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Hydraulic Conductivity and Compatibility of Bentonite for Hydraulic Containment Barriers
High-swelling sodium bentonite (Na-bentonite) commonly is used in engineered containment barriers for hydraulic control and containment of liquid-phase contaminants. Such barriers include compacted liners that comprise bentonite-amended natural soils (i.e., sands, silts, and clays); manufactured geosynthetic clay liners (GCLs) that comprise thin (~ 10 mm) sheets of Na-bentonite sandwiched between two porous geotextiles; highly compacted bentonite buffers for high-level nuclear waste disposal; and soil-bentonite (SB) vertical cutoff walls. The primary role of the bentonite in all of these barriers is to serve as a high-swelling, low-hydraulic conductivity, k, material (k < 10-10 m/s) to minimize seepage of liquids (groundwater, leachates in landfills, pure-phase organic liquids, etc.) and migration of contaminants (e.g., heavy metals, radionuclides, organic compounds, etc.) through the barriers. A primary concern with bentonite-based barriers used for such containment applications is the potential for incompatibility between the bentonite and the liquid being contained, resulting in increase in k and concomitant decrease in the performance of the barrier. With this concern in mind, the purpose of this paper is to provide a review of the factors and potential impacts resulting from such incompatibility (Δk > 0) in several different types of bentonite based-barriers, including traditional GCLs that rely solely upon bentonite as the primary hydraulic-resistant material, compacted soil-bentonites (CSBs), and soil-bentonite backfills (SBBs) used in vertical cutoff walls for control of contaminated groundwater. The results show that the potential for significant incompatibility in bentonite-based barriers (i.e., Δk ranging from one to three or more orders of magnitude) generally increases with decrease in the amount of bentonite in the barrier, increase in the initial void ratio of the barrier, and/or increase in the composition and concentration of dissolved chemical species (solutes) contained in the permeant liquid. Values of k back-calculated from the results of consolidation tests based on Terzaghi's theory typically are unconservatively low and, therefore, should not be relied upon for assessing the performance of bentonite-based barriers.
Hydraulic Conductivity and Compatibility of Bentonite for Hydraulic Containment Barriers
High-swelling sodium bentonite (Na-bentonite) commonly is used in engineered containment barriers for hydraulic control and containment of liquid-phase contaminants. Such barriers include compacted liners that comprise bentonite-amended natural soils (i.e., sands, silts, and clays); manufactured geosynthetic clay liners (GCLs) that comprise thin (~ 10 mm) sheets of Na-bentonite sandwiched between two porous geotextiles; highly compacted bentonite buffers for high-level nuclear waste disposal; and soil-bentonite (SB) vertical cutoff walls. The primary role of the bentonite in all of these barriers is to serve as a high-swelling, low-hydraulic conductivity, k, material (k < 10-10 m/s) to minimize seepage of liquids (groundwater, leachates in landfills, pure-phase organic liquids, etc.) and migration of contaminants (e.g., heavy metals, radionuclides, organic compounds, etc.) through the barriers. A primary concern with bentonite-based barriers used for such containment applications is the potential for incompatibility between the bentonite and the liquid being contained, resulting in increase in k and concomitant decrease in the performance of the barrier. With this concern in mind, the purpose of this paper is to provide a review of the factors and potential impacts resulting from such incompatibility (Δk > 0) in several different types of bentonite based-barriers, including traditional GCLs that rely solely upon bentonite as the primary hydraulic-resistant material, compacted soil-bentonites (CSBs), and soil-bentonite backfills (SBBs) used in vertical cutoff walls for control of contaminated groundwater. The results show that the potential for significant incompatibility in bentonite-based barriers (i.e., Δk ranging from one to three or more orders of magnitude) generally increases with decrease in the amount of bentonite in the barrier, increase in the initial void ratio of the barrier, and/or increase in the composition and concentration of dissolved chemical species (solutes) contained in the permeant liquid. Values of k back-calculated from the results of consolidation tests based on Terzaghi's theory typically are unconservatively low and, therefore, should not be relied upon for assessing the performance of bentonite-based barriers.
Hydraulic Conductivity and Compatibility of Bentonite for Hydraulic Containment Barriers
Shackelford, Charles D. (author) / Sample-Lord, Kristin M. (author)
Geo-Congress 2014 ; 2014 ; Atlanta, Georgia
2014-02-24
Conference paper
Electronic Resource
English
Calcium and Sodium Bentonite for Hydraulic Containment Applications
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