桩在饱和土中水平振动的辐射阻尼简化算法

将适用于单相土－桩系统的Novak的平面应变假设和Gazetas的分象限假设推广到饱和土－桩系统中。通过简化后的微分方程推导了饱和土－桩系统辐射阻尼系数的解析解答。最后用算例说明了饱和土中两个压缩波的特性，比较了饱和土和单相土的单位桩长辐射阻尼系数，比较了简化算法和三维有限元方法求得的桩头幅射阻尼比，结果证明简化算法在一定条件下适用于计算层饱和土－桩系统的辐射阻尼。     

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.     

Vertical dynamic response of a pipe pile in saturated soil layer

An analytical solution is developed in this paper to investigate the vertical time-harmonic response of a pipe pile embedded in a viscoelastic saturated soil layer. The wave propagation in the saturated soil is simulated by Biot’s 3D poroelastic theory and that in the pipe pile is simulated by 1D elastodynamic theory. Potential functions are applied to decouple the governing equations of the soil. The analytical solutions of the outer and inner soil in frequency domain are obtained by the method of separation of variables. The vertical response of the pipe pile is then obtained based on the continuity assumption of the displacement and stress between the pipe pile and both the outer and inner soil. The solution is compared with existing solutions to verify the validity. Numerical examples are presented to analyze the vibration characteristics of the pile.     

饱和软土中打入式预制桩单桩承载力的时效性

饱和软土中打入式预制桩承载力的时效性问题早已为学术界所共识,并已在工程实践中得到了验证。但对上海地区饱和软土层中的打入式预制桩的休止时间对单桩承载力的影响规律,尚待进一步研究。结合近期完成的一项实际工程的现场实测静载荷试验资料,对预制桩的静载荷试验的间歇时间问题进行了有益的探讨。饱和软土中的打入式预制桩,在沉桩两周后一定时间内,复压单桩极限承载力平均提高了将近单桩设计最大加载值的30％。     

饱和土坡降雨变形的数值模拟

基于Biot两相饱和多孔介质固结理论,采用有效应力有限单元法对降雨作用下饱和土质边坡的性状进行了数值模拟。对于土的本构行为,采用了一个可以考虑“松冈-中井破坏准则”的弹塑性模型来模拟。首先对降雨作用下边坡变形的数值分析方法进行了简要介绍。然后,应用这种方法,对一个边坡的工程实例进行了降雨变形分析。计算结果较好地描述了边坡降雨变形的发展情况,反映了降雨作用下边坡性状的基本特征,并得到了一些有益的结论。     

Application of a high-cycle accumulation model to the analysis of soil liquefaction around a vibrating pile toe

High residual pore pressure observed in the vicinity of piles driven in saturated soil indicates that the soil around the pile may be liquefied. In the present paper, the problem of deformation of saturated sand around a vibrating pile is formulated with the use of a high-cycle accumulation model capable of describing a large number of cycles. The problem is solved numerically for locally undrained conditions in spherically symmetric formulation suitable for the lower part of a cylindrical closed-ended pile near the toe. The aim of the study is to calculate the evolution of the liquefaction zone around the pile for a large number of cycles. A parametric study is carried out to show how the growth of the liquefaction zone depends on the pile displacement amplitude, the relative soil density, the effective stress in the far field and the pore fluid compressibility.     

饱和土中管桩的水平动阻抗研究

为了考察桩、土主要参数对饱和土中管桩水平振动的影响,将土体分为桩周饱和土和桩芯饱和土两部分,利用多孔介质理论的饱和土控制方程建立了饱和土-管桩的耦合振动模型。在考虑桩周饱和土和桩芯饱和土边界条件的情况下,运用势函数解耦的方法对桩周饱和土和桩芯饱和土的水平振动进行了求解。在考虑桩周饱和土和桩芯饱和土对管桩作用的情况下对饱和土中管桩的水平振动进行了求解,得到了管桩桩顶的水平动力阻抗,并分析了主要桩、土参数对管桩水平动力阻抗的影响。研究表明：管桩内外半径、桩周土和桩芯土剪切模量比、泊松比之比对管桩水平动力阻抗的影响较大,低频时液-固耦合系数比对管桩水平动力阻抗有一定的影响,而阻尼比之比对管桩水平动力阻抗阻尼因子有一定的影响。     

