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: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=636193
• 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-consolidationMorgenstern 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°CWhen 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 soilsThe 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百分之四十。北方拥有世界一流的矿产、石油和天然气储量，是一个拥有巨大经济机遇的地方。北方的可持续资源开发需要设计和建设基础设施，如道路、挡水结构、管道、采矿设施、港口、机场和建筑物。北方也处于气候变化影响和适应的最前线。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。如果充分了解冻融效应并适应气候变化趋势，就能提供充分的保护。本研究计划解决了几个问题：• 二维或三维环境中的解冻固结；• 温度高于-1 °C 时富含冰的土壤的蠕变行为；• 解冻材料的剪切强度和边坡稳定性。解冻固结Morgenstern 和 Nixon (1971) 研究了 一维公式中的解冻固结过程并使用分析技术及其固有的简化。他们的分析表明，解冻土壤中的孔隙压力分布与解冻固结比 R 相关，R 是解冻速率和解冻前沿排水速率的耦合参数。主要假设是解冻的土壤在解冻完成之前不会沉降。不用说，在富含冰的土壤中，解冻沉降率高达 70%，在分析过程中忽略沉降会导致设计过于保守。该研究提案使用现代计算工具得出流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解冻土壤中的排水、解冻前沿传播和固结与地表的移动边界耦合起来。将建立新的孔隙压力图，并提出分析具体问题（地基、道路、管道和土坝、融化斜坡中的边坡稳定性）的方法。温度高于-1°C时富冰土的蠕变行为当冻土受到载荷时，它将响应瞬时变形和随时间变化的变形。速率效应取决于温度和应力，并随冻土中冰的数量而变化。在文献中发现大量冻土数据的温度低于-1°C。然而，考虑到每百年几度的气候变化，需要对温度高于-1℃的富含冰的土壤进行更多的研究。这对于冰透镜平行于倾斜地面形成的斜坡的情况尤其重要。这些斜坡的蠕动速度可能高达 2m/年，与瑞士阿尔卑斯山冰川的行为相同。实验室测试将在控制在特定温度且变化小于0.05°C的环境室中进行，以获得蠕变参数和本构方程。 Flex-PDE 将用于利用高温参数研究斜坡和其他结构的行为。解冻土壤的抗剪强度拟议的研究还将研究解冻土壤的抗剪强度与孔隙压力消散程度之间的关系。可用的数据很少，并且需要在解冻期间进行适当的设计，以确保永久冻土上建造的结构的稳定性。