土体变形的尺度及转动效应研究与有限元分析

发布时间：2018-03-03 07:25

本文选题：尺度效应　切入点：颗粒转动　出处：《华南理工大学》2016年博士论文　论文类型：学位论文

【摘要】：土体是由跨越多个数量级尺度的矿物颗粒、水和空气通过一定方式聚集而成的非连续颗粒介质,其宏观力学特性与土颗粒尺寸和颗粒运动行为细节密切相关,具有非常显著的颗粒尺度及转动效应。但经典连续介质力学建立在宏观尺度上,无法表征土颗粒尺度及其转动;离散力学方法多针对单一尺度的均匀颗粒体系且计算量庞大;而应变梯度塑性理论一般适用于金属材料,能否应用于土体介质尚待研究。本文通过土体特性影响试验,总结出颗粒性质和颗粒尺度对土体宏观力学性质的影响规律,并利用“基体-增强颗粒”胞元结构模型,提出了一种可考虑颗粒尺度和转动效应的土体弹塑性理论(以下简称“尺度理论”),同时,借助ABAQUS用户子程序接口二次开发了相应的有限元程序。数值模拟和理论分析表明,所发展的有限元方法可较好地解决经典弹塑性理论存在的问题,合理地预测土体变形过程中因颗粒尺度及转动效应引起的特殊力学行为。基于上述研究工作,取得的成果主要有如下几个方面:(1)根据矿物成分与粒度成分土体特性影响试验总结颗粒性质和颗粒尺度对土体宏观力学性质的影响规律和不同尺度颗粒间的相互作用规律,并利用“基体-增强颗粒”土体胞元模型,在本构关系中引入表达颗粒尺度的内禀尺度因子和反映转动变形的转动变量,以及包含内禀尺度因子的等效剪应变和等效剪应力,进而基于能量法则和Von Mises屈服准则进行理论推导,建立了一种可以考虑颗粒尺度及转动效应的土体弹塑性理论。(2)借助大型通用商业有限元软件ABAQUS所带的UEL用户自定义单元子程序接口,二次开发了基于尺度理论的有限元计算程序,并采用该程序分析了孔洞应力集中问题的尺度及转动效应。通过与经典弹塑性理论有限元计算结果对比,验证了所开发程序的正确性,揭示出应力集中与颗粒尺度和颗粒转动的内在关联性,从变形机制上解释了尺度理论的合理性。(3)利用本文所发展的尺度理论有限元方法,对土体软化和变形局部化现象展开了相应的数值模拟和理论分析,研究表明:土体变形局部化过程中,尺度理论可较好地解决经典弹塑性理论遇到的数值计算困难和计算结果的严重网格依赖性,并借此进一步分析剪切带的发生和发展过程与颗粒尺度和颗粒转动的关联规律,揭示出由于土体颗粒性特征产生的特殊变形行为和变形机制。(4)利用本文所发展的尺度理论有限元方法,对具有工程尺寸的地基承载力问题和边坡滑动问题进行模拟,实现了土体软化非线性变形的全过程计算,其结果表现出与经典弹塑性理论不同的土体变形行为。除此之外,还探讨了颗粒尺度对土体变形和荷载特性的影响规律,并给出考虑颗粒尺度及转动效应的土体变形和破坏机制,为今后工程灾害防治提供理论与数据参考。
[Abstract]:Soil mass is a discontinuous granular medium, which is composed of mineral particles that span many orders of magnitude, and water and air gather in a certain way. Its macroscopic mechanical properties are closely related to the size of soil particles and the details of particle motion behavior. But the classical continuum mechanics is based on the macroscopic scale, which can not represent the soil particle size and its rotation, and the discrete mechanics method is mostly aimed at the homogeneous particle system with a single scale and has a large amount of calculation. However, the strain gradient plasticity theory is generally applicable to metal materials, and whether it can be applied to soil media remains to be studied. In this paper, the effects of particle properties and particle size on the macroscopic mechanical properties of soil are summarized through the soil characteristic influence test. Based on the cell structure model of "matrix reinforced particles", a soil elastoplastic theory (hereinafter referred to as "scale theory"), which can consider particle size and rotational effect, is proposed. With the help of ABAQUS user subroutine interface, the corresponding finite element program is developed twice. Numerical simulation and theoretical analysis show that the developed finite element method can solve the problems of classical elastoplastic theory. The special mechanical behavior caused by particle size and rotational effect during soil deformation can be reasonably predicted. The main achievements are as follows: (1) based on the experiments of the influence of mineral composition and particle size composition on soil properties, the effects of particle properties and particle size on the macroscopic mechanical properties of soil and the interaction between particles of different scales are summarized. Using the "matrix reinforced particle" soil cell model, the intrinsic scale factor representing particle size and the rotational variable reflecting rotational deformation are introduced into the constitutive relation, as well as equivalent shear strain and equivalent shear stress including intrinsic scale factor. Then based on the energy law and Von Mises yield criterion, a theoretical derivation is made. In this paper, a soil elastoplastic theory, which can consider particle size and rotational effect, is established. The UEL user-defined element subroutine interface is developed with the help of the large commercial finite element software ABAQUS. The finite element calculation program based on scale theory is developed for the second time, and the scale and rotational effect of the stress concentration problem of holes are analyzed by using the program. The results are compared with the results of finite element calculation based on classical elastic-plastic theory. The correctness of the developed program is verified, and the inherent relationship between stress concentration and particle size and particle rotation is revealed. The rationality of the scale theory is explained from the deformation mechanism.) the scale theory finite element method developed in this paper is used. Numerical simulation and theoretical analysis of soil softening and deformation localization are carried out. The results show that: in the process of soil deformation localization, The scale theory can solve the difficulty of numerical calculation and the serious grid dependence of the results of classical elastic-plastic theory, and further analyze the correlation law between the occurrence and development of shear band and particle size and particle rotation. It is revealed that the special deformation behavior and deformation mechanism caused by the particle characteristics of soil mass are simulated by using the scale theory finite element method developed in this paper, and the problems of bearing capacity of foundation and slope sliding with engineering size are simulated. The calculation of soil softening nonlinear deformation is realized. The results show that the deformation behavior of soil is different from that of classical elastoplastic theory. In addition, the influence of particle size on soil deformation and load characteristics is also discussed. The mechanism of soil deformation and failure considering particle size and rotation effect is also given, which can provide theoretical and data reference for engineering disaster prevention and control in the future.
【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TU433

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