堆石体多尺度模型与宏细观力学特性研究

发布时间：2018-04-28 17:04

本文选题：堆石体 + 多尺度　；参考：《武汉大学》2015年博士论文

【摘要】：高堆石坝建设的快速发展对堆石体的宏细观力学特性研究提出了更高要求。堆石体自身的多尺度结构和典型的非线性、非均匀、离散性、各向异性等使得人们对其宏细观变形机理的认识还不够深入,现行的本构模型和设计理论还不能完全满足工程实践的需求。目前,堆石体应力变形的研究方法主要是采用基于连续介质模型的有限元方法进行,它能够在宏观层面上基本等效地得到堆石体的应力变形特性,但难以反映堆石体在细观尺度上的演变过程,如颗粒破碎、颗粒滑移等重要特征。离散元或者以离散元为基础的多尺度数值试验不受试验尺寸的限制,并能够区分影响堆石体力学性能的各种因素,同时也可以方便地监测堆石体内部结构在加载过程中的演化过程,数值试验的这些优势一方面为研究堆石体的细观变形机理或宏观力学特性产生机制提供了新的途径,另一方面也可为完善堆石体的本构关系提供理论依据。因此,有必要从细观数值方法入手,以多尺度方法为手段,从宏细观角度研究堆石体的力学特性。多尺度方法是研究堆石体等复杂颗粒体系的一种有效思路。本文提出了一种分阶耦合有限元-离散元的多尺度模拟方法,分析和推导了该多尺度方法中的关键关系式,构建了相应计算框架。该多尺度方法采用有限元模拟边值问题,并从对应于每个高斯积分点的离散颗粒集合体提取本构关系用于整体求解。该方法既能避免传统连续方法对基于唯象假定的本构关系的依赖,又能克服单纯离散元不能有效模拟大尺度工程问题的缺点,同时还可以将宏观响应与颗粒材料的细观机制有效关联。通过堆石体双轴压缩多尺度数值试验,对堆石颗粒材料的宏细观特性进行了系统的研究。宏观力学响应表现出围压相关性与非对称的应变局部化现象；剪切带内外以及边缘积分点表现出不同的局部响应；在细观组构方面,分析了加载过程中配位数的演化规律、颗粒的运动规律以及接触力链的发展,从细观层次解释了堆石颗粒体系的力学性质；颗粒集合体的接触力分布具有非均匀性与空间各向异性,剪切带内颗粒集合体的主应力发生了偏转,各向异性程度更加明显；分析了各向异性系数的演化过程以及不同各向异性来源对总体各向异性的贡献权重；研究了加载过程中颗粒集合体能量的演变。随着表征元颗粒数目的增多,接触法向的分布越均匀、各向异性程度越小,但在软化行为的模拟方面有一定差别。数值算例充分展示了该多尺度模拟方法在颗粒材料基本特性研究及其实际工程应用方面良好的运用前景。对随机散粒体不连续变形(SGDD)方法中的接触力学模型、弹塑性应力应变关系、时域离散和积分等方面进行了简要介绍。以实际工程筑坝料为例,对堆石颗粒形状进行了分析和模拟,发展了堆石颗粒随机生成方法。该算法可生成不同颗粒形状、不同孔隙率、不同级配的颗粒集合体,在细观尺度上实现了堆石颗粒几何形态与空间分布的精细化描述。在随机散粒体不连续变形方法的基础上,引入内聚力模型,将准脆性材料离散为实体单元与无厚度界面单元,并对界面单元的刚度等参数进行推导,通过界面单元的起裂、扩展和失效,实现了岩体等准脆性材料开裂扩展的数值模拟。该方法能够显式地模拟三维颗粒破碎现象,不需要在裂缝尖端重新剖分网格,确保了数值计算的稳定性,提高了计算效率。数值模型中,损伤与断裂只发生在界面单元上,实体单元仅发生弹性变形,界面单元的应力状态达到破坏准则后,运用基于断裂能的损伤演化模型,界面单元失效后从模型中删除,之前由界面单元相连的实体单元转为接触状态。以巴西劈裂试验等算例对该方法进行了验证,较好地模拟了裂纹的开裂萌生与扩展。在分析颗粒破碎力学机制的基础上,应用该方法模拟了堆石体的颗粒破碎。基于多尺度力学模型与随机散粒体不连续变形方法,建立了堆石体的数值试验平台。数值试验平台能够模拟刚性或柔性边界条件,提供位移或应力加载方式,提取颗粒集合体的宏观力学指标。在详细阐述数值试验过程的基础上,分别研究了堆石体的缩尺效应和锚固效应。以水布垭面板堆石坝主次堆石料为研究对象,建立了考虑颗粒破碎与颗粒强度尺寸效应的散粒体数值模型,重点研究了颗粒强度的尺寸效应以及试样的尺寸对堆石体力学特性的影响,分析了缩尺后堆石体力学特性的变化规律。将砾石锚固试验进行数值实现,分别建立了不同锚杆间距和不同颗粒粒径的数值试样,数值模拟结果能够较好地反映不同加锚散粒体结构的变形规律与锚固效应,散粒体材料表现出的宏观特性与其细观组构的演化密切相关。
[Abstract]:The rapid development of the construction of high rockfill dams has put forward higher requirements for the study of the macro and meso mechanical properties of rockfill. The multi-scale structure of the rockfill body and the typical nonlinear, non-uniform, discrete, anisotropic and so on make people's understanding of its macro and meso deformation mechanism not deep enough, and the existing constitutive model and design theory can not be finished. At present, the research method of stress and deformation of rockfill is mainly based on the finite element method based on continuous medium model. It can basically equivalently obtain the stress and deformation characteristics of rockfill body at the macroscopic level, but it is difficult to reflect the evolution process of rockfill body on the meso scale, such as particle breakage and particle. The multi scale numerical test based on discrete element or discrete element is not limited by the test size, and can distinguish the factors that affect the mechanical properties of the rockfill, and can also conveniently monitor the evolution of the internal structure of the rockfill in the loading process. These advantages of numerical experiments are studied on the one hand. A new way is provided for the mechanism of the meso deformation and the mechanism of macroscopic mechanical properties. On the other hand, it can provide a theoretical basis for improving the constitutive relation of rockfill. Therefore, it is necessary to study the mechanical properties of the rockfill body from the meso scale method by the meso numerical method and the multi scale method. This paper presents a multi-scale simulation method for the multiscale coupled finite element discrete element method, analyzes and derives the key relation in the multiscale method, and constructs the corresponding calculation framework. The multiscale method uses finite element method to simulate the boundary value problem and corresponds to each Gauss. This method can not only avoid the dependence of the traditional continuous method on the constitutive relation based on the phenomenological hypothesis, but also overcome the shortcomings that the simple discrete element can not effectively simulate the large scale engineering problem. At the same time, the macroscopic response and the microscopic mechanism of the granular material can be effective. The macro and mesoscopic characteristics of rockfill particles are systematically studied by the multiscale numerical test of rock mass biaxial compression. The macroscopic mechanical response shows the localized strain localization and the asymmetric strain localization. The local response of the shear zone and the edge integration points shows different local responses; in the meso