Geosynthetic Clay Liners Specimens Research Articles

Transport parameters for PFOA and PFOS migration through GCL's and composite liners used in landfills

The effect of applied stress (20, 60, and 150 kPa) on the diffusion of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) through a geosynthetic clay liner (GCL) is examined. The diffusion coefficients deduced from GCL diffusion tests for PFOA and PFOS decrease linearly with decreasing final bulk GCL void ratio (increasing applied stresses). The different components of the same GCL are also tested for PFOA and PFOS sorption. No statistically significant sorption of PFOA is observed for any of the components of the GCL. However, some sorption of PFOS onto the cover and carrier geotextiles of the GCL is observed with in an average distribution coefficient, Kd ∼2.22 ml/g for the GCL. Permeants containing different PFAS compounds are tested to assess their impact on the Geomembrane (GMB) - GCL interface transmissivity in composite liners. Results show PFAS concentrations up to 20 ppm had negligible impact on the GMB-GCL interface transmissivity. Lastly, the GCL specimens extracted from the diffusion tests are tested for hydraulic conductivity. No impact of PFAS is seen on the hydraulic conductivity of GCLs subjected to high applied loads, but a small increase is seen on the GCLs subjected to relatively low applied stresses.

Internal erosion and permeability of Na CMC-treated and PAM-treated geosynthetic clay liners

This paper investigates the occurrence of internal erosion and the variation of the permeability of geosynthetic clay liner (GCL) with respect to its geotextile component, polymer type and polymer amount added to its bentonite component, hydraulic head, and subgrade material by performing extensive triaxial permeability tests on the GCL specimens. To do this, Na carboxymethyl cellulose (CMC) and polyacrylamide (PAM) were treated with the bentonite component of the GCLs. Then, the GCLs were placed over poorly graded gravel (GP) and poorly graded sand (SP). Consequently, they were tested with two different woven geotextile components under the hydraulics heads of 0.3 m and 10 m. Results showed that only GCLs tested with woven geotextile, having lower tensile strength, lower mass/area and lower thickness over the gravel at a hydraulic head of 10 m, experienced internal erosion. Critically, Na CMC and PAM treatment caused 2–2.5 orders of magnitude decrease in the permeability. Actually, 2% Na CMC and 1% PAM treatment by dry mass were found to be the optimum polymer contents. Both the environmentally friendly biopolymer Na CMC and the synthetic polymer PAM can effectively be treated with Ca bentonite to enhance the hydraulic performance of the GCLs.

Self-healing of laboratory eroded defects in a GCL on silty sand

The self-healing of five geosynthetic clay liners (GCLs) with laboratory simulated down-slope erosion defects (quasi-circular holes and linear slits where there is little or no bentonite) upon hydration from Godfrey silty sand subgrade with wfdn = 16% under an overburden stress σv = 20 and 100 kPa is examined. While there was an up to 9.6 mm reduction in hole diameter/slit width, none of the defects fully self-healed. The self-healing of these laboratory eroded specimens with a swell index of 10.2 ± 1.7 ml/2 g after hydration is generally smaller than that of the corresponding virgin GCLs. GCLs with powdered bentonite with an initial SI of 32 ml/2 g generally self-healed better and the intact specimens had a lower hydraulic conductivity than GCLs with granular bentonite with an initial SI of 24–26 ml/2 g. Higher mass per unit area of bentonite and overburden stress led to better self-healing. Ponding of distilled (DI) water above the GCL increased self-healing of GCL slightly more than simulated synthetic landfill leachate (SSL). The post-hydration hydraulic conductivity, k, of GCL specimens with holes/slits is shown to be about 1–3 orders of magnitude higher than that of the intact GCL specimen.

Mechanical and osmotic consolidation of geosynthetic clay liners: a laboratory study

This study aims to assess the effect of pore water salinity (sodium chloride (NaCL) solution) on the consolidation behaviour of GCLs (geosynthetic clay liners) using one-dimensional oedometer test apparatus. The experiments include two testing conditions: (1) an investigation of mechanical consolidation of GCL specimens saturated with water having different salinity levels, and (2) an investigation of the effect of pore water salinity on the volume change of GCL specimens under different constant vertical stress levels (i.e. osmotic consolidation). The mechanical consolidation test results indicated that the compression and swelling indices decrease as the liquid salinity increases, whereas an elastic hysteresis volume change behaviour was observed in the osmotic consolidation test results. The results of this study also show that the compression and swelling indices, and the hydraulic conductivity of a GCL specimen are almost reversible when it is subjected to an osmotic cycle.

