EAGER: Analysis of the Depositional Fabric and Deformation Characteristics of Sands Using 3-D Computed X-Ray Tomography and DEM Simulation

了解砂土在不同荷载条件下的行为是能够为所有类型的结构设计基础的一个重要方面。最大的挑战之一是准确了解沙子的沉积方式如何影响它们的特性。因此，这一早期概念探索性研究赠款项目的目标是一项国际合作努力，以评估使用计算机X射线断层扫描技术来产生不同环境中沉积的沙子和淤泥的三维图像。计算机X射线层析成像涉及使用高能光束来获得微观物体的高分辨率三维图像。这项技术已经用实验室制备的颗粒状材料和均匀沙子的样品进行了演示。然而，到目前为止，还没有对从自然沉积物中收集的未受干扰的样品进行同样的尝试。因此，该项目的实际方面是开发必要的实验室技术，利用计算机X射线断层成像技术对未受干扰的样品成像，以确定颗粒组合的实际沉积几何形状。这些数据将允许使用先进的粒子跟踪数值模型来分析沉积模式对这些材料的机械性能的影响。最终目标是开发出针对特定材料及其沉积模式的更细微的岩土分析和设计方法。总体而言，这项工作代表了对先进技术的早期探索，利用了颗粒媒体可视化和模拟的最新发展。该奖项致力于美国国家科学基金会“促进科学进步”的使命。这项研究的主要目的是探索使用计算机X射线层析成像来证明不同的沉积环境和沉积物来源产生不同类型的组构，这些组构是该环境的特征。这将允许开发不同来源材料和沉积环境的织物类型特征的数据库。然后，该数据库将提供特定于当地和区域地质环境的预期材料行为的基线属性。假设扫描方法可以充分标准化，这一目标应该可以实现，因为新西兰、日本、智利和加利福尼亚州正在开发关于最近沉积物原位性质的广泛数据库。然后将探索先进的可视化和数字高程模型模拟工具，以开发自然沉积的沙子和淤泥的微观力学行为的真实的数学描述。挑战在于能够准确地表示颗粒的几何形状，然后以数字方式跟踪颗粒的运动及其在接触点的相互作用。目前，这种类型的详细数值模拟仅在具有相对开放组构的砂粒组合上进行了演示。因此，我们的目标是将最新技术扩展到更紧密的颗粒堆积和更复杂的几何形状，以探索织物对天然沉积物变形特征的影响。这应该允许未来在使用多尺度本构模型模拟颗粒沉积物行为的最先进技术方面取得进展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the behavior of sands under different loading conditions is an important aspect of being able to design foundations for all types of structures. One of the great challenges is obtaining an accurate understanding of how the way the sands were deposited affects their properties. Thus, the objective of this EArly-concept Grant for Exploratory Research (EAGER) project is an international cooperative effort to evaluate the use of computed X-ray tomography to produce 3-D images of sands and silts deposited in different environments. Computed X-ray tomography involves the use of high energy beam to obtain high resolution 3-D images of microscopic objects. The technique has been demonstrated using samples of granular materials and uniform sands prepared in the laboratory. However, to-date the same has not been attempted with undisturbed samples collected from natural deposits. Thus, the practical aspect of the project is the development of the necessary laboratory techniques for imaging undisturbed samples using computed X-ray tomography in order to determine the actual depositional geometry of the grain assemblage. These data will then allow analysis of the influence of the mode of deposition on the mechanical properties of these materials using advanced particle tracking numerical models. The ultimate goal is the development of more nuanced approach to geotechnical analysis and design tailored to a specific material and its mode of deposition. Overall, this effort represents an early exploration of advanced techniques, taking advantage of the latest developments in visualization and simulation of granular media. This award addresses the NSF mission "to promote the progress of science." The principal objective of this research is to explore the use of computed X-Ray tomography to demonstrate that different depositional environments and sources of sediments produce different types of fabric that are characteristic of that environment. This will allow the development of a data base of types of fabric characteristic of different source materials and depositional environments. This data base will then provide baseline attributes of expected material behavior that are specific to the local and regional geologic setting. Assuming that the scanning methodology can be sufficiently standardized, this goal should become quite achievable with the extensive data bases of the in-situ properties of recent sediments being developed in New Zealand, Japan, Chile, and California, in particular. Advanced visualization and DEM simulation tools will then be explored to develop a realistic mathematical description of the micro-mechanical behavior of naturally deposited sands and silts. The challenge is in being able to accurately represent the grain geometry and then numerically track the movement of grains and their interaction at points of contact. At present this type of detailed numerical simulation has been demonstrated only on an assemblage of sand grains with relatively open fabric. Thus, the objective is to extend the state of the art to a more compact grain packing and more complex geometry in order to explore the influence of fabric on the deformation characteristics of natural deposits. This should allow for future advances in the state of the art of modeling the behavior of granular sediment using multi-scale constitutive models.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.