Thermo-Hydraulic-Mechanical Properties of Frozen and Thawing Soils

冻结和解冻土壤的热水力机械特性

• 批准号: RGPIN-2014-06037
• 负责人: Konrad, JeanMarie
• 金额: $ 2.04万
• 依托单位: Université Laval
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611989
• 关键词: Thermo; Hydraulic; Mechanical; Properties; Frozen

The North is forty percent of Canada’s land mass. With world-class mineral, oil and gas deposits, the North is a place of tremendous economic opportunity. Sustainable resource development in the North requires to design and build infrastructures such as access roads, water retaining structures, pipelines, mining installations, ports, airports and buildings. The North is also on the front line of climate change impacts and adaptation. Strong environmental protection is an essential component of sustainable development, especially in a permafrost environment. Adequate protection is provided if the freeze-thaw effects are well understood and adapted to the climate change trends. This research proposal addresses several issues: • Thaw-consolidation in a two of three dimensional environment; • Creep behaviour of ice-rich soils at temperatures higher than -1 °C; • Shear strength of thawed materials and slope stability. Thaw-consolidation Morgenstern and Nixon (1971) have studied the thaw-consolidation process in a one-dimensional formulation and using analytical techniques with its inherent simplifications. Their analysis showed that the pore pressure distribution in the thawed soil can be related to the thaw-consolidation ratio, R, which is a parameter coupling thaw rate and rate of water drainage away from the thaw front. The main assumption was that the thawed soil did not settle until thaw was complete. Needless to say that thaw settlements van reach up to 70% in ice rich soils and neglecting settlement during the analysis leads to overly conservative design. This research proposal uses modern computing tools to derive a solution in which the processes are fully coupled. Flex-PDE will allow to couple drainage in the thawed soil, thaw front propagation and consolidation with a moving boundary at the surface in one, two or three dimensional environments. New pore pressure charts will be established and a methodology for analysis specific problems (foundations, roads, pipelines and earth dams, slope stability in thawing slopes) will be proposed. Creep behaviour of ice-rich soils at temperatures higher than -1°C When a frozen soil is subjected to a load, it will respond with an instantaneous deformation and a time-dependent deformation. The rate effects are temperature- and stress-dependent and vary with the amount of ice present in the frozen soil. In the literature one finds a significant amount of data for frozen soils are temperature lower than -1°C. However, considering a climatic change of several degrees per hundred years, more study need to be conducted for ice-rich soils at temperatures higher than -1°C. This is particularly important for the case of slopes in which ice lenses have formed parallel to the sloping ground. These slopes may display creep rates as high as 2m/year, identically to the behaviour of glaciers in the Swiss Alps. Laboratory tests will be conducted in environmental chambers controlled to a specific temperature with a variation of less than 0.05°C in order to obtain creep parameters and constitutive equations. Flex-PDE will be used to study the behaviour of slopes and other structure using the parameters at high temperatures. Shear strength of thawed soils The proposed research will also investigate the relationship between shear strength and degree of pore pressure dissipation in thawing soils. Little data is available and is needed for adequate design during thaw for ensuring stability of structures built on permafrost.

北部占加拿大陆地面积的40%。北方拥有世界级的矿产、石油和天然气储量，是一个蕴藏着巨大经济机会的地方。北方的可持续资源开发需要设计和建设基础设施，如通路、蓄水结构、管道、采矿设施、港口、机场和建筑物。 朝鲜也站在气候变化影响和适应的第一线。强有力的环境保护是可持续发展的重要组成部分，特别是在永久冻土环境中。如果充分了解并适应气候变化趋势，就能提供充分的保护。 这项研究提案涉及几个问题： ·融化--在二维和三维环境中进行巩固； ·富冰土壤在温度高于-1摄氏度时的蠕变行为； ·解冻材料的抗剪强度和斜坡稳定性。 解冻-固结 Morgenstein和Nixon(1971)在一维公式中研究了融化-固结过程，并使用分析技术对其进行了内在简化。他们的分析表明，融化土中的孔压分布与融化固结比R有关，R是一个耦合融化速率和远离融化前沿的排水速率的参数。主要的假设是，融化的土壤在融化完成之前不会下沉。不用说，在富含冰的土壤中，融化的沉降量可能高达70%，在分析过程中忽略沉降量会导致设计过于保守。这项研究建议使用现代计算工具来推导出一个过程完全耦合的解决方案。FLEX-PDE将允许在一维、二维或三维环境中将融化土壤中的排水、融化前沿传播和固结与地表移动边界相结合。将建立新的孔压图表，并提出分析具体问题(地基、道路、管道和土坝、融化斜坡中的斜坡稳定性)的方法。 -1℃以上富冰土壤的蠕变特性 当冻土受到荷载作用时，它将以瞬时变形和时变变形响应。速率效应依赖于温度和应力，并随冻土中存在的冰量而变化。在文献中，人们发现有相当数量的冻土温度低于-1°C。然而，考虑到每一百年几度的气候变化，对于温度高于-1°C的富冰土壤，需要进行更多的研究。这对于冰透镜与坡地平行形成的斜坡的情况尤其重要。这些斜坡的蠕变速度可能高达2米/年，与瑞士阿尔卑斯山的冰川行为相同。为了获得蠕变参数和本构方程，实验室试验将在控制在低于0.05°C的特定温度下的环境箱中进行。FLEX-PDE将用于研究在高温下使用参数的斜坡和其他结构的行为。 融化土的抗剪强度 拟议的研究还将调查融化土中抗剪强度与孔压消散程度之间的关系。几乎没有数据可用，在融化期间需要进行适当的设计，以确保在永久冻土上建造的结构的稳定性。