真空排水预压下土体变形的应力路径分析

通过室内试验, 对真空排水预压下土体变形特性进行了应力路径分析, 测定软土地基在真空预压加固后应力路径的改变对沉降量的影响, 论证真空排水预压加固软土地基不能消除其剪应力引起的剪切变形, 结合实例, 计算其后期沉降量与固结沉降量的比值, 并推算软土地基在真空预压下其最终沉降量计算公式的修正系数。     

饱和土–隧道动力响应的2.5维有限元–边界元耦合模型

针对饱和土中异形隧道的三维动力响应问题,建立了2.5维有限元与边界元耦合模型.将隧道结构视为弹性体,采用2.5维有限元建立隧道模型;将地基土视为饱和多孔介质,采用2.5维边界元建立饱和土体模型.借助组合辅助问题基本解消除了边界积分方程的奇异性.利用饱和土与隧道接触面的位移、面力连续和完全透水或完全不透水边界条件,实现2.5维有限元和边界元模型的耦合求解.模型具有计算效率高、适用范围广的优点.通过与完全透水和完全不透水边界条件下轴对称问题的半解析解以及单相介质的2.5维有限元与边界元耦合模型对比,验证了本文模型的正确性.最后利用该模型计算了饱和土体中类矩形隧道在移动载荷作用下的三维动力响应,分析了不同土体渗透性下位移及孔隙水压力沿隧道轴向、环向和深度的分布规律.结果表明:(1)孔隙水压力随土体渗透性增大而显著减小,位移受土体渗透性影响小;(2)位移及孔隙水压力在隧道环向主要分布在距载荷作用点两侧约2 m的范围内;(3)孔隙水压力沿深度的衰减比土体位移快,且孔隙水压力和轴向位移沿深度的分布受土体渗透性影响大.     

流变性地层基坑开挖过程中土体长时位移预测

软土基坑开挖更易导致施工事故的发生,因此有必要对该类基坑施工过程进行变形预测分析。本文引入改进的Singh-Mitchell蠕变模型及土体位移时效系数概念,提出了利用三轴流变试验数据和三维FEM模拟瞬时结果的软土基坑开挖过程中土体长时位移预测方法并给出了计算步骤。以宁波地铁车站基坑施工为案例,预测了土体长时水平位移和分层沉降量,并与现场监测结果进行了比较分析。结果表明,模型预测值与监测结果趋势一致。     

某软土深基坑工程时间效应有限元分析

软土地区的深基坑因土体的固结作用和流变性而具有了时间效应。本文以Biot固结有限元法为基础,用三元件模型中的第一个线性弹簧模拟固结作用,弹性模量考虑了开挖应力路径和应力历史的影响;另外一部分(KELVIN模型)来模拟土体的流变性,以实际变形的反演来得到两个参数的大致取值,再对基坑的变形情况以及进一步开挖进行分析。假定为正常固结饱和粘土,平面应变问题。通过对某饱和软粘土地基深基坑开挖工程实例的分析,得到的挡墙水平位移曲线与实测曲线很吻合,表明程序较好地反映出基坑的时间效应。     

考虑次固结的软土地基一维非线性固结理论

将软黏土变形分为有效应力变化引起的变形和次固结引起的变形,推导了软土新型应力应变关系。然后结合Davis固结理论,建立了考虑次固结的一维非线性固结控制方程,并对其进行解析求解。通过与数值方法对比,验证了解析解的可靠性。在此基础上,分析了次固结对软土地基固结沉降的影响。结果表明:考虑次固结的孔压消散速度与固结速度较不考虑次固结的慢;忽略次固结将低估软黏土地基的工后沉降。     

欧拉描述的大变形固结理论

以往大变形固结理论主要基于一般的固体力学模型,其控制方程忽视了固结过程中排水引起 的质量变化. 提出饱和土的连续介质模型,并基于连续介质力学的公理体系推导了反映质量 变化的欧拉描述的大变形固结控制方程. 发现传统固结理论中：(1)忽视了渗流速度对土体平衡条件的影响;(2)决定土体平衡的总应力张量只有在土体变形速度和渗流速度方向相同时才具有对称性等. 在忽略变质量效应等条件下,传统理论成为本文理论的特例. 通过算例 的有限元分析,比较了欧拉描述与两种物质描述方法的差别,得到初步结论：(1)欧拉描述 方法计算的地基沉降量要小于物质描述方法的结果;(2)欧拉描述方法计算的侧向位移偏大 于两种物质描述结果.     

