上海深厚饱和覆盖土层的动力耦合地震反应分析

上海的第四纪沉积土层呈水平层状分布，市区的土层厚度约为270－290m，年平均地下水位0.5-0.7m。上海地区上覆深厚、饱和的沉积土层，对土层的地震反应特性具有重要的影响。基于动力耦合理论，将上海深厚饱和覆盖土层视为由固相和液相组成的两相饱和多孔介质，建立了能够反映上海土层深厚、饱和特点的地震反应计算模型。然后应用该模型，以El Centro,Taft，苏南和唐山地震波作为基岩输入加速度，对深度280m的上海深厚覆盖土层进行了动力耦合地震反应计算，并对加速度、振动孔隙水压力和地基震陷结果进行了分析。     

Parametric study on seismic ground response by finite element modelling

In this paper the results of 2D FE analyses of the seismic ground response of a clayey deposit, performed adopting linear visco-elastic and visco-elasto-plastic constitutive models, are presented. The viscous and linear elastic parameters are selected according to a novel calibration strategy, leading to FE results comparable to those obtained by 1D equivalent-linear visco-elastic frequency-domain analyses. The influence of plasticity on the numerical results is also investigated, with particular reference to the relation between the hysteretic and viscous damping effects. Finally, different boundary conditions, spatial discretisation and time integration parameters are considered and their role on the FE results discussed.     

Numerical simulation of mitigation for liquefaction-induced soil deformations in a sandy ground improved by cement grouting

This paper presents a numerical study of mitigation for liquefaction during earthquake loading. Analyses are carried out using an effective stress based, fully coupled, hybrid, finite element-finite differences approach. The sandy soil behavior is described by means of a cyclic elastoplastic constitutive model, which was developed within the framework of a nonlinear kinematic hardening rule. In theory, the philosophies of mitigation for liquefaction can be summarized as two main concepts, i.e. prevention of excess pore water pressure generation and reduction of liquefaction-induced deformations. This paper is primarily concerned with the latter approach to liquefaction mitigation. Firstly, the numerical method and the analytical procedure are briefly outlined. Subsequently, a case-history study, which includes a liquefaction mitigation technique of cement grouting for ground improvement of a sluice gate, is conducted to illustrate the effectiveness of liquefaction countermeasures. Special emphasis is given to the computed results of excess pore water pressures, displacements, and accelerations during the seismic excitation. Generally, the distinctive patterns of seismic response are accurately reproduced by the numerical simulation. The proposed numerical method is thus considered to capture the fundamental aspects of the problems investigated, and yields results for design purposes. From the results in the case, excess pore water pressures eventually reach fully liquefied state under the input earthquake loading and this cannot be prevented. However, liquefaction-induced lateral spreading of the foundation soils can be effectively reduced by the liquefaction mitigation techniques. An erratum to this article can be found at     

深厚土层流固多向地震全耦合动力响应分析

根据上海地区典型土层的力学特性,拟合得到简化亚塑性边界面模型的动力计算参数,同时考虑流、固耦合以及地震多向作用的耦合,以San Fernando1971年地震记录的加速度时程曲线为输入地震波,对上海280 m深典型地层的地震反应进行了分析,得到了有意义的结果。     

Seismic analysis of laterally loaded pile under influence of vertical loading using finite element method

An efficient analytical approach using the finite element (FE) method, is proposed to calculate the bending moment and deflection response of a single pile under the combined influence of lateral and axial compressive loading during an earthquake, in both saturated and dry homogenous soil, and in a typical layered soil. Applying a pseudo-static method, seismic loads are calculated using the maximum horizontal acceleration (MHA) obtained from a seismic ground response analysis and a lateral load coefficient (a) for both liquefying and non-liquefying soils. It is observed that for a pile having l/d ratio 40 and embedded in dry dense sand, the normalized moment and displacement increase when the input motion becomes more severe, as expected. Further increasing of a from 0.1 to 0.3 leads to increase in the normalized moment and displacement from 0.033 to 0.042, and 0.009 to 0.035, respectively. The validity of the proposed FE based solution for estimating seismic response of pile is also assessed through dynamic centrifuge test results.     

Simulation of the progressive failure of an embankment on soft soil

A pragmatic strain-softening constitutive model, which is based on Modified Cam Clay, was applied to the simulation of the progressive failure of an embankment constructed on a deposit of sensitive (strain-softening) clay in Saga, Japan. A comparison of the predictions for this case indicates that if softening is ignored, only relatively small deflections and consolidation settlements are predicted, especially after construction. In contrast, for the case where softening is included in the analysis, progressive failure within the clay induces large shear deformations and finally failure of the embankment is predicted. This comparison suggests that softening-induced progressive failure should be considered in the design of embankments on such soils, and the residual strength of the deposit may have an important influence on the overall factor of safety of the construction. Detailed analyses of predicted excess pore water pressures, shear strains and shear stress levels in the ground indicate that considering the strain-softening process: (a) is associated with the buildup of excess pore water pressure; (b) promotes strain localization; and (c) results generally in a larger zone of soil involved in the failure.     