Barrier properties of a geosynthetic clay liner using polymerized sodium bentonite

The hydraulic and swelling properties of a polymerized bentonite (PB), and the self-healing capacity of a geosynthetic clay liner (GCL) using the PB as the core material (PB-GCL) were investigated experimentally. Five different test liquids included of deionized water, NaCl solutions (0.1 M and 0.6 M) and CaCl2 solutions (0.1 M and 0.6 M) were used in this study. The PB exhibited a higher free swelling index (FSI) than that of the untreated bentonite (UB) for all test liquids. For permeability test, under a given void ratio (e), the value of k of the PB is much lower than that of the UB in NaCl and CaCl2 solutions. The PB-GCL specimens demonstrated a higher self-healing capacity than that of the corresponding GCL specimens using the UB (UB-GCL). Specifically, when using a 0.6 M CaCl2 solution for a 20-mm-diameter damage hole, the UB-GCL specimen provided a zero healing ratio (healed damage area/total damage area), but the PB-GCL specimen demonstrated an approximately 76% healing ratio. The results from this study indicate that the PB-GCL provided better barrier performance against cationic liquids with higher cation valence and concentrations compared to that of the UB-GCL.

Exhumation and performance of an Antarctic composite barrier system after 4 years exposure

An Antarctic biopile using a composite liner (high-density polyethylene geomembrane (GMB) over a geosynthetic clay liner (GCL)) was constructed on a coarse granular subgrade to contain hydrocarbon-contaminated soil and leachate. The soil was remediated after 4 years and the biopile was decommissioned. The liner was exhumed to assess the properties and performance of the GMB and GCL. There was no significant change in the GMB index properties. Although cobbles and coarse gravel of the subgrade had left indentations in the GMB, implying tensile strains that could impact long-term performance, there were no holes. There was significant variability in the hydration of the GCL (from 10% to 220%) and in the underlying subgrade soil water content (from 5% to 30%). This reflects the complexity of the subgrade and groundwater flow in the Antarctic environment. The exhumed GCL specimens had low hydraulic conductivity (1 × 10−11 to 7 × 10−11 m/s) at 13 kPa. Soil samples from below the composite liner showed no detectable hydrocarbons and confirmed no migration through the barrier. It is concluded that the composite barrier contained the leachate and biopile soil over the 4 years in service in the extreme Antarctic conditions.

Hydraulic conductivity of geosynthetic clay liners to inorganic waste leachate

Hydraulic conductivity (k) tests were conducted to evaluate how the permeation of solidified/stabilized inorganic hazardous waste (SIHW) leachate affected the k values of two geosynthetic clay liners (GCLs): a natural sodium bentonite GCL (GCL-N) and a sodium-activated calcium bentonite GCL (GCL-S). The two GCLs were permeated with distilled water (DW) and a SIHW leachate. The effects of the type of bentonite, effective stress and prehydration were assessed. At effective stress of 30 kPa, the k to DW was 1.5 × 10–11 m/s and 5.1 × 10–11 m/s for GCL-N and GCL-S, respectively. In contrast, at the same effective stress, permeation with SIHW leachate caused the k to increase by factors ranging from 1.2 to 3733 for GCL-N and from 86 to 5294 for GCL-S, respectively. Compared with GCL-N, GCL-S had poorer hydraulic performance. Increasing the effective stress and prehydration with DW reduced the detrimental effect induced by permeation with SIHW leachate. Some GCL specimens maintained low k values to SIHW leachate even though the corresponding bentonites had small or modest swell indexes in SIHW leachate. The results of this study suggest that further evaluation is needed before using swell index test to assess the effect of SIHW leachate on the hydraulic performance of GCLs.

Direct shear testing of GCLs at elevated temperature and in a non-standard solution

The objective of this study was to develop, verify, and assess a direct shear apparatus to measure the internal shear strength of geosynthetic clay liners (GCLs) when exposed to elevated temperature and non-standard hydration solutions. Shear boxes were developed to facilitate testing 300 mm square and 150 mm square specimens. Preliminary experiments documented the effectiveness of a GCL gripping system and a two-stage hydration procedure. Direct shear experiments were performed to evaluate the new apparatus with respect to the following variables: (i) specimen size; (ii) GCL peel strength; (iii) GCL heat treatment; (iv) test temperature; and (v) hydration solution. Direct shear results were verified via comparison to literature, which also supported the use of 150 mm square GCL specimens to measure internal shear behavior and shear strength. Shear tests on heat-treated and non-heat-treated GCLs at 20°C and 80°C yielded a 40% reduction in internal peak strength with increase in temperature. Hydration in a high-alkaline synthetic mining solution indicated a loss in peak strength with increasing hydration times from 15 to 60 days. A systematic reduction in peak and large-displacement shear strength with increasing normal stress was observed for 60 days’ hydration in the alkaline solution relative to hydration for 4 days in de-ionized water.

