Deep-sea polymetallic nodules are fundamental to the development of future green energy, and developing tracked mining vehicles (TMVs) that can adapt to complex deep-sea environments is crucial for the commercial mining of these resources. To optimize the design of the walking mechanism and the selection of operating parameters for the TMV, ensuring safe, stable, and efficient operation on soft deep-sea sediments, this paper studies the vehicle's traction performance under various track tensions and traveling speeds using multibody dynamics simulation. Simulation results show that the independently designed TMV has sufficient passability on different terrains, confirming the design's validity. The study also analyzes the effects of track tension and traveling speed on key performance indicators such as traction and track slip rate, finding that an optimal tension of 100 kPa and a speed of 0.7 m/s provide sufficient traction and stability for the vehicle's walking mechanism. This research provides a crucial foundation for the rational design optimization of the walking mechanism parameters for deep-sea polymetallic nodule TMVs, enhancing their operational performance and mining efficiency.

The design of a tracked mining vehicle (TMV) that can efficiently and safely travel on the deep seabed is the core technology in the deep-sea polymetallic nodule mining system, and one of the main aspects influencing the TMV's driving performance and efficiency is its travel speed. To overcome the current limitations of low mining vehicle efficiency and susceptibility to slipping and sinking, this study investigates the impact of travel speed on vehicle performance based on laboratory model experiments and numerical simulation methods. Initially, track driving model experiments were conducted, revealing that traction force increases with travel speed, analyzing the influence on the stage-wise variation of shear strength-displacement relationship between the track and sediment interface. An optimized traction force calculation model was proposed, and applied in multi-body dynamics software and validating its rationality. Multi-body dynamics simulation experiment results indicate a significant increase in the settlement amount of TMVs with increasing travel speed. However, the magnitude of the travel speed changes the variation pattern of settlement amount with travel displacement, and it was found that the slip rate during stable vehicle traveling is positively correlated with travel speed. The impact of travel speed on the performance of TMVs traveling on sediment eroded by jets in actual engineering was also analyzed. It is found that excessive or insufficient travel speed is detrimental to the performance of TMVs. In this study, when the travel speed is 0.7 m/s, the effect of weakening the mechanical strength of eroded sediment on TMV's driving performance is relatively small. This research provides a scientific theoretical basis for improving mining vehicle efficiency and enhancing mining capability.

The design and working state parameters of the tracked mining vehicle (TMV), a vital piece of equipment in the development system for deep-sea polymetallic nodule mineral resources, have a significant influence on the TMV's traction performance. This study aims to reveal the mechanism of track-sediment interaction during the walking process of TMVs and obtain a more accurate and reasonable evaluation model for the traction performance of TMVs. The main factors influencing TMV's traction performance were determined theoretically, and numerous track shear sediment model tests were carried out in light of this. The results showed that the grounding-specific pressure has a significant impact on the traction performance of TMVs, and the track's maximum traction increases with the grounding-specific pressure. With the increase of the grouser pitch-to-height ratio (GPH), the track traction initially increases, and then stabilizes after a GPH of 1.15, and there is a weakening effect of traction in multi-grouser tracks. The experimental results found that the traveling speed has a significant impact on the track traction. The relationship functions between the attenuation coefficient and GPH, the speed influence coefficient and traveling speed, and the track traction calculation model that considering the impacts of grouser pitch and traveling speed were provided. The study's findings can offer a theoretical foundation grounded in science for designing structural parameters and choosing working state parameters for TMVs.

The hydraulic double-row jet collector is widely used due to its high collection efficiency. Deep-sea sediments are usually characterized by high water content and semi-fluid dynamics, and there are few studies on the erosion properties of such sediments under jets. Resulting in the failure to accurately assess the efficiency and disturbance of a two-row jet collector. In this paper, the flow field characteristics are simulated for different double-row jet parameters (jet outlet pressure, nozzle-to-seabed height, target distance and number of nozzles). The erosion of a high water content, semi-fluid dynamic sediment layer (similar to the deep sea) under a double-row jet is experimentally investigated. According to the results from study, the jet flow field had a powerful central flow field, and decayed to both sides gradually. The formulas of flow field attenuation distribution in the upper jet zone and the maximum axial pressure are proposed. Moreover, the experiments showed that the erosion holes on the surface layer was mainly a "bowl" shape with a flat bottom and concave side, which had self-similarity. The erosion depth grew with the increase of jet outlet pressure, decreased with the increase of the nozzle height to the seabed. With the increase of target distance, the erosion depth first increased and then decreased. A new model of the erosion depth-time and erosion depth prediction are proposed. These results can provide theoretical reference for flow field calculation in nodule mining operation with double-row jet collector. It may have potential benefits on melioration of the collection efficiency and reduction of the jet disturbance.

