Evolution of Contact Shear Resistance and Arching in Silica Sand

颗粒状岩土材料的时间依赖行为是人们对其特性了解最少的，而颗粒状材料中的拱起是一种难以捉摸的现象，没有工程分析所需的明确数学框架。本研究解决了硅砂颗粒之间的接触随时间的演变，以及其对强度、刚度和砂拱形成的影响。这项研究旨在发现控制土壤行为的微观过程。寻求颗粒状地质材料中颗粒间接触和拱起之间的联系，目的是在工程分析中更明智地使用拱起。这项研究的双重目的是促进科学的进步，以及将研究成果应用于国家基础设施的发展而产生的社会效益。土壤的行为通常是用现象学模型来描述的，该模型预测了它们在工程尺度上对荷载和荷载持续时间的响应。然而，这些模型并不能解释它们所描述的行为的物理原因。为了对物质行为施加任何影响，需要发现行为的起源。本研究解决了为什么硅砂接触表现出时间依赖性行为，导致接触剪切阻力和刚度随时间变化的基本问题。构建新一代晶粒尺度试验装置，用于复杂载荷下的晶粒接触试验。接触测试将产生接触行为的数学描述，随后将扩展到谷物接触网络和工程尺度行为。本文将研究源自粒间接触处的物质性质演化过程对土体内拱形成的影响。不同的单元方法和有限元分析都将进行，以深入了解颗粒材料中难以捉摸的拱状现象。研究成果将以工程应用为例加以说明。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The time-dependent behavior of granular geomaterials is among the least understood of their characteristics, and arching in granular materials is an elusive phenomenon without the definitive mathematical framework needed for engineering analyses. This research addresses time-dependent evolution of contacts between silica sand grains, with its consequences on strength, stiffness, and arching formation in sand. This study seeks to discover microscopic processes which govern the behavior of soils. A link between evolution of inter-grain contacts and arching in granular geomaterials is sought, with a goal of a more informed use of arching in engineering analyses. The twofold purpose of the study is in promoting progress in science, and in benefits to society stemming from application of the research results in the development of national infrastructure. Behavior of soils is typically described by phenomenological models that predict their response to loads and load duration on the engineering scale. These models, however, do not explain the physical cause of the behavior they describe. In order to exercise any influence over the material behavior, the origin of the behavior needs to be discovered. This research addresses the fundamental question of why silica sand contacts exhibit time-dependent behavior that leads to time-dependent evolution of contact shear resistance and stiffness. A new generation of grain-scale testing apparatus will be constructed to test grain contacts subjected to complex loads. Testing of contacts will give rise to a mathematical description of contact behavior, which, subsequently, will be upscaled to the networks of grain contacts, and to the engineering scale behavior. The influence of the evolution process of material properties that originates at inter-grain contacts on formation of internal arches in soil masses will be studied. Both the distinct element approach and finite element analysis will be carried out to gain insight into the elusive phenomenon of arching in granular materials. The outcomes of the research will be illustrated with engineering applications.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.