Gas permeability of partially hydrated geosynthetic clay liner under two stress conditions

The results of a series of gas permeability tests, with monitoring of gravimetric/volumetric moisture content and total suction, on a commercially available needle-punched geosynthetic clay liner (GCL) are presented. GCL specimens were partially hydrated with deionised water under 2 and 20 kPa confinement prior to testing. The tests were conducted at differential pressures ranging from 1 to 10 kPa. Gas permeability was found to decrease with an increase in gravimetric/volumetric moisture content and a decrease of suction. The effect of the preconditioning stress was found to be more pronounced at gravimetric moisture contents greater than 40% (25% apparent degree of saturation, 0·30 m3/m3 volumetric moisture content), and suctions less than 1·6 MPa.

Water retention and swelling behaviour of granular bentonites for application in Geosynthetic Clay Liner (GCL) systems

Geosynthetic Clay Liner (GCL) systems are used as efficient hydraulic barriers in landfills for the disposal of hazardous municipal wastes. Along with geotextiles, bentonite materials are chosen as one of the primary components of GCLs due to their high retention, adsorption, and swelling capacities. GCLs are manufactured using bentonites at a high total suction and hydrated through the uptake of liquid from the subsoil and the confined material as soon as they are installed. Bentonites may exhibit considerable volume change upon wetting. Depending on the confinement stress, the void ratio may significantly increase with a decrease in suction, particularly at higher degrees of saturation. To improve the hydraulic performance of GCLs, the swelling of the bentonites induced by the hydration should be limited when GCLs reach low suction values. The change in the hydrated void ratio is related to the pore structure evolution of the bentonites at different hydration levels. An improved understanding of the water retention and the void ratio evolution of bentonite materials during swelling is required, with particular attention given to the applications of GCL systems. The aim of this paper is to characterise the water retention and the swelling behaviour of granular bentonites for applications in GCLs. MX-80 granular bentonite, with an optimised grain size distribution, and Volclay GC-50 granular bentonite were selected, and their water retention behaviour was determined based on a new methodology. Reconstituted GCL specimens with MX-80 and Volclay GC-50 granular bentonites were tested with the same methodology to determine the water retention behaviour. An analysis of the water retention behaviour of the granular bentonites and reconstituted GCLs indicates that an adsorption mechanism controls the water retention behaviour for a wide range of total suction values. An analysis of the swelling potential of the granular bentonites indicates a significant increase in the hydrated void ratio for lower suction values. The increase in the void ratio is attributed to the modification of the smectite particles in the hydration path that results in new pore levels emerging in the bentonite structure. This change in the void ratio is expected to influence the hydraulic performance of the GCL in terms of diffusion and hydraulic conductivity.

Water vapour adsorption and desorption in GCLs

Super-saturated salt solutions are used to control relative humidity (RH) and to infer the hydration (water uptake and loss) behaviour of three needle-punched geosynthetic clay liners (GCLs) with respect to time under conditions of both free swell and 20 kPa applied stress. It is shown that RH and applied stress play a key role in the hydration behaviour with time when GCL specimens were in equilibrium with water vapour. It was also observed that water uptake and loss was affected by the bentonite form (powdered or granular) and mineralogy of the bentonite. However, the effect of GCL structure (i.e. difference in geotextiles and bonding of needle-punched fibres to the carrier geotextile) on their hydration behaviour for GCLs with similar form of bentonite was not significant for RH ≤ 97.7%. The effect of GCL structure became more apparent at 100% RH (for all GCLs). The results presented in this study can be used to better assess the hydration of GCLs in field applications such as waste containment liners and cover systems at different RH and overburden stress conditions.

Hydraulic Conductivity of Geosynthetic Clay Liners to Recirculated Municipal Solid Waste Leachates

AbstractTests were conducted to assess how permeation with actual recirculated leachate from municipal solid waste (MSW) landfills affects the hydraulic conductivity and exchange complex of geosynthetic clay liners (GCLs). Long-term hydraulic conductivity tests were conducted (∼1 to 5 years) on GCL specimens with conventional sodium bentonite using seven recirculated MSW leachates and one conventional (nonrecirculated) MSW leachate as permeant liquids. Effects of stress and temperature were also assessed. Hydraulic termination criteria were achieved for all tests, and chemical termination criteria were achieved for nearly all. The long-term hydraulic conductivity of the GCL specimens to recirculated leachates (1.0–2.0×1011 m/s) was slightly less than the long-term hydraulic conductivity to the conventional leachate (2.0×10−11 m/s). Furthermore, the ratio of the hydraulic conductivity to recirculated MSW leachate to the hydraulic conductivity to DI water for GCL specimens (1.4–2.9) fell within the range...

