Evolution of Contact Shear Resistance and Arching in Silica Sand

颗粒岩土材料的时间相关行为是对其特性了解最少的材料之一，而颗粒材料中的拱化是一种难以捉摸的现象，没有工程分析所需的明确的数学框架。这项研究解决了硅砂颗粒之间接触随时间的演变，以及它对强度、硬度和砂中拱形形成的影响。这项研究试图发现支配土壤行为的微观过程。在颗粒岩土材料中寻找颗粒间接触的演化和拱化之间的联系，目的是在工程分析中更明智地使用拱化。这项研究的双重目的是促进科学进步，以及将研究成果应用于发展国家基础设施而造福社会。土体的特性通常由现象学模型描述，这些模型预测土体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。这项研究解决了为什么硅砂接触表现出随时间变化的行为这一基本问题，这导致了接触剪切阻力和刚度随时间的演变。将建造新一代颗粒尺寸测试装置，用于测试复杂载荷下的颗粒接触。对接触的测试将产生接触行为的数学描述，随后将被提升到颗粒接触网络和工程规模的行为。将研究起源于颗粒间接触的材料性质的演变过程对土体内部拱形形成的影响。为了深入了解颗粒材料中难以捉摸的拱形现象，我们将采用离散元方法和有限元分析方法。这项研究的结果将通过工程应用进行说明。这一奖项反映了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。

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.