structure, the analysis is analyzed. The evolution law of the coordination number, the movement law of particles and the development of contact force chain during the loading process, the mechanical properties of the particle system are explained from the meso level. The contact force distribution of the particle aggregate has non uniformity and spatial anisotropy, the main stress of the granular aggregate in the shear zone is deflected, the degree of anisotropy is the degree of anisotropy. It is more obvious that the evolution process of the anisotropy coefficient and the contribution weight of different anisotropy sources to the overall anisotropy are analyzed. The evolution of the energy of the particle aggregate during the loading process is studied. With the increase of the number of particles, the more uniform distribution of the contact method and the smaller the anisotropy, but the modulus of the softening behavior. The numerical examples fully demonstrate the good application prospect of the multi-scale simulation method in the research of the basic properties of granular materials and the practical engineering applications. The contact mechanics model, the elastic plastic stress stress stress relation, the time domain discrete and integral in the random granular discontinuous deformation (SGDD) method are carried out. Taking the actual engineering damming materials as an example, the shape of rockfill particles is analyzed and simulated, and the random generation method of rockfill particles has been developed. This algorithm can generate particles with different particle shapes, different porosity and different gradations, and the fine description of the geometric shape and spatial distribution of rockfill particles is realized on the meso scale. On the basis of the random granular discontinuous deformation method, the cohesive force model is introduced to discrete the quasi brittle material into the solid element and the non thickness interface element, and the stiffness and other parameters of the interface element are derived. Through the initiation, expansion and failure of the interface unit, the numerical simulation of the crack propagation of the quasi brittle materials, such as rock body, is realized. The method can be used to simulate the three-dimensional particle breakage clearly. It does not need to re divide the mesh at the tip of the crack, which ensures the stability of the numerical calculation and improves the calculation efficiency. In the numerical model, the damage and fracture only occur on the interface unit, the solid element only takes place elastic deformation, and the stress state of the interface unit reaches the failure criterion, and the application base is used. In the damage evolution model of fracture energy, the interface unit is deleted from the model after failure, and the solid element connected by the interface unit is turned into contact state before the failure. The method is verified by the example of Brazil splitting test, and the crack initiation and propagation are simulated well. On the basis of the analysis of the mechanical mechanism of the particle breakage, the application of this method is used. This method simulates the particle breakage of rockfill. Based on the multi scale mechanical model and the random granular discontinuous deformation method, the numerical test platform of the rockfill body is established. The numerical test platform can simulate the rigid or flexible boundary conditions, provide the displacement or stress loading mode and extract the macroscopic mechanical indexes of the grain aggregate. On the basis of the numerical test process, the scale effect and the anchorage effect of the rockfill body are studied. The bulk material model of the primary and secondary piles of the Shuibuya concrete face rockfill dam is taken as the research object. The size effect of the particle size and the size effect of the particle strength is established. The size effect of the particle strength and the size of the specimen to the rockfill body are studied. The change law of mechanical properties of the rockfill body after the scale is analyzed. The numerical realization of the gravel anchorage test is carried out, and the numerical samples with different bolt spacing and different particle size are set up respectively. The numerical simulation results can better reflect the deformation law and anchorage effect of different anchorage granular structures. The macroscopic characteristics are closely related to the evolution of meso structure.

【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TV41

【参考文献】