The benthic plume generated by nodule mining operations has garnered significant attention due to its intricate environmental impact and the limitations of existing plume control techniques. Prior research has suggested that temperature effects can facilitate the aggregation of suspended sediments; however, a more detailed understanding is needed. In this study, a series of experiments were conducted to examine the sedimentation behavior of the benthic plume and the influence of temperature on its sedimentation process. Suspension concentrations of the plume were monitored over an hour, while flocs characteristics were investigated at 30 and 60-min intervals. A novel function describing the relationship between temperature effects and concentration changes was developed. Results indicate that higher temperatures can accelerate the deposition process by approximately 3–6 times, emphasizing the necessity to consider low water temperatures in laboratory studies of benthic plumes. Moreover, the integration of temperature effects and micro-eddies in plume aggregation research may offer new opportunities for developing advanced plume control and separation methods.

The threshold of the sediment initial movement is closely related to marine structure scour. In complex marine environment, the relative density of seabed is usually changed by liquefaction and scour that is caused by currents and waves. It affects the scour depth and scour time scale which have been noted recently. However, the effect of relative density on sediment movement was mostly ignored in previous studies. In this paper, a series of tests were conducted to investigate the incipient motion under different relative density conditions on different seabeds. Subsequently, the internal friction force was introduced to describe the relative density effect, and an incipient motion model was built. Accordingly, a unified sediment incipient motion velocity function that considers relative density is proposed. Based on this function, the critical bed shear stress was assessed. A new theory was then evaluated in terms of the critical bed shear stress. Finally, the percentage of internal friction force to the whole resistance was discussed. Results indicated the significance of considering the relative density effect in predicting small-sized sediment movement. The new function provides better prediction accuracy with an acceptable error of 20%. Additionally, the discussion of the internal friction force gives a potential avenue to quantify interparticle force.

Rigid piles are common foundations for offshore wind turbines. Scour around piles leads to the loss of surrounding soil, which seriously threatens the safe operation of offshore wind turbines. However, most of the existing experimental studies on the scour effects on marine foundations are carried out in the test box without a hydraulic environment, resulting in deviations between the test results and the actual ocean engineering. Therefore, a test method to study scour effects on the lateral response of rigid piles is proposed. The key to this test method lies in the design of four types of parameters: pile, soil, hydraulic (wave and current), and load. Considering the characteristics of scour tests and scour effects tests, the design method of the four types of parameters is proposed. Combined with an example, the test method is described in detail. Subsequently, the defects of this test method are discussed. The research shows that this test method is a good attempt to study the loss of lateral ultimate capacity and the increase of cyclic cumulative deformation of rigid piles under real scour conditions.

In the complex marine environment, the seabed will undergo geomechanical phenomena such as pore water pressure dissipation and reconsolidation, resulting in cyclic changes in seabed density. However, the changes in the relative density of the seabed were mostly ignored in the previous studies. In this paper, a series of scouring experiments of the pile with different seabed relative densities (loose, medium dense, and dense) are conducted. Results show that the scour history process of the pile differs across different seabeds, and the scour time scale of the pile increases with the increase of relative density. The critical motion shear stress between particles rises with the increase of relative density. The equilibrium scour depth of the pile decreases with the increase of relative density. The study finds that the existing empirical equations of scour are less applicable to the loose and dense seabed. Therefore, the paper derives novel empirical formulas for the scour history process, scour time scale and equilibrium scour depth of pile, which applies to the seabed with different densities. The prediction errors are 10%–20%. The results of this paper have potential engineering implications for proposing new scour protection methods.