考虑横向拉伸影响的FGM板的静态分析

在三阶剪切变形理论的基础上,添加关于厚度坐标z的幂函数项,并假设板结构的上下表面剪切力为0,提出了一种考虑横向拉伸影响的高阶剪切变形理论。并且研究了简支边界条件下受静态载荷作用的功能梯度材料矩形板的静态弯曲行为。基于虚功原理推导出了功能梯度矩形板的基本方程,利用Navier双三角级数法计算了功能梯度材料矩形板在静态载荷作用下沿厚度方向的位移及应力分布的数值结果。计算结果与三维精确解理论、其他高阶剪切变形理论得到的数值结果进行了比较。对比结果表明,改进的考虑横向拉伸影响的高阶剪切变形理论的正确性和优越性。     

基于物理中面FGM简支梁的弯曲行为

基于一阶非线性梁理论,利用物理中面概念导出了FGM梁的基本方程,分析了热载荷作用下简支FGM梁的弯曲行为.当坐标面置于功能梯度材料(FGM)梁的物理中面上时,其本构方程中,面内力与弯矩并不耦合,使得问题的控制方程以及边界条件得以简化.分析中假设功能梯度材料性质只沿梁厚度方向、并按成分含量的幂指数形式变化;利用打靶法数值地求解了所得方程.数值结果表明:热载荷作用下,夹紧FGM梁发生过屈曲变形,而简支梁则发生较为复杂的热弯曲变形;在同一热载荷作用下,简支FGM梁将会产生三种构形问题;剪切变形对夹紧FGM梁的热变形影响比简支梁更明显.     

ONE-DIMENSIONAL NONLINEAR CONSOLIDATION THEORY FOR SOFT GROUND WITH CONSIDERATION OF SECONDARY CONSOLIDATION1)

将软黏土变形分为有效应力变化引起的变形和次固结引起的变形,推导了软土新型应力应变关系。然后结合Davis固结理论,建立了考虑次固结的一维非线性固结控制方程,并对其进行解析求解。通过与数值方法对比,验证了解析解的可靠性。在此基础上,分析了次固结对软土地基固结沉降的影响。结果表明：考虑次固结的孔压消散速度与固结速度较不考虑次固结的慢;忽略次固结将低估软黏土地基的工后沉降。     

离心模型试验边界效应分析

通过对模型土进行加卸载的离心模型试验，分析边界摩擦力对土体变形的影响。由试验可以得到土层表面的弹性变形曲线，根据模型土体的位移边界条件，假设土层的位移函数，运用最小势能原理，求出边界磨擦力的大小，以及离心机加载过程中，在惯性力场和边界摩擦力作用下，模型土体的位移计算公式。通过试验和计算认为，在离心模型试验中，边界摩擦力对粘性土体的位移场有很大影响，应采取一定的措施减小摩擦力。     

平面应变 Biot 固结的解析层元

提出用解析层元法有效地解决任意深度单层土的平面应变 Biot 固结问题. 从 Biot 固结问题的控制方程出发, 采用特征值法在 Laplace-Fourier 变换域内推导出一个精确对称的解析层元刚度矩阵. 通过表示单层土广义力和广义位移之间关系的解析层元, 并结合土层的边界条件, 推导出土层任意点的解答; 物理域内的真实解可以通过 Laplace-Fourier 数值逆变换进一步获得. 通过数值计算验证理论的正确性, 研究了土层性质及时间因素对固结的影响.}      

圆球土样Biot固结的级数解

给出了圆球土样Biot固结的封闭级数解，该解由满足非齐次边界条件的弹力学角与满足齐次边界条件的渗注 动态解的叠加构成，通过算例，探讨了圆球土样的Biot固结规律和影响Manadel-Cryer效应的因素。     

