Progress 08/01/04 to 07/31/07
Outputs
This competitive grant is being transfered to the University of Arizona. We continued theoretical and experimental studies on hydraulic and swelling properties of clays with focus on confinement conditions. Preliminary results indicate the existence of a critical clay content at which clay soils exhibit lowest permeability and porosity. This has potential implications for agricultural water management and numerous geotechnical engineering applications. To gain better understanding regarding initiation and evolution of surface crack networks in active clay soils we performed well controlled dehydration experiments in conjunction with X-Ray Computed Tomography (CT) observations. We also initiated experiments with polyacrylamide (PAM) amended clays to investigate if the addition of non-ionic, cationic, or anionic PAM reduces crack formation. We developed novel computer codes for spatial analysis of 3-dimensional X-Ray CT images and refined the scanning procedure to obtain
higher quality images. These observations provide new insights regarding effects of solution chemistry (concentration and ion valence) and drying conditions on formation and evolution of surface cracks in clay soils. The newly developed codes and scanning procedure were utilized in a collaborative project with Yakov Pachepsky (USDA EMSL Beltsville) aimed at studying pathogen transport in macroporous and structured soils. Soil structure greatly affects the ability of soil to transmit and to retain water, chemicals, and colloidal particles that can carry contaminants or be contaminants themselves, e.g. pathogenic microorganisms. Results were disseminated through two refereed publications, and abstracts and presentations at national and international meetings.
Impacts
Knowledge and data regarding clay-solute interactions and application of polyacrylamide (PAM) additives gained from the proposed project will benefit water management in agricultural fields and rangelands with swelling soils, leading to improved infiltration and water use efficiency. Due to the sensitivity of clay soils to irrigation water quality, gained knowledge could also benefit salinity and sodicity management by quantifying the impact of irrigation strategy and application of additives on soil hydraulic properties. Sustainable use and protection of water resources is a growing societal concern, especially in arid regions such as the Pacific Northwest. Insights gained from the project will also contribute to more efficient and cost effective performance-based design of bentonite landfill covers and liners and provide potential strategies for remediation and improvement of existing waste containment systems. Society has and will continue to generate large amounts
of hazardous waste that require save long-term storage, recycling, destruction, or treatment. Besides a myriad of technical and engineering problems associated with waste management, treatment and containment are significant economical factors. The Environmental Protection Agency (EPA) estimates that over 217,000 contaminated sites within the United States need remediation over the next 30 years at a total cost of $187 billion.
Publications
- Tuller, M. and Or, D. 2006. Hydraulic Properties of Swelling Clay-Sand Mixtures: Microscale Modeling and Measurements. In: G.A. Miller, C.E. Zapata, S.L. Houston, D.G. Fredlund (Eds.), Unsaturated Soils, Geotechnical Special Publication 147(2):2186-2197, ASCE, Reston, VA.
- Gebrenegus, T., Tuller, M. and Muhunthan, B. 2006. The Application of X-ray Computed Tomography for Characterization of Surface Crack Networks in Bentonite-Sand Mixtures. In: J. Desrues, G. Viggiani, and P. Besuelle (Eds.), Advances in X-Ray Tomography for Geomaterials, pp. 207-212, ISTE Publishing Company, ISBN:1905209606.
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Progress 01/01/05 to 12/31/05
Outputs
We used and developed cutting edge research equipment to measure hydraulic and swelling properties (Volume Change Measuring Device; Flexible Wall Permeameter) of clay-sand mixtures, and to visualize pore structural changes with hydration state and solute chemistry at different scales (Environmental Scanning Electron Microscopy (ESEM); X-Ray Computed Tomography (CT)). We completed a comprehensive series of experiments to determine the effects of fluid chemistry (concentration and ion valence) and confinement stress on swelling potential and saturated hydraulic conductivity of clays. We conducted a comprehensive study with X-Ray CT to visualize spatial and transient phase distributions at the meso- and macro-scales. In addition we applied Environmental Scanning Electron (ESEM) microscopy to determine structural changes at the micro-scale. Another direct outcome of this project during the reporting period was the development of a novel method to determine soil specific
surface area from measuring the water content - potential relationship under dry conditions. Results were disseminated through two refereed publications, a master's thesis, and four abstracts and presentations at national and international meetings.
Impacts
Current and future results will contribute to agriculture, environmental management, and geotechnical engineering by: (1) elucidation of basic aspects of flow and transport processes in an evolving pore space; (2) development of physically based predictive models for hydraulic properties of swelling soils; (3) providing new insights into salinity and sodicity management of agricultural clay soils; (4) providing advanced design criteria for caps and barriers used for hydraulic isolation of hazardous waste. Furthermore, the results of this project should enhance understanding of clay dispersion and surface sealing with consequent erosion hazards and enhanced colloid-facilitated transport of agrochemicals.
Publications
- Tuller, M. and Or, D. 2005. Water films and scaling of soil characteristic curves at low water contents, Water Resour. Res., Vol. 41, No. 9, W0940310.1029/2005WR004142.
- Viola, R., Tuller, M., Or, D. and Drasdis, J. 2005. Microstructure of Clay-Sand Mixtures at Different Hydration States. In A. Tarantino, E. Romero, Y.J. Cui (Eds.), Advanced Experimental Unsaturated Soil Mechanics, Taylor & Francis, Leiden, The Netherlands, pp.437-442.
- Gebrehawariat, K. 2005. Saturated Permeability and Volume Change Behavior of Na-Bentonite - Sand Mixtures. Master Thesis, University of Idaho, June 2005, pp. 72.
