波浪作用下斜坡上单桩周围海床孔隙水压力响应特性试验研究

单桩基础周围斜坡海床中的波致孔隙水压力响应与纯斜坡海床存在较大差异。为了解不同波高、波周期条件下,单桩基础周围波浪传播变形及其对斜坡海床孔压振荡响应的影响,在波浪水槽末端铺设了长6 m、坡度1∶16的斜坡砂床进行试验。通过改变桩身位置和波浪参数,测量斜坡段各处波面形态,采集单桩周围孔隙水压力,分析了桩身位置及波浪参数对斜坡海床孔压响应的影响。结果表明：相同入射波条件下,随距坡脚水平距离增加,波高、近底流速和桩周孔隙水压力幅值都随之增大;桩周孔隙水压力幅值分布规律为：桩前孔压幅值明显大于桩侧与桩后孔压幅值。当Keulegan-Carpenter数大于6时,随着波高和波周期增大,马蹄涡产生的负压区使得桩侧海床孔隙水压力与纯斜坡海床孔隙水压力差值迅速增加。     

波浪引起海床内部孔隙迁移试验研究

本文通过室内方形水槽开展了波浪荷载对孔隙迁移过程影响的试验研究。结果表明,对于松软土体,波浪荷载会导致土体发生剪切破坏形成滑动层,而孔隙水则会在累积孔压作用下沿着滑动层形成的孔隙发生迁移。波浪荷载导致土体内部孔隙迁移,其迁移过程受外界荷载以及土体性质影响显著。含气泡的孔隙会在波浪循环荷载过程中的负压作用和气体自身浮力作用的共同影响下发生迁移,循环荷载中的负压作用越强,含气泡的孔隙越容易发生迁移。孔隙向上迁移后会导致底部土体的密实度增加而上方土体的密实度下降。土体的松软程度会影响滑动面的形成,越松软的土体越容易形成滑动面。相比于密实土体,孔隙在滑动面中更容易发生迁移。     

沙质海床对波浪的响应及其稳定性研究的回顾

本文简要回顾了前人关于沙质海床在波浪作用下的响应，液化和稳定性等方面问题和研究状况。对各研究中所采用的计算模型、计算方法、应用范围以及存在的问题作了较为系统的评述。此外对各问题的最新研究成果也作了简要的介绍，最后讨论了该领域中有待于进一步研究的问题。     

波浪作用下孔隙海床-管线动力相互作用分析

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。     

波浪作用下沙床中的孔隙水压力响应模型实验研究

本文介绍了在波浪水槽中进行的波浪作用下沙床中的孔隙水压力量测实验，并给出和分析了部分实验数据，实验中的波浪采用和规则波和不规则波。沙床采用了均质沙床和分层沙床，同时对沙床上有直立墙的模型也进行了实验。     

波浪作用下粉土中的孔压响应及其在粉土海床稳定性评价中的应用

粉土在波浪等动荷载作用下极易发生液化破坏,而孔隙水压力在粉土动力学行为中扮演了一个很重要的角色,其发展变化会直接影响到土体的稳定性。因此,通过室内波浪作用下的粉土孔压响应模型试验探讨了孔压与波浪之间的响应情况,发现波浪能量的影响沿土层深度递减,水深条件相同时,响应的孔压随波高的增大而增加,当波浪作用足够长时间后粉土发生液化破坏,此时粉土内累积的孔压小于上覆土体的自重应力。根据结果提出了1种评价粉土海床稳定性的方法。     

浅水区波浪非线性效应对砂质海床动力响应的影响

以广义Biot动力固结理论为基础,运用一阶椭圆余弦波和二阶Stokes波等非线性波浪理论考虑浅水区波浪荷载的非线性效应,在时域上采用有限元方法对非线性波浪力作用下饱和砂质海床的动力响应进行了数值求解,并与线性波浪作用下海床动力响应特性进行了对比分析。结果表明,随着波长与水深之比L／d及无量纲参数T(g/d)^1/2的增大,非线性波浪对海床动力响应的影响增大。与线性波浪理论相比,孔隙水压力与有效应力幅值的增大效应非常显著。因此在近海海洋建筑物设计与工程场地评价中,波浪力的非线性特性必须引起注意。     

