Multiscale Thermo-Hydro-Mechanical Analysis of Thawing/Freezing Cycles in Partially Saturated Soils: Application to Stability of Permafrost Layers and Climate Change

部分饱和土壤解冻/冻结循环的多尺度热水力机械分析：在多年冻土层稳定性和气候变化中的应用

• 批准号: RGPIN-2020-06480
• 负责人: Pouragha, Mehdi
• 金额: $ 1.89万
• 依托单位: Carleton University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=741240
• 关键词: Multiscale; Thermo; Hydro; Mechanical; Analysis

The permafrost layers in the Northern Canada regions are most sensitive to climate change effects since the thawing of frozen soil leads to degradation of strength and substantial instabilities. The geo-environmental impacts of permafrost landslide can be catastrophic for infrastructure and the environment since the mechanical instabilities induce significant deflections to, for instance, major pipelines residing in these zones, with ensuing potential of hazardous materials being released into the environment. More direct environmental effects such as loss of vegetation coverage, and the release of the methane trapped in permafrost layers are also among consequences of landslides in cold regions. Notwithstanding the prevalence of landslide instabilities in the permafrost regions, the current state of research in this field relies strongly on empirical observations and phenomenological approaches. The lack of coherent analytical studies is primarily due to the challenges associated with incorporating phase change phenomenon (thawing/freezing) into the multiscale calculation of stress and strain, as well as the modification thereof strength parameters. The objective of the current research is to develop a physically sound theoretical framework of multiphasic soil-water-ice-air systems where the overall deformational and strength behavior of permafrost soil is explained within a Thermo-Hydro-Mechanical (THM) framework, in terms of simpler interactions at the particle scale. The research is built upon my previous analysis of multiphasic soils where the crucial, but often overlooked, effect of soil/water /air interfaces are coherently incorporated into the formulation of stress and strain. While inheriting the subtleties of my previous analysis of unsaturated soils, the current research will further develop the mechanics of frozen soils by incorporating the thermal effects and phase change of interpore water, transport aspects and the ensuing deformational characteristics. The overall degradation of strength parameters of thawing permafrost soil is naturally accounted for at microscopic scale by disappearance of the cohesive ice bonds, as well as by the irreversible deformations upon continual thawing/freezing cycles caused by fluctuating temperatures in the active layer. The research will, in short term, contribute towards better understanding of the physics underlying the geomechanical instabilities in the permafrost layers, enhancing the accuracy of our real-scale modelling and predictions, as well as increasing the safety and reliability of current and future designs of infrastructure in the North. Furthermore, in the long term, such fundamental insights in the basic components contributing to the soil's behavior will eventually be used to devise effective strategies to contain and prevent numerous landslides in the cold regions.

加拿大北部地区的永久冻土层对气候变化的影响最为敏感，因为冻土的融化会导致强度下降和严重的不稳定。永久冻土滑坡对地质环境的影响可能对基础设施和环境造成灾难性影响，因为机械不稳定性会导致这些地区的主要管道等发生重大偏转，从而可能导致有害物质释放到环境中。寒冷地区山体滑坡还会造成更直接的环境影响，例如植被覆盖范围的丧失以及永久冻土层中甲烷的释放。 尽管永久冻土地区普遍存在滑坡不稳定现象，但该领域的研究现状在很大程度上依赖于经验观察和现象学方法。缺乏连贯的分析研究主要是由于将相变现象（解冻/冻结）纳入应力和应变的多尺度计算及其强度参数的修改所面临的挑战。当前研究的目标是开发一个多相土壤-水-冰-空气系统的物理合理的理论框架，其中永久冻土的整体变形和强度行为在热-水-机械（THM）框架内解释，粒子尺度上更简单的相互作用。这项研究建立在我之前对多相土壤的分析基础上，其中至关重要但经常被忽视的土壤/水/空气界面的影响被连贯地纳入应力和应变的公式中。在继承我之前对非饱和土分析的精妙之处的同时，当前的研究将通过结合孔隙间水的热效应和相变、传输方面以及随后的变形特征来进一步发展冻土力学。解冻永久冻土土的强度参数的整体退化在微观尺度上自然地被解释为内聚冰键的消失，以及由活动层中的温度波动引起的连续解冻/冻结循环中的不可逆变形。在短期内，该研究将有助于更好地了解永久冻土层地质力学不稳定性背后的物理原理，提高我们真实规模建模和预测的准确性，并提高当前和未来设计的安全性和可靠性。北部基础设施建设。此外，从长远来看，对土壤行为基本组成部分的这些基本见解最终将用于制定有效的策略，以遏制和预防寒冷地区的大量山体滑坡。