土体颗粒尺度效应的理论与试验研究

发布时间：2018-02-05 02:47

本文关键词： 颗粒尺度效应数字图像处理多尺度胞元体内禀长度　出处：《华南理工大学》2014年博士论文　论文类型：学位论文

【摘要】：土体介质在复杂多变的条件下形成了以固相、液相和气相等物质为基本成分的组合物。固相物质在经历风化、搬运、沉积和冲刷等自然作用力后形成了大小差异明显的颗粒材料，，包括小至微米级的黏粒、大至数十厘米以上的卵石、块石，颗粒尺度跨越了6~7个数量级。不同尺度土颗粒的无序空间排列形成了土体介质承受自身重力及外力荷载的颗粒骨架，对土体介质复杂的物理力学特性产生关键性的影响。土体的各粒径颗粒以不同的组合形成的土体微细观结构，其物理力学特性受到颗粒的尺寸、形状和级配等颗粒特征强烈的影响，呈现显著的颗粒尺度效应。为了解决传统连续介质力学无法对颗粒尺度效应现象进行解释的问题，通过建立具有多尺度特征的土体胞元模型，阐述各尺度土体颗粒相互作用的力学机理，引入刻画土体微结构特征的材料内禀长度参数，建立宏观力学性质与微观结构特征相互关联的力学模型。本文完成的理论与试验研究工作及其结论有以下几个方面： (1)通过数字图像处理技术对加强颗粒的几何特征进行测定，获得了颗粒粒度特征的分布规律。测试结果表明，对具有同一岩性和生产工艺的不同粒径加强颗粒，其二维投影的形状参数具有相似的分布规律；颗粒短轴具有明显的对称性，呈典型的标准正态分布，方形筛孔对颗粒短轴有良好的筛分性。 (2)基于土体的多尺度模型，分析颗粒加强土体的力学模型。根据不同粒径颗粒的作用力类型，划分基体材料与加强颗粒；计算协调微裂纹密度与平均应变梯度，获得颗粒加强土体流动应力的计算方法。分析结果表明颗粒加强土体的强度由基体材料的性质和加强颗粒的粒度特征共同决定，协调微裂纹的萌生与发展对应变能的消耗作用表现为土体力学性能的提高，颗粒加强土体强度的尺度效应由土体胞元的强化引起。 (3)研究基体水理性质与加强颗粒粒度特征对土体颗粒尺度效应的影响及其机理。根据试验结果分析，基体液性指数的减小强化了土体颗粒间的作用，削弱了水分子对接触颗粒的润滑力；加强颗粒含量的增加使得土体胞元数量随着增加，提高了胞元体对土体的强化作用；加强颗粒粒径的减小加剧了单位体积土体对剪切应变能的消耗；颗粒加强土体的流动应力与颗粒体表面积呈近似的线性关系。 (4)基于颗粒加强土体的流动应力计算方法，分析了可变内禀长度的影响因素。由分析结果可知，土体的内禀长度反映了基体材料与加强颗粒的物理力学性质，揭示了两种材料耦合程度对力学性能的影响，刻画了土体内部非均质微胞元的结构特征尺寸。土体内禀长度的表达式不仅包含了加强颗粒的粒度特征与基体的剪切强度性质，还综合反映了基体的能量储存与释放的能力、抗剪特征、受力变形的非线性和塑性特征。 (5)基于可变内禀长度的试验研究结果，分析内禀长度的变化规律及其影响因素的敏感性。分析结果表明，可变内禀长度随应变的增加而趋于稳定值；内禀长度随液性指数的增加呈先增加后减小的变化规律；内禀长度随加强颗粒含量的增加而呈非线性增长，增幅亦随加强颗粒含量的增加而增加；内禀长度随加强颗粒粒径的减小以非线性的规律减小，加强颗粒含量越大则非线性越明显。
[Abstract]:The soil medium in complex conditions formed by solid phase, liquid phase and gas composition of equal material as the basic component of the solid material handling. After weathering, erosion, deposition and other natural forces after the formation of the granular material size difference is obvious, including small micron clay, to tens of centimeters above the pebble. Stone size across the 6~7 orders. The disordered spatial arrangement of different scales of soil particles formed skeleton soil under their own gravity and external load, the soil physical and mechanical properties of complex production key. The effects of soil fine soil particles formed by the combination of different views the structure, physical and mechanical properties by the particle size, shape and gradation and particle characteristics of strong, showing remarkable grain size effect. In order to solve the traditional continuum mechanics without Method to explain the problem of particle size effects, soil cell model through the establishment of the multi-scale feature, describes the mechanical mechanism of the scale of soil particle interaction, the characterization of soil microstructure of the material length scale parameter, the mechanics model is established in macroscopic mechanical properties and microstructure characteristics related to each other.
The theoretical and experimental research work completed in this paper and its conclusions are as follows:
(1) to strengthen the geometric characteristics of particles were measured by digital image processing technology, the distribution of particle size characteristics. The test results show that with the same lithology and production process of different size particles strengthen, its shape parameter 2D projection has similar distribution; with obvious symmetry short particle axis, was typical of the standard normal distribution, square sieve on particle short axis has good screening.
(2) multiscale model of soil based on the mechanical model of soil particles. According to the analysis of strengthening the different particle types of force, division of matrix material and strengthening particles; coordination of micro crack density and average strain gradient, particle strengthening the soil flow stress calculation method. Analysis results show that the strength of soil particle strengthening is determined by the properties of matrix material and strengthen the particle size characteristics, coordination of micro crack initiation and development of the strain energy consumption performance for improving the mechanical properties of soil particles, strengthen the scale effect of soil strength caused by soil cell enhancement.
(3) on the base of water physical properties and enhance the particle size characteristics influence on the scale effect of soil particles and its mechanism. Based on the analysis of the test results, the matrix liquid index decreased to strengthen the soil particle particle interactions, weaken the lubricating capacity of water molecule on the contact of particles; particle content increased the number of soil cell with the increase, improve the strengthening effect of the cell element of soil; strengthen the decrease of the particle size increased the unit volume consumption of soil shear strain energy; soil flow is a linear relationship of the approximate surface area and particle strengthening.
(4) to strengthen the soil particle flow stress calculation method based on the analysis of the influence factors in the intrinsic variable length. The analysis result shows that the intrinsic length of soil reflects the base material and strengthen the physical and mechanical properties of particles, reveals the influence of two kinds of materials on the mechanical properties of the coupling degree, describe the soil the heterogeneous characteristics of micro cellular structure element size. The expression length in soil contains not only the shear strength properties of reinforced particles and matrix grain size characteristics, but also reflects the ability of energy storage and release matrix, shear characteristics, nonlinear deformation and plastic characteristics.
(5) results in variable length based on sensitivity variation and influence factors analysis in length. The analysis results show that the intrinsic variable length with the increase of strain tends to a stable value; showed a trend of first increase and then decrease with the increase of the length of the intrinsic liquid index; intrinsic length with the increase of reinforcement particle content and nonlinearly increase with increasing growth, also strengthen the content of particles increases; the intrinsic length increases with the decrease of the particle size in order to strengthen the rule of nonlinear decreases, the reinforcement particle content greater nonlinear is more obvious.

【学位授予单位】：华南理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU43

【参考文献】