饱和黏弹性地基土中管桩纵向振动研究

用解析方法在频率域内研究考虑质量耦合效应的饱和黏弹性地基土中管桩的纵向振动特性。基于Biot理论,采用薄层法,推导得到饱和黏弹性地基土的位移、应力等的表达式。将管桩等效为一维弹性杆件处理。根据界面连续性条件,给出饱和黏弹性地基土中管桩的纵向振动一般分析方法和桩顶动力复刚度的表达式。在该基础上,对比分析饱和地基土中实心桩和管桩纵向振动特性。通过算例分析,考察桩周土和桩芯土的力学参数对桩顶刚度因子和等效阻尼的影响。研究表明,饱和黏弹性地基土中实心桩和管桩的纵向振动有明显的差异。     

Load transfer from an elastic pile to a saturated porous elastic soil

The quasi-static development of the force, pore pressure and displacement is obtained in the system of a circular elastic pile partially embedded in a saturated porous elastic soil, and loaded axially on the top. The porous elastic soil is governed by Biot's theory. The problem is decomposed into two systems, namely, an extended porous elastic half-space in the absence of the pile characterized by the material constants of the medium, and a fictitious pile represented by a Young's modulus equal to the difference between the Young's moduli of the real pile and the medium. The problem is found to be governed by a Fredholm integral equation of the second kind. Laplace transforms are applied to time functions involved, and Hankel transforms to the radial coordinate of which the origin is at the centre of the pile. Numerical solutions are obtained for final and initial solutions for various practical values of the parameters involved.     

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。     

饱和土中单桩融沉附加力的试验研究

为探讨人工冻结法施工不稳定含水表土层地下工程中的冻融灾害，通过物理模拟试验，研究了饱和土冻融过程中土层的融沉规律、土层对单桩产生的竖向融沉附加力变化规律，分析了土层性质及主要冻结参数对附加力的影响。研究表明，饱和冻土在融沉初期会产生明显的热胀效应：粘土、砂质粘土的融化固结速度明显低于砂土：最大融沉负摩擦力达3.012kPa：砂土的最大负摩擦力分别是粘土、砂质粘土的1.34和2.25倍：饱和冻土融沉的过程能对桩产生明显的工程灾害效应。     

基于虚土桩模型的三维饱和介质中浮承桩纵向振动特性分析

基于Biot波动理论提出了一种桩底饱和虚土桩模型,同时考虑桩周、桩底土体三维波动效应及饱和特性,建立了三维饱和黏弹性土、虚土桩和实体桩完全耦合振动定解问题。采用势函数求解得出饱和土体位移解,并利用饱和土-桩界面耦合条件,求解得出桩顶纵向振动动力阻抗解析解答。将所得解退化到已有解析解进行对比验证,并在此基础上对浮承桩纵向振动特性进行参数化分析,计算结果表明:桩底饱和土层厚度越大,桩顶动刚度和动阻尼曲线振幅及共振频率越小,且当桩底饱和土层厚度增大到一定程度后,振幅呈现大、小峰值交替现象;桩周饱和土体孔隙率仅对桩顶动力阻抗曲线振幅产生明显影响,而桩底饱和土体孔隙率对桩顶动力阻抗曲线共振幅值和共振频率均影响显著;随桩周、桩底饱和土体剪切模量的增加,桩顶动力阻抗曲线共振幅值水平均明显降低,且受桩周饱和土体剪切模量影响更为突出。     