- Tuller, M. and Gebrehawariat, K. 2005. Saturated Hydraulic Conductivity and Swelling Properties of Clay Soils. Geophysical Research Abstracts, Vol.7, 02498, 2005, SRef-ID: 1607-7962/gra/EGU05-A-02498, ISSN: 1029-7006, European Geosciences Union.
- Gebrenegus, T. and Tuller, M. 2005. Quantitative Characterization of Surface Crack Networks in Sand-Bentonite Mixtures with X-Ray Computed Tomography. INRA Environmental & Subsurface Science Symposium, September 19-21, 2005, Big Sky, MT. https://www.b-there.com/breg/esss05/Gebrenegus.pdf
- Tuller, M. and Gebrehawariat, K. 2005. Effects of Solution Chemistry and Confining Pressure on Saturated Hydraulic Conductivity of Bentonite-Sand Mixtures. SSSA Annual Meeting Abstracts, Nov. 6-10, Salt Lake City, UT. On CD.
- Gebrenegus, T. and Tuller, M. 2005. X-Ray Computed Tomography for Qualitative and Quantitative Characterization of Surface Crack Networks in Clay Soils. SSSA Annual Meeting Abstracts, Nov. 6-10, Salt Lake City, UT. On CD.
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Progress 01/01/04 to 12/31/04
Outputs
From 08/01/2004 to 12/31/2004 we accomplished the following tasks: (1) Measurement of Saturated Hydraulic Conductivity and Swelling Potential of Bentonite-Sand Mixtures. We used a fully automated latest technology flexible wall permeameter setup to measure saturated hydraulic conductivity of Wyoming sodium bentonite - Ottawa silica sand mixtures. To investigate effects of solution chemistry we used deionized water and 0.5 and 1.0M sodium chloride solutions as permeants and varied the bentonite content between 0-50 percent. Obtained results reveal that for all investigated liquids there is a sharp initial decrease in permeability until a critical clay content is reached. After this critical clay content we see a slight increase. This can be explained by differing spatial arrangement of sand grains relative to the clay matrix. At low clay contents sand grains form a rigid skeleton with clay matrix occupying part of the intergranular pore space. At certain critical clay
content the matrix starts dominating, completely filling pores and pushing sand grains apart. The slight increase in permeability at higher clay contents is due to increasing mesopore space as more and more sand is replaced by bentonite. It is interesting to note that the critical clay content is highly dependent on the permeant liquid concentration. Samples saturated with deionized water show the lowest permeability at around 20% bentonite content, whereas the critical bentonite content for 1.0M NaCl saturated samples is at around 40%. Permeability and critical clay content are strongly related to the swelling potential, which was measured with a novel volume change apparatus. (2) Observation of spatial and transient phase distributions in bentonite-sand mixtures with X-ray Computed Tomography (CT). We started a series of experiments to test the suitability of X-ray CT for: (a) observation of development and evolution of surface crack networks as related to clay hydration state; and
(b) potential anisotropic distribution of liquid, gaseous, and solid phases. First results indicate strong dependence of crack porosity on clay content and drying rate. Mixtures with low clay content (e.g., 10%) develop finer crack networks with higher porosity than high clay content mixtures. Due to limitations of our computer hardware we are currently not able to achieve the required rendering resolution for meaningful assessment of crack topology and tortuosity. Results also reveal that all phases and interfaces of interest can be clearly resolved with X-ray CT. (3) Observation of clay microstructure with Field Emission Scanning Electron Microscopy (FESEM) and Environmental Scanning Electron Microscopy (ESEM). We conducted a series of observations of clay microstructure as related to hydration state and solution chemistry with FESEM and ESEM. Preliminary results reveal that ESEM is the more suitable technology for observation of hydrated media, as it does not require specific
sample preparation. Preliminary results were disseminated through 4 abstracts and conference presentations.
Impacts
During the first 5 months of this project we tested and modified cutting-edge techniques for measurement of hydraulic conductivity and swelling potential, and observation of pore structure. These techniques are currently not state-of-the-art in the soil and environmental sciences. On the long term results of our efforts should significantly contribute to improved salinity and sodicity management practices in irrigated agricultural areas. Furthermore, insights gained from this study will enhance understanding of clay dispersion and surface sealing, and lead to improved management guidelines for prevention of soil erosion and colloid facilitated transport of agrochemicals.
Publications
- Viola, R., Tuller, M. and Islam, M.R. 2004. Microscopic Observations of Pore Space Geometry in Clay-Sand Mixtures under Varying Hydration States. SSSA Annual Meeting Abstracts, Oct. 31-Nov. 4, Seattle, WA. On CD, abstract 4546.
- Ghebrehawariat, K., Tuller, M. and Or, D. 2004. Saturated Hydraulic Conductivity and Volume Change of Clay-Sand Mixtures. SSSA Annual Meeting Abstracts, Oct. 31-Nov. 4, Seattle, WA. On CD, abstract 4835.
- Gebrenegus, T., Tuller, M. and Muhunthan, B. 2004. Visualization and Quantification of Spatial Phase Arrangement in Bentonite-Sand Mixtures with X-Ray Computed Tomography. SSSA Annual Meeting Abstracts, Oct. 31- Nov. 4, Seattle, WA. On CD, abstract 4860.
- Gebrenegus, T., Tuller, M. and Muhunthan, B. 2004. Visualization of Spatial and Transient Phase Distributions in Porous Materials with X-Ray Computed Tomography. INRA Environmental & Subsurface Science Symposium "Environmental and Subsurface Science Applied to Energy, Nuclear, and National Security Research", September 20-22, 2004, Spokane, WA. http://ww.b-there.com/breg/esss04/Poster_Beyene.doc.
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