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。 粘土由非常细（2 μ m）、带电、化学活性颗粒组成，其行为和组装受到作用于较小颗粒（即，分子和界面）尺度。 不同种类的粘土矿物广泛存在于自然地质环境中，通常以聚集体或簇的形式存在，其相互作用控制着基础设施设计和建设中使用的富含粘土的土壤的宏观工程性质。 虽然基于微观力学的实验和计算研究已经大大提高了对砂（粒径大于75 μ m）行为的理解，但粘土颗粒性质的重要性尚未得到广泛研究。 这个合作项目旨在开发和验证一个新的多尺度框架，用于理解宏观（即，通过研究基本粘土颗粒的微尺度聚集和所得粘土聚集体之间的相互作用，该项目将提供开发可用于地下工程的粘土力学特性的下一代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（例如，粘土页岩等）。 该研究将直接影响未来的岩土工程和地质力学学生的教育，通过创建与粘土行为的小规模测量和多尺度建模相关的在线模块。研究工作包括一个多尺度实验，原子和粗粒度的多尺度模拟一个共同的粘土矿物，伊利石的紧密集成的程序。 该研究涉及以下主要任务：1）在一系列孔隙水化学条件下单个粘土骨料行为的建模和实验验证; 2）开发新的建模技术和实验方法，用于研究骨料-骨料相互作用和结构（即，颗粒取向和取向分布函数的定量测量）;和3）通过与粘土性质的宏观测量比较来验证多尺度模型预测。 实验测量将利用马萨诸塞州阿默斯特大学（UMass）现有的实验室设施以及阿贡国家实验室的分析设施，而马萨诸塞州理工学院（MIT）的数值模拟将利用NSF eXtreme科学和工程发现环境（XSEDE）国家超级计算资源。 通过开发一个框架来理解基于颗粒的粘土微观力学，该研究旨在提供一个创新的多尺度视角来解释基于连续体的粘土性质的基础，如粘聚力和蠕变，迄今为止只能通过宏观方法从现象学上观察。 长期目标是推广该方法，使复杂的天然土壤，包括不同的粘土矿物与淤泥和沙子大小的颗粒以及不同的孔隙水化学的混合物的机械性能的自下而上的预测。

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.