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1.
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
2.
Haixia Xu 《Ocean Engineering》2011,38(7):860-867
Seabed instability caused by soil liquefaction due to build-up of excess pore pressure within the sedimentary seabed represents a serious threat to coastal structures. Models of varying sophistication exist for predicting the liquefaction process but most previous calculations are limited to regular waves while the real waves are random. In this study, a numerical study of liquefaction potential of a sand bed under narrow-band random waves is carried out employing ensemble modelling techniques. The aim of the work is to investigate the effect of random waves on excess pore pressure build-up and liquefaction processes and study the probability distribution of the maximum liquefaction depth. The computational results using a 1D liquefaction model indicate that the random wave-induced liquefaction can be much deeper than that of the corresponding regular waves with the largest individual waves in the random wave time series playing a dominant role in determining the maximum liquefaction depth. It is also found that the time for the maximum liquefaction depth to be reached can vary considerably from one random wave series to another, which suggests that in random waves notable densification may occur within the same timeframe as that for liquefaction. 相似文献
3.
Wei-Yun Chen Guo-Xing Chen Chen-Cong Liao Hong-Mei Gao 《Marine Georesources & Geotechnology》2013,31(8):924-935
AbstractIn this paper, a 2D poro-elastoplastic model for wave-induced dynamic response in an anisotropic seabed is derived analytically. The seabed is treated as a porous medium and characterized by Biot’s consolidation equations. The soil plasticity and wave non-linearity are included in the model and both the pore fluid and the soil skeleton are assumed to be compressible. The nonlinear ocean waves are respectively considered as progressive and standing waves. The previous experimental data is used to validate the proposed model. Numerical results demonstrate that the influence of nonlinear wave components should not be ignored without committing substantial error. A significant difference between progressive and standing waves is also observed for the development of residual pore pressure, as well as the distribution of liquefied zone. A detailed parametric investigation reveals that the nonlinear wave-induced seabed response is also affected significantly by cross-anisotropic soil parameters. 相似文献
4.
The evaluation of the wave-induced liquefaction potential is particularly important for coastal engineers involved in the design of marine structures. Most previous investigations of the wave-induced liquefaction have been limited to two-dimensional non-breaking waves. In this paper, the integrated three-dimensional poro-elastic model for the wave-seabed interaction proposed by [Zhang, H., Jeng, D.-S., 2005. An integrated three-dimensional model of wave-induced pore pressure and effective stresses in a porous seabed: I. A sloping seabed. Ocean Engineering 32(5/6), 701–729.] is further extended to simulate the seabed liquefaction potential with breaking wave loading. Based on the parametric study, we conclude: (1) the liquefaction depth due to breaking waves is smaller than that of due to non-breaking waves; (2) the degree of saturation significantly affects the wave-induced liquefaction depth, and no liquefaction occurs in full saturated seabed, and (3) soil permeability does not only significantly affect the pore pressure, but also the shear stresses distribution. 相似文献
5.
近海区域广泛分布着第四纪新沉积的松散海洋土,波浪荷载作用下松散海床会发生液化进而对近海结构物的稳定性存在巨大威胁。本文采用中国科学院流体-结构-海床相互作用数值计算模型FSSI-CAS 2D,选用Pastor-Zienkiewicz-Mark Ⅲ（PZⅢ）弹塑性本构研究了波浪诱发的松散海床液化问题。分析了波浪荷载引起的松散海床内超孔隙水压力、有效应力以及应力角的时程变化特性,并预测了松散海床的渐进液化过程。计算结果表明,波浪荷载作用下松散海床内残余孔压会累积增长,海床表面最先发生液化,然后逐渐向下发展至液化最大深度。同时指出海床内超孔隙水压力的竖向分布特征和应力角的变化时程均可以作为判断海床液化的间接参数。最后,通过应力状态分析,讨论了海床渐进式液化的发展过程和趋势。 相似文献
6.
