基于PFC3D的粗粒土三轴试验细观数值模拟
发布时间：2018-10-10 11:41
【摘要】：细观力学特性是粗粒土力学特性的主要研究内容之一。目前，试验及测试技术都无法获取其细观力学参数，粗粒土宏观力学特性内在作用机制不能得到很好的揭示。PFC作为离散元方法的一种，是细观分析的主要手段之一。在PFC三轴数值模拟试验中，建立既高效又反应室内试样颗粒级配的数值模型是三轴数值模拟的基础，选择各细观参数值的调节顺序及调节程度是提高三轴数值模拟效率的关键，采用不同的细观分析方法揭示粗粒土宏观力学特性内在机制是三轴数值模拟试验的最终目的。因此，，本文基于室内三轴试验研究成果，开展PFC三轴数值试验研究，提出了高效数值建模方法和新的细观分析方法，分析细观参数对宏观力学特性的影响，并进行了各细观参数力学及变形敏感性排序。本文主要研究工作及成果如下： 1）基于已有的室内大型三轴试验数据，自编程序，建立PFC3D三轴数值试验模型。 2）首次提出采用加权平均数方法生成模型中的颗粒，避免粒径较小的颗粒数目庞大导致的计算效率的降低。同时根据颗粒粒径的加权平均数生成方法，能够很好的得到三轴数值试验应力应变曲线结果。 3）从细观角度分析不同围压下剪切过程中颗粒位移场和颗粒转动速度场的变化规律，并根据其变化情况分析室内三轴试验宏观力学特性现象的细观本质。 4）首次将测量模型运用到三轴数值试验模型中，通过自编测量模型程序，采用133个测量球体对试样内部裂隙分布进行检测，根据量球环内的颗粒配位数、孔隙度以及体应变在剪切过程中的变化规律分析剪切面在三轴模型中的空间分布，得到三轴数值试验的空间剪切面。 5）进行了各细观参数对粗粒土强度以及变形的敏感性影响分析，其中包括：孔隙度、颗粒配位数、颗粒法向刚度与切向刚度之比（kn/ks）、颗粒粒径分布、剪切速率以及摩擦系数等细观参数。得出各细观参数对粗粒土峰值强度的敏感性排序为：kn/ks摩擦系数剪切速率颗粒粒径分布孔隙度配位数。
[Abstract]:Meso-mechanical properties are one of the main contents of mechanical properties of coarse grained soils. At present, testing and testing techniques can not obtain its meso-mechanical parameters, and the internal mechanism of macroscopic mechanical properties of coarse grained soil can not be well revealed. PFC, as a discrete element method, is one of the main means of meso-analysis. In the PFC triaxial numerical simulation test, it is the foundation of triaxial numerical simulation to establish a numerical model that is both efficient and responsive to indoor sample particle gradation. The key to improve the efficiency of triaxial numerical simulation is to select the adjusting order and degree of each meso-parameter value. The ultimate purpose of triaxial numerical simulation test is to reveal the internal mechanism of macroscopic mechanical properties of coarse grained soil by using different meso-analytical methods. Therefore, based on the research results of indoor triaxial test, the PFC triaxial numerical test is carried out, and an efficient numerical modeling method and a new mesoscopic analysis method are proposed to analyze the influence of mesoscopic parameters on the macroscopic mechanical properties. The order of mechanical parameters and deformation sensitivity is also given. The main work and results of this paper are as follows: 1) based on the data of large scale triaxial test, a program is developed. The PFC3D triaxial numerical test model is established. 2) the weighted average method is used to generate the particles in the model for the first time to avoid the reduction of computational efficiency caused by the large number of smaller particles. At the same time, according to the weighted average of particle size, The results of stress and strain curves of triaxial numerical tests can be obtained well. 3) the variation law of particle displacement field and particle rotation velocity field during shearing under different confining pressures are analyzed from the view of meso. According to its variation, the meso nature of macroscopic mechanical characteristics of indoor triaxial test is analyzed. 4) the measurement model is first applied to the triaxial numerical test model. The fracture distribution in the specimen was measured by 133 measuring spheres. The spatial distribution of the shear surface in the triaxial model was analyzed according to the variation of particle coordination number, porosity and volume strain in the measuring sphere ring during the shear process. The spatial shear plane of triaxial numerical test was obtained. 5) the effects of various meso-parameters on the strength and deformation sensitivity of coarse grained soil were analyzed, including porosity, particle coordination number, The ratio of normal stiffness to tangential stiffness (kn/ks), particle size distribution, shear rate, friction coefficient and so on. The sensitivity of the meso-parameters to the peak strength of coarse-grained soil is in the order of 1: KN / KS friction coefficient shear rate particle size distribution porosity coordination number.
【学位授予单位】：三峡大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU411
本文编号：2261631
[Abstract]:Meso-mechanical properties are one of the main contents of mechanical properties of coarse grained soils. At present, testing and testing techniques can not obtain its meso-mechanical parameters, and the internal mechanism of macroscopic mechanical properties of coarse grained soil can not be well revealed. PFC, as a discrete element method, is one of the main means of meso-analysis. In the PFC triaxial numerical simulation test, it is the foundation of triaxial numerical simulation to establish a numerical model that is both efficient and responsive to indoor sample particle gradation. The key to improve the efficiency of triaxial numerical simulation is to select the adjusting order and degree of each meso-parameter value. The ultimate purpose of triaxial numerical simulation test is to reveal the internal mechanism of macroscopic mechanical properties of coarse grained soil by using different meso-analytical methods. Therefore, based on the research results of indoor triaxial test, the PFC triaxial numerical test is carried out, and an efficient numerical modeling method and a new mesoscopic analysis method are proposed to analyze the influence of mesoscopic parameters on the macroscopic mechanical properties. The order of mechanical parameters and deformation sensitivity is also given. The main work and results of this paper are as follows: 1) based on the data of large scale triaxial test, a program is developed. The PFC3D triaxial numerical test model is established. 2) the weighted average method is used to generate the particles in the model for the first time to avoid the reduction of computational efficiency caused by the large number of smaller particles. At the same time, according to the weighted average of particle size, The results of stress and strain curves of triaxial numerical tests can be obtained well. 3) the variation law of particle displacement field and particle rotation velocity field during shearing under different confining pressures are analyzed from the view of meso. According to its variation, the meso nature of macroscopic mechanical characteristics of indoor triaxial test is analyzed. 4) the measurement model is first applied to the triaxial numerical test model. The fracture distribution in the specimen was measured by 133 measuring spheres. The spatial distribution of the shear surface in the triaxial model was analyzed according to the variation of particle coordination number, porosity and volume strain in the measuring sphere ring during the shear process. The spatial shear plane of triaxial numerical test was obtained. 5) the effects of various meso-parameters on the strength and deformation sensitivity of coarse grained soil were analyzed, including porosity, particle coordination number, The ratio of normal stiffness to tangential stiffness (kn/ks), particle size distribution, shear rate, friction coefficient and so on. The sensitivity of the meso-parameters to the peak strength of coarse-grained soil is in the order of 1: KN / KS friction coefficient shear rate particle size distribution porosity coordination number.
【学位授予单位】：三峡大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU411
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