Micromechanics of unsaturated porous media across the saturation regimes: Applications to stability and resilience of geostructures under climate change

饱和状态下不饱和多孔介质的微观力学：在气候变化下地质结构稳定性和恢复力中的应用

• 批准号: RGPIN-2022-03180
• 负责人: Wan, Richard
• 金额: $ 4.52万
• 依托单位: University of Calgary
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=749441
• 关键词: Micromechanics; unsaturated; porous; media; across

In nature, unsaturated porous media are ubiquitous, e.g., footprints in sand and snowballs. How water occupies pore spaces of a soil such as in a slope is crucial-the cyclical wetting and drying of soils due to fluctuating climate can be disastrous, triggering landslides by liquefaction. Global warming is also causing permafrost thaw, creating soil moisture changes that cascade into CO2 release and landslides in the Canadian North. The central question is: How does water saturation in soils lead to distinct capillary regimes that can spontaneously modify their behaviour from solid to fluid state? How do we mathematically describe such a brutal transition that translates into a wetting collapse of geostructures? It turns out that this longstanding question has microstructural origins, being intimately linked to the loss of suction between grains. Whereas most studies take rather a phenomenological view that does not go deep into the physics of the microstructure, thus hindering progress, the proposed research investigates formidable issues such as how grain contacts, water menisci and interfaces between phases in an unsaturated soil evolve as water saturation increases (decreases) during wetting (draining). A multiscale approach is thus mandated where an element volume capturing all the local microstructural complexities of fluid and solid interactions is studied, and thereafter statistically upscaled to establish relationships between stress, strain, and capillary stresses at the continuum level for the analysis of a geostructure. A new framework is developed that underscores the collective interactions of water and air in pore spaces coupled with solid particles through discrete element modelling for solids and the Lattice Boltzmann method for water and air. This facilitates the modelling of complex formation, coalescence, and rupture of water menisci in the pore space. Unsaturated constitutive laws that account for these transitions are developed and implemented into a Material Point Method computational code. This groundbreaking modelling paradigm provides a powerful tool that can precisely analyze the complex response of geostructures against climatic fluctuations, especially flow-type failures. The research program will significantly advance the knowledge in unsaturated soil mechanics by elucidating the dynamics of wetting and drying under climatic fluctuations. The developed computational tool will offer quantitative analysis of existing geostructures combined with field monitoring and machine learning for mitigating geohazards. Building on existing successes, this goal will be achieved through the training of HQP in interlinked tasks, and in collaboration with industry and an international research network. The highly impactful nature of the research in the light of growing uncertainly around climate change today, such as the recent flooding and landslide events in Europe, makes this proposal an extremely valuable endeavour.

在自然界中，不饱和多孔介质是普遍存在的，例如，沙滩上的脚印和雪球水如何占据土壤的孔隙空间，例如在斜坡中，这是至关重要的--由于气候波动，土壤的周期性变湿和变干可能是灾难性的，会因液化而引发山体滑坡。全球变暖也导致永久冻土融化，造成土壤水分变化，导致加拿大北部的二氧化碳释放和山体滑坡。核心问题是：土壤中的水饱和度如何导致不同的毛细管制度，可以自发地修改其行为从固体到流体状态？我们如何从数学上描述这种转化为地质结构湿塌的残酷转变？事实证明，这个长期存在的问题有微观结构的根源，与谷物之间吸力的丧失密切相关。虽然大多数研究采取现象学的观点，不深入到微观结构的物理学，从而阻碍了进展，但拟议的研究调查了一些棘手的问题，如颗粒接触，水渗透和非饱和土壤中各相之间的界面如何随着润湿（排水）过程中水饱和度的增加（减少）而演变。因此，一个多尺度的方法是强制执行的元素体积捕获所有的局部微观结构的复杂性的流体和固体的相互作用进行了研究，然后统计放大，以建立应力，应变和毛细管应力之间的关系，在连续体水平的地质结构的分析。开发了一个新的框架，强调通过固体的离散元建模和水和空气的格子玻尔兹曼方法与固体颗粒耦合的孔隙空间中的水和空气的集体相互作用。这有利于模拟复杂的形成，聚结，并在孔隙空间中的水凝胶破裂。不饱和本构关系，占这些过渡的开发和实施到一个材料点法计算代码。这种开创性的建模范式提供了一种强大的工具，可以精确分析地质结构对气候波动的复杂响应，特别是流动型故障。该研究计划将通过阐明气候波动下的湿润和干燥动力学来显着推进非饱和土力学的知识。开发的计算工具将提供现有地质结构的定量分析，结合现场监测和机器学习，以减轻地质灾害。在现有成功的基础上，这一目标将通过在相互关联的任务方面对人力资源规划人员进行培训，并与工业界和国际研究网络合作来实现。鉴于当今气候变化的不确定性越来越大，例如欧洲最近发生的洪水和山体滑坡事件，这项研究具有高度影响力，因此这项建议是一项极其宝贵的努力。