随机波浪作用下海床动力响应及液化的理论分析

运用随机波浪理论,基于广义Biot动力固结理论,建立了能够考虑波浪荷载随机特性影响的计算海床动力响应及液化深度的解析数值模型,并从时域上进行求解分析.通过与传统线性规则波浪荷载作用下海床动力响应及液化深度的数值结果的对比分析,详细讨论了考虑波浪荷载的随机特性对于求解海床动力响应及液化深度的影响程度.结果表明,根据随机波浪理论计算得到的海床中的超孔隙水压力、水平有效应力、竖向有效应力、剪应力表现出较强的不规则性,其幅值沿着海床深度方向的变化趋势与根据线性规则波浪理论计算得到结果的变化趋势基本相同,但在同数量级上更大,同时计算得到的海床最大液化深度明显大于根据线性规则波浪理论计算得到的结果.因此,在海洋地基设计和自由场地安全评估时应该合理地考虑波浪荷载的随机特性.     

粉质海床波浪响应的数值模拟及试验研究

针对波浪荷载作用下粉质海床的动力响应问题,结合波浪槽模型试验研究的结果,提出了一种粉质海床在波浪作用下超静孔隙水压力增长的数值分析方法。计算结果表明：该方法能较好地拟合试验数据,揭示粉质海床孔隙水压力发展的机理,能运用于海床液化势的评价分析。     

Short-crested wave-induced soil response in a porous seabed of infinite thickness

Waves reflecting obliquely from structures establish short-crested waves which are conducive to scour of the bed adjacent to them. The pore pressures and effective stresses induced by this wave system are derived analytically for an unsaturated, anisotropic soil matrix of infinite depth in a three-dimensional domain. Verification is available by the solutions being readily reduced to the two-dimensional cases of the progressive and standing wave, for which some closed-form solutions are available. It is shown that wave obliquity is coupled with soil permeability. The effects of wave obliquity, relative water depth, soil stiffness and soil permeability on wave-induced pore pressure are discussed in detail.     

波浪作用下黄河三角洲粉质土海床动力响应分析

应用饱和土动力固结理论和Pastor-Zienkiewicz III动力本构关系,对波浪作用下黄河三角洲粉质土海床的动力响应特征进行了有限元分析,应用总超孔压准则对海床进行了液化判别,并将计算结果与现场观测资料进行对比。结果表明：波浪导致的海床超孔压由瞬态孔压和累积孔压两部分组成;相比均质海床,拥有表面硬层的海床瞬态孔压沿深度衰减更快,累积孔压在表层增长速度更大;不同波浪条件下,瞬态孔压值及其变化趋势较为一致,累积孔压则具有较大的不同。年平均波浪条件下海床不会发生液化;5 a和50 a一遇极端波浪条件下,考虑三维效应和具有表面硬层的海床更容易液化,最大液化深度在海床表面以下2～3 m范围内。计算所得的海床最大液化深度与实测的黄河三角洲海底灾害地貌深度有较好的一致性,表明了文中方法的有效性和合理性。     

Effects of principal stress rotation on wave-induced soil response in a poro-elastoplastic sandy seabed

In this study, a constitutive model is developed in order to investigate wave–seabed interactions. This model takes into account the impact of principal stress rotation (PSR) and is based on the generalized plasticity theory, in which plastic strain generated by PSR is considered an additional item in the constitutive relationship of soil. The normalized loading direction and plastic flow direction were determined based on the stress tensor invariant. Comparisons between the present model and previous Hollow Cylinder Apparatus tests and geotechnical centrifugal wave tests show good agreement. Numerical results show the effects of PSR on predictions of liquefaction potential due to: (a) the cumulative impact of plastic strain in the seafloor and (b) the buildup of pore pressure. Parametric study shows that the model parameters, including the wave and seabed parameters, have significant effects on the wave-induced soil liquefaction.

