CAREER: Mobility of Unfrozen Water in Frozen Soil

Project Info

Lead Researcher(s)

Margaret M. Darrow
Mining and Geological Engineering
University of Alaska Fairbanks
Box 755800
Fairbanks, AK 99775-5800
Phone: (907) 474-7303
Fax: (907) 474-6635
margaret.darrow@alaska.edu

Funding

The “Mobility of Unfrozen Water in Frozen Soil” project is funded by the National Science Foundation CAREER program under Award No. CMMI-1147806.

Project Summary

Abstract

The long-term research goal is to improve understanding of frozen ground behavior as it interacts with thermal changes in the environment, an essential knowledge base for predicting permafrost response to climate change and for developing robust building design in cold regions. Research objectives are to: (1) measure mass and molecular mobility of unfrozen water (water that remains liquid at sub-freezing temperatures) 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 (a parameter related to mineral surface charge) of cation-treated soil particles at subfreezing temperatures. Measurements will provide a unique data set allowing for correlation among and between the amount of mobile water in a frozen soil and the soil’s physicochemical properties as a function of temperature – key variables influencing soil freezing and thawing processes. The long-term educational goal is to increase the number of engineering graduates from underrepresented groups. Achievement is predicated on educational objectives: (1) recruiting undergraduate students from the Alaska Native Science and Engineering Program (ANSEP) to participate in CAREER research, and (2) including ANSEP students in K-8 outreach through a hands-on geotechnical engineering module delivered to middle school-aged students. The PI’s background in soils and frost heave research, as well as having been a high school teacher in rural Alaska, provides unique skills and experiential insight to ensure success in performing the proposed research and in accomplishing the educational goals.

Intellectual Merit

Historically, microscale phenomena associated with unfrozen water has been challenging to measure and therefore is 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, and soil micro-fabric. Several novel and complementary experimental methods will be developed, such as: (1) repeatable methodology with a quantified accuracy using the NMR method; (2) quantitative examination of soil micro-fabric using CT scanning, XRD, and SEM methods; and (3) unprecedented quantification of zeta potential with decreasing temperature for typical soil minerals, which will increase understanding of unfrozen water mobility via modification of fluid viscosity. Results will be quantified and used to develop a model of unfrozen water in freezing soils based on theoretical principles such as streaming potential. Relationships among unfrozen water thickness, viscosity, and connectivity as determined through soil micro-fabric analysis, will provide understanding of how water moves through frozen soil, leading to improved models of heat and mass transport and frost heave.

Broader Impact

Research results will lead toward making accurate predictions of: (1) Water mobility and hydraulic conductivity in frozen soils; (2) Permafrost thaw rates with increasing global temperatures; (3) Frost heave susceptibility and magnitude; and (3) Frozen soil strength. Yields will result in: (1) Improved planning tools for Arctic communities relocating due to permafrost instability; (2) Cost-effective, robust designs accompanied by less structural damage and safety risks for a variety of civil structures, including buried chilled gas pipelines and liquefied natural gas storage tanks; (3) Improved northern regions site characterization techniques; (4) Novel methods used in frost heave reduction through cation treatments; and (5) Improved slope stability analysis in permafrost soils. Involving undergraduate ANSEP students will promote development of engineering professionals with strong outreach skills, capable of addressing engineering problems unique to Alaska and the Arctic, a critical combination for successful development and long-term viability of rural Alaska. Introducing hands-on engineering activities to middle school-aged students will promote early interest in engineering, potentially increasing numbers of engineering graduates.

Project News

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In April 2016, undergraduate research assistant Heni Barnes (BS student, Geological Engineering) presented a summary of her work for UAF’s Undergraduate Research Day. Heni is completing the measurements of cation-treated clays using a zeta potential analyzer.

 

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In April 2014, undergraduate research assistants Timothy Nick (BS student, Civil Engineering; pictured on left) and Yan Mio (BS, Geological Engineering; pictured on right) presented summaries of their work in the laboratory at UAF’s 7th Annual Research Day. Timothy developed a laboratory procedure for preparing and testing clay samples using a zeta potential analyzer, and Yan developed methods for soil sample preparation for NMR testing and verified thermal stability of the NMR system.

 

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In April 2013, undergraduate research assistants Yan Miao (BS student, Geological Engineering; pictured on the left) and Ralph Sinnok (BS, Civil Engineering; pictured on the right) presented a summary of their work on sample preparation as a poster at UAF’s 6th annual Undergraduate Research Day. Yan developed methods for crushing bulk rock samples into soil with a suitable clay-sized particle distribution, and Ralph refined laboratory procedures for exchanging surface cations on clay particles.

 

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PI Margaret Darrow taught a geotechnical engineering module to 7th and 8th graders at the Watershed School in Fairbanks, Alaska. The outreach activity consisted of a laboratory activity followed by a tour of the US CRREL permafrost tunnel. The middle-school aged students were introduced to general concepts of frozen ground and geotechnical engineering, such as bearing capacity, soil classification, and thaw strain, gained hands-on experience identifying different types of soil and how each responds to being frozen, and saw ice wedges and ice-rich soil in the 3D environment of the permafrost tunnel.

Photos by AUTC News.