波浪作用下海床瞬态剪切破坏深度的计算分析

鉴于弹性本构模型的简便性,目前波浪作用下海床瞬态剪切破坏深度的计算一般都是基于海床的多孔弹性介质模型,这种方法不能考虑塑性单元不平衡应力的重分配,而如果将海床视为多孔理想弹塑性介质进行波浪作用下的瞬态响应分析,则可以克服上述缺陷。为此,以波浪作用下砂质、粉砂质海床瞬态响应模型为例,基于Mohr-Coulomb屈服准则,对不同海床计算参数条件下上述2种计算方法的结果进行了对比分析。结果表明,将海床视为多孔理想弹塑性介质时海床瞬态剪切破坏深度大于等于海床为多孔弹性介质时的计算结果;随着海床计算参数的变化,2种方法计算结果的变化趋势较为一致,且在砂质、粉砂质海床常见计算参数范围内,2种方法计算结果的差值在一个相对固定的范围内变化。     

波浪作用下海床的有效应力分析

波浪作用下海床的稳定性分析是海洋工程地质评价的重要内容。海床的稳定性可通过计算分析其随时间变化的有效应力场来评估。本文建议了一个周期荷载作用下土体的本构模型 ,并用于计算波浪作用下海床的应力与变形。采用Biot固结理论和有限单元法 ,分析了海床的动态应力场与孔隙水压力场。波浪作用下两种渗透系数时有效应力的动态变化过程结果对比 ,反映了渗透消散作用对海床有效应力变化的影响     

The Mechanism Analysis of Seafloor Silt Liquefaction Under Wave Loading

The sediment in Chengbei area of the Huanghe (Yellow River) subaqueous delta is the object of a reseach project in this article. The accumulating and dissipating effects following the change of time are considered first in the study area and the distributing curves of excess pore water pressure along with time and depth in the soil stratum are gained; the possibility of silt liquefaction is evaluated using the computing values and the affecting depth of liquefaction is given. This paper quantitatively analyzes the dynamic response of seafloor soil under the cyclic loading of waves and makes an inquiry into the instable mechanism of soil.     

Pore Water Pressure Buildup Under Cyclic Rotation of Principal Stress and Stability Evaluation of Seabed Deposit

- The cyclic rotation of principal stress direction with a constant amplitude is the characteristics of cyclic stress in seabed deposit induced by travelling waves. Presented in the paper are the results obtained from tests simulating the cyclic stress characteristics, with emphasis laid on the buildup of pore water pressure in soil samples. Regression analysis of test data shows that the pore water pressure can be expressed as the function of the number of cycles of cyclic loading, or as the function of generalized shear strain. Using the results thus obtained, the possibility of failure of seabed deposit under cyclic loading induced by travelling waves can be evaluated. The comparison with the results of conventional cyclic torsional shear tests shows that neglect of the effect of the cyclic rotation of the principal stress direction will result in considerable over-estimation of the stability of seabed deposit.     

A Coupling Model of Nonlinear Wave and Sandy Seabed Dynamic Interaction

In the paper,a weak coupling numerical model is developed for the study of the nonlinear dynamic interaction between water waves and permeable sandy seabed.The wave field solver is based on the VOF(Volume of Fluid)method for continuity equation and the two-dimensional Reynolds Averaged Navier Stokes(RANS)equations with a k-ε closure.The free surface of cnoidal wave is traced through the PLIC-VOF(Piecewise Linear Interface Construction).Biot's equations have been applied to solve the sandy seabed,and the u-p finite element formulations are derived by the application of the Galerkin weighted-residual procedure.The continuity of the pressure on the interface between fluid and porous medium domains is considered.Laboratory tests were performed to verify the proposed numerical model,and it is shown that the pore-water pressures and the wave heights computed by the VOF-FEM models are in good agreement with the experimental results.It is found that the proposed model is effective in predicting the seabed-nonlinear wave interaction and is able to handle the wave-breakwater-seabed interaction problem.     

Laboratory Study on the Hydraulic Conductivity and Pore Pressure of Sand-Silt Mixtures

The hydraulic conductivity plays a major role on the excess pore pressure generation during monotonic and cyclic loading of granular soils with fines. This paper aims to determine how much the hydraulic conductivity and pore pressure response of the sand-silt mixtures are affected by the percentage of fines and void ratio of the soil. The results of flexible wall permeameter and undrained monotonic triaxial tests performed on samples reconstituted from Chlef River sand with 0, 10, 20, 30, 40, and 50% nonplastic silt at an effective confining stress of 100 kPa and two relative densities (D_r = 20, and 91%) are presented and discussed. It was found that the pore pressure increases linearly with the increase of the fines content and logarithmically with the increase of the intergranular void ratio. The results obtained from this study reveal that the saturated hydraulic conductivity (k) of the sand mixed with 50% low plastic fines can be, on average, four orders of magnitude smaller than that of the clean sand. The results show also that the hydraulic conductivity decreases hyperbolically with the increase of the fines content and the intergranular void ratio.     

