Seabed structures and foundations related to deep-sea resource development:A review based on design and research

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.

Optimal design for rubber concrete layered periodic foundations based on the analytical approximations of band gaps and mapping relations

The seismic performance of rubber concrete-layered periodic foundations are significantly influenced by their design,in which the band gaps play a paramount role.Aiming at providing better designs for these foundations,this study first proposes and validates the analytical formulas to approximate the bounds of the first few band gaps.In addition,the mapping relations linking the frequencies of different band gaps are presented.Furthermore,an optimal design method for these foundations is developed,which is validated through an engineering example.It is demonstrated that ensuring the superstructure’s resonance zones are completely covered by the corresponding periodic foundation’s band gaps can achieve satisfactory vibration attenuation effects,which is a good strategy for the design of rubber concrete layered periodic foundations.

Frequency-dependent viscoelasticity effects on the wave attenuation performance of multi-layered periodic foundations

In this paper,layered periodic foundations(LPFs)are numerically examined for their responses to longitudinal and transverse modes in the time and frequency domains.Three different unit-cells,i.e.,2-layer,4-layer,and 6-layer unit-cells,comprising concrete/rubber,concrete/rubber/steel/rubber,and concrete/rubber/steel/rubber/lead/rubber materials,respectively,are taken into account.Also,the viscoelasticity behavior of the rubber is modeled with two factors,i.e.,a frequency-independent(FI)loss factor and a linear frequency-dependent(FD)loss factor.Following the extraction of the complex dispersion curves and the identification of the band gaps(BGs),the simulations of wave transmission in the time and frequency domains are performed using the COMSOL software.Subsequent parametric studies evaluate the effects of the rubber viscoelasticity models on the dispersion curves and the wave transmission for the longitudinal and transverse modes.The results show that considering the rubber viscoelasticity enhances the wave attenuation performance.Moreover,the transverse-mode damping is more sensitive to the viscoelasticity model than its longitudinal counterpart.The 6-layer unit-cell LPF exhibits the lowest BG,ranging from 4.8 Hz to 6.5 Hz.

Dynamic Response of Foundations during Startup of High-Frequency Tunnel Equipment

The specialized equipment utilized in long-line tunnel engineering is evolving towards large-scale,multifunctional,and complex orientations.The vibration caused by the high-frequency units during regular operation is supported by the foundation of the units,and the magnitude of vibration and the operating frequency fluctuate in different engineering contexts,leading to variations in the dynamic response of the foundation.The high-frequency units yield significantly diverse outcomes under different startup conditions and times,resulting in failure to meet operational requirements,influencing the normal function of the tunnel,and causing harm to the foundation structure,personnel,and property in severe cases.This article formulates a finite element numerical computation model for solid elements using three-dimensional elastic body theory and integrates field measurements to substantiate and ascertain the crucial parameter configurations of the finite element model.By proposing a comprehensive startup timing function for high-frequency dynamic machines under different startup conditions,simulating the frequency andmagnitude variations during the startup process,and suggesting functions for changes in frequency and magnitude,a simulated startup schedule function for high-frequency machines is created through coupling.Taking into account the selection of the transient dynamic analysis step length,the dynamic response results for the lower dynamic foundation during its fundamental frequency crossing process are obtained.The validation checks if the structural magnitude surpasses the safety threshold during the critical phase of unit startup traversing the structural resonance region.The design recommendations for high-frequency units’dynamic foundations are provided,taking into account the startup process of the machine and ensuring the safe operation of the tunnel.

Performance of composite foundations with different load transfer platforms and substratum stiffness over silty clay

The semi-rigid pile-supported composite foundation is widely used in highway projects due to its effectiveness in increasing the bearing capacity and stability of foundations.It is crucial to understand the stress distribution across the embankment width and the behaviour of unreinforced foundations.Thus,five centrifuge tests were conducted to examine the bearing and deformation behaviours of NPRS(Non-Connected Piled Raft Systems)and GRPS(GeosyntheticReinforced Pile-Supported systems)with varying substratum stiffness,then a comparative analysis was conducted on embankment settlement,pressures underneath the embankments,and axial forces along the piles.The results indicated that greater substratum stiffness correlates with reduced settlement and deformation at various depths.Deformation occurring 5 meters from the embankment toe includes settlement in NPRS and upward movement in GRPS.The potential sliding surface is primarily located within the embankment in NPRS,whereas it may extend through both the embankment and foundation in GRPS.The pile-soil stress ratio and efficiency in NPRS are higher than in GRPS across the embankment.The axial force borne by end-bearing piles is significantly greater than that by floating piles.As the buried depth increases,the axial force in GRPS initially rises then declines,whereas in NPRS,it remains relatively constant within a certain range before decreasing.This study aids in assessing the applicability of composite foundations in complex railway environments and provides a reference for procedural measures under similar conditions.

