3D Printed Particle Analogs for Coarse-grained Soils: Interpretation Framework

该项目涉及利用3D打印颗粒类似物进行粗粒土壤行为的基础研究。这些合成类似物将解决岩土工程中普遍存在的挑战，因为土壤是天然材料，其性质由其地质历史决定，其行为取决于数十个变量，包括颗粒形态和大小、级配和土壤状态。开发一种解释框架，包括基于颗粒组成材料刚度的压缩和剪切响应的标准化，将允许对由不同材料组成的土壤的响应进行定量研究。它还将允许数值模拟（例如离散元素建模，DEM）结果的验证。本研究:(i)提供系统和独立控制土壤类似物颗粒特性的能力，这可以改变当前的研究能力，以研究对许多应用都很重要的土壤行为方面，如渗透、污染物输送、细菌和真菌生长、侵蚀、承载能力、界面摩擦和土压力；（ii）促进来自工程和科学领域不同学科的研究人员之间的跨学科知识转移，如化学、机械和材料科学工程和物理学，他们研究不同颗粒材料（如土壤、粉末和颗粒）中的现象；（iii）促进在研究中使用3D打印，以改变岩土工程领域当前的实验研究技术；（iv）通过培训当地中学的教师和为本科生提供研究机会，在整个教育过程中增加西班牙裔学生的参与。许多研究人员通过不同土壤或土壤类似物的实验、离散元建模（DEM）模拟或先进的成像技术，对土壤行为进行了定性理解。阻碍使用这些工具构建定量理解的两个主要障碍是：(i)目前的实验方法无法系统地改变天然土壤颗粒的一个特征，同时保持其他特征不变（影响对天然土壤研究的解释），（ii）缺乏一个框架，允许独立于组成材料特性差异的行为研究（影响对土壤类似物研究的解释）。本研究项目的假设是3D打印土壤类似物的响应可以直接定量地了解自然土壤的响应。在颗粒尺度和单元尺度的一维压缩试验中量化了颗粒接触变形的影响，在三轴压缩剪切试验中表征了颗粒接触与土骨架变形的耦合效应。这些实验见解与基于刚度的归一化方案相结合，该方案考虑了组成材料特性的差异，构成了一个框架，允许直接比较仅受颗粒特性和土壤状态影响的自然和模拟土壤的响应。开发的3D打印土壤类似物和解释框架将允许系统和独立的颗粒形状、表面粗糙度和尺寸处方，以详细研究粗颗粒土壤的行为。这将促进在颗粒和单元尺度上理解颗粒组成材料刚度对土壤压缩和剪切响应的影响，并将颗粒刚度的影响纳入临界状态土力学的框架中。

This project concerns the utilization of 3D printed particle analogs for the fundamental study of coarse-grained soil behavior. These synthetic analogs will address the pervasive challenge in geotechnical engineering caused by the fact that soils are natural materials whose properties are defined by their geologic history, and whose behavior depends on dozens of variables, including particle morphology and size, gradation, and soil state. Development of an interpretation framework, consisting of normalization of the compression and shear responses based on the stiffness of the particles constituent material stiffness, will allow for quantitative study of the response of soils comprised of different materials. It will also allow for validation of results from numerical simulations (e.g. Discrete Element Modeling, DEM). This research: (i) provides the ability to systematically and independently control particle properties of soil analogs, which can transform current research capabilities to study aspects of soil behavior that are important for many applications, such as seepage, pollutant transport, bacterial and fungal growth, erosion, bearing capacity, interface friction, and earth pressures, (ii) facilitates the trans-disciplinary transfer of knowledge among researchers from different disciplines within engineering and the sciences, such as chemical, mechanical and material science engineering and physics, who investigate phenomena in different granular materials such as soils, powders, and grains, (iii) promotes use of 3D printing in research to transform current experimental research techniques within geotechnical engineering, and (iv) increases the involvement of Hispanic students through the entire educational track by training teachers from local middle schools and providing research opportunities to undergraduate students. Qualitative understanding of soil behavior has been achieved by many researchers through experiments on different soils or soil analogs, Discrete Element Modeling (DEM) simulations, or advanced imaging techniques. The two major barriers that have deterred the construction of quantitative understanding using these tools are: (i) the inability of current experimental methods to systematically change one characteristic of natural soil particles, while keeping the others unchanged (affecting interpretation of studies on natural soils), and (ii) the lack of a framework that allows for study of behaviors independently from differences in constituent material properties (affecting interpretation of studies on soil analogs). The hypothesis of this research project is that the response of 3D printed soil analogs can provide direct and quantitative understanding of the response of natural soils. The effects of particle contact deformation are quantified in particle- and element-scale 1D compression tests, and the coupled effect of particle contact and soil skeleton deformation are characterized in triaxial compression shear tests. These experimental insights, in combination with a stiffness-based normalization scheme that accounts for differences in constituent material properties, comprise a framework that allows for direct comparison of the response of natural and analog soils that is only influenced by particle characteristics and soil state. The developed 3D printed soil analogs and interpretation framework will allow for systematic and independent prescription of particle shape, surface roughness, and size for the detailed study of the behavior of coarse-grained soils. This will advance the understanding of the influence of particle constituent material stiffness on the compression and shear response of soils at the particle- and element-scales, and incorporate the effect of particle stiffness on the framework of critical state soil mechanics.