沙脊沙波泥沙数学模型的研究 总被引：1，自引：0，他引：1
在剪切水流条件下,基于水沙两相流动量方程,推导出描述海底沙脊沙波内在演变规律的基本方程。将此方程与二维浅水环流方程、波浪折射-绕射方程进行耦合,建立大范围海区平面二维波、流、泥沙数学模型,并结合海区实际观测水文地质、潮汐、波浪、泥沙资料进行模型验证。通过对比分析发现,数值模拟值与实测站位观测值二者吻合较好,表明了模型的可靠性。应用此模型对东方1-1气田穿越的大范围海底沙脊沙波在相应海动力条件下的移动规律及演变趋势进行定量预测,结果显示,随着时间的推移,沙脊沙波移动距离逐年递增,但发展变化趋势基本稳定。 相似文献
7.
Based on Biot＇s consolidation theory, a two-dimensional model for computation of the seabed response to waves is presented with the finite element method. Numerical results for different wave conditions are obtained, and the effects of wave non-lineafity on the wave-induced seabed response are examined. Moreover, the wave-induced momentary liquefaction in uniform and inhomogeneous seabeds is investigated. It is shown that the wave non-linearity affects the distribution of the wave-induced pore pressure and effective stresses, while the influence of wave non-linearity on the seabed liquefaction potential is not so significant. 相似文献
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10.
Response of a porous seabed around breakwater heads 总被引：1，自引：0，他引：1
The evaluation of wave-induced pore pressures and effective stresses in a porous seabed near a breakwater head is important for coastal engineers involved in the design of marine structures. Most previous studies have been limited to two-dimensional (2D) or three-dimensional (3D) cases in front of a breakwater. In this study, we focus on the problem near breakwater heads that consists of incident, reflected and diffracted waves. Both wave-induced oscillatory and residual liquefactions will be considered in our new models. The mistake in the previous work [Jeng, D.-S., 1996. Wave-induced liquefaction potential at the tip of a breakwater. Applied Ocean Research 18(5), 229–241] for oscillatory mechanism is corrected, while a new 3D boundary value problem describing residual mechanism is established. A parametric study is conducted to investigate the influences of several wave and soil parameters on wave-induced oscillatory and residual liquefactions around breakwater heads. 相似文献
11.
基于广义Biot动力理论和Longuet-Higgins线性叠加模型,构建波浪-海床-管线动态响应的有限元计算模型,求解随机波作用下,多层砂质海床中管线周围土体孔隙水压力和竖向有效应力的分布。采用基于超静孔隙水压力的液化判断准则,得出液化区的最大深度及横向范围,从而判断海床土体液化情况。考虑海洋波浪的随机性,将海床视为多孔介质,海床动态响应计算模型采用u-p模式,孔隙水压力和位移视为场变量。并考虑孔隙水的可压缩性、海床弹性变形、土体速度、土体加速度以及流体速度的影响,忽略孔隙流体惯性作用。参数研究表明:土体渗透系数、饱和度以及有效波高等参数对海床土体孔隙水压力、竖向有效应力和液化区域分布有显著影响。 相似文献
12.
The stability of a porous seabed under wave and current loadings is particularly important for engineers to design marine structures such as submarine pipelines, breakwaters, and offshore platform foundations. Most previous investigations of dynamic response of marine structures and seabed have only considered the influence of wave loading, but the important influence of current is ignored. Even if the influence of current is considered, the interaction mechanism of both loadings has not been clearly elaborated. Based on the Biot’s dynamic theory and combined two-dimensional nonlinear progressive wave and uniform current theory, the interaction mechanism of wave and current loadings and the influence of current on wave characteristic are analyzed by numerical computations. The influence of current velocity, different permeability, and stratification in seabed on the effective stresses and pore pressures of seabed is discussed in detail. Further, the stability of seabed is evaluated through the liquefaction analysis of seabed, which will provide important reference frames to improve the design and construction of marine structures. 相似文献
13.
