Conductivity Of Geosynthetic Clay Liners Research Articles

Freeze–thaw cycling concurrent with cation exchange and the hydraulic conductivity of geosynthetic clay liners

A study was conducted to assess the effect of cation exchange concurrent with freeze–thaw cycling on the hydraulic conductivity of a geosynthetic clay liner (GCL). GCLs were prehydrated by contact with silica flour moistened with synthetic subgrade pore water and subsequently permeated with a solution representing the pore water in the cover soil over a tailings facility. Control tests were conducted using the same procedure, except deionized (DI) water was used as the permeant liquid to preclude cation exchange from the permeant liquid. The GCLs were subjected to 1, 3, 5, 15, and 20 freeze–thaw cycles, and the hydraulic conductivity and exchange complex were determined before and after freeze–thaw cycling to assess chemical changes that occurred during freezing, thawing, and permeation. GCLs undergoing freeze–thaw cycling experienced little to no cation exchange through 5 freeze–thaw cycles. After 20 freeze–thaw cycles, 50% of the sodium (Na+) initially in the exchange complex was replaced by calcium (Ca2+). Dissolution of calcite within the bentonite is a likely source of the Ca2+. Hydraulic conductivity of the GCLs exposed to freeze–thaw cycling was lower than the hydraulic conductivity of a new GCL permeated with DI water (<2.2 × 10−11 m/s). A small increase in hydraulic conductivity (∼2.3 times), which may have been caused by cation exchange, occurred between 15 and 20 freeze–thaw cycles, but the hydraulic conductivity remained below the hydraulic conductivity of a new GCL unexposed to freeze–thaw cycling and permeated with DI water.

Erratum for “Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners” by Sabrina L. Bradshaw, Craig H. Benson, and Joseph Scalia IV

Erratum for “Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners” by Sabrina L. Bradshaw, Craig H. Benson, and Joseph Scalia IV

Fluid loss as a quick method to evaluate hydraulic conductivity of geosynthetic clay liners under acidic conditions

This study investigates the performance of bentonite components of geosynthetic clay liners (GCLs) when exposed to aggressive leachates using the fluid loss test and provides a possible quick method for estimating the effect of acidic conditions on hydraulic conductivity. Fluid loss generally increases with increasing acid concentrations. Hydraulic conductivity values back-calculated from the fluid loss tests (kFL) are compared with the values measured using a flexible-wall permeameter (kTri). Generally, the predicted hydraulic conductivity values are conservative (kFL/kTri > 1) under water and low acid concentrations (≤0.015 mol/L). However, the back-calculated hydraulic conductivity is shown to be nonconservative (kFL/kTri < 1) at high acid concentrations (≥0.125 mol/L).

Impact of bentonite form on the thermal evolution of the hydraulic conductivity of geosynthetic clay liners

Several field observations have confirmed that engineered liner systems of municipal solid waste landfills could be subjected to temperatures up to 60°C over the course of their lifetime. These elevated temperatures are reportedly due to ongoing bio-degradation of the waste and, as reported by several authors, can have a significant impact on the service life of the geosynthetic components of engineered lining systems in addition to the already established effects on landfill processes. The preliminary study reported here aimed to experimentally assess the effect of temperature on the hydraulic conductivity of geosynthetic clay liners containing different forms (i.e. granular and powder) of sodium bentonite. The experimental programme involved conducting constant-head hydraulic conductivity tests using a modified Rowe cell capable of withstanding temperatures up to 60°C. A theoretical interpretation of the observed test results reveals that the initial microstructure of the bentonite core and its evolution under a thermo-mechanical effect could control the thermal evolution of geosynthetic clay liners' hydraulic conductivity.

Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners

AbstractExperiments were conducted to evaluate cation exchange during hydration of geosynthetic clay liners (GCLs) used in composite hydraulic barriers and the effect on their hydraulic conductivity. GCLs arranged in a composite barrier configuration were hydrated by contact with moist compacted subgrades (two clays, one silt, and one sand) under a confining stress of 10 kPa for 30 days to 1 year. No measurable exchange occurred in GCLs hydrated for 30 days. For hydration periods longer than 30 days, the exchange increased as the duration of hydration increased. The exchange during subgrade hydration had no measurable effect on the hydraulic conductivity to deionized (DI) water. However, if the GCL was desiccated after hydration, the hydraulic conductivity increased more than 1,000-fold. Dissolution of calcite within the bentonite during permeation with DI water also induced the replacement of sodium by calcium; however, this additional exchange had no measurable effect on the hydraulic conductivity to DI...

