The Role of Fabric on the Behavior of Granular Materials Subjected to Cyclic Loading

预测颗粒材料的循环行为仍然是一项重大的工程挑战，过去几十年开发的现有计算机模型还没有充分捕捉到这一挑战。颗粒材料的循环行为在许多应用中是至关重要的，包括地震荷载下的土壤行为和近海的清洁能源收集。目前的模型中缺少的一环是包含内部颗粒结构(织物)，它被认为控制颗粒材料的整体行为，特别是在材料经历载荷反转的循环载荷下。这项研究的目的是通过仔细研究织物的影响来扩展计算机模型对承受循环载荷的颗粒材料的预测能力。这项研究将使用尖端的计算、实验和现场技术来开发沙子等颗粒状材料的下一代模型。这项研究是加州理工学院和挪威岩土研究所合作进行的。此外，该项目将有助于对本科生和研究生的培训。本科生将通过加州理工大学的夏季本科生研究奖学金参与进来。这项研究也将对继续扩大国际岩土工程教育基础设施，特别是美国和欧洲之间的教育基础设施产生重大影响。本研究的工作假设是，连续统行为是在相邻颗粒相互作用的尺度上编码的。这些相互作用建立了一个应力路径网络或结构，可以动态适应不断变化的载荷条件；产生了像力链这样的介观特征，这是颗粒状材料所独有的。其结果是，织物的演化导致材料的介观尺度和连续统响应的连续变化。缺乏能够准确预测颗粒材料循环行为的连续介质模型可以归因于普遍缺乏对作为循环载荷的函数的组构的演变以及它如何影响颗粒材料行为的理解。本研究旨在通过完成三个中心研究任务来填补这一空白：1：固有结构的表征和重构；2：循环应力路径下的结构演化建模；3：结构演化关系的连续描述和验证。这项研究将激励新的实验仪器的设计，并激发新一代颗粒材料的预测本构模型。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。

Predicting the cyclic behavior of granular materials remains a major engineering challenge that is not yet sufficiently captured by existing computer models developed in the last few decades. Cyclic behavior of granular materials is critical in a large number of applications, including soil behavior under earthquake loading and clean energy harvesting offshore. A missing link in the current models is the inclusion of internal granular structure (fabric), which is known to control the overall behavior in granular materials, especially under cyclic loads where the material experiences load reversals. The objective of this research is to extend the predictive capability of computer models for granular materials subjected to cyclic loading by carefully investigating the effects of the fabric. This research will use cutting edge computational, experimental and in situ techniques to develop next-generation models for granular materials such as sands. This research is a collaboration between Caltech and the Norwegian Geotechnical Institute. Furthermore, this project will contribute to the training of students at the undergraduate and graduate levels. Undergraduate students will be involved via the summer undergraduate research fellowship at Caltech. This research will also have significant impact on continuing to expand the international educational infrastructure in geotechnical engineering, especially between the United States and Europe.The working hypothesis of this research is that continuum behavior is encoded at the scale where neighboring grains interact. These interactions establish a stress path network, or fabric, that adapts dynamically to changing loading conditions; giving rise to meso-scale features like force chains, which are unique to granular materials. The upshot of this is that the evolution of fabric induces continuous change in the meso-scale and the continuum response of the material. The dearth of continuum models capable of predicting accurately the cyclic behavior of granular materials could be attributed to a general lack of understanding of how fabric evolves as a function of cyclic loading and how it influences the granular material behavior. This research aims to fill this gap by accomplishing three central research tasks: 1: Characterization and reconstitution of inherent fabric; 2: Modeling fabric evolution in cyclic stress paths; 3: Continuum description and validation of fabric evolution relations. This research will motivate the design of new experimental apparatuses and inspire a new generation of predictive constitutive models for granular materials.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.