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

EAGER：使用 3D 计算机 X 射线断层扫描和 DEM 模拟分析沙子的沉积结构和变形特征

• 批准号: 1853056
• 负责人: Nicholas Sitar
• 金额: $ 29.98万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-11-15 至 2021-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1853056&HistoricalAwards=false
• 关键词: EAGER; Analysis; Depositional; Fabric; Deformation

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.

了解沙子在不同载荷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。巨大的挑战之一是准确了解沙子的沉积方式如何影响其特性。因此，这个早期概念探索性研究资助 (EAGER) 项目的目标是一项国际合作努力，以评估计算机 X 射线断层扫描的使用，以生成不同环境中沉积的沙子和淤泥的 3D 图像。计算机 X 射线断层扫描涉及使用高能束来获取微观物体的高分辨率 3D 图像。该技术已通过实验室制备的颗粒材料和均匀沙子样品进行了验证。然而，迄今为止，尚未对从天然沉积物中采集的未受干扰的样品进行过同样的尝试。因此，该项目的实际方面是开发必要的实验室技术，使用计算机 X 射线断层扫描对未受干扰的样品进行成像，以确定颗粒组合的实际沉积几何形状。然后，这些数据将允许使用先进的粒子跟踪数值模型分析沉积模式对这些材料机械性能的影响。最终目标是开发针对特定材料及其沉积模式的更细致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，利用了颗粒介质可视化和模拟的最新发展。该奖项体现了美国国家科学基金会“促进科学进步”的使命。本研究的主要目的是探索使用计算机 X 射线断层扫描来证明不同的沉积环境和沉积物来源会产生具有该环境特征的不同类型的织物。这将允许开发不同来源材料和沉积环境的织物特征类型的数据库。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。假设扫描方法能够充分标准化，那么随着新西兰、日本、智利和加利福尼亚州正在开发的最新沉积物原位特性的广泛数据库，这一目标应该可以实现。然后将探索先进的可视化和 DEM 模拟工具，以对自然沉积的沙子和淤泥的微观机械行为进行真实的数学描述。挑战在于能够准确地表示颗粒几何形状，然后以数字方式跟踪颗粒的运动及其在接触点处的相互作用。目前，这种详细的数值模拟仅在具有相对开放的结构的沙粒组合上进行了验证。因此，我们的目标是将现有技术扩展到更紧凑的颗粒堆积和更复杂的几何形状，以探索织物对自然沉积物变形特征的影响。这应该有助于使用多尺度本构模型对颗粒沉积物行为进行建模的最先进技术的未来进步。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力优点和更广泛的影响审查进行评估，被认为值得支持标准。