ジオシンセティッククレイライナーの透水係数に及ぼす1,4-ジオキサンおよびビスフェノールAの影響評価

ジオシンセティッククレイライナーの透水係数に及ぼす1,4-ジオキサンおよびビスフェノールAの影響評価

Hydraulic Conductivity of Geosynthetic Clay Liners Exhumed from Landfill Final Covers with Composite Barriers

Geosynthetic clay liners GCLs were exhumed from composite barriers, i.e., geomembrane over GCL in final covers at four sites after 4.7 to 6.7 years to evaluate the in-service condition. Monovalent bound cations were replaced by divalent cations in all GCLs, with near complete exchange at two-thirds of the sampling locations. Hydraulic conductivity was measured using two dilute solutions commonly used as permeant water: standard water SW, 0.01M CaCl2 solution and type II deionized water DW. Hydraulic conduc- tivities to SW varied over four orders of magnitude, whereas identical specimens i.e., from same sample had hydraulic conductivities to DW consistently 310 10 m /s. Higher hydraulic conductivities and sensitivity to permeant water did not correspond directly to the amount of cation exchange. Exhumed GCLs with higher gravimetric higher water contents 50% exhibited a gel structure indicative of osmotic hydration and had lower hydraulic conductivities to both SW and DW, regardless of the amount of sodium Na replaced by divalent cations. These GCLs with higher water contents were placed on subgrade having water content in excess of optimum water content standard Proctor. Conditions that promote rapid hydration and osmotic swell in a GCL are recommended to ensure that a GCL in a composite barrier maintains low hydraulic conductivity 510 11 m /s, even if the native Na is ultimately replaced by divalent cations. Subgrade with water contentoptimum water content is recommended. DOI: 10.1061/ASCEGT.1943-5606.0000407 CE Database subject headings: Geosynthetics; Clay liners; Landfills; Hydraulic conductivity; Barriers; Composite materials; Water content. Author keywords: Geosynthetic clay liner; Landfill; Final cover; Hydraulic conductivity; Cation exchange; Hydration; Osmotic swell; Crystalline swell; Preferential flow.

Hydraulic conductivity of geosynthetic clay liners to tailings impoundment solutions

The results of a comprehensive testing program conducted to evaluate the hydraulic conductivity ( k) of two geosynthetic clay liners (GCLs) considered as a liner component for a tailings impoundment at a proposed zinc and copper mine are reported. The two GCLs were permeated with a relatively low ionic-strength ground water (GW) from the mine site and two electrolyte solutions, a process water (PW) and a simulated leachate (SL), with chemical compositions consistent with those expected during operation of the impoundment. A total of 22 flexible-wall tests were performed to determine the effects of prehydration with the GW, type of GCL, type of permeant liquid, and duration of the back-pressure stage of the test. The k values for both GCLs permeated with the GW were 1.7 × 10 −9 cm/s, which is within the range 1–3 × 10 −9 cm/s typically reported for GCLs permeated with low ionic-strength liquids, such as deionized water. However, the mean values of k based on permeation of duplicate specimens of both types of GCL with either PW or SL relative to the values of k based on permeation with GW, or k/ k w , ranged from a factor of 200 (2.3 orders of magnitude) to a factor of 7600 (3.9 orders of magnitude). Thus, both tailings impoundment solutions had significant adverse impacts on the hydraulic performance of both GCLs. Given the overall range of k/ k w values, factors such as prehydration, type of GCL, type of permeant liquid, and duration of back pressure, were relatively insignificant. The results of this study serve to emphasize the need to perform hydraulic conductivity testing using site specific materials.

Characterization of humic substances in landfill leachate and impact on the hydraulic conductivity of geosynthetic clay liners

A detailed characterization was performed on the humic substances present in landfill leachate derived from the older (10-year) and younger (6-month) municipal landfill cells at a site in Inchion, Korea. The characterization focused on the humic and fulvic acid components of the leachate, relying on information gleaned from the UV/visible spectroscopy, molecular weight distribution, and Fourier transform infrared spectroscopy. The effect of the leachates, and specific components of the leachates, on the hydraulic conductivity of a geosynthetic clay liner (GCL), was evaluated. The humic acid extracted from the older leachate was composed primarily of high molecular weight and aromatic compounds, which is typical for humic acids. However, the humic acid extracted from the younger leachate showed characteristics more similar with fulvic acids, indicating that the younger humic acid was at the initial stage of humification. The hydraulic conductivity of the GCLs to the humic and fulvic acids of the older and younger leachate was similar to those permeated with the distilled deionized water (DI). However, the hydraulic conductivity of the samples tested with the raw leachate was more than 200 times the DI value. This fact suggests that cations present in leachate, rather than humic substances, are the key factor in the increase of the permeability.

Research on anti-seepage properties of geosynthetic clay lines in landfills

In recent years, geosynthetic Clay liners (GCLs) are widely used in different kinds of anti-seep-age projects and the anti-seepage availabilities of GCLs are regarded as increasingly important by engineers. Anti-seepage effectiveness of GCLs involves at least two aspects, such as Hydraulic conductivity of GCLs under engi-neering practice conditions, and Absorption ability of bentonite in GCLs in the course of liq-uid permeation. In this paper, Hydraulic con-ductivity tests are performed to obtain seepage coefficient of GCLs, taking liquids such as dis-tilled, deioned water and landfill leachate, and solutions with single-species cation as the hy-dration and permeation liquid. The results Show that cation valence, cation concentration and hydration ionic radius in hydration and permea-tion liquids have influences on hydraulic con-ductivity of GCLs.