     

近海欠密实砂质海床内波致渐进液化特征研究

利用一个经过广泛验证的数值模型FSSI-CAS 2D为计算工具,采用砂土的高级本构模型Pastor-Zienkiewicz-Mark III (PZIII) 描述海床砂土的动态力学行为,定量研究松散海床地基土在波浪作用下,其内部的液化过程和特征,以加深对波致海床液化特征、性质的认识。计算结果分析表明,开发的耦合数值模型FSSI-CAS 2D能够很好地捕捉到波浪作用下欠密实海床的动力响应特征,以及海床内的累积液化过程等一些列的非线性物理现象。研究表明,波浪导致的松砂海床液化是一个渐进过程,海床表面首先液化,并逐渐向下扩展。     

A semi-analytical solution for the transient response of one-dimensional unsaturated single-layer poroviscoelastic media

This paper develops a semi-analytical solution for the transient response of an unsaturated single-layer poroviscoelastic medium with two immiscible fluids by using the Laplace transformation and the state-space method. Using the elastic–viscoelastic correspondence principle, we first introduce the Kelvin–Voigt model into Zienkiewicz’s unsaturated poroelastic model. The vibrational response for unsaturated porous material can be obtained by combining these two models and assuming that the wetting and non-wetting fluids are compressible, the solid skeleton and solid particles are viscoelastic, and the inertial and mechanical couplings are taken into account. The Laplace transformation and state-space method are used to solve the basic equations with the associated initial and boundary conditions, and the analytical solution in the Laplace domain is developed. To evaluate the responses in the time domain, Durbin’s numerical inverse Laplace transform method is used to obtain the semi-analytical solution. There are three compressional waves in porous media with two immiscible fluids. Moreover, to observe the three compressional waves clearly, we assume the two immiscible fluids are water and oil. Finally, several examples are provided to show the validity of the semi-analytical solution and to assess the influences of the viscosity coefficients and dynamic permeability coefficients on the behavior of the three compressional waves.     

板-复合地基动力分析半解析元法

将复合地基视为横观各向同性材料,利用半解析数值方法的基本原理分析板-复合地基动力相互作用问题,克服有限元法中人为设定计算边界的弊端,提高了计算精度,并将三维问题转化为一维问题计算,显著减少了计算工作量。通过改变复合地基置换率、加固深度和桩土模量比,研究了板-复合地基体系动力特性的变化规律。计算结果表明,增大加固深度、置换率和桩土模量比对系统频率和振幅均有影响,并使频率有一定的提高,动力基础设计时,应注意复合地基置入对基础动力特性改变的影响。     

单层非饱和多孔介质一维瞬态响应半解析解

基于Zienkiewicz提出的非饱和多孔介质波动理论,考虑两相流体和固体颗粒的压缩性以及惯性、黏滞和机械耦合作用,采用半解析的方法获得了一类典型边界条件下单层非饱和多孔介质一维瞬态响应解。首先推导出无量纲化后以位移表示的控制方程,并将其写成矩阵形式;然后,将边界条件齐次化,求解控制方程所对应的特征值问题,得到了满足齐次边界条件的特征值和相对应的特征函数。根据变异系数法并利用特征函数的正交性,得到了一系列仅黏滞耦合的关于时间的二阶常微分方程及相应的初始条件。在此基础上,运用精细时程积分法给出了常微分方程组的数值解。最后,通过若干算例验证了结果的正确性并探讨了单层非饱和多孔介质一维瞬态动力响应的特点。该方法可推广应用于其他典型的边界条件。     

波浪导致黄河口海床沉积物超孔压响应现场试验研究

黄河口海床特殊的工程地质性质与复杂的工程动力稳定性问题,均与海床沉积物在波浪荷载作用下的孔压动力响应密切相关。在现代黄河水下三角洲潮间带岸滩选择4个典型研究点,现场模拟波浪作用对原状海床沉积物实施循环加载,利用孔隙水压力观测、沉积物强度测试、样品采集与实验室土工测试等方法手段,测定黄河口原状海床沉积物在循环荷载作用不同阶段的孔压响应与强度变化。研究发现,黄河口原状海床沉积物在经历循环加载过程中,典型的超孔压响应可分为逐渐累积、部分消散、快速累积、累积液化和完全消散5个阶段,分别对应沉积物强度的衰减、增大、衰减、丧失和恢复过程,沉积物的粒度组成与结构性强弱决定了超孔压的具体响应模式。波浪导致原状海床液化深度受沉积物的干密度、孔隙比、饱和度等初始物理性质影响显著,细颗粒组分的相对含量高低也在很大程度上控制着沉积物的液化特性。     