分数导数模型描述的饱和土桩纵向振动分析

土体具有黏弹性性质,为了更好地考虑饱和土体固相土骨架的黏弹性性质,在分数导数理论和多孔介质理论的基础上,将土体视为液固饱和两相介质,并利用分数导数模型来描述饱和土固相土骨架的应力-应变关系,建立分数导数模型描述的饱和土的控制方程。在三维轴对称情况下,利用势函数和分离变量法研究了分数导数模型描述的饱和土中桩的振动问题。分析了模型参数对饱和土中桩的竖向振动的影响。研究表明,分数导数模型描述的饱和土的控制方程应用范围更广,模型参数对桩的竖向振动有较大的影响。     

基于土体三维波动模型的饱和土中管桩竖向振动

基于土体的三维波动模型研究了饱和土中单个管桩的竖向振动。将桩周土和桩芯土视为两相多孔介质,管桩视为等截面的圆管杆单元。在考虑桩周饱和土和桩芯饱和土径向位移和竖向位移的情况下,建立了基于土体三维波动模型的饱和土-管桩竖向耦合振动模型。借助势函数和分离变量法并考虑土体边界条件,求解了考虑土体三维波动的桩周饱和土和桩芯饱和土的竖向振动。在此基础上,考虑管桩桩端边界条件,利用三角函数正交性求解了饱和土中单个管桩的竖向振动,得到了管桩桩顶的竖向复刚度。通过数值算例,对比分析了土体三维波动模型解和不考虑土体径向位移的简化模型解的计算结果,分析了主要桩、土参数对饱和土中管桩竖向振动的影响。研究表明：当管桩壁较薄时且低频时不应忽略土体径向位移的影响,在动态刚度因子和等效阻尼随频率变化曲线峰值峰谷处不宜忽略土体液相的影响,管桩壁不宜过薄。管桩壁厚、长径比、桩芯饱和土与桩周饱和土密度比、剪切模量比以及桩-土模量比对饱和土中管桩竖向振动有较大影响,在进行管桩设计时需要综合考虑相关参数。     

Dynamic characteristics of a large‐diameter pile in saturated soil and its application

This study theoretically investigates the dynamic response of an end‐bearing pile embedded in saturated soil considering the transverse inertial effect of the pile. The saturated soil surrounding the pile is described by Biot poroelastic theory, and the pile is represented by a Rayleigh‐Love rod because both the vertical and radial displacements at the soil‐pile interface are considered. The potential function decomposition method and variable separation method are introduced to solve the governing equations of the soil, in which the vertical and radial displacement components are coupled. The governing equation of the pile is solved using the continuity conditions at the pile‐soil interface. Next, the velocity admittance in the frequency domain and the velocity response in the time domain at the pile top are presented based on the Laplace transform and inverse Fourier transform, respectively. Subsequently, the reduced solution is compared with a 1‐dimensional model solution to verify the validity, and the influences of the slenderness ratio of the pile on the transverse inertial effect of the pile are analyzed. Moreover, Poisson ratio, the slenderness ratio of the pile, and the pile‐soil modulus ratio are studied. Finally, the theoretical and measured curves in the engineering project are compared, and the results demonstrate the good application prospects of the solution presented in this article.     

基于相对变形方法的桩后土拱模型试验研究

为分析桩后土拱在滑动过程中的动态演化过程,设计了一种新型的土体相对变形监测系统,开展了物理模型试验和滑体强度参数分析试验,基于试验监测数据,引入了两个无量纲参数表征滑体相对变形程度和不均匀变形程度。试验结果表明：（1）基于桩后土拱变形与传递侧向力曲线特征,土拱演化可分为弹性形成阶段、塑性发展阶段和破坏阶段3个阶段。在破坏阶段观察到显著的三维破坏特征,在水平面上,土拱表现出成层的拱圈挤出破坏;在竖直面上,表现出中下部的滑体土率先开裂并塌落,然后在顶部出现悬链形状的裂缝。（2）随相对变形变化,桩后滑体强度参数在滑动过程中是处于一个动态的强化过程,就强化程度而言,黏聚力较内摩擦角更敏感。（3）前期相对靠后的滑体的相对变形程度与参数强化程度分别高于相对靠前的滑体和桩间滑体,因此,桩周滑体裂缝在向后发展过程中逐渐向桩间中心线发生偏转,在裂缝贯通后形成稳定支撑的拱形结构。     

