Towards a Unified Unsaturated Soil Mechanics Framework for Interpretation of Frozen and Unfrozen Soils

在加拿大的许多地区，冬季冻土的热-水-力学行为与一年中其余时间的未冻土相比有很大的不同。然而，饱和土力学原理在加拿大的岩土工程实践中被广泛应用，忽略了冻土和未冻土中吸力的影响。最近，联合国政府间气候变化专门委员会(IPCC)表示，全球变暖效应将导致到2030年，年气温比工业化前水平高1.5摄氏度。这种气温上升可能会导致极端洪水、干旱时间延长和土壤温度的显著变化。换句话说，全球变暖效应对岩土基础设施的设计提出了挑战。通过这项研究建议，将制定一个统一的框架，以合理解释非饱和土热-水-力学行为，考虑冻结和未冻结条件，包括气候变化的影响。短期目标将是在渥太华大学岩土实验室对各种典型的加拿大土壤进行全面的实验研究，这些土壤包括沙土、冰川土、膨胀土、粉质粘土和敏感粘土。这些研究的结果将用于开发膨胀土中桩基础设计的框架、冻土和未冻土中路面的力学模型以及膨胀粘土的边坡稳定性分析。这项研究计划的长期目标将是了解加拿大各种土壤的热-水-力学耦合行为的复杂机制。来自安大略省交通部(MTO)、渥太华大学和其他预期机构的额外资金将为未来十年的一些目标提供部分支持。预期影响这项研究计划有望朝着开发一种新的框架向前迈进一步，该框架将非饱和土力学扩展到冻土和未冻土，并考虑到气候变化，以便合理设计各种岩土基础设施。申请人从以前的探索奖助金中获得的研究工作被纳入了MTO的人行道设计中。此外，申请人早期对非饱和土壤行为的研究正在南非岩土工程实践手册中实施，并被加拿大开发的商业软件Geo-SLOPE广泛使用。预计目前的一些研究可能会出现在加拿大基础工程手册中，该手册建议包括与非饱和土特性相关的最新发展。最后，这项研究将培养3名博士、2名硕士和3名BASC学生，他们将获得基于非饱和土力学的岩土基础设施设计方面的高级知识和技能。

The thermo-hydro-mechanical behavior of a frozen soil during winter in many regions of Canada is significantly different in comparison to unfrozen soil during the remainder of the year. However, saturated soil mechanics principles are widely used in Canadian geotechnical practice ignoring influence of suction in both frozen and unfrozen soils. Recently, the UN Intergovernmental Panel on Climate Change (IPCC) suggested that global warming effects would contribute to an increase in annual temperatures of 1.5oC above pre-industrial level temperatures by 2030. This temperature rise would likely contribute to extreme floods, extended drought periods and significant variations in soil temperatures. In other words, global warming effects offer challenges to the design of geotechnical infrastructure. Through this research proposal, a unified framework will be developed for the rational interpretation of thermo-hydro-mechanical behavior of unsaturated soils taking into account frozen and unfrozen conditions including climate change effects. The short-term objectives will be directed towards undertaking comprehensive experimental studies at the University of Ottawa geotechnical laboratory on a variety of typical Canadian soils; namely, sand, glacial till, expansive soil, silty clay and sensitive clay. The results of these studies will be used in the development of a framework for the design of pile foundations in expansive soils, mechanistic models for pavements in frozen and unfrozen soils and slope stability analyses of expansive clays. The long-term objectives of this research program will be directed towards understanding the complex mechanics of the coupled thermo-hydro-mechanical behavior of various Canadian soils. Additional funding from Ministry of Transportation of Ontario (MTO), University of Ottawa and other anticipated agencies will provide partial support for some of the objectives over the next decade. Expected impact This research program is expected to be step forward towards the development of a novel framework that extends the mechanics of unsaturated soils for frozen and unfrozen soils taking account of the climate changes for the rational design of various geotechnical infrastructure. The applicant's research work from the previous Discovery grants is incorporated into the design of pavements by the MTO. Also, the applicant's earlier research on the unsaturated soils behavior is being implemented in the South Africa Geotechnical Practice manual and is widely used by the Geo-slope, commercial software developed in Canada. It is expected that some of the present studies may find place into the Canadian Foundation Engineering Manual which is proposing to include state-of-the-art developments related to unsaturated soil behavior. Finally, this research will train 3 PhD, 2 MASc and 3 BASc students, who will acquire advanced knowledge and skills in the design of geotechnical infrastructure based on the mechanics of unsaturated soils.