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 sinkage of underwater landing robots deployed on loose seabed sediment over extended periods poses a significant challenge. Excessive sinkage can significantly reduce the locomotion performance of robots or even cause them to become trapped in the sediment. The study investigates the long-term sinkage behavior of underwater landing robots on seabed sediments using numerical simulations. Focusing on varying pressure source geometries and sediment mechanical properties, this research identifies distinct stages of sediment sinkage: transient, viscoelastic, and stable creep. A time-dependent pressure-sinkage model is established to predict sinkage behavior over extended durations, accounting for the effects of pressure magnitude, pressure source geometry, and sediment characteristics. Results demonstrate significant differences in sinkage depth between cylindrical and plate pressure sources, with maximum disparities reaching 158 mm under high-pressure conditions. The study further reveals that sediment parameters such as density, cohesion, and internal friction angle significantly influence sinkage, particularly in later stages, whereas loading rates affect initial but not long-term sinkage. The findings provide valuable insights for optimizing underwater landing robot designs and operational strategies, especially for long-term seabed deployments on complex sediment types. This research offers guidance for mitigating excessive sinkage risks and improving stability in underwater environments with varied sedimentary conditions.

This article presents a review of the equipment used in the process of determining the mechanical strength of soil, in particular with regards to the vertical loads applied. Here, devices incorporating the bevameter approach, i.e. medium and large-scale testers, are discussed. The bevameter technique is described in detail, along with the most common mathematical models relating to the vertical pressure applied to the soil and its compaction. The paper also highlights important phenomena for this type of experiment, such as the scale effect, wall effect, multipass effect, and slip sinkage effect. The article presents the reasons for which plate testers are currently the most commonly used tester type for soil penetration tests for the purpose of terramechanics, including the Next Generation NATO Reference Mobility Model that is currently under development. Investigations towards the influence of the penetration rate on soil penetration are also addressed. Furthermore, the authors also present a selection of their own results of currently ongoing research on the subject of potential influence of the plate grouser on plate sinkage. The results already obtained have made it possible to identify phenomena that are not taken into account in the current research methods, in turn resulting in the development of an innovative plate tester for investigating the sinkage of the running gear components of machines and vehicles in fragmented media.

The discrete element method (DEM) has been extensively utilized to investigate the mechanical properties of granules, particularly their microscopic behavior, overcoming limitations in field tests such as cost, time consumption, and soil condition restrictions. To ensure the development of reliable DEM simulations, proper contact model selection and parameter calibration are essential. In this research, a DEM parameter calibration method that could represent the nonlinear relationship between clayey soil pressure and sinkage at different moisture contents was proposed. Firstly, the sinking modulus K and the soil deformation exponent n were identified to reflect the nonlinear pressure-sinkage relationship. Then, sensitive DEM parameters on the soli pressure-sinkage relationship were investigated and calibrated, and the effect of moisture content on them was explored. Finally, the transfer of soil internal stress during subsidence was analyzed using the constructed discrete element model. The average error of the sinking modulus K and the soil deformation exponent n between the DEM and the experimental result at four moisture contents were 4.7% and 4.9%, respectively. The relative error of soil internal stress between simulation and experiment was 6.7%, 4.4%, and 9.7% at depths of 50 mm, 100 mm, and 150 mm, respectively. The soil particle trajectory, soil internal stress distribution, and variations during plate pressure-sinkage progress were analyzed by the constructed DEM model. The results demonstrated good agreement with theoretical models and experimental findings. The proposed clayey soil DEM modeling process that considers the pressure-sinkage nonlinear relationship at different moisture contents can be applied in machine-soil research.