CAREER: Mobility of Unfrozen Water in Frozen Soil

这项学院早期职业发展(CALEAR)奖支持的研究将提高我们对冻土在与周围环境中的热变化相互作用时的行为的理解。了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(即在冻结土壤中有多少水在低于冰点的温度下保持液态，以及它是如何运动的)。从历史上看，与未冻结水相关的微尺度现象一直难以测量，而且对此了解甚少。这项研究使用最先进的测量技术的创新组合来量化土壤冻结和解冻过程中假设的关键变量之间的关系，即未冻水含量和移动性、土壤Zeta电位(与矿物表面电荷有关的参数)和土壤微结构。具体地说，PI将(1)使用脉冲核磁共振(NMR)方法测量冷冻阳离子处理土壤中未冻水的质量和分子流动性；(2)将这些测量与使用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；以及(3)将这些测量与零冻结温度下阳离子处理土壤颗粒的Zeta电位相关联。从阿拉斯加原住民科学与工程计划(ANSEP)招募的学生将通过向中学生提供的实践岩土工程模块参与这项职业研究和K-8推广。准确预测冻土系统的热量和质量平衡、冻土强度和冻胀幅度-所有这些都取决于未冻水-将支持规划对气候变化的永久冻土反应，并将促进更有效和经济的寒冷地区的工程设计。这一职业研究的结果可用于改进热量和质量传输模型、冻胀模型和冻土蠕变模型，包括增强的未冻水含量函数，该函数将考虑未冻水的流动性及其对土壤特定物理化学性质的依赖。改进的模型将产生深远的影响，包括：为科学界研究退化的永久冻土释放甲烷作出贡献；为由于不稳定的永久冻土而必须搬迁的北极社区提供规划工具；提高对冻土中不稳定斜坡的分析精度；为埋藏的冷冻天然气管道等项目提供更具成本效益的设计，同时减少结构破坏和安全风险；在教育方面，让ANSEP学生参与这项研究将鼓励代表不足的学生群体成为具有强大拓展技能的工程专业人员，他们可以回到阿拉斯加农村，激励下一代工程师。增加阿拉斯加土著学生对冻土工程的参与将产生一支更强大、训练有素的劳动力队伍，能够解决北极特有的岩土问题，这对他们社区的长期生存和北极的成功开发至关重要，北极是能源资源开发的下一个前沿。让中学生参加实践工程活动，接触与当地环境相关的问题，将促进他们早期对工程的兴趣，这将成为工程生涯的一部分。

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.