Evaluation of Hydraulic Conductivity of Sodium Bentonite GCL Overlaps to Saline Solutions
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Gastelo Diaz, Jackeline Liliana
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Abstract
Current regulation established for disposal of solid waste (e.g., municipal solid waste, and coal combustion residuals) requires disposal facilities that include a composite liner consisting of a geomembrane overlying a 0.6-m-thick clay liner. A sustainable alternative is to use of geosynthetic clay liners (GCLs) in lieu of a conventional clay liner, because GCLs have a low hydraulic conductivity (k<10-10 m/s), take much less air space due to their thickness (5 - 10mm), and easy to install. A Geosynthetic clay liner (GCL) consists of one layer of sodium bentonite sandwiched between two layers of geotextile that can be woven or non-woven. Many studies have been performed to understand and evaluate the hydraulic conductivity of GCLs that come in contact with various leachates (Daniel et al. 1997; Petrov and Rowe 1997; Shackelford et al. 2000; Ashmawy et al. 2002; Katsumi et al. 2008; Bradshaw and Benson 2014; Tian et al. 2016). However, these studies did not investigate the hydraulic conductivity of GCL in the region where the pieced of the GCL are overlapped during installation to cover large areas. If the hydraulic conductivity of the region where the GCL pieces are overlapped is higher than the hydraulic conductivity of the GCL itself, these areas will potentially control the bulk hydraulic conductivity of GCL layer installed in the landfill liner system. Therefore, proper evaluation of this phenomenon is very important and is lacking in the literature. Hydraulic conductivity was evaluated for the overlap of Sodium Bentonite (Na-B) Geosynthetic clay liners (GCLs) permeated with leachate characteristics of Municipal Solid Waste (MSW) landfills under four effective stress conditions (20, 100, 250, 500 kPa). The Na-B GCLs had different combination of geotextiles, one of them was nonwoven-nonwoven (NW-NW) while the other was nonwoven-woven (NW-W). The hydraulic conductivity of the (NW-NW) was higher compare to the (NW-W). Two overlap construction methods were evaluated: the Supplemental bentonite and Cut method. Hydraulic conductivities were similar at 20kPa, Supplemental bentonite method give a similar hydraulic conductivity compare to the Cut method at higher effective stress. A conceptual model of the flow paths featuring horizontal flow through the geotextiles was proposed and tested to explain the direction of the flow.
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This thesis has been embargoed for 5 years and will not be available until November 2024 at the earliest.
Keywords
Geosynthetic clay liners, Overlap, Geotextiles, Hydraulic conductivity, Transmissivity