Influence of Incomplete Soil Plugs on Bearing Capacities of Bucket Foundations in Clay

Due to the uneven seabed and heaving of soil during pumping,incomplete soil plugs may occur during the installation of bucket foundations,and the impacts on the bearing capacities of bucket foundations need to be evaluated.In this paper,the contact ratio(the ratio of the top diameter of the soil plug to the diameter of the bucket)and the soil plug ratio(the ratio of the soil heave height to the skirt height)are defined to describe the shape and size of the incomplete soil plug.Then,finite element models are established to investigate the bearing capacities of bucket foundations with incomplete soil plugs and the influences of the contact ratios,and the soil plug ratios on the bearing capacities are analyzed.The results show that the vertical bearing capacity of bucket foundations in homogeneous soil continuously improves with the increase of the contact ratio.However,in normally consolidated soil,the vertical bearing capacity barely changes when the contact ratio is smaller than 0.75,while the bearing capacity suddenly increases when the contact ratio increases to 1 due to the change of failure mode.The contact ratio hardly affects the horizontal bearing capacity of bucket foundations.Moreover,the moment bearing capacity improves with the increase of the contact ratio for small aspect ratios,but hardly varies with increasing contact ratio for aspect ratios larger than 0.5.Consequently,the reduction coefficient method is proposed based on this analysis to calculate the bearing capacities of bucket foundations considering the influence of incomplete soil plugs.The comparison results show that the proposed reduction coefficient method can be used to evaluate the influences of incomplete soil plug on the bearing capacities of bucket foundations.

Local Scour Mechanisms and Prediction Methods Around Offshore Wind Turbine Foundations:Insights and Future Directions

Local scour around offshore wind turbine foundations presents a considerable challenge due to its potential influence on structural stability,driven by hydrodynamic forces.While research has made strides in comprehending scouring mechanisms,notable complexities persist,specifically with newer foundation types.Addressing these limitations is vital for advancing our understanding of scour mechanisms and for improving mitigation strategies in offshore wind energy development.This review synthesizes current findings on local scour across various offshore foundations,encompassing field observations,data-driven approaches,turbulence-sediment interactions,scour evolution processes,influencing factors,and numerical model advancements.The objective is to enrich our understanding of local scour mechanisms.In addition,future research directions are outlined,including the development of robust arti-ficial intelligence models for accurate predictions,the exploration of vortex structure characteristics,and the refinement of numerical models to strengthen prediction capabilities while minimizing computational efforts.

Design Optimization of a Lattice Tower: Structure and Foundations

Produced in power plants, electrical energy is transported to places of consumption via the electricity network. At the heart of this network are the supports that allow electricity to be efficiently transported over long distances, guaranteeing the security and supply of energy to the various centers of use. In the construction of a line, supports occupy an important part in terms of safety and construction cost. It is therefore essential to optimize their use to reduce the cost of transmission lines. This work addresses this problem, which focuses on the optimal utilization of X-lattice towers in the construction of overhead power lines. The challenge is to reconcile the search for optimal cost and respect for the design, resistance and service constraints of the structure. To do this, a parameter having a strong correlation with the weight, foundation and construction cost of the X-lattice tower for 161 kV lines is determined as an important cost variable. This parameter is the wheelbase of the towers. The junction point between the structure and the foundations is obtained by measuring the forces at the base of the tower following the lowering of the loads. These efforts make it possible to size foundations which are of the inverted or isolated sole type. The results obtained reveal that from 8 meters in width, the wheelbase gradually changes until the optimum is obtained at 6.29 meters. With this wheelbase, the production cost is optimal. It clearly emerges from this study that the construction of lattice pylons with a wheelbase of approximately 6.29 meters makes it possible to optimize the cost of construction of 161 kV lines in the Republic of Benin.

Estimation of Undrained Bearing Capacity for Offshore Soft Foundations with Cyclic Load

The degradation strength of soils under cyclic loading is studied and a method for determining the cyclic degradation strength with cyclic triaxial tests is given in the paper. Furthermore, a dum my static method for estimating the undrained bearing capacity for offshore soft foundation under wave loads is developed. It can consider the effect of the difference of cyclic stress for different parts of the foundation on both the degradation strength of the foundation soil and the bearing capacity so that the estimated result can better reflect the real condition of foundation under cyclic loading. The method can be applied to plane and space problem.

