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1.
Experimental investigations are carried out on wave-induced pressures and uplift forces on a submarine pipeline (exposed, half buried and fully buried) in clayey soil of different consistency index both in regular and random waves. A study on scour under the pipeline resting on the clay bed is also carried out. It is found that the uplift force can be reduced by about 70%, if the pipeline is just buried in clay soil. The equilibrium scour depth below the pipeline is estimated as 42% of the pipe diameter for consistency index of 0.17 and is 34% of the pipe diameter for consistency index of 0.23. The results of the present investigations are compared with the results on sandy soil by Cheng and Liu (Appl. Ocean Res., 8(1986) 22) to acknowledge the benefit of cohesive soil in reducing the high pore pressure on buried pipeline compared to cohesionless soil. 相似文献
2.
The wave pressure and uplift force due to random waves on a submarine pipeline (resting on bed, partially buried and fully buried) in clayey soil are measured. The influence of various parameters viz., wave period, wave height, water depth, burial depth and consistency index of the soil on wave pressures around and uplift force on the submarine pipeline was investigated. The wave pressures were measured at three locations around the submarine pipeline (each at 120° to the adjacent one). It is found that the wave pressure and uplift force spectrum at high consistency index of the soil is smaller compared to that of low consistency index. Just burying the pipeline (e/D=1.0) in clayey soil reduces the uplift force to less than 60% of the force experienced by a pipeline resting on the seabed (e/D=0.0) for Ic=0.33. 相似文献
3.
Wave-induced liquefaction in a porous seabed around submarine pipeline may cause catastrophic consequences such as large horizontal displacements of pipelines on the seabed, sinking or floatation of buried pipelines. Most previous studies in relation to the wave and seabed interactions with embedded pipeline dealt with the wave-induced instaneous seabed response and possible resulting momentary liquefaction (where the soil is liquefied instantaneously during the passage of a wave trough), using theory of poro-elasticity. Studies for the interactions between a buried pipeline and a soil undergoing build-up of pore pressure and residual liquefaction have been comparatively rare. In this paper, this complicated process was investigated by using a new developed integrated numerical model with RANS (Reynolds averaged Navier–Stokes) equations used for governing the incompressible flow in the wave field and Biot consolidation equations used for linking the solid–pore fluid interactions in a porous seabed with embedded pipeline. Regarding the wave-induced residual soil response, a two-dimensional poro-elastoplastic solution with the new definition of the source term was developed, where the pre-consolidation analysis of seabed foundation under gravitational forces including the body forces of a pipeline was incorporated. The proposed numerical model was verified with laboratory experiment to demonstrate its accuracy and effectiveness. The numerical results indicate that residual liquefaction is more likely to occur in the vicinity of the pipeline compared to that in the far-field. The inclusion of body forces of a pipeline in the pre-consolidation analysis of seabed foundation significantly affects the potential for residual liquefaction in the vicinity of the pipeline, especially for a shallow-embedded case. Parametric studies reveal that the gradients of maximum liquefaction depth with various wave and soil characteristics become steeper as pipeline burial depth decreases. 相似文献
4.
Experimental investigation on the wave-induced pore pressure around shallowly embedded pipelines 总被引：1，自引：1，他引：0
A series of regular wave experiments have been done in a large-scale wave flume to investigate the wave-induced pore pressure around the submarine shallowly embedded pipelines.The model pipelines are buried in three kinds of soils,including gravel,sand and silt with different burial depth.The input waves change with height and period.The results show that the amplitudes of wave-induced pore pressure increase as the wave period increase,and decay from the surface to the bottom of seabed.Higher pore pressures are recorded at the pipeline top and the lower pore pressures at the bottom,especially in the sand seabed.The normalized pressure around pipeline decreases as the relative water depth,burial depth or scattering parameters increase.For the silt seabed,the wavelet transform has been successfully used to analyze the signals of wave-induced pore pressure,and the oscillatory and residual pore pressure can be extracted by wavelet analysis.Higher oscillatory pressures are recorded at the bottom and the lower pressures at the top of the pipeline.However,higher residual pressures are recorded at the top and the lower pressures at the bottom of the pipeline. 相似文献
5.
海底滑坡作为常见的海洋地质灾害,对海洋油气工程安全产生巨大威胁。海床土体失稳引起滑坡体滑动,会对海底管道产生拖曳作用。基于计算流体动力学方法(CFD)建立海底滑坡体对管道作用的评估模型,采用H-B模型描述块状滑坡体并与试验比较验证,分析不同海床倾斜度滑坡对管道的作用并拟合表达式;研究了海底管道在滑坡作用下的力学响应,并采用极限状态方法开展海底滑坡作用下管道结构极限安全分析,探讨了管道埋地状态时的极限安全界限,建立滑坡作用下管道结构安全分析方法。研究表明:滑坡对管道作用力与海床倾角呈现正相关,而覆土层厚度对作用力影响较小;随着不排水抗剪强度的减小,允许的滑坡宽度和速度均增加,表明土体不排水抗剪强度与引起的拖曳力呈正相关;滑坡土体宽度对极限安全速度影响较大。 相似文献
6.