Torsional dynamic response of a large‐diameter pipe pile in viscoelastic saturated soil

An analytical solution is developed in this paper to investigate the dynamic response of a large‐diameter end‐bearing pipe pile subjected to torsional loading in viscoelastic saturated soil. The wave propagation in saturated soil and pile are simulated by Biot's two‐phased linear theory and one‐dimensional elastic theory, respectively. The dynamic equilibrium equations of the outer soil, inner soil, and pile are established. The solutions for the outer and inner soils in frequency domain are obtained by Laplace transform technique and the separation of variables method. Then, the dynamic response of the pile is obtained on the basis of the perfect contacts between the pile and the outer soil as well as the inner soil. The results in this paper are compared with that of a solid pile in elastic saturated soil to verify the validity of the solution. Furthermore, the solution in this paper is compared with the classic plane strain solution to verify the solution further and check the accuracy of the plane strain solution. Numerical results are presented to analyze the vibration characteristics and illustrate the effect of the soil parameters and the geometry size of the pile on the complex impedance and velocity admittance of the pile head. Finally, the displacement of the soil at different depth and frequency is analyzed. Copyright © 2014 John Wiley & Sons, Ltd.     

考虑横向效应饱和黏弹性土层中桩的纵向振动

由于饱和土中土体颗粒与孔隙水的相互作用以及桩与土体的不同渗透率,饱和土体中桩基的力学行为与单相土中桩基力学行为有很大的差别。基于饱和多孔介质理论,考虑桩纵向振动时的横向变形及惯性效应,将桩等效为Rayleigh-Love杆,在频率域中研究了饱和黏弹性土层中端承桩纵向振动的动力特性,给出了饱和黏弹性土层和桩纵向振动时动力响应的解析解及桩头复刚度的解析表达式。通过数值计算,给出了桩头动刚度因子和阻尼随激励频率的响应,考察了饱和土物性参数、桩土模量比、桩长径比、泊松比等参数对桩头刚度因子和阻尼的影响。研究表明,对于大直径桩,当外载荷激励频率较大时桩横向效应对桩头刚度因子和阻尼有显著的影响     

基于薄层法的饱和土桩纵向振动研究

在饱和多孔介质理论的基础上,将桩周土体看作液固饱和两相介质,借助于Novak薄层理论得到了饱和土层的竖向动力阻抗,研究了饱和土中桩的纵向耦合振动,并对比分析了采用三维模型和薄层法的结果,验证了结果的正确性。分析讨论了桩土主要力学参数对饱和土-桩耦合体系动力行为的影响。研究结果表明,桩的长径比、桩土模量比等对饱和土桩耦合体系纵向振动的影响相对较大,而土的黏滞阻尼系数和液固耦合系数的影响相对较小。     

饱和黏性土蠕变变形试验研究

结合苏锡常地区地面沉降研究,用单向固结仪研究饱和黏性土在复杂荷载作用下的蠕变变形特征。试验土样取自苏锡常地区第2弱透水层。研究结果表明,在初次加载时黏性土具有明显的蠕变性,在双对数坐标中蠕变变形与时间呈直线关系,且直线斜率随荷载水平增大而减小,但在荷载水平达到一定值后斜率变化不大;在初次卸载时黏性土仍有明显的回弹蠕变,特别是在卸载水平较高时,卸载回弹蠕变变形与应力和时间的关系仍可用幂函数表示;在循环荷载作用下,加卸载达到变形稳定的时间随循环次数增加而减小。当循环荷载最大值小于土样的先期固结压力时,土样在2次加卸载循环后达到弹性变形状态;当循环荷载最大值等于土样的先期固结压力时,土样在5次加卸载循环后达到弹性变形状态。