The evolution of morphology and fabric of a sand during shearing
The evolution of morphology and fabric of a sand during shearing
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DOI：
10.25560/62618
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
J. Fonseca
中科院分区：
文献类型：
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作者：
J. Fonseca
在过去的50年里，实验研究一再表明，沙子的机械行为对材料结构很敏感，即，颗粒的排列。到目前为止，定量描述砂组构的尝试相对较少。事实上，我们对颗粒运动和相互作用与颗粒材料（包括沙子）的宏观尺度响应之间联系的大多数理解来自离散元建模（DEM）和具有简单理想形状的“模拟”沙子的实验。本研究的目的是定量地描述真实的颗粒形态和组构，以及它们在载荷作用下的演变。研究的材料是Reigate砂（来自英格兰东南部），一种地质上古老的砂，在其完整的状态下，表现出显着的颗粒互锁和nobonding。为探讨织物对土力学响应的影响，对密度相近的原状土和重塑土进行了三轴压缩试验。在剪切变形的三个不同阶段用环氧树脂浸渍试样，并使用X射线显微断层扫描法对每个试样的小芯进行扫描。为了获得体素尺寸为5μm的三维高分辨率图像，探索了不同的系统和扫描参数（0.018d50）和识别单个颗粒和限定每个颗粒-颗粒接触的表面所需的质量水平。颗粒尺寸和形状的定量表明，破碎颗粒的破碎，沿着现有的裂缝，发生在完整土壤的重组和剪切过程中，这是一种使用侵入性技术如筛分析无法观察到的现象。在每个加载阶段，根据颗粒取向、接触法线、分支向量和空隙取向对组构方向数据的分布进行统计分析。结果表明，在材料沉积过程中形成的初始颗粒取向组构倾向于在剪切过程中持续存在，而接触法线似乎沿着峰后区域的大主应力方向重新取向。在剪切带内观察到不同的图案，因为颗粒和接触法线似乎朝向剪切平面的方向旋转。从断层扫描数据的测量补充了定性描述的形态和织物，使用SEM和光学显微镜图像的薄切片。
Over the past 50 years, experimental studies have repeatedly demonstrated that the mechanical behaviour of sand is sensitive to the material fabric, i.e., the arrangement of the grains. Up until now there have been relatively few attempts to describe quantitatively the fabric of sands. In fact, most of our understanding of the link between the particle movements and interactions and the macro-scale response of granular materials, including sand, comes from discrete element modelling (DEM) and experiments on “analogue” sands with simple, idealized shapes. The aim of this study had been to describe quantitatively the particle morphology and fabric of reals and and their evolution under loading. The material investigated was Reigate sand (from Southeast England), a geologically old sand which, in its intact state, exhibits significant grain interlocking and nobonding. To explore the effects of fabric on the mechanical response of the soil, intact and reconstituted specimens both having similar densities were tested under triaxia lcompression. The specimens were impregnated with an epoxy resin at three different stages of shear deformation and small cores from each specimen were scanned using X-ray micro-tomography. Different systems and scanning parameters were explored in order to obtain three-dimensional high-resolution images with a voxel size of 5μm(0.018d50) and a quality level required for the identification of the individual particles and the surface defining each particle-particle contact.The quantification of particle size and shape has shown that breakage of fractured grains, along existing fissures, occurs both during reconstitution and shearing ofthe intact soil, a phenomenon that cannot be observed using invasive techniques such as sieve analysis. Statistical analyses of the distribution of fabric directional data in terms of particle orientations, contact normals, branch vectors and void orientations were carried out at each loading stage. It has been shown that the initial particle orientation fabric that develops during the deposition of the material tendsto persist during shearing, while the contact normals seem to be reorientated along the direction of the major principal stress in the post-peak regime. Different patterns were observed within the shear band as both the particles and the contact normals appeared to rotate towards the direction of the shear plane. The measurements from the tomographic data were complemented with a qualitative description of the morphology and fabric using SEM and optical microscope images of thin sections.