Effects of a cover layer on wave-induced pore pressure around a buried pipe in an anisotropic seabed 总被引：1，自引：0，他引：1
In engineering practice, a cover layer of coarser material has been used to protect a buried marine pipeline from wave-induced seabed instability. However, most previous investigations of the wave–seabed–pipe interaction problem have been concerned only with such a problem either in an isotropic single layer or a rigid pipe. This paper proposes a two-dimensional finite element model by employing the principle of repeatability to investigate the wave-induced soil response around a buried pipeline. The elastic anisotropic soil bahavior and geometry of cover layer are included in the present model, while the pipe is considered to be an elastic medium. This study focuses on the effects of a cover layer (including thickness B and width W of the cover layer) on the wave-induced pore pressure in the vicinity of a buried pipeline. 相似文献
7.
Submarine pipelines are always trenched within a seabed for reducing wave loads and thereby enhancing their stability. Based on Biot's poroelastic theory, a two-dimensional finite element model is developed to investigate non-linear wave-induced responses of soil around a trenched pipeline, which is verified with the flume test results by Sudhan et al. [Sudhan, C.M., Sundar, V., Rao, S.N., 2002. Wave induced forces around buried pipeline. Ocean Engineering, 29, 533–544] and Turcotte et al. [Turcotte, B.R., Liu, P.L.F., Kulhawy, F.H., 1984. Laboratory evaluation of wave tank parameters for wave-sediment interaction. Joseph H. Defree Hydraulic Laboratory Report 84-1, School of Civil and Environmental Engineering, Cornell University]. Non-linear wave-induced transient pore pressure around pipeline at various phases of wave loading is examined firstly. Unlike most previous investigations, in which only a single sediment layer and linear wave loading were concerned, in this study, the influences of the non-linearity of wave loading, the physical properties of backfill materials and the geometry profile of trenches on the excess pore pressures within the soil around pipeline, respectively, were explored, taking into account the in situ conditions of buried pipeline in the shallow ocean zones. Based on the parametric study, it is concluded that the shear modulus and permeability of backfill soils significantly affect the wave-induced excess pore pressures around trenched pipeline, and that the effect of wave non-linearity becomes more pronounced and comparable with that of trench depth, especially at high wave steepness in shallow water. 相似文献
8.
The stability of submarine pipelines has been extensively studied by coastal engineers in recent years. Seismic-induced pore pressure and effective stresses in the saturated porous seabed and pipeline are the main important factors in the analysis of foundation stability around submarine pipelines. The majority research of the seismic-induced dynamic response around an offshore pipeline has been limited to two-dimension cases. In this paper, a three-dimensional finite element model including buried pipeline is established by extending DYNE3WAC. Based on the proposed numerical model, a parametric study is conducted to examine the effects of soil characteristics and pipeline configurations on the seismic-induced soil response around offshore pipelines. 相似文献
9.
波浪作用下孔隙海床-管线动力相互作用分析 总被引：1，自引：0，他引：1
波浪作用下海床中的孔隙水压力与有效应力是影响海底管线稳定性的主要因素。然而,在目前的海床响应分析中一般将管线假定为刚性,并不能合理地考虑海床与管线之间的相互作用效应,同时也没有考虑土体和管线加速度对海床动力响应的惯性影响,从而无法确定由此所引起的管线内应力。为此考虑管线的柔性,分别采用饱和孔隙介质的Biot动力固结理论和弹性动力学理论列出了海床与管线的控制方程,进而采用摩擦接触理论考虑海床与管线之间的相互作用效应,基于有限元方法建立了海床-管线相互作用的计算模型及其数值算法。通过变动参数对比计算讨论了管线几何尺寸、海床土性参数对波浪所引起的管线周围海床孔隙水压力和管线内应力的影响。 相似文献
10.
《Coastal Engineering》1986,10(1):33-48
For the response of an undisturbed seabed to water waves there exists a number of solutions. Based on the concept of linear consolidation theory they all lead to the result that the pore pressure satisfies the Laplace equation, at least when incompressibility of the pore fluid is assumed. This suggests that the flow around an embedded object, e.g. a submarine pipeline, is also governed by the Laplace equation, either exactly or approximately. In this paper a number of such problems is solved using complex function theory and the technique of conformal mapping. The hydrodynamical force is calculated from the solution for the pore pressure. A good agreement is obtained with existing solutions. A comparison is also made with a numerical solution based on the finite-element method. It is concluded that the hydrodynamical force acting upon a submarine pipeline is about ten to thirty percent of the buoyancy of the pipe depending on the maximum wave load and the burial depth. 相似文献
11.