Influence of vertical loads on lateral response of pile foundations in sands and clays

Although the load applied to pile foundations is usually a combination of vertical and lateral components,there have been few investigations on the behavior of piles subjected to combined loadings.Those few studies led to inconsistent results with regard to the effects of vertical loads on the lateral response of piles.A series of three-dimensional(3D) finite differences analyses is conducted to evaluate the influence of vertical loads on the lateral performance of pile foundations.Three idealized sandy and clayey soil profiles are considered:a homogeneous soil layer,a layer with modulus proportional to depth,and two-layered strata.The pile material is modeled as linearly elastic,while the soil is idealized using the Mohr-Coulomb constitutive model with a non-associated flow rule.In order to confirm the findings of this study,soils in some cases are further modeled using more sophisticated models(i.e.CYsoil model for sandy soils and modified Cam-Clay(MCC) model for clayey soils).Numerical results showed that the lateral resistance of the piles does not appear to vary considerably with the vertical load in sandy soil especially at the loosest state.However,the presence of a vertical load on a pile embedded in homogeneous or inhomogeneous clay is detrimental to its lateral capacity,and it is unconservative to design piles in clays assuming that there is no interaction between vertical and lateral loads.Moreover,the current results indicate that the effect of vertical loads on the lateral response of piles embedded in twolayered strata depends on the characteristics of soil not only surrounding the piles but also located beneath their tips.

Transverse free vibration analysis of a tapered Timoshenko beam on visco-Pasternak foundations using the interpolating matrix method

The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the eff ects of the Winkler coeffi cient, Pasternak coeffi cient and damping coeffi cient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary diff erential equations with variable coeffi cients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verifi ed through two numerical examples. The infl uences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with diff erent taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam.

Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

Windows Presentation Foundations的项目部署和性能优化

针对Windows Presentation Foundation（WPF）这一全新的Windows应用程序的图形引擎技术,该文简要介绍了WPF的基本知识,并针对WPF的优缺点,通过个人的项目开发经历,讨论和总结在实际WPF应用程序项目中会遇到的界面开发代码结构设计和应用程序性能两大问题。该文主要研究如何合理部署WPF应用程序前台界面开发的代码结构;以及如何正确处理WPF应用程序的性能问题。

Study of vibrating foundations considering soil-pile-structure interaction for practical applications

An investigation of soil-pile-structure interaction is carried out, based on a large reciprocating compressor installed on an elevated concrete foundation （table top structure）. A practical method is described for the dynamic analysis, and compared with a 3D finite element （FE） model. Two commercial software packages are used for dynamic analysis considering the soilpile-structure interaction （SPSI）. Stiffness and damping of the pile foundation are generated from a computer program, and then input into the FE model. To examine the SPSI thoroughly, three cases for the soil, piles and superstructure are considered and compared. In the first case, the interaction is fully taken into account, that is, both the superstructure and soil-pile system are flexible. In the second case, the superstructure is flexible but fixed to a rigid base, with no deformation in the base （no SSI）. In the third case, the dynamic soil-pile interaction is taken into account, but the table top structure is assumed to be rigid. From the comparison beteen the results of these three cases some conclusions are made, which could be helpful for engineering practice.

NONLINEAR RESPONSES OF A FLUID-CONVEYING PIPE EMBEDDED IN NONLINEAR ELASTIC FOUNDATIONS

The nonlinear responses of planar motions of a fluid-conveying pipe embedded in nonlinear elastic foundations are investigated via the differential quadrature method discretization （DQMD） of the governing partial differential equation. For the analytical model, the effect of the nonlinear elastic foundation is modeled by a nonlinear restraining force. By using an iterative algorithm, a set of ordinary differential dynamical equations derived from the equation of motion of the system are solved numerically and then the bifurcations are analyzed. The numerical results, in which the existence of chaos is demonstrated, are presented in the form of phase portraits of the oscillations. The intermittency transition to chaos has been found to arise.

State-of-the-art review of some artificial intelligence applications in pile foundations

Geotechnical engineering deals with materials（e.g. soil and rock） that, by their very nature, exhibit varied and uncertain behavior due to the imprecise physical processes associated with the formation of these materials. Modeling the behavior of such materials in geotechnical engineering applications is complex and sometimes beyond the ability of most traditional forms of physically-based engineering methods. Artificial intelligence（AI） is becoming more popular and particularly amenable to modeling the complex behavior of most geotechnical engineering applications because it has demonstrated superior predictive ability compared to traditional methods. This paper provides state-of-the-art review of some selected AI techniques and their applications in pile foundations, and presents the salient features associated with the modeling development of these AI techniques. The paper also discusses the strength and limitations of the selected AI techniques compared to other available modeling approaches.