非线性波浪作用下海底管线-海床动力响应分析

确定波浪荷载作用下海底埋置管线和海床的响应是海底管线设计中的关键问题。目前大多数研究只是考虑了管线、海床在线性推进波作用下的响应,并没有考虑管线与海床之间的相互作用效应。采用接触摩擦理论,考虑管线与海床之间的相互作用效应,基于有限元方法研究了非线性波浪作用下海底埋置管线和多孔海床相互作用问题。数值计算结果表明,在计算中如果忽略波浪非线性项,既有可能低估海底管线内应力及管线周围海床中孔隙水压力,也有可能高估海底管线内应力及管线周围海床中孔隙水压力。     

A semi-analytical solution for swelling around a borehole

Previous field and laboratory studies have shown that the creation of a borehole in a saturated cohesive soil mass induces significant pore water suctions in the vicinity of the hole. The dissipation of these pore water suctions (swelling) leads to local increases in the moisture content and hence a softening of the soil around the hole. This softening may have important consequences for the stability of the hole and also for the ultimate load capacity of any foundation elements (bored piles or drilled shafts) constructed in these holes. This paper presents a semi-analytical solution for the radial dissipation of pore water pressure around a freshly created, vertical hole. It is assumed the soil deforms elastically during the swelling process. The solutions are presented in the form of isochrones of excess pore water pressure and may be used to obtain estimates of the time required for the soil around the hole to swell and therefore to soften. Both permeable and impermeable borehole interfaces have been considered, together with either no support for the hole or partial support provided by hydrostatic pressure within the hole.     

强震作用下松散海床地基的动力响应

海上和沿海区域砂性土地基在强震作用下需同时考虑液化、震陷以及流滑效应。选用杨朝晖叠套屈服面模型,提出了获取计算参数的简化方法,用OpenSees验证了该模型模拟液化的能力;开发了OpenSees与ANSYS的接口,对处于强震地区、地基土为松散砂性土的印尼某进水明渠堤坝进行了非线性有限元动力计算,判断了场地的液化情况,预测了堤坝及地基的震陷量和侧向流滑,计算结果对该类地基的加固处理具有一定的指导意义     

A semi-analytical solution procedure for predicting damage evolution at interfaces

A semi-analytical solution procedure is developed to predict damage evolution at the interface between two dissimilar geologic materials. The procedure consists of an analytical field solution within each finite element, and a numerical scheme for simulating structural responses. For static problems, an incrementaliterative solution strategy is constructed through the use of an initial elasticity stiffness matrix, and an evolving-localization constraint in terms of a suitable measure of damage at the most severely damaged element. For simplicity, one-dimensional problems are considered to illustrate the features of the proposed procedure, and future research is discussed based on the preliminary results obtained.     

分布热源作用下单裂隙岩体三维水流-传热的半解析计算方法

针对高放射性核废物地下处置库近场饱和裂隙岩体环境,提出一种由分布热源、饱和单裂隙和两侧无限大岩石构成的三维水流-传热简化模型,建立了控制微分方程和基于拉氏变换域格林函数的积分方程;采用矩形单元把裂隙面域离散化,利用极坐标下的解析方法计算包含奇点的单元积分,利用数值方法计算分布热源和不包含奇点的单元积分,建立拉氏变换域的线性代数方程组,求解后,利用拉氏数值逆变换,计算任意时刻裂隙水和岩石的温度分布。对两个无内热源、流场确定的计算模型进行了计算,与仅考虑岩石沿裂隙面法向一维热传导的解析解进行了对比。计算分析了分布热源作用下饱和单裂隙岩体的三维水流-传热特征及其对裂隙水流速、岩石热传导系数和热源热流集度的敏感度。计算结果表明：与直接采用高斯数值积分相比,提出的解析法奇异积分精度较高;就裂隙水温度而言,单裂隙岩体三维水流-传热半解析计算方法与解析法得到的结果基本一致,但由于半解析计算方法考虑了岩石的三维热传导,使得裂隙水的上游温度较低,而下游温度较高;无分布热源作用时,岩石热传导系数越大,裂隙水温度越低;裂隙水流速越大,裂隙进水温度对裂隙水和岩石温度分布的影响越明显;由于受到裂隙水流动传热的作用,分布热源对裂隙水温度和岩石温度的影响在裂隙水流的下游区域比较显著。     

