Development of Micromechanically-Based Models for Unsaturated Geomaterials

与基础设施、能源和环境相关的新出现的地质力学问题对岩土工程的基本原理提出了挑战。例如，不饱和、热和耦合条件需要超越传统理论的分析，这些理论本质上大多是现象学的。最简单的情况下，不饱和度是指存在不止一种流体，例如：液体和气体通过孔隙空间内的界面分离。这导致不饱和介质的行为与干燥或完全饱和的情况有很大不同。事实上，不饱和度赋予介质明显的内聚力、更高的强度和刚度，这是湿度和温度的函数。在变化的水力和热负荷（例如气候波动或气体条件）下，强度的增加会消失。因此，强度可能会迅速丧失，导致地质结构自发塌陷失效。***本研究的总体目标是对作为多相系统的地质材料的不饱和条件进行更根本的科学研究。这将通过探索各种尺度直至颗粒和孔隙尺度（包括水弯液面）来实现。通过认识新现象，我们对不饱和介质的理解将得到扩展，这些新现象对于在判断、质量和安全方面改进工程实践中的设计至关重要。所采用的方法是多尺度的，探讨各个相（包括分隔它们的界面）对通过机械力相互接触的颗粒施加的压力的性质。一个重要的方面是阐明界面内存在的界面张力对多相流的作用，以及非饱和地质材料的强度、变形和破坏特征。***该研究以数学方式检验了异质随机颗粒组件中的力传递，颗粒由离散液体弯月面连接作为代表性的基本体积。因此，可以通过了解颗粒堆积和液桥统计数据的均质化方案来计算出包括界面在内的各个相的应力贡献。这将阐明许多由界面张力驱动的众所周知的过程，例如作为饱和度函数的毛细管应力或吸力应力。与之前的工作相比，该分析将涵盖液体弯月面的空间分布、固体骨架的织物各向异性、温度，并确定控制强度和变形的有效应力。除了确定不饱和介质中应力张量的各个组成部分外，还将按照能量方法导出相关的应变张量。***这项研究的应用包括有毒废物处理、多孔介质中的污染物传输以及地质构造中的二氧化碳注入。**

Emerging geomechanics problems associated with infrastructure, energy and the environment present challenges to basic tenets of geotechnical engineering. For instance, unsaturated, thermal and coupled conditions demand analyses that go beyond traditional theories which are mostly phenomenological in nature. Unsaturation in the simplest case refers to the presence of more than one fluid, e.g. liquid and gas separated by interfaces within the pore space. This results in the behaviour of an unsaturated medium being vastly different from the dry or fully saturated case. In fact, unsaturation confers the medium with an apparent cohesion, a higher strength and stiffness that are a function of moisture and temperature. This gain in strength is evanescent under varying hydraulic and thermal loads such as climatic fluctuations or gassy conditions. As such, strength could be rapidly lost causing spontaneous collapse failures in geostructures.***The overall goal of this research is to pursue a more fundamentally scientific study of unsaturated conditions in geomaterials as multiphasic systems. This will be accomplished by exploring the various scales down to the particle and pore scales, including the water menisci. Our understanding of unsaturated media will be extended by recognizing new phenomena key to the improvement of design in engineering practice in terms of judgement, quality and safety. The adopted approach is multiscale, probing into the nature of the pressures exerted by the individual phases, including interfaces separating them, on particles that are in mutual contact through mechanical forces. An important aspect will be to elucidate the role of interfacial tension that exists within interfaces on multiphase flow, as well as the strength, deformation and failure characteristics of unsaturated geomaterials.***The proposed research mathematically examines force transport in a heterogeneous random granular assembly with particles connected by discrete liquid menisci as a representative elementary volume. As such, stress contributions from the various phases, including the interfaces, can be worked out through a homogenization scheme knowing the statistics of the grain packing and liquid bridges. This will elucidate many well-known processes driven by interfacial tension such as capillary or suction stresses as a function of saturation. In contrast to previous work, the analysis will encompass the spatial distribution of liquid menisci, fabric anisotropy of solid skeleton, temperature, and identify an effective stress that controls strength and deformations. Besides determining the various components of the stress tensor in an unsaturated medium, the associated strain tensor will also be derived following an energy approach.***Applications of this research include toxic waste disposals, contaminant transport in porous media, and CO2 injection in geological formations.**