CAREER: Mobility of Unfrozen Water in Frozen Soil

该学院早期职业发展（CAREER）奖支持研究，这将提高我们对冻土如何与周围环境中的热变化相互作用的理解。 理解土壤冻结和融化过程的一个关键因素是预测未冻结水的质量分数和流动性的能力（即在冻土中低于冰点的温度下有多少水保持液态，以及它如何移动）。 从历史上看，与未冻水相关的微尺度现象一直难以测量，而且人们对其了解甚少。 本研究采用最先进的测量技术的创新组合，以量化土壤冻融过程中假设的关键变量之间的关系，即未冻水含量和流动性，土壤zeta电位（与矿物表面电荷相关的参数），和土壤微结构。 具体而言，PI将（1）使用脉冲核磁共振（NMR）方法测量冻结阳离子处理土壤中未冻结水的质量和分子流动性;（2）将这些与使用X射线计算机断层扫描（CT）扫描，X射线衍射（XRD）和扫描电子显微镜（SEM）方法测量的土壤微团聚体形成和微结构相关联;和（3）将这些测量与阳离子处理的土壤颗粒在低于冰点温度下的zeta电位相关联。 从阿拉斯加土著科学与工程项目（ANSEP）招募的学生将通过向中学生提供的动手岩土工程模块，参与这项CAREER研究和K-8推广活动，提高学生准确预测冻土系统热量和质量平衡、冻土强度、和冻胀幅度--所有这些都取决于未冻水--将支持冻土对气候变化的响应规划，并将促进寒冷地区更有效和更经济的工程设计。 从这个CAREER研究的结果可以用来改善热量和质量传输模型，冻胀模型，并通过将增强的未冻水含量的功能，这将占未冻水的流动性和它的依赖于土壤特定的物理化学性质的冻土蠕变模型。 改进后的模型将产生深远的影响，包括：有助于科学界研究不断退化的永久冻土层释放的甲烷;作为由于永久冻土层不稳定而必须搬迁的北极社区的规划工具;提高冻土层不稳定斜坡的分析准确性;从而使设计更具成本效益，同时减少结构损坏和安全风险，例如埋地冷冻气体管道;在教育方面，让ANSEP学生参与这项研究将鼓励代表性不足的学生群体成为具有强大外联技能的工程专业人士，他们可以回到阿拉斯加的农村，激励下一代工程师。 增加阿拉斯加原住民学生在冻土工程的参与将导致一个更强大，训练有素的劳动力，能够解决北极独特的岩土工程问题，这是他们的社区的长期生存能力和成功发展的关键北极，在能源资源开发的下一个前沿。 让中学生接触动手工程活动和与当地环境密切相关的问题，将促进对工程的早期兴趣，从而可以进入工程职业生涯。

This Faculty Early Career Development (CAREER) award supports research that will improve our understanding of how frozen ground behaves as it interacts with thermal changes in the surrounding environment. A key element in understanding soil freezing and thawing processes is the ability to predict the mass fraction and mobility of unfrozen water (that is, how much water remains liquid at below-freezing temperatures within frozen soils, and how it moves). Historically, microscale phenomena associated with unfrozen water has been challenging to measure and poorly understood. This research uses an innovative combination of state-of-the-art measurement techniques to quantify relationships among hypothesized key variables in soil freezing and thawing processes, namely unfrozen water content and mobility, soil zeta potential (a parameter related to mineral surface charge), and soil micro-fabric. Specifically, the PI will (1) measure mass and molecular mobility of unfrozen water in frozen cation-treated soils using pulsed nuclear magnetic resonance (NMR) methods; (2) correlate these with measurements of soil micro-aggregate formation and micro-fabric using X-ray computed tomography (CT) scanning, X-ray diffraction (XRD), and scanning electron microscopy (SEM) methodologies; and (3) correlate these measurements to zeta potential of cation-treated soil particles at sub-freezing temperatures. Students recruited from the Alaska Native Science and Engineering Program (ANSEP) will participate in this CAREER research and in K-8 outreach through a hands-on geotechnical engineering module delivered to middle school-aged students.The ability to accurately predict heat and mass balance of frozen soil systems, frozen soil strength, and frost heave magnitude - all of which depend on unfrozen water - will support planning for permafrost response to climate change, and will facilitate more efficient and economic engineering design for cold regions. Results from this CAREER research may be used to improve heat and mass transport models, frost heave models, and models of frozen soil creep by incorporating enhanced unfrozen water content functions, which will account for unfrozen water mobility and its dependence on soil-specific physicochemical properties. The improved models will have far-reaching effects, including: contributing to the scientific community studying methane release from degrading permafrost; serving as planning tools for Arctic communities that must relocate due to unstable permafrost; increasing the analysis accuracy of unstable slopes in frozen ground; resulting in more cost-effective designs accompanied by less structural damage and safety risks for projects such as buried chilled gas pipelines; and predicting frost heave susceptibility and magnitude more accurately, which will support design of safer, more durable roads in cold regions.In terms of education, involving ANSEP students in this research will encourage underrepresented student groups to become engineering professionals with strong outreach skills, who can return to rural Alaska to inspire the next generation of engineers. Increasing the involvement of Alaskan Native students in frozen ground engineering will result in a stronger, highly-trained workforce, capable of addressing geotechnical problems unique to the Arctic, which is critical for the long-term viability of their communities and for the successful development of the Arctic, the next frontier in energy resource development. Exposing middle school-aged students to hands-on engineering activities and to problems germane to their local environment will promote an early interest in engineering that can segue into an engineering career.