Field observations show that silt is not always loose and that silt consolidation is common. In the study reported here, the characteristics of pile scour in consolidated silt (CS) under clear-water conditions were investigated and compared with those in loose silt. Experiments were performed to study the dimensions of equilibrium scour holes in CS, and the results show that the scour depth and radius in CS are smaller than those in loose silt, but the slope angle in CS is larger and the scour depth is inversely proportional to the dry density. It is found that the scour characteristics in CS differ from those in commonly used fine sand and silt, and most of the existing scour equations cannot predict the scour depth in CS. A mathematical relationship between the scour hole dimensions and the maximum scour depth applicable to CS is established, and a new equation is proposed for computing the maximum scour depth in CS with an error of less than 25%. The present work offers theoretical guidance for the design of scour prevention of piles and scour hole repair in CS.

In this study, the entire evolution process of consolidated silt in a silty seabed under the action of waves is reproduced via a flume experiment. The response of pore water pressure in the seabed, variation of soil strength, and change in characteristic parameters of the soil particles are studied. From the experiment, the silty seabed is inferred to undergo two stages, i.e., failure and reconsolidation, finally forming a high-strength consolidated silt layer. The rapid accumulation of pore water pressure in the seabed under the action of waves provides the initial conditions for the formation of consolidated silt. The shear of the wave and seepage of pore water pressure provide power for the reconsolidation of the seabed. Macroscopically, reconsolidation of an unstable seabed results in consolidated silt. Microscopically, consolidated silt is the product of coarsening, homogenization, and embedment of particles. The hardening mechanism of consolidated silt is driven by increases in the internal friction angles of the particles and existence of hardening forces between the particles. The empirical formula for the internal hardening force of consolidated silt is obtained experimentally.

This study develops a new form of composite beam theory to study the connections of fiber reinforced polymers (FRPs), reinforced concrete beams, and closed-form solutions of four typical connections are derived and discussed. Comparisons with experimental data also show agreement. The maximum strain incompatibility of the mechanically anchored FRP system at two ends appears at the position where the first-order derivative of the applied bending moment M-ex' is zero or at the boundary positions. Compared with strain incompatibility, the slip is more critical for determining the composite behavior of the FRP-reinforced structure. The first-order derivative function of the slip is strain incompatibility. It is demonstrated that the structural response of this FRP system can be improved theoretically by introducing additional mechanical anchors at the critical locations from the slip perspective. (C) 2022 American Society of Civil Engineers.

The influence of the seabed geotechnical properties on the scour development mechanism of the pile is ignored in the majority of the studies, which leads to a low accuracy of the scour depth prediction equation. This paper presents an experimental study on scour of the pile in sand with different seabed geotechnical properties (i.e. the friction angle, the density and the seepage force of the sand). The seabed stress equation, scour mechanism and scour depth prediction equation of the pile are found. The pile scour depth decreases with an increase in the relative densities of sand. The sand friction angle is the main micro parameter of the scour mechanism, and the seabed stress has a positive correlation with the relative density of sand. The seepage force of the sand has little effect on the scour depth of the pile. A scour protection method regarding reducing the scour depths of the pile by increasing the sand density is given. Finally, the effect of seabed consolidation on the scour depth of the pile is discussed.

Local scouring is a severe threat to the safety of offshore wind turbines, and it cannot be eliminated completely by traditional protection methods. In this paper, to improve seabed scouring resistance, a new local scouring countermeasure—grouting protection—is proposed, and flume scouring tests are reported. It is found that after grouting, the micro-morphological characteristics of the soil are changed, with the internal friction angle and cohesion of the seabed soil being improved significantly. The grouted seabed has different modes during the development of scouring, i.e., cracking, peeling off, incipient motion, and abrasion. Further analysis shows that the critical shear stress of grouted seabed particles is much greater than that of ungrouted ones, and the ultimate scouring depth of grouted seabed is much lower than that of ungrouted seabed. The protective effect of grouting on local scouring is fully verified: compared with collar protection, grouting protection is more reliable under weak hydrodynamic action, and compared with riprap protection, grouting protection is more efficient under extreme hydrodynamic action.

This paper aims at optimizing the shear connectors distribution in sandwich structures and thus improving both deformation and stress state performance under service load. Different from traditional uniform shear connectors configuration, two shear connectors configurations are presented and analyzed theoretically. A further analysis from slip characteristics leads to a novel slip control setup and by limiting the slip at critical locations, for example at +/- l / 4 location, stress and deflection can be significantly reduced. Additionally, common load cases are discussed and closed form solutions are provided in details. It is concluded that shear connectors optimization would reduce the stress and deflection while achieving better economy and thermal efficiency. This methodology and theory are not limited to sandwich structures and can be readily applied to other types of composite structures.