黄河三角洲饱和地基土地震响应数值分析

根据黄河三角地区特殊土层的力学性质,以天津波水平向加速度时程曲线为输入地震波,在3 %,10 %和63 %三种超越概率情况下,对黄河三角洲20 m深度土层的地震反应进行数值分析,研究了孔压和动剪应力的变化。与室内动三轴试验得到的破坏孔压和动剪应力进行比较,判断土层的液化破坏情况。研究结果表明,在3 %超越概率下大部分地层均液化,在10 %超越概率下少部分地层被破坏,在63 %超越概率下大部分地层均不液化。采用破坏动剪应力比和破坏孔压比的判别结果相吻合。     

深埋地下结构静动力耦合响应分析的边界条件设置方法

针对深埋地下结构的荷载环境特点,提出了深埋地下结构静动力耦合计算过程中边界条件的合理设置方法。该方法通过构建边界上的力系来平衡计算区域的初始地应力,然后将该力系设置成阶跃函数形式的动荷载作用于边界,并与后续的动荷载共同作用。研究表明,一次完整的地下结构静动力耦合分析过程,边界条件必须经过变换设置才能得到合理的计算结果。另外,只要计算软件具有黏性边界条件设置功能就能准确地完成地下结构静动力耦合响应分析。算例分析显示,该边界条件设置方法精度和效率高,简单适用。     

城市垃圾填埋场的地震响应及稳定性分析

对典型构型填埋场的二维地震响应进行了详细计算,目的是考察不同强度地震动作用下填埋场的稳定性,评价影响填埋场稳定性的主要因素,及各因素之间的相对重要性。计算结果显示：（1）覆盖层的稳定性主要依赖于垃圾土的材料属性、填埋场高度、输入地震动的频谱特性、以及场地条件等参数;（2）衬垫层的稳定性取决于输入地震动的加速度峰值、卓越周期和填埋场的基本自振周期。     

次塑性模型及饱和砂土动力弹塑性响应分析

提出了一个新的次塑性模型并用试验作了初步验证,建议用异步交叉迭代显式差分有限元求解固液耦合动力弹塑性问题。利用次塑性模型以及动力固结有限元计算程序,对一简单饱和砂土地基的动力弹塑性响应进行了分析,取得了合理的结果。     

Seismic response of flexible cantilever retaining walls with dry backfill

Failure of retaining walls during earthquakes has occurred many times in the past. Although significant progress has been made in analysing the seismic response of rigid gravity type retaining walls, considerable difficulties still exist in the seismic-resistant design of the flexible cantilever type of retaining walls because of the complex nature of the dynamic soil–structure interaction. In this paper the seismic response of cantilever retaining walls with dry backfill is simulated using centrifuge modelling and numerical modelling. It is found that bending moments on the wall increased significantly during an earthquake. After the end of base shaking, the residual moment on the wall was significantly higher than the moment under static loading. The numerical simulation is able to model quite accurately the main characteristics of acceleration, bending moment, and displacement recorded in the centrifuge test.     

饱和土一维简谐响应解析解的求解和应用:I求解

对于饱和土一维简谐响应的u-w和u-p方程，通过消元分别将二阶微分方程组变为一个四阶的微分方程。求解此微分方程则得到一维简谐响应的通解。对于特定的边值问题，通过求解描述边界条件的线性方程组得到满足边界条件的解析解。此解析解可用于饱和土动力响应研究的诸多方面。     

Numerical and analytical investigation of compressional wave propagation in saturated soils

In geotechnical earthquake engineering, wave propagation plays a fundamental role in engineering applications related to the dynamic response of geotechnical structures and to site response analysis. However, current engineering practice is primarily concentrated on the investigation of shear wave propagation and the corresponding site response only to the horizontal components of the ground motion. Due to the repeated recent observations of strong vertical ground motions and compressional damage of engineering structures, there is an increasing need to carry out a comprehensive investigation of vertical site response and the associated compressional wave propagation, particularly when performing the seismic design for critical structures (e.g. nuclear power plants and high dams). Therefore, in this paper, the compressional wave propagation mechanism in saturated soils is investigated by employing hydro-mechanically (HM) coupled analytical and numerical methods. A HM analytical solution for compressional wave propagation is first studied based on Biot’s theory, which shows the existence of two types of compressional waves (fast and slow waves) and indicates that their characteristics (i.e. wave dispersion and attenuation) are highly dependent on some key geotechnical and seismic parameters (i.e. the permeability, soil stiffness and loading frequency). The subsequent HM Finite Element (FE) study reproduces the duality of compressional waves and identifies the dominant permeability ranges for the existence of the two waves. In particular the existence of the slow compression wave is observed for a range of permeability and loading frequency that is relevant for geotechnical earthquake engineering applications. In order to account for the effects of soil permeability on compressional dynamic soil behaviour and soil properties (i.e. P-wave velocities and damping ratios), the coupled consolidation analysis is therefore recommended as the only tool capable of accurately simulating the dynamic response of geotechnical structures to vertical ground motion at intermediate transient states between undrained and drained conditions.     