大直径单桩基础是海上风电应用广泛的一种基础形式,严格控制桩基泥面处的位移是保证基础稳定和风机安全运营的关键因素.通过数值方法建立了单桩—海床的三维模型,将可以描述海洋砂土超固结性和结构性的弹塑性本构模型通过UMAT子程序嵌入有限元软件ABAQUS中,桩基承受的波浪荷载通过Morison方程进行计算模拟.针对无波浪荷载、仅作用于海床的波浪荷载、同时作用于桩基和海床的波浪荷载三种情况,分析了海床土的动力响应以及桩基的水平位移之间的差异,探讨了海床土体参数对桩基水平变形的影响.研究结果表明海床土体液化会导致桩基水平变形增加,海床土渗透性、超固结性、结构性对桩基水平位移影响显著,研究成果可为海上风电单桩基础的设计与运维提供参考. 相似文献
14.
In this study, a mathematical integrated model is developed to investigate the wave-induced sloping seabed response in the vicinity of breakwater. In the present model, the wave model is based on the Volume-Averaged/Reynolds Averaged Navier–Stokes (VARANS) equations, while Biot's consolidation equation is used to govern the soil model. The influence of turbulence fluctuations on the mean flow with respect to the complicated interaction between wave, sloping seabed and breakwater are obtained by solving the Volume-Averaged k − ϵ model. Unlike previous investigations, the phase-resolved absolute shear stress is used as the source of accumulation of residual pore pressure, which can link the oscillatory and residual mechanisms simultaneously. Based on the proposed model, parametric studies regarding the effects of wave and soil characteristics as well as bed slopes on the wave-induced soil response in the vicinity of breakwater are investigated. Numerical results indicate that wave-induced seabed instability is more likely to occur in a steep slope in the case of soil with low relative density and low permeability under large wave loadings. It is also found that, the permeability of breakwater significantly affect the potential for liquefaction, especially in the region below the breakwater. 相似文献
15.
C. C. Liao 《Marine Georesources & Geotechnology》2013,31(9):1149-1150
AbstractThe excess pore pressure accumulation is a key factor when estimating the formation mechanism of large pockmarks, as it determines the liquefaction potential of marine sediments due to water waves. The governing equations for excess pore pressure may have different forms for various types of sediments and then shall reflect the cyclic plasticity of the soil. For water waves propagating over a porous seabed, the liquefaction area induced by waves is generally progressive, which indicates that the liquefaction area will move forward following the wave train. Therefore, the excess pore pressure accumulation can be used to explain the occurrence of the large pockmarks, but the dimension of the pockmark may be related to the heterogeneity of sediment or the wave properties affected by the topography in the subaqueous Yellow River Delta. 相似文献
16.
He Guangna Cao Yalin
Professor Dalian University of Technology Dalian .
Former Postgruate Student Dalian University of Technology Dalian 《中国海洋工程》1995,(2)
Based on unified equivalent harmonic loading on seabed foundation and energy approach suggested by the authors, the development of dynamic pore water pressure and stability of soil foundation for the vibration of ocean gravity structures excited by random wave loading are analysed. It may be seen that the present method for the study of dynamic problems of ocean gravity structure soil foundations is more reasonable and convenient. 相似文献
17.
The multi-spring shear mechanism plastic model in this paper is defined in strain space to simulate pore pressure generation and development in sands under cyclic loading and undrained conditions,and the rotation of principal stresses can also be simulated by the model with cyclic behavior of anisotropic consolidated sands.Seismic residual deformations of typical caisson quay walls under different engineering situations are analyzed in detail by the plastic model,and then an index of liquefaction extent is applied to describe the regularity of seismic residual deformation of caisson quay wall top under different engineering situations.Some correlated prediction formulas are derived from the results of regression analysis between seismic residual deformation of quay wall top and extent of liquefaction in the relative safety backfill sand site.Finally,the rationality and the reliability of the prediction methods are validated by test results of a 120 g-centrifuge shaking table,and the comparisons show that some reliable seismic residual deformation of caisson quay can be predicted by appropriate prediction formulas and appropriate index of liquefaction extent. 相似文献
18.
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
19.
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
20.
The impact of wave loads and pore-water pressure generation on initiation of sediment transport 总被引：3，自引：0，他引：3
Edward C. Clukey Fred H. Kulhawy Philip L. -F. Liu George B. Tate 《Geo-Marine Letters》1985,5(3):177-183
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported. 相似文献