Multi-scale modeling of coupled multiphysics processes in geomaterials: Theoretical and experimental study

在岩土工程和环境工程以及能源生产的各个方面，例如废物处理（包括核废料）和土壤污染问题中，已经观察到多物理场过程和不同程度的相互耦合，其中热效应增加了多相耦合的复杂性。油气工业中页岩等致密岩水力破裂过程中的水-力学相互作用与水入渗引起的边坡破坏。对于这些复杂的工程问题，仅仅对各个物理过程单独进行分析是不够的。相反，在分析中考虑它们的相互耦合是至关重要的。这些过程涵盖了不同的尺度，从颗粒大小到更大的工程尺度。因此，需要在多尺度上考虑各种耦合的多物理场过程来研究相关基础设施的性能。

Multiphysics processes and different levels of mutual coupling have been observed in various aspects of geotechnical and environmental engineering and of energy production, such as waste disposal (including nuclear waste) and soil pollution problems where heat effects add to the complexity of multi-phase couplings, hydro-mechanical interactions during hydraulic fracture of shale or other tight rocks in oil and gas industry and slope failure induced by infiltration of water into the ground surface. It is not sufficient to solely carry out analysis on each physical process separately for these complicated engineering problems. Instead, it is crucial to consider their mutual coupling in the analysis. These processes cover different scales, from particle size to much larger engineering scales. Therefore, it is required to study the performance of relevant infrastructures by considering various coupled multiphysics processes on multi-scales. The main objectives of the research are to understand the coupled effects of different physics processes (particularly fluid flow and stress-induced deformation) on underlying mechanisms of instability and degradation in geomaterials. Thereafter, a mathematical framework will be developed across scales to describe material behavior, with micromechanical aspects of soil behaviour being properly taken into account. The research consists of theoretical analysis, laboratory tests and numerical modelling of soil behaviour involving mechanical, hydraulic and environmental processes. The experimental study includes the characterization of internal structure on particle level using X-ray micro-CT digital image analysis and laboratory tests on engineering soil properties to understand the effect of different processes, such as stress-induced deformation, internal structure change and water flow. The mathematical work will develop a new multi-scale, multi-phase formulation that penetrates down to details of grain activity at the particle-scale, and back to the macro-scale through a micromechanical analysis and homogenization. The mathematical framework, after being implemented into a computer modelling code and validated against benchmark problems, will be used to analyze a variety of practical problems such hydraulic fracture of rock. The proposed research is unique in that it accounts for the effect of coupled hydro-mechanical-environmental processes on the behaviour of geomaterials. The developed multi-scale modeling methods employ information at the grain level for larger scale simulations for difficult problems, such as seasonal deterioration of highway pavements, hydraulic fracture of rock, as well as for the impact of climate change on geotechnical infrastructures. Six graduate students will be trained in the proposed research. Clearly, each would become a highly trained researcher at the end of the project.