Submarine pipelines that transport crude oil and natural gas are often in a complex marine geological environment and may become unstable and fail upon impact by submarine landslides. Previous research has mostly focused on the impact forces exerted by submarine landslides on suspended pipelines, but the impact of submarine landslides on pipelines laid on the seafloor at various impact angles, θ, have been relatively infrequently discussed, and the effects of suspended height, H, on the impact forces exerted by submarine landslides on pipelines have not been thoroughly investigated. In this study, based on the Herschel–Bulkley model, the impact forces exerted by a submarine landslide on laid-on or suspended pipelines at various impact angles θ were simulated using the computational fluid dynamics (CFD) approach. Equations for calculating the axial and normal drag coefficients of a submarine pipeline were proposed. The CFD numerical simulation results were rearranged based on the soil mechanics approach. By comparing the parameters, an essentially corresponding relationship was found between the soil mechanics and CFD approaches when the equations were used to calculate the impact forces exerted by a submarine landslide on a pipeline. In addition, a semi-analytical expression for the failure envelope was provided. Furthermore, the effects of H on the forces on a pipeline were discussed, and an equation for calculating the acting forces on a pipeline along the flow direction of a submarine landslide that comprehensively accounts for the effects of θ and H was proposed. The lift force was discussed preliminarily and the results provide a basis for further investigation. The achievement of this study is applicable for selecting locations of submarine pipeline routes and for designing submarine pipelines. 相似文献
12.
波致海底缓倾角无限坡滑动稳定性计算分析探讨 总被引：1，自引：1，他引：0
波浪作用下海底无限坡滑动稳定性计算的极限平衡法中,忽略了坡体水平向应力状态的影响,为此,针对波浪作用下海底缓倾角无限边坡的特点,提出直接基于滑动面处土体应力状态的滑动稳定性计算方法(简称应力状态法),并分析了其适用范围。对具体算例的分析表明,应力状态法计算得出的安全系数大于极限平衡法的安全系数,且随着滑动面深度的增加、土体泊松比以及边坡坡角的增大,两种计算方法得出的安全系数的差异会逐渐增大;对于波浪作用下的海底缓倾角无限边坡,在失稳时极可能沿具有一定厚度的滑动带而不是单一的滑动面而滑动,且波致最大剪应力所在的深度,常常不是斜坡体最易失稳滑移的深度。 相似文献
13.
An experimental study of seabed responses around a marine pipeline under wave and current conditions 总被引：1，自引：0，他引：1
Experiments on three types of soil (d50=0.287, 0.057 and 0.034 mm) with pipeline(D=4 cm) either half buried or resting on the seabed under regular wave or combined with current actions were conducted in a large wave flume to investigate characteristics of soil responses. The pore pressures were measured through the soil depth and across the pipeline. When pipeline is present the measured pore pressures in sandy soil nearby the pipeline deviate considerably from that predicted by the poro-elasticity theory. The buried pipeline seems to provide a degree of resistance to soil liquefaction in the two finer soil seabeds. In the silt bed, a negative power relationship was found between maximum values of excess pore pressure pmax and test intervals under the same wave conditions due to soil densification and dissipation of the pore pressure. In the case of wave combined with current, pore pressures in sandy soil show slightly decrease with time, whereas in silt soil, the current causes an increase in the excess pore pressure build-up, especially at the deeper depth. Comparing liquefaction depth with scour depth underneath the pipeline indicates that the occurrence of liquefaction is accompanied with larger scour depth under the same pipeline-bed configuration. 相似文献
14.
Recently, the security and stability of submarine pipelines have attracted much attention in ocean engineering. In this paper, pipelines with a streamlined contour (wedge, airfoil, double-ellipse, and arc-angle hexagon) are designed in hopes of defending against the impact of submarine landslides, and the computational fluid dynamics (CFD) approach is used to investigate the interaction between submarine landslides and streamlined pipelines. The results show that the peak interactional force is more representative of the hazard level of pipelines imposed by submarine landslides. It is also found that the streamlined pipelines possess a significant advantage in reducing the drag force and lift force of landslide–pipeline interaction with a maximum lessening percentage of 66.32 and 40.17%, compared with a conventional circular pipeline. In addition, the influence of applying streamlined pipelines to engineering is briefly discussed, and the empirical equation for estimating the drag force and lift force of streamlined pipelines induced by landslides is recommended based on the numerical test results. 相似文献
15.
