Collaborative Research: Multi-scale Modeling and Measurement of Clay Aggregate Behavior

这项研究的目的是促进对粘土作为工程材料的力学行为的理解。粘土包含非常细的(2微米)带电的化学活性颗粒，其行为和组装受到较小(即分子和界面)尺度上单个颗粒上的物理化学力的强烈影响。不同种类的粘土矿物广泛存在于自然地质环境中，通常以团聚体或团簇的形式存在，其相互作用控制着用于基础设施设计和建设的富含粘土的土壤的宏观工程性质。虽然基于细观力学的实验和计算研究大大提高了对沙子(粒度大于75um)行为的理解，但粘土的颗粒性的重要性还没有得到广泛的研究。该合作项目旨在开发和验证一个新的多尺度框架，通过研究基本粘土颗粒的微观聚集以及生成的粘土集合体之间的相互作用来理解粘土的宏观(即连续尺度)力学性质。该项目将提供开发可用于地下工程的下一代粘土力学特性本构模型所需的基本理解，最终降低与基础设计、地下施工和地质能源资源(如粘土页岩等)的使用相关的风险和成本。这项研究将通过创建与粘土行为的小尺度测量和多尺度建模相关的在线模块，直接影响到未来岩土工程和岩土力学专业学生的教育。这项研究工作包括一个紧密结合的多尺度实验、原子化和粗粒度的多尺度模拟程序，对一种常见的粘土矿物伊利石进行模拟。这项研究的主要任务包括：1)在一系列孔隙水化学条件下对单个粘土集料的行为进行建模和实验验证；2)开发研究集料-集料相互作用和组构的新的建模技术和实验方法(即颗粒取向和取向分布函数的定量测量)；3)通过与粘土性质的宏观测量进行比较，验证多尺度模型预测的有效性。实验测量将使用马萨诸塞大学阿默斯特分校(UMA)现有的实验室设施以及阿贡国家实验室的分析设施，而麻省理工学院(MIT)的数值模拟将利用NSF极端科学和工程发现环境(XSEDE)的国家超级计算资源。通过建立一个理解基于颗粒的粘土微观力学的框架，这项研究旨在提供一个创新的多尺度视角来解释基于连续介质的粘土特性的基本基础，如粘聚力和蠕变，这些特性迄今只能通过宏观方法从现象上观察到。长期目标是推广这一方法，以便能够自下而上地预测复杂的天然土壤的力学性质，这些土壤包括不同粘土矿物与粉砂和沙子大小的颗粒的混合物，以及不同的孔隙水化学。

The goal of this research is to advance the understanding of the mechanical behavior of clays as engineering materials. Clays comprise very fine ( 2 um), electrically charged, chemically active particles whose behavior and assembly are strongly affected by physico-chemical forces operating on individual particles at the smaller (i.e., molecular and interfacial) scales. Clay minerals of different varieties occur widely in natural geological environments and are generally found in the form of aggregates or clusters whose interactions control the macroscopic engineering properties of clay-rich soils used in the design and construction of infrastructure. While micromechanics-based experimental and computational research has advanced significantly the understanding of the behavior of sands (particle sizes greater than 75um), the importance of the particulate nature of clays has not been extensively investigated. This collaborative project aims to develop and validate a new multiscale framework for understanding the macroscopic (i.e., continuum scale) mechanical properties of clays by studying the microscale aggregation of elementary clay particles and the interactions between the resultant clay aggregates. The project will provide the fundamental understanding needed to develop the next generation of constitutive models for mechanical properties of clays that can be used for subsurface engineering, ultimately reducing risks and costs associated with the design of foundations, underground construction and use of geological energy resources (e.g., clay shales, etc.). The research will impact directly upon the education of future geotechnical engineering and geomechanics students through the creation of online modules related to the small-scale measurement and multiscale modeling of clay behavior. The research work comprises a closely-integrated program of multiscale experimentation, atomistic and coarse-grained multiscale simulations for one common clay mineral, illite. The research involves the following main tasks: 1) modeling and experimental validation of individual clay aggregate behavior under a range of porewater chemistry conditions; 2) development of new modeling techniques and experimental methods for investigating aggregate-aggregate interactions and fabric (i.e., quantitative measurement of particle orientation and of orientation distribution function); and 3) validation of multiscale model predictions through comparison with macroscopic measurements of clay properties. Experimental measurements will use existing laboratory facilities at the University of Massachusetts Amherst (UMass) as well as the analytical facilities at the Argonne National Laboratory, while numerical simulations at the Massachusetts Institute of Technology (MIT) will take advantages of NSF eXtreme Science and Engineering Discovery Environment (XSEDE) national supercomputing resources. By developing a framework for understanding particulate-based clay micromechanics, the research aims to provide an innovative multiscale perspective for explaining the underlying basis of continuum-based clay properties such as cohesion and creep, which have to date only been observed phenomenologically via macroscopic approaches. The long-term goal is to generalize the methodology to enable bottom-up prediction of mechanical properties for complex natural soils that comprise mixtures of different clay minerals with silt- and sand-sized particles as well as varying porewater chemistry.