The scour around the bucket foundation has a significant impact on the response and stability of the bucket foundation. A series of tests have been carried out to estimate the effect of scour on the cyclic response of the bucket foundation under waves and currents. It is found that the scour depth S-d/d of the bucket increases with the increase in Fr-a. The top displacement of the bucket increases with the increase of wave height and scour depth. When the wave force accounts for more than 90% of the wave flow force (0.05 < Fr-a < 0.5), at the same wave height, the scour depth can increase more than 0.6 d, the rotation angle can increase by 120-200%. This article proposes an empirical relationship with an error of 10-20% for evaluating the bucket foundation rotation angle under scour, which can provide a relevant reference for the design of the bucket foundation.

Under a scouring action, scouring holes occur around a suction bucket foundation and have different depths and widths. The loss of soil in scouring holes causes changes in the stress history of the remaining soil. In this study, considering the stress history, scouring depth, scouring width, and length-diameter ratio, we conducted a horizontal static loading model test of a suction bucket foundation in sand. We obtained a variation law for the ultimate bearing capacity of the foundation considering three aspects: displacement change, soil pressure distribution, and turning point position. In addition, we summarized the relationship between horizontal loads and displacements at different aspect ratios. We also demonstrated the influence of scouring factors on the distribution of soil pressure and the rotation point and revealed the mechanism influencing the scouring depth, scouring width, and history of stress on the horizontal bearing capacity of a suction bucket foundation.

The energy transmission and variation law during rock damage are studied. Consequently the energy based criterion for rock damage is obtained. Based on analyzing the energy distribution law in rock mass, the geostress condition for Zonal Disintegration Phenomenon (ZDP) is studied. The criterion for ZDP in terms of strain energy is thus established. The forming mechanism for ZDP is revealed. Additionally the sensitive factors and the influences on ZDP are determined. An equivalent excavation model is proposed to investigate the releasable strain energy. Therefore, the energy-based criterion for anchoring ZDP is established with the Energy analysis of anchor bolt. Meanwhile, the number of bolts to control the ZDP formation is calculated in this paper. Finally, a model test is compared with the theoretical result and testifies the criterion. (C) 2017 Elsevier Ltd. All rights reserved.

A superposition-iteration (S-I) model is proposed to simulate the jet grouting pre-reinforcing impact for a shallow-buried tunnel. The common model is deduced by theoretical (force equilibrium) analysis and then transformed into the numerical formulation. After applying it to an actual engineering problem, the most obvious deficiency was found to be continuous error accumulation, even when the parameters change slightly In order to address this problem, a superposition-iteration model is developed based on the basic assumption and superposition theory. First, the additional deflection between two successive excavation steps is determined. This is caused by the disappearance of the supporting force in the excavated zone and the soil pressure in the disturbed zone. Consequently, the final deflection can be obtained by repeatedly superposing the additional deflection to the initial deflection in the previous steps. The analytical solution is then determined with the boundary conditions. The superposition-iteration model is thus established. This model was then applied and found to be suitable for real-life engineering applications. During the calculation, the error induced by the ill-conditioned problem of the matrix is easily addressed. The precision of this model is greater compared to previous models. The sensitivity factors and their impact are determined through this superposition-iteration model.

Suction bucket foundation is a typical type for offshore turbines. Scour caused by wave and current can reduce the stability of foundation and then endanger the whole structure. This paper details a series of suction bucket model tests performed in sand under wave cyclic loading. The model tests investigate the effect of scour on stability of bucket foundation by artificially excavated scour hole around the foundation. It is revealed that the behavior of foundation bearing capacity can be divided into two stages: the initial cyclic stage and the final stage (showing either cyclic stability or cyclic failure). When the wave circulation is stable, the sand on the front and back sides of the foundation is suspected to be liquefied. With the increase in scour depth, the stability of foundation is gradually reduced, the behavior of foundation gradually changes from a state of cyclic stability to cyclic failure, and the number of waves that can be withstood is drastically reduced. Finally, the height of the center of rotation of the suction bucket was observed to descend with the increase in scour depth.