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.

加拿大北部地区的多年冻土层对气候变化的影响最敏感，因为冻结土壤会导致力量和实质性不稳定的降解。多年冻土滑坡的地理环境影响可能是对基础设施和环境的灾难性的，因为机械不稳定性会引起大量偏转，例如，在这些区域中，主要的管道中的主要管道会导致随之而来的危险材料的潜力被释放到环境中。更直接的环境影响，例如植被覆盖率的丧失以及被困在多年冻土层中的甲烷的释放也是寒冷地区滑坡的后果之一。 尽管在多年冻土区域中流行的不稳定性的率很高，但该领域的当前研究状态在很大程度上依赖于经验观察和现象学方法。缺乏相干分析研究主要是由于将相变现象（解冻/冻结）纳入压力和应变的多尺度计算以及其强度参数的修改所带来的挑战。当前研究的目的是开发一个多相土壤冰 - 冰 - 空气系统的物理理论框架，在该系统中，在粒子尺度上的简单相互作用方面，在热 - 热机械（THM）框架中解释了永久冻土土壤的总体变形和强度行为。这项研究是基于我对多相土壤的先前分析而建立的，在这些土壤中，土壤 /水 /空气界面的关键但经常被忽略的影响相干地纳入了压力和应变的配方中。在遗传了我先前对不饱和土壤的分析的细微之处，当前的研究将通过纳入室间水，传输方面和随之而来的变形特征的热效应和相变，进一步发展冷冻土壤的机制。通过粘性冰键的消失以及通过不断融化/冻结的周期，由于有效层的波动温度而导致的不变变形，自然而然地以微观量表来解释融化的多年冻土土壤强度参数的总体降解。这项研究将在短期内有助于更好地理解永久冻土层中的地质力学不稳定性的基础物理学，从而提高了我们的实际建模和预测的准确性，并提高了北部基础设施的当前和未来设计的安全性和可靠性。此外，从长远来看，对促成土壤行为的基本组成部分的这种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许多滑坡。