Oscillatory soil response and liquefaction in an unsaturated layered seabed

The subject of wave-induced soil response in a real seabed has attracted the attention of geotechnical and coastal engineers over the last three decades, for which several basic theories have been developed. However, the evaluation of soil liquefaction has not been attempted theoretically in a seabed with multiple sub-layers, in which homogeneity in soil properties can be assumed within each layer. In this study, a semi-analytical approach is presented for obtaining solutions for the pore pressure and effective stresses in a non-cohesive layered seabed of finite thickness subject to a system of three-dimensional waves. Based on the numerical results for a layered seabed, influences of soil characteristics (relative layer thickness, permeability ratio and shear modulus) on seabed responses are described. Special attention is given to the effect of placing a coarser material as a top layer for protecting an underlayer of finer sediment. Although only a three-layered seabed is explicitly solved in this study, the procedure outlined can readily be extended to a multi-layered soil system. The three-dimensional solutions can also be applied to the two-dimensional progressive or standing wave systems.     

A semi-analytical solution for saltwater intrusion with a very narrow transition zone

The Henry saltwater intrusion problem provides a semi-analytical solution that is largely used for benchmarking density-dependent groundwater flow models. The major drawback of this problem arises from the high dispersion value used by Henry (represented by the dimensionless parameter b?=?0.1). Finding a stable semi-analytical solution for small values of b is challenging due to the low convergence of the corresponding nonlinear system. In this work, an accurate semi-analytical solution is developed in the case of a very narrow transition zone corresponding to b?=?0.005. About 6,330 terms are used in the Fourier series to accurately represent the solution. The resolution of the corresponding highly nonlinear system is made possible by the modified Powell hybrid algorithm due to the analytical evaluation of the Jacobian, which drastically reduces the computational time. The new test problem is also investigated numerically using different numerical methods and different mesh sizes to show its high worthiness, compared to the standard Henry problem, for benchmarking density driven flow codes.     

Wave-induced soil response in an unsaturated anisotropic seabed of finite thickness

An analytical solution for the wave-induced soil response is developed for a seabed of finite thickness subject to a three-dimensional (3-D) wave system produced by two intersecting waves of equal properties. These 3-D exact solutions for the pore pressure and effective stresses, proposed for a non-cohesive soil matrix of finite depth in a homogeneously unsaturated and anisotropic condition, are readily reducible to the limiting two-dimensional cases of progressive and standing waves, for which no explicit solutions are available for finite thickness. The effects of soil isotropy, degree of saturation, seabed thickness and grain size on the wave-induced pore pressure are discussed in detail. The explicit solutions presented in this study for the wave-induced pore pressure and effective stresses should benefit the laboratory experiments and field monitoring programs carried out in soil of finite depth.     

Tide-induced hydraulic response in a semi-infinite seabed with a subaqueous drained tunnel

In this study, analytical solutions for tide-induced pore pressure, seepage force and water inflow into a subaqueous drained tunnel are developed. The results are compared with numerical solutions from a commercial software. The effects of the soil permeability, shear modulus, lining thickness and buried depth of the tunnel on tide-induced pore pressure, seepage force and water inflow are discussed. Larger tide-induced pore pressure and seepage force are obtained for smaller tunnel depth and higher soil permeability. The phase lags of the maximal tide-induced pore pressure at different depths are determined and investigated.     

地下结构对渗流场阻隔问题的解析~半解析法

针对当前地下空间开发引起的地下水渗流场变化量化评价需要,本文就渗流场受地下结构阻隔后的稳定流状态下的流量及各部位(上游段、阻隔段和下游段)的水位计算公式进行了探讨,分别导出了上、下阻隔两种情况下的承压水问题的解析解和潜水问题的半解析解,并利用数值试验直观解释了一些阻隔现象,以及获得了小水力梯度条件下潜水问题半解析解可以用同条件下的承压水问题解析解来近似的结论。