Numerical Simulation of Seabed Response and Liquefaction due to Nonlinear Waves

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.     

波浪作用下埕岛海域海底土液化分区

根据埕岛海域表层沉积物特征,结合该区的波浪实测资料推算的波浪要素,利用动三轴实验得到研究区土体在循环荷载作用下孔隙水压力的增长与振动次数的关系,计算研究区内海底土层的液化可能性和液化所需的时间,并根据土体在不同水深情况下达到液化所需的时间对研究海域进行了液化分区。结果显示,7-8 m等深线之间的海底土体由于受到波浪破碎作用的影响,最易发生液化,液化影响深度也最深,自该海域向近岸和远海,液化可能性降低;土层埋深为2.5 m以浅时,研究区大部分区域液化可能性为高,而到埋深为4 m时土层液化可能性明显降低。     

胜利油田浅海区域海底土层的液化判别方法分析

针对胜利油田海上石油勘探开发区(埕岛油田)的海底饱和粉土(砂土)液化判别问题,结合工程研究实例,对土层液化判别的各种方法进行对比分析,指出了当前各种方法的局限性和不足,为海底土层的液化判别分析提供了新思路。     

Characteristics of Pore Water Pressure of Saturated Silt Under Wave Loading

The characteristics of dynamic stress in the seabed under wave loading are constant principal stress and continuous rotation of the principal stress direction.Cyclic triaxial-torsional coupling shear tests were performed on saturated silt by the hollow cylinder apparatus under different relative densities,deviator stress ratios and vibration frequencies to study the development of pore water pressure of the saturated silt under wave loading.It was found that the development of pore water pressure follows the trend of "fast～steady～drastic".The turning point from fast to steady stage is not affected by relative density and deviator stress ratio.However,the turning point from steady to drastic stage relies on relative density and deviator stress ratio.The vibration cycle for the liquefaction of saturated silt decreases with increasing deviator stress ratio and increases with relative density.The vibration cycle for the liquefaction of the saturated silt increases with vibration frequency and reaches a peak value,after which it decreases with increasing vibration frequency for the relative density of 70%.But the vibration cycle for the liquefaction of saturated silt increases with vibration frequency for the relative density of 30%.The development of pore water pressure of the saturated silt is influenced by relative density and vibration frequency.     

Characteristics of Excess Pore Water Pressure of Nanjing Saturated Fine Sand Under the Interaction of Wave and Earthquake Loading

A stress path with continuous rotation of the principal stress direction and continuous alteration of amplitude of deviatoric stress difference under the interaction of wave and earthquake loading was proposed based on the characteristics of the stress path under wave and earthquake loading, respectively. Using a GDS dynamic hollow cylinder apparatus, a series of cyclic triaxial-torsional coupling shear tests were performed on Nanjing saturated fine sand via the stress path mentioned previously under different relative densities, effective initial confining pressures, plastic fines contents, and loading frequencies to study the development of excess pore water pressure (EPWP) of saturated sand under the interaction of wave and earthquake loading. It was found that the development of EPWP follows the trend of fast-steady-mutative-drastic, which is different from that under the cyclic triaxial test or wave loading. The number of cycles causing initial liquefaction (N_L) of saturated sand increases remarkably with relative densities. However, the relationships between N_L and effective initial confining pressures, plastic fines content, or loading frequencies are more complex.     

动荷载作用下海底粉土的孔压响应及其动强度

本文选用近海分布较广的粉土为研究对象 ,利用室内动三轴试验结果 ,找出动荷载作用下粉土的动应力应变关系 ,分析模拟波浪荷载作用下粉土中的孔压响应、临界循环次数 ,确定波浪作用下粉土的应力状态、破坏临界循环次数 ,判断不同深度处的粉土发生液化的可能性及发生液化所需要的时间 ;研究粉土在动荷载作用下的强度降低 ,为海上工程设计和施工提供科学依据。