Most previous investigations related to composite breakwaters have focused on the wave forces acting on the structure itself from a hydrodynamic aspect. The foundational aspects of a composite breakwater under wave-induced cyclic loading are also important in studying the stability of a composite breakwater. In this study, numerical simulations were performed to investigate the wave-induced pore water pressure and flow changes inside the rubble mound of the composite breakwater and seabed foundation. The validity and applicability of the numerical model were demonstrated by comparing numerical results with existing experimental data. Moreover, the present model clearly has shown that the instantaneous directions of pore water flow motion inside the seabed induced by surface waves are in good agreement with the general wave-induced pore water flow inside the seabed. The model is further used to discuss the stability of a composite breakwater, i.e., the interaction among nonlinear waves, composite breakwater and seabed. Numerical results suggest that the stability of a composite breakwater is affected by not only downward shear flow generating on the seaward slope face of the rubble mound but, also, a high and dense pore water pressure gradient inside the rubble mound and seabed foundation. 相似文献
16.
《Coastal Engineering》2001,44(2):153-190
This paper summarizes the results of the European Union Marine Science and Technology (EU MAST) III project “Scour Around Coastal Structures” (SCARCOST). The summary is presented under three headings: (1) Introduction; (2) Flow and scour processes with the subheadings: flow and scour processes around vertical cylinders; flow and scour processes at detached breakwaters; flow and scour processes at submerged breakwaters; and the effect of turbulence on sediment transport; and (3) Sediment behaviour close to the structure with the subheadings: field measurement and analysis of wave-induced pore pressures and effective stresses around a bottom seated cylinder; non-linear soil modelling with respect to wave-induced pore pressures and gradients; wave-induced pressures on the bottom for non-linear coastal waves, including also wave kinematics; development of a numerical model (linear soil modelling) to calculate wave-induced pore pressures—the effect of liquefaction on sediment transport; penetration of blocks in non-consolidated fine soil; and cyclic stiffness of loose sand.The paper also includes a discussion of the role of scale effects in laboratory testing and the applicability of the results obtained in supporting engineering design. 相似文献
17.
18.
Wave-induced seabed instability in front of a breakwater 总被引：2，自引：0，他引：2
D.S. Jeng 《Ocean Engineering》1997,24(10):887-917
The wave-induced soil response in a porous seabed has become an important factor for the stability of offshore facilities, because many marine structures may have failed due to seabed instability and concomitant subsidence. An analytical solution is presented for the wave-induced soil response under the action of a three-dimensional wave system. Based on this general solution, the mechanism of seabed instability is then investigated. The general solutions for pore pressure and effective stresses are readily reducible to two dimensions for progressive waves, and are compared to theoretical and experimental work available. Some dominant factors affecting the wave-induced seabed instability are discussed; including permeability, seabed thickness and degree of saturation. 相似文献
19.
Wave interaction with a concentric porous cylinder system 总被引：1，自引：0，他引：1
This is a theoretical investigation of wave interaction with a concentric surface-piercing two-cylinder system. The exterior cylinder is porous and considered to be thin in thickness and the interior cylinder is impermeable. Both cylinders are rigidly fixed at the sea bed. The fluid motion is idealized as a linearized potential flow. The free-surface elevation and the total net hydrodynamic forces acting on both cylinders are determined analytically. The wave-induced overturning moments are also evaluated. It is found that, with the existence of the exterior porous cylinder, the hydrodynamic force acting on the interior cylinder is reduced if compared to the force exerted on the interior cylinder by a direct wave impact. The reduction of the wave amplitude around the leeward side of the outer porous cylinder is shown from the free-surface computations. In this paper, results are also presented to illustrate the effects of wave parameter and structural porosity on this wave and cylinder interaction problem. The role played by the ratio of radii of the inner and outer cylinders is duscussed. 相似文献
20.
Models based on the theoretical framework of soil mechanics are presented to evaluate storm wave-induced silty seabed instability and geo-hazards through a case study in the Yellow River delta. First, the transient and residual mechanisms of wave-induced pore pressure are analyzed. Three typical models (i.e., elastic model, pore pressure development mode and elasto-plastic model) are proposed to calculate wave-induced stresses in the seabed. Next, mechanisms and calculation methods of wave-induced seabed instability modes such as scour, liquefaction, seepage instability and shear slide are proposed. Typical results of storm wave-induced excess pore pressure and seabed instability are given and relevant discussions are made. At last, the formation mechanism of geo-hazards in the Yellow River delta is analyzed based on the proposed mechanism and calculated results. Results and analysis indicate that both transient and residual mechanisms are important to storm wave-induced response of silty seabed and hence the elasto-plastic model is more appropriate. Complete liquefaction does not happen, while other types of instability occur mostly within 2–6 m under the seabed surface. Wave-induced scour, seepage instability and shear slide are all possible instability modes under the 1-year storm waves, and scour is predominant for the 50-year storm waves. The formation mechanism of geo-hazards such as shallow slide and storm wave reactivation, pockmarks, silt flow and gully, disturbed stratum and hard crust in the Yellow River are well explained based on the proposed mechanisms and calculated results of storm wave-induced silty seabed instability. 相似文献