-sea mining machine is a crucial component of the seabed mining system. However, due to the unique mechanical properties of deep-sea sediments, the machine often encounters problems like slipping and sinking during operation. Traditional model testing struggles to analyze the interaction between tracks and soil on a microscopic level. This study uses an MBD-DEM coupling method to simulate track-soil interactions, revealing the impact of grouser shape, spacing, track plate spacing, ground pressure, and pretension on the machine's performance. The results show that the grouser causes the most soil disturbance when entering and exiting the soil, providing significant traction during entry, though some grousers face resistance while moving. Increasing grouser spacing initially boosts traction but later decreases it, as too small or too large spacing affects thrust and soil utilization. Enlarging track plate spacing reduces motion resistance and increases traction. Raising ground pressure also enhances traction but increases soil disturbance. Setting pretension to 12% of the machine's weight results in smoother operation. Additionally, the study considered the impact of biomimetic grousers on traction under multi-grouser conditions and designed more efficient grousers, providing theoretical guidance for the structural design of deep-sea mining machine tracks.

With the increasing development demand of the modern energy industry, heightened focus has been directed toward the exploitation of deep-sea polymetallic mineral resources. The water jet-sediment coupling under the jet action plays a crucial role in the collection processes. Understanding this mechanism is essential for achieving both efficient collection and minimal environmental disturbance. In this paper, from the deep-sea sediments to which the polymetallic nodules (PMNs) adhere, the characteristics of sediments are studied, focusing on physical and mechanical properties, cementation effects, rheological, and dynamic properties. Upon this foundation, the evolving patterns of flow field structure and characteristics (changes of pressure and velocity), jet-induced sediment erosion and plume generation (erosion pattern, disturbance volume), as well as the characteristics of nodules stripping-movement (such as lift-up force and movement law) are analyzed. Furthermore, following an analysis of the jet-sediment coupling mechanism, the technical applications of jet collection (collection structure design and operation parameter matching) are discussed. Finally, the existing problems and future research directions are discussed. This research reviews the coupling mechanism of water jet and sediment in the process of jet collection, which provides a reference for the design of collection equipment with high efficiency and low-disturbance characteristics.

To ensure the safe performance of deep-sea mining vehicles (DSMVs), it is necessary to study the mechanical characteristics of the interaction between the seabed soil and the track plate. The rotation and digging motions of the track plate are important links in the contact between the driving mechanism of the DSMV and seabed soil. In this study, a numerical simulation is conducted using the coupled Eulerian-Lagrangian (CEL) large deformation numerical method to investigate the interaction between the track plate of the DSMV and the seabed soil under two working conditions: rotating condition and digging condition. First, a soil numerical model is established based on the elasto-plastic mechanical characterization using the basic physical and mechanical properties of the seabed soil obtained by in situ sampling. Subsequently, the soil disturbance mechanism and the dynamic mechanical response of the track plate under rotating and digging conditions are obtained through the analysis of the sensitivity of the motion parameters, the grouser structure, the layered soil features and the soil heterogeneity. The results indicate that the above parameters remarkably influence the interaction between the DSMV and the seabed soil. Therefore, it is important to consider the rotating and digging motion of the DSMV in practical engineering to develop a detailed optimization design of the track plate.