Swell index, oedopermeametric, filter press and rheometric tests for identifying the qualification of bentonites used in GCLs
ABSTRACT Geosynthetic clay liners (GCLs) are used in landfill liner applications and there is a need for a better control of the properties of the bentonite in the GCL received on site, particularly in the European context where a wide variety of bentonites can be encountered. This paper presents the results of a project aimed at a rapid identification of the nature of the bentonite in a given GCL. The interaction between the bentonite and the fluid was increased by producing dispersions then testing its structure within a few hours with filter press tests and flow curves. The results of those tests were compared with swell index tests, electrical conductivity values and oedopermeametric tests. Eight GCLs were studied. Two of these GCLs contained natural calcium bentonites; they presented poor swelling properties and high permittivities. The dispersions had a low viscosity and their filtration under pressure led to large amounts of filtrate. A further two GCLs contained natural sodium bentonites and the remaining four contained sodium-activated calcium bentonites. Their permittivities, swell indices and filtrate masses were similar; however, their rheometrical behaviours were different due to a difference in the values of electrical conductivity. Thus it seems that electrical conductivity measurements and rheological tests can provide a good and fast way of identifying the nature of the bentonite contained in GCLs.
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ABSTRACT: The potential shrinkage of eight different geosynthetic clay liners (GCLs) subjected to wetting and drying cycles is examined. It is shown that the initial (e.g, off-the-roll) moisture content may affect the initial shrinkage but did not notably affect the final equilibrium shrinkage. For GCLs with granular bentonite and wetted to a moisture content of about 60% (or greater) in the hydration phase, the actual moisture content did not appear to affect the magnitude of the final equilibrium shrinkage. However, it did affect the rate of shrinkage. Specimens brought to about 100% moisture content in each cycle reached a constant shrinkage value much faster than those brought to about 60% in each wetting cycle. GCLs containing powdered bentonite generally shrank more than those containing granular bentonite. All of the powdered bentonite specimens continued a slow accumulation of strain with increasing cycles, even up to 75 cycles. The shrinkage of a needle-punched GCL with a thermally treated scrim-reinforced nonwoven carrier geotextile and granular bentonite was less than that for a needle-punched GCL with a simple nonwoven carrier and granular bentonite. For some products, there was considerable variability in GCL shrinkage for specimens from the same roll and tested under nominally identical conditions, whereas for other products, the variability was relatively small. The shrinkage strain required to cause the loss of a 150–300 mm panel overlap is shown to be able to be mobilized in about five wet-dry cycles in the experiments reported.Journal of Geotechnical and Geoenvironmental Engineering 11/2011; 137(11). DOI:10.1061/(ASCE)GT.1943-5606.0000522 · 1.47 Impact Factor
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ABSTRACT: The hydration and subsequent hydraulic performance of geosynthetic clay liners (GCLs) depend on the water-retention curve (WRC) of the GCL. Because of the inherent difficulty in obtaining the WRC for these materials, limited data exists regarding the WRCs of GCLs in the literature. In this study, high-capacity tensiometers and capacitance relative humidity sensors were used to quantify the water-retention behavior of GCLs for four different GCL products that vary both in materials (woven and nonwoven geotextiles) and in fabrication detail (thermal treatment and needle-punching). The water-retention behavior was investigated under wetting and drying paths; we present results in terms of gravimetric and volumetric moisture content and bulk GCL void ratio. The WRCs of the different GCL products showed significant variation among wetting and drying curves, indicating that both needle-punching and thermal treatment have a significant effect on the swelling behavior of the GCL and its WRC. Theoretical equations were fit to the experimental data, establishing the parameters that can be used for numerical modeling of these four GCL products.Journal of Geotechnical and Geoenvironmental Engineering 11/2011; 137(11). DOI:10.1061/(ASCE)GT.1943-5606.0000526 · 1.47 Impact Factor
- GBR-C 2k10, Würzburg, Germany; 09/2010