Plane strain consolidation of a multi-layered soil with anisotrpic permeability and compressible constituents

对多层地基的平面应变固结问题进行了研究,并同时考虑了土体的渗透各向异性和孔隙 流体的可压缩性. 从平面应变Biot固结的控制方程出发,对时间t, 坐标z和x进行 Laplace和Fourier变换,建立了地基表面(z=0)和任意深度z处的基本量 在Laplace-Fourier变换域内的传递矩阵关系. 利用传递矩阵 法,结合土层连续条件和边界条件,并应用Laplace-Fourier逆变换技术,推导出渗透各向 异性可压缩多层地基平面应变固结的理论解. 基于该解,编制了计算程序,并进行了 数值计算. 讨论了土体的渗透各向异性、孔隙流体的可压缩性以及地基的分层特性对地基固 结的影响,分析结果表明：土体的渗透各向异性、孔隙流体的可压缩性,以及地基的分层特 性对地基的固结行为有着重要的影响.     

BIOT’S CONSOLIDATION ANALYSIS FOR CYLINDRICAL SOIL-SAMPLE BASED ON HANSBO’S FLOW1)

诸多黏性土渗流试验表明,在低水力梯度下渗流会出现明显偏离Darcy定律的现象. 为了分析渗流的非Darcy特性对固结过程 的影响,引入Hansbo渗流方程描述圆柱土样内的渗流,重新推导轴对称条件下的Biot固结方程,并给出方程的Crank--Nicolson有限 差分格式. 通过与Darcy渗流条件下轴对称Biot固结方程解析解的对比,验证计算方法的有效性. 然后分析Hansbo模型参数对圆柱 土样固结过程的影响. 计算结果表明：与Darcy渗流相比,Hansbo渗流会延缓圆柱土样的固结过程. 随着Hansbo渗流参数m或I¹的增大,在固结前期,Mandel--Cryer效应会更加显著,即孔隙水压力峰值将提高,且达到该峰值的时间 会延迟;在固结中后期,孔压消散滞后的现象也更加明显. 不过,Hansbo渗流对位移的影响很小.     

Finite and transversely isotropic elastic cylinders under compression with end constraint induced by friction

This paper derives an exact solution for the non-uniform stress and displacement fields within a finite, transversely isotropic, and linear elastic cylinder under compression with a kind of radial constraint induced by friction between the end surfaces of the cylinder and the loading platens. The main feature of the present work is the introduction of a general solution form for Lekhnitskii’s stress function such that the governing equation and all end and curved boundary conditions of the cylinder are satisfied exactly. Two different solutions were obtained corresponding to the real or complex characteristic roots of the governing equation, depending on the combination of the elastic material constants. The solution by Watanabe [Watanabe, S., 1996. Elastic analysis of axi-symmetric finite cylinder constrained radial displacement on the loading end. Structural Engineering/Earthquake Engineering JSCE 13, 175s–185s] for isotropic cylinders under compression test can be recovered as a special case. Our numerical results show that both the non-uniform stress distribution and the difference between the apparent and the true Young’s moduli of the cylinder are very sensitive to the anisotropy of Young’s moduli, Poisson’s ratios and shear moduli. A more distinct bulging shape of the cylinder is expected when anisotropy in shear modulus is strong, the cylinder is relatively short, and the end constraint is large. The bulging shape, however, does not depend strongly on anisotropy of either Poisson’s ratio or Young’s modulus.     

饱和地基任意形状衬砌内部均布突加荷载作用下的动力响应

地下衬砌结构经常会受到内部动荷载的作用,内荷载引起的衬砌结构的动应力集中备受关注.论文利用波函数展开法和Laplace变换,推导了饱和土中突加荷载作用下衬砌结构和土体的位移、应力、孔压表达式.应用复变函数和保角变换,将任意形状边界映射为圆形边界,利用饱和土和衬砌结构的连续条件和边界条件,求得了任意形状衬砌结构的动力响应...     