饱和土表面在水平集中荷载作用下的瞬态反应

分析了水平集中荷载作用在半空间饱和土表面时的瞬态问题。利用Laplace-Hankel变换对非轴对称Biot固结方程进行解耦，利用Laplace-Hankel数值逆变换得到半空间饱和土在时域内的数值解。退化到线弹性中的解与文献中的结果进行比较，验证了文中结果的正确性和数值逆变换的可靠性.可以用于研究地震工程中地震波的传播以及饱和土与结构之间相互作用等问题。     

Exact solution for the 1D transient response of saturated single-layer poroviscoelastic media

The basic equations for fluid-saturated porous media proposed by Biot are modified by replacing the classical linear elastic model of the solid skeleton with the Kelvin–Voigt model. Thus, the new theory can take into account the viscoelastic effect of the solid skeleton. After the establishment of appropriate boundary and initial conditions, a time-domain series solution for the transient response of a fluid-saturated single-layer poroviscoelastic medium is obtained by using the finite Fourier transform and the corresponding analytical inverse transform. Several numerical examples are provided to illustrate the validity of the exact solution and to investigate the influence of the viscosity coefficient, permeability coefficient, and load frequency on the transient response of a fluid-saturated single-layer poroviscoelastic medium.     

How the response spectrum of non-liquefied loose-to-medium sand deposits is affected by the groundwater level

This study examines the water level influence on the seismic response of sand deposits. The seismic ground response of a sand deposit for two cases was computed: groundwater level near the surface and at great depth. The ratio of soil factors computed for both cases evaluates the influence of having the water table near the surface. This parameter is small when the full range of periods is considered, but rises to ∼1.15 when narrowing the range of periods to 0.2–0.6 s, corresponding to the plateau of Eurocode 8 ground type C response spectrum. So, the water level effect is of the same magnitude of the existing soil factor in seismic codes.     

Lateral dynamic response of a pipe pile in saturated soil layer

This paper presents an analytical solution for the lateral dynamic response of a pipe pile in a saturated soil layer. The wave propagations in the saturated soil and the pipe pile are simulated by Biot's three‐dimensional poroelastic theory and one‐dimensional elastic theory, respectively. The governing equations of soil are solved directly without introducing potential functions. The displacement response and dynamic impedances of the pipe pile are obtained based on the continuous conditions between the pipe pile and both the outer and inner soil. A comparison with an existing solution is performed to verify the proposed solution. Selected numerical results for the lateral dynamic responses and impedances of the pipe pile are presented to reveal the lateral vibration characteristics of the pile‐soil system. Copyright © 2015 John Wiley & Sons, Ltd.     

饱和土中单桩水平瞬态响应研究

基于Biot动力固结方程,应用Novak薄层方法研究了饱和土中单桩在水平冲击荷载作用下的动力响应问题。首先引入势函数对方程解耦,再通过算子分解和分离变量法,结合初始边界条件,并联立桩基振动微分方程,推导了Laplace变换域内桩身位移函数及内力表达式。采用Laplace逆变换的优化模型求得了时域内瞬态响应的封闭解。将该解退化到单相介质条件下的桩顶位移-时间曲线与已有的边界元方法的结果基本吻合,验证了解答的正确性。参数分析结果表明：桩-土模量比、长径比、渗透系数对桩身位移均影响显著,而同条件下长径比超过一特定值后则影响较小,且桩土模量比是影响桩身弯矩大小及其分布的重要参数。     

饱和土地下源u-P形式解答动力响应计算

一直以来,由Biot孔隙弹性动力方程得到的饱和土地下源Green函数都是u-w形式（u为固相介质位移,w为流相相对于固相的平均位移）。应用两相介质纵波解耦理论,得到了饱和土半空间地下点源荷载的u-P形式（P为孔压）Green函数频域解答;克服了u-w形式Green函数在边界元（BEM）积分时的增根影响。再由Hankel反演,结合Somigliana表象积分,完成BEM计算。并以计算结果分析了地下集中力作用时,饱和土位移、孔压、排水量等动力特性,这对地铁等交通工程、地震工程、土-结构动力相互作用（SSI）的响应计算都具有较重要应用价值。