Correlating Index Properties and Hydraulic Conductivity of Geosynthetic Clay Liners

Three index properties (liquid limit, sedimentation volume, and swell index) of two sodium bentonites from geosynthetic clay liners (GCLs) are correlated with the hydraulic conductivity (k) of the same GCLs to evaluate the suitability of index properties for evaluating chemical compatibility. Deionized water (DIW) and calcium chloride (Ca Cl2 ) solutions were used for hydration (index tests) and permeation (hydraulic conductivity tests). In general, increasing the Ca Cl2 concentration caused each index property to decrease and the hydraulic conductivity to increase relative to values obtained with DIW, with the strongest correlations obtained with the liquid limit. The correspondence between index properties and hydraulic conductivity differed by index property, the quality of the bentonite, and the effective stress applied during the hydraulic conductivity test. Thus, correlations used for compatibility assessments are specific to the bentonite in the GCL and the stress conditions being applied. Results ...

Impact of Bentonite Quality on Hydraulic Conductivity of Geosynthetic Clay Liners

The differences in hydraulic conductivity for two geosynthetic clay liners (GCLs) containing different qualities of bentonite are evaluated based on permeation with water and chemical solutions containing 5, 10, 20, 50, 100, and 500 mM CaCl2. The GCL with the higher quality bentonite (GCL-HQB) is characterized by a greater content of sodium montmorillonite (86 versus 77%), a higher plasticity index (548 versus 393%), and a higher cation exchange capacity (93 versus 64 meq/ 100 g) relative to the GCL with the lower quality bentonite (GCL-LQB). The tests using CaCl2 solutions as permeant liquids were continued until chemical equilibrium between the influent and effluent was established, resulting in test durations that ranged from less than 1 to more than 900 days. The hydraulic conductivity for GCL-HQB, kHQB ,i s,33 lower than the hydraulic conductivity for GCL-LQB, kLQB, when specimens of both GCLs are permeated with water. However, the hydraulic conductivity for GCL-HQB is always higher than that for GCL-LQB when the specimens are permeated with the CaCl2 solutions. For example, kHQB/ kLQB ranges from 2.0 to 2.6 for the tests performed using 5, 10, and 20 mM CaCl2 solutions as the permeant liquids, whereas the kHQB/ kLQB values are ,230, ,100, and ,40 for the tests performed using 50, 100, and 500 mM CaCl2 solutions as the permeant liquids, respectively. Thus, the GCL with the higher quality bentonite is more susceptible to chemical attack than the GCL with the lower quality bentonite.

Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids

Fundamental factors and testing considerations affecting the evaluation of the hydraulic conductivity of geosynthetic clay liners (GCLs) permeated with non-standard liquids (i.e., liquids other than water) are discussed and supported with test data. Both aggregate-size distribution and montmorillonite content of the bentonite portion of the GCL have a potential effect on the hydraulic conductivity of GCLs. Other factors affecting the hydraulic conductivity of GCLs permeated with non-standard liquids include thickness of the adsorbed layer, prehydration of the GCL, void ratio of the GCL, and test duration. Results show that non-standard liquids containing both high concentrations of monovalent cations (e.g., 0.6 M NaCl) as well as low concentrations of divalent cations (e.g. 0.0125 M CaCl 2) can cause significant increases (⩾1 order of magnitude) in hydraulic conductivity provided the test is performed sufficiently long to allow for exchange of adsorbed cations. Results also indicate that termination of hydraulic conductivity tests involving prehydrated GCLs before chemical equilibrium is established may result in measured hydraulic conductivities that do not represent equilibrium and may be unconservatively low. Finally, control of average effective stress is more important than control of hydraulic gradient when evaluating the hydraulic conductivity of GCLs.

Hydraulic Conductivity of Geosynthetic Clay Liners after Freeze-Thaw

Hydraulic conductivity tests were performed in large tanks on intact (single panel) and overlapped samples of three geosynthetic clay liners (GCLs) that had been subjected to freeze-thaw cycles. The compressive stress applied to the GCLs (7.6–12.4 kPa) was selected to simulate final cover systems for landfills. Laboratory flexible-wall permeameter tests were also performed. With the exception of one overlapped GCL, all three GCLs withstood three freeze-thaw cycles without a significant change in hydraulic conductivity. An overlapped, geotextile-encased, stitch-bonded GCL did undergo a 1,000-fold increase in hydraulic conductivity after one freeze-thaw cycle, but the overlapped area contained stitches, which are left off the edges of the full-sized material that is deployed in the field. In general, the tests showed that GCLs can withstand at least three freeze-thaw cycles without significant changes in hydraulic conductivity.