Numerical simulation on behavior of pile foundations under cyclic axial loads

On the basis of the two dimensional finite element analysis model, the pile foundations' mechanical effect of the rigid pile composite foundation under the dynamic load was researched. Through the research, the development law and deformation property of axial force of pile body, shaft resistance of pile, and cumulative settlement of pile head under vertical cyclic dynamic loads were concluded. Through the comparison and analysis of the test results of dynamic models, the test results of Poulos(1989) and cumulative settlement model of the single pile under cyclic loads were confirmed. Based on the above research, Fortran language was adopted to introduce the soil attenuation factor, the secondary development of relevant modules of ABAQUS was carried out, and the effect of soil attenuation factor on dynamic property of pile-soil was discussed further.

Simplified approach for design of raft foundations against fault rupture.Part II:soil-structure interaction

This is the second paper of two, which describe the results of an integrated research effort to develop a four-step simplified approach for design of raft foundations against dip-slip （normal and thrust） fault rupture. The first two steps dealing with fault rupture propagation in the free-field were presented in the companion paper. This paper develops an approximate analytical method to analyze soil-foundation-structure interaction （SFSI）, involving two additional phenomena： （i） fault rupture diversion （Step 3）; and （ii） modification of the vertical displacement profile （Step 4）. For the first phenomenon （Step 3）, an approximate energy-based approach is developed to estimate the diversion of a fault rupture due to presence of a raft foundation. The normalized critical load for complete diversion is shown to be a function of soil strength, coefficient of earth pressure at rest, bedrock depth, and the horizontal position of the foundation relative to the outcropping fault rupture. For the second phenomenon （Step 4）, a heuristic approach is proposed, which ＂scans＂ through possible equilibrium positions to detect the one that best satisfies force and moment equilibrium. Thus, we account for the strong geometric nonlinearities that govern this interaction, such as uplifting and second order （P-△） effects. Comparisons with centrifuge-validated finite element analyses demonstrate the efficacy of the method. Its simplicity makes possible its utilization for preliminary design.

Empirical methods for determining shaft bearing capacity of semi-deep foundations socketed in rocks

Semi-deep foundations socketed in rocks are considered to be a viable option for the foundations in the presence of heavy load imposed by high-rise structures, due to the low settlement and high bearing capacity. In the optimum design of semi-deep foundations, prediction of the shaft bearing capacity, rs, of foundations socketed in rocks is thus critically important. In this study, the unconfined compressive strength(UCS), qu, has been applied in order to investigate the shaft bearing capacity. For this, a database of 106 full-scale load tests is compiled with UCS values of surrounding rocks, in which 34 tests with rock quality designation(RQD), and 5 tests with rock mass rating(RMR). The bearing rocks for semi-deep foundations include limestone, mudstone, siltstone, shale, granite, tuff, granodiorite, claystone, sandstone, phyllite, schist, and greywacke. Using the database, the applicability and accuracy of the existing empirical methods are evaluated and new relations are derived between the shaft bearing capacity and UCS based on the types of rocks. Moreover, a general equation in case of unknown rock types is proposed and it is verified by another set of data. Since rock-socketed shafts are supported by rock mass(not intact rock), a reduction factor for the compressive strength is suggested and verified in which the effect of discontinuities is considered using the modified UCS, qu(modified), based upon RMR and RQD in order to take into account the effect of the rock mass properties.

Lateral response of pile foundations in liquefiable soils

Liquefaction has b e e n a m ain cause o f dam ag e to civil en g in eerin g stru ctu res in seism ically active areas.The effects o f dam ag e o f liquefaction o n d eep foundations are v ery d estructive. Seism ic beh av io r o f pilefoundations is w idely discussed by m any researchers for safer an d m ore econom ic design purposes. Thisp a p e r p resen ts a p se u d o -static m eth o d for analysis o f piles in liquefiable soil u n d e r seism ic loads. A freefieldsite resp o n se analysis using th ree-d im en sio n al （3D） num erical m odeling w as p erfo rm ed to d e te rmine kin em atic loads from lateral g ro u n d disp lacem en ts an d inertial loads from vib ratio n o f th e supe rstru ctu re . The effects o f various p aram eters, such as soil layering, k in em atic and inertial forces,b o u n d ary con d itio n o f pile h ead an d gro u n d slope, o n pile resp o n se w e re studied. By com paring th enum erical results w ith th e centrifuge te s t results, it can be concluded th a t th e use o f th e p-y curves w ithvarious d eg rad atio n factors in liquefiable sand gives reasonable results.