Transient hydraulic behavior of two GMBs–GCLs composite liners

In general, interface transmissivity is obtained based on measurements of the steady-state flow in composite geomembranes (GMBs) – geosynthetic clay liners (GCLs). However, transient flow rate has not been studied prior to this study. It has been already noticed that its consideration can lead to an important increase in predicted effluent volumes penetrating the liner, the subgrade soil and the ground water. The goal of the study presented herein is to study the transient state by quantifing the reduction in flow rate with time for two different composite liners. In these composite liners, a needle-punched GCL was combined to a high-density polyethylene GMB. The first GCL contained granular sodium bentonite and the second GCL contained powdered sodium bentonite. While the GCLs hydrated their water content and deformation were quantified. To this aim, various tests were conducted over various periods of time, corresponding to different flow rate values through the composite liner. Relationships between the flow rate and water uptake of the GCL on one side and swell on the other side are given for both GCLs. The results show that the mass per unit area in addition to the granulometric distribution of bentonite in GCL specimens may affect the hydration process and the flow rate evolution through composite liners. In addition, For both GCLs, the deformation follows the same trend of evolution with water content.

Restricted salt diffusion in a geosynthetic clay liner

The influence of semipermeable membrane behaviour on salt diffusion through a geosynthetic clay liner (GCL) was investigated by conducting multi-stage membrane tests on four GCL specimens at different effective stresses (σ′ = 34·5–242 kPa) in flexible-wall cells. Each test was conducted by circulating five source potassium chloride solutions, sequentially from lowest to highest concentration (Co = 3·9, 6·0, 8·7, 20, 47 mM), across the top specimen boundary, while circulating de-ionized water across the bottom boundary. Membrane efficiency coefficients (ω) were determined from differential pressure measurements, and effective salt-diffusion coefficients [Formula: see text] were inferred from boundary electrical conductivities. Increases in [Formula: see text] with increasing Co were observed for all specimens and were correlated to decreases in ω. In each case, [Formula: see text] decreased linearly toward zero as ω → 1, regardless of the applied σ′. These results support the hypothesis from pore-scale physical modelling that [Formula: see text] for GCLs exhibiting membrane behaviour may be expressed as a linear function of the quantity 1 − ω.

Laboratory investigation of self-healing properties on geosynthetic clay liners with flaw

Abstract The objective of this paper is to evaluate the self- healing properties of a commercially-available geosynthetic clay liner (GCL) using flexible-wall permeameter. The GCLs are produced by the same factory, but the contents of bentonite are different. Also the hydraulic conductivities (HC) of GCLs with no defect are different. In this study, specimens were completely saturated under the backpressure of 20 kPa before the test. Permeability tests were performed on GCL specimens with penetrating flaw and also on specimens permeated with distilled water and CaCl2 solutions. The test results were presented and discussed. Experimental results showed that the GCL with penetrating flaw did not exhibit complete self-healing in the case of flaw. After 120 days, the hydraulic conductivity increased by approximately an order of magnitude. In addition, CaCl2 solutions had a significant influence on the hydraulic conductivity. The research findings might be of interest to researchers and engineers who design liners for landfills and other liquid containment facilities

Altered geosynthetic clay liners: effect on the hydraulic performance of composite liners

This study evaluates how alteration of geosynthetic clay liners (GCLs) affects the hydraulic behaviour of a composite liner when the geomembrane presenting a hole is overlying a GCL. Interface transmissivity experiments were performed on GCL specimens that were exhumed from field sites. The results reveal different trends in the flow rates, which decrease differently to their steady state values. The steady state flow rates obtained and the calculated interface transmissivities are of the same order of magnitude as results obtained with a virgin GCL. The transient flow rate results are discussed in relation with the GCLs parameters. Based on these results, a new equation is derived that links interface transmissivity to the hydraulic conductivity of GCLs that have been altered by the environment. Considering large transient flow rates in calculations result in a greater leakage volume penetrating the liner when compared to calculations of infiltrated volumes considering only steady state leakage volume for a period of time of 1, 10 or 30 years. From a practical point of view, this suggests the introduction of a factor of safety of 1.67 when calculating the flow rate in composite liners in order to take into account the alteration by the environment of GCLs.

Effect of stress on water retention of needlepunched geosynthetic clay liners

Geosynthetic clay liners (GCLs) are placed at the bottom of waste disposