超固结土热黏弹塑性本构关系

热黏弹塑性本构模型是描述土在温度（热）和时间（黏）耦合作用下的应力-应变关系的本构模型。在一些新型岩土工程诸如高放核废料地质处置、地热资源开发与贮存的建设中,需要同时考虑温度和时间对土的影响,所以建立一个热黏弹塑性本构模型具有理论和实际意义。将温度变化对黏土体积和强度参数的影响引入笔者之前提出的超固结土等向应力-应变-时间关系,建立了一个等向应力条件下的应力-应变-时间-温度关系。随后,基于该关系推导了屈服面硬化定律,并将其与超固结土统一硬化模型的屈服方程和流动法则结合,建立了超固结土的热黏弹塑性本构模型。最后,使用新模型预测室内试验,证明新模型能够反映时间和温度对土体积、一维压缩曲线和前期固结压力的耦合影响。     

不同固结条件下黏土数值化建模的研究

研究了不同初始固结压力条件对黏土本构关系的影响。进行了2组不同固结条件下的排水压缩试验,即等压固结条件和K0固结条件。采用数值建模方法,以 和 为硬化参数的双屈服面模型为框架,通过对试验数据空间的反演获得两种不同初始条件下的黏土弹塑性本构关系,并在整个应力场 可视化。将该数值模型嵌入有限元程序对三轴压缩试验进行数值模拟,并与试验曲线及相同路径下的剑桥模型和Duncan-Chang模型关系曲线进行对比。结果表明,数值建模方法有较好的容错性,能很好地反映应力历史的影响,能模拟真实应力路径。     

非饱和土的水力和力学特性及其弹塑性描述

简单回顾了非饱和土本构模型研究的发展历程,总结了近几年非饱和土弹塑性本构模型最新研究成果,重点介绍了能统一模拟非饱和土水力性状和力学性状耦合的弹塑性本构模型。通过对建立模型过程中的几个核心问题讨论,较详细地说明该类模型的结构、性能以及相关问题。非饱和土水力性状的滞回性用假定存在饱和度弹性区间的弹塑性过程来模拟;该类耦合模型不仅考虑了吸力对非饱和土水力性状和力学性状的影响,还考虑了饱和度对应力-应变关系和强度的影响以及土体变形对土-水特征曲线的影响。用同一套模型参数,耦合模型可统一预测在吸力控制或含水率控制下沿各种应力路径下非饱和土的水力-力学特性,并简单介绍了膨胀性非饱和土的弹塑性本构模型以及耦合模型在有限元数值计算中的应用。     

非饱和土化学-水力-力学耦合行为数值模拟

在描述非饱和土力学本构行为的Gens-Alonso模型[1]的基础上,结合化学浓度对前固结压力的软化公式[2],并考虑了化学浓度对黏聚力的软化作用,建立了描述非饱和土化学-水力-力学耦合行为的本构模型。对包括化学-水力-力学本构关系、流体流动和污染物传输的控制方程的平衡方程组进行有限元离散,并采用此非饱和土化学-水力-力学耦合行为的数值模型对非饱和土中隧道周围化学-水力-力学耦合过程进行了模拟,对纯粹的力学响应、弹性化学力学响应、弹塑性化学力学响应 3 种情况进行了分析,数值结果显示了化学浓度作用下隧道周围的体积变化量和应力状态比单纯的力学响应有较大的提高,隧道表面的收缩量也有明显的增大。数值模拟的结果显示了该方法对模拟非饱和土复杂的耦合行为的可行性。     

低渗透煤层气-水流固耦合数学模型及数值模拟

基于有效应力原理,结合弹塑性几何方程、本构方程及平衡方程建立了应力场控制方程。依据流体力学中的质量守恒原理建立了煤层气、水和煤岩体固体颗粒的渗流场方程;以上方程再配以辅助方程和定解条件构成了应力作用下煤层 气-水流固耦合的数学模型,并对简化模型进行了单相流流-固耦合数值模拟分析,得到了压力动态分布曲线,分析了耦合和非耦合情况对压力分布的影响,进一步为煤层气流-固耦合分析提供了一定的理论基础。     

不同应力路径下水土耦合超固结黏土分叉分析

基于超固结黏土三维弹塑性本构模型,导出水-土耦合部分排水条件下饱和黏土应变局部化的萌生条件,求出在不同应力路径下,单相和水-土耦合条件下超固结土分叉的三维解析解和数值解。理论分析表明,应力罗德角 为-30°、15°和30°时,无论是单相条件,还是水土耦合两相介质条件,该模型均无分叉现象产生;应力罗德角为0°时,单相条件下该模型有分叉现象产生,水土耦合不排水条件下该模型无分叉现象出现,水-土耦合部分排水条件下分叉与否则与参数选取有关;应力罗德角为-15°时,无论是单相条件,还是水-土耦合条件,该模型均有分叉现象产生。利用嵌入了上述本构模型的有限元软件ABAQUS,对单相和水-土耦合条件下的多单元立方体应变局部化分叉现象进行数值分析。分析表明,在应力罗德角为 30°时,单相条件和水土耦合条件下都无分叉现象产生;应力罗德角为15°时,单相条件下有分叉现象产生,水-土耦合不排水条件下无分叉现象出现,水-土耦合部分排水条件下何时分叉则与渗透系数大小有关;应力罗德角为-15°和0°时,单相条件和水土耦合条件下该模型均有分叉现象产生。同一应力路径下数值解相对于理论解更易出现分叉。     

基于广义位势理论的接触面本构模型一般表述

基于广义位势理论建立的岩土体材料本构模型以及岩土体材料与结构接触面本构模型原理相通,只是前者是在三轴剪切试验条件下的三维应力空间建模,后者是在单剪试验条件下的二维应力空间建模。单剪试验条件下土与结构的接触面问题可以看作是法向与切向应力空间上的二维问题,其试验结果可以表达成由应力、应变组成的二维矢量。结合接触面力学特性,确定应力空间中的势函数以及塑性状态方程,可以推导出双重势面接触面弹塑性本构方程的一般表达式。进一步取两个势函数分别为法向应力和切向应力,建立简化双重势面接触面弹塑性模型的本构方程,该方程可直接应用于有限元等数值分析。结合试验实例对建模方法的合理性进行验证,模型拟合效果良好。研究结果表明,基于广义塑性位势理论建立接触面本构模型无需推求塑性势函数和屈服函数,可以直接得到弹塑性刚度矩阵,且建模方便。     

不同应力路径下砂土的神经网络弹塑性本构模型研究

基于多种应力路径下砂土的加载、卸载和再加载过程的三轴排水试验数据，研究了三种应力路径对屈服面的影响，其结果表明，不同应力路径对砂土的本构模型有着不可忽视的作用。在此基础上，建立了砂土的弹塑性神经网络模型，对相应路径下的本构关系进行了学习。实例分析表明，该模型能够很好地描述具体应力路径下的本构关系，神经网络建模方法具有方便、容错性强的特点，对岩土力学快速、高效数值方法的进一步发展具有重要的参考价值。同时，在这种弹塑性应力-应变关系中，笔者并没有使用塑性势函数，这在目前的弹塑性本构关系的建模中是一种新的尝试。     

砂土液化变形的有限元-无网格耦合方法

通过构造Biot固结理论u-p方程的无网格伽辽金-有限元耦合方法,对砂土液化变形问题进行了数值模拟。对于饱和砂土,采用Oka等提出的弹塑性本构模型,同时采用更新的Lagrange计算格式推导了控制方程。耦合方法能够发挥有限元和无网格各自的优点,既避免了由于单元变形扭曲而引起的计算中断,也可节约计算时间,算例验证了该方法在地震液化问题中的有效性。     

考虑冻融循环的季冻区高等级公路路基填土本构模型研究

在季冻区高等级公路路基场地取土,制成重塑土试件进行冻融循环试验。而后对经历不同冻融循环次数的土体进行三轴固结排水（CD）剪切试验,测得应力、应变数据。在大量试验数据的基础上,遵循岩土本构变化规律,以岩土弹塑性力学为理论基础,在p-q空间,以椭圆方程拟合体变屈服面,以抛物线方程拟合剪切屈服面,采用塑性关联流动,得到考虑冻融循环条件下融土的弹塑性本构方程。通过编程计算后,对比计算与试验结果,证明该双屈服面本构模型能够较为准确地预估冻融循环土体的应力-应变关系,该本构模型对季冻区路基土体长期稳定性分析和工程预测具有重要参考意义。     

Decoupling Conditions for Elasto-plastic Consolidation Question Based on Numerical Modeling Method

INTRODUCTION Theconsolidationofsaturatedsoilisanimpor tantsubjectingeomechanics.Biot(1941)proposed thethree dimensionalconsolidationtheory,whichis basedontheprincipleofeffectivestress,continuity conditionsandequilibriumequations.Theremarka blesuccessofthistheoryistheanalysisofthetime dependenteffectandcouplingeffectofsoilandpore water.Thus,thetheoryisaclassictheoryinsatu ratedsoilstatistics.Itwasalmostunfeasibletoperformanalysesof thistheorywithoutthedevelopmentofhigh speed computersandnu…     

Finite element modelling of three-phase flow in deforming saturated oil reservoirs

A numerical simulation is presented for three-dimensional three-phase fluid flow in a deforming saturated oil reservoir. The mathematical formulation describes a fully coupled governing equation systen which consists of the equilibrium and continuity equations for three immiscible fluids flowing in a porous medium. An elastoplastic soil model, based on a Mohr–Coulomb yield surface, is used. The finite element method is applied to obtain simultaneous solutions to the governing equations where displacement and fluid pressures are the primary unknowns. The final discretized equations are solved by a direct solver using fully implicit procedures. The developed model is used to investigate the problems of three-phase fluid flow in a deforming saturated oil reservoir.     

Finite element modelling for simulating the surface subsidence above a compacting hydrocarbon reservoir

The surface subsidence above a compacting saturated oil reservoir is the main topic of this paper. From a literature review, it is obvious that extensive efforts have been conducted for investigating this phenomenon in various situations. Herein, a numerical model, based on the finite element method, was used for simulating three-dimensional three-phase fluid flow in a deforming saturated oil reservoir. The mathematical formulation describes a fully coupled governing equation system which consists of the equilibrium and continuity equations for three immiscible fluids flowing in a porous media. An elastoplastic soil model, based on a Mohr Coulomb yield surface, was utilized. The finite element method was applied to obtain simultaneous solutions to the governing equations where the displacements and the fluid pressures are the primary unknowns. The final discretized equations are solved by a direct solver using fully implicit procedures. A linear analysis was used to study the stability conditions of the present model. Finally, a series of simulations were conducted to indicate the validity and the utility of the developed model.     

变荷载下层状非饱和土地基全耦合固结特性研究

非饱和土是地球表层土体一种常见的存在形式。与经典的饱和土Biot固结理论相比,非饱和土固结理论还亟待发展。基于Fredlund非饱和土双应力变量固结理论,放弃传统理论固结过程中骨架总应力不变的假设,推导出变荷载作用下非饱和土全耦合轴对称固结理论的控制方程组。通过Laplace-Hankel变换处理变量t和r,所得的控制方程被处理为常微分方程组;扩展的精细积分法将被进一步运用求解方程组以得到层状非饱和土地基在变换域内的固结解答,而最终的解答将通过Laplace-Hankel逆变换技术求得。将非饱和土地基退化为饱和土地基,与现有文献结果进行对比,验证所提方法结果的可靠性;最后,提供3个数值算例,以讨论加载时间T0、孔隙水关于净应力的体积变化系数m1w以及土体分层性对非饱和土固结特性的影响。     

Numerical solution for consolidation and desiccation of soft soils

The consolidation and desiccation behaviour of soft soils can be described by two time‐dependent non‐linear partial differential equations using the finite strain theory. Analytical solutions do not exist for these governing equations. In this paper, we develop efficient numerical methods and software for finding the numerical solutions. We introduce a semi‐implicit time integration scheme, and show numerically that our method converges. In addition, the numerical solution matches well with the experimental result. A boundary refinement method is also developed to improve the convergence and stability for the case of Neumann type boundary conditions. Interface governing equations are derived to maintain the continuity of consolidation and desiccation processes. This is useful because the soil column can undergo desiccation on top and consolidation on the bottom simultaneously. The numerical algorithms has been implemented into a computer program and the results have been verified with centrifuge test results conducted in our laboratory. Copyright © 2001 John Wiley & Sons, Ltd.     

深隧道围岩分区破裂的数学模拟

该研究为先前深隧道围岩分区破裂现象内变量梯度塑性模型的进一步发展。利用应变梯度模型研究了深隧道围岩的分区破裂现象。作为额外的状态变量,在此引入应变梯度这一新变量。利用虚功原理得到了深隧道围岩的平衡方程、边界条件和流动准则,利用Clausius-Duhem不等式获得了岩体的本构方程。对于圆形深隧道,由上述模型的一般方程得到了弹性变形情况下、具有下降段的弹塑性变形情况下和不考虑弹性变形的塑性变形情况下圆形深隧道围岩的支配方程,得到了解析解,并讨论了解析解的性质。这一模型不仅扩展了隧道围岩的经典弹塑性模型,也为下一步数值研究深隧道围岩的分区破裂现象奠定了理论基础。     

Scattering of a plane wave by a lined cylindrical cavity in a poroelastic half-plane

The focus of this contribution is to develop a complex variable function method to solve the two-dimensional scattering of plane waves by a lined cylindrical cavity in the poroelastic half-plane. The poroelastic half-plane is based on Biot’s dynamic theory, and the governing equations are solved by reduction to three Helmholtz equations. The lining structure can be treated as an elastic material and decoupled into two Helmholtz equations. Here, the large circle assumption is applied to simulate the half-plane boundary. By using appropriate boundary conditions and continuity conditions, the unknown coefficients in the potentials can be determined. Selected numerical results are presented in this paper.     

Dual-porosity elastoplastic analyses of non-isothermal one-dimensional consolidation

A numerical solution, using the finite difference method, and based on a porothermo-elasto-plastic formulation for dual-porosity one-dimensional consolidation has been presented. The model is fully coupled to ensure the interactive behavior of fluid flow, heat flow and solid deformations in the conservation of momentum, mass and energy equations. A bi-linear stress-strain relationship is used to accommodate elastoplastic deformation behavior. A double effective stress law, proposed by Elsworth and Bai (1992), is applied to describe constitutive relationships among the stresses, pressures and temperatures. In order to examine the dual-porosity and thermal effects on the soil consolidation individually, isothermal and non-isothermal consolidations for a dual-porosity column are analyzed. In comparison to the single porosity approach, the present study shows that the pore pressure dissipation is faster and Mandel's effect (Mandel, 1953) is more pronounced at early times of the source disturbance for dual-porosity consolidation. One of the significant parameters affecting the dual-porosity consolidation is the fracture spacing (fracture density); the smaller the fracture spacing, the faster the column drainage.