Modeling shear localization along granular soil–structure interfaces using elasto-plastic Cosserat continuum

The current study presents finite element simulations of shear localization along the interface between cohesionless granular soil and bounding structure under large shearing movement. Micro-polar (Cosserat) continuum approach is applied in the framework of elasto-plasticity in order to overcome the numerical problems of localization modeling seen in the conventional continuum mechanics. The effects of different micro-polar kinematic boundary conditions, along the interface, on the evolution and location of shear band are shown by the numerical results. Furthermore, shear band thickness is also investigated for its dependence on the initial void ratio, vertical pressure and mean grain size. Here, the distribution and evolution of static and kinematic quantities are the main focuses regarding infinite layer of micro-polar material during plane shearing, especially with advanced large movement of bounding structure. The influence of such movement has not been investigated yet in the literature. Based on the results obtained from this study, shear localization appears parallel to the direction of shearing. It occurs either in the middle of granular layer or near boundaries, regarding the assumed micro-polar kinematic boundary conditions at the bottom and top surfaces of granular soil layer. Narrower shear band is observed in lower rotation resistance of soil particles along the interface. It is emphasized that the displacement magnitude of bounding structure has significant effect on the distribution and evolution of state variables and polar quantities in the granular soil layer. However, continuous displacement has no meaningful effect on the thickness of shear band. Here, smooth distributions of void ratio and shear stress components are obtained within the shear band, what the other previous numerical investigations did not receive. Despite indirect linking of Lade’s model to the critical state soil mechanics, state variables tend towards asymptotical stationary condition in large shear deformation.     

Flexural gravity wave motion over poroelastic bed

Using Biot’s consolidation theory, effect of poroelastic bed on flexural gravity wave motion is analyzed in both the cases of single-layer and two-layer fluids. The model for the flexural gravity waves is developed using linear water wave theory and small amplitude structural response in finite water depth. The effects of permeability and shear modulus of poroelastic bed and time period on flexural gravity wave motion are studied by analyzing the dispersion relation, phase speed, plate deflection, interface elevation and pressure distribution along water depth. Various results for surface gravity waves are analyzed as special cases. The study reveals that bed permeability retards the hydrodynamic pressure distribution along the water depth significantly compared to shear modulus whilst, floating plate deflection decreases significantly with change in shear modulus compared to permeability of the poroelastic bed. The present study can be generalized to analyze various wave–structure interaction problems over poroelastic bed.     

解析法求解成层渗透各向异性地基Biot固结轴对称问题

采用解析法研究成层渗透各向异性地基,该法从渗透各向异性Ｂｉｏｔ固结轴对称问题的基本方程（静力平衡方程,物理方程及渗透连续方程）出发,利用Ｌａｐｌａｃｅ～Ｈａｎｋｅｌ变换及有关矩阵理论等,得到Ｂｉｏｔ固结基本量不同深度之间的传递矩阵。利用传递矩阵,边界条件以及Ｌａｐｌａｃｅ～Ｈａｎｋａｌ逆变换技术可求解多层渗透各向异性地基体系,采用更为有效的Ｆ．Ｄｕｒｂｉｎ的方法实现Ｌａｐｌａｃｅ逆变换。编制了计算     

A continuum approach to the analysis of the stress field in a fiber reinforced composite with a transverse crack

The stress field in a periodically layered composite with an embedded crack oriented in the normal direction to the layering and subjected to a tensile far-field loading is obtained based on the continuum equations of elasticity. This geometry models the 2D problem of fiber reinforced materials with a transverse crack. The analysis is based on the combination of the representative cell method and the higher-order theory. The representative cell method is employed for the construction of Green’s functions for the displacements jumps along the crack line. The problem of the infinite domain is reduced, in conjunction with the discrete Fourier transform, to a finite domain (representative cell) on which the Born–von Karman type boundary conditions are applied. In the framework of the higher-order theory, the transformed elastic field is determined by a second-order expansion of the displacement vector in terms of local coordinates, in conjunction with the equilibrium equations and these boundary conditions. The accuracy of the proposed approach is verified by a comparison with the analytical solution for a crack embedded in a homogeneous plane.Results show the effects of crack lengths, fiber volume fractions, ratios of fiber to matrix Young’s moduli and matrix Poisson’s ratio on the resulting elastic field at various locations of interest. Comparisons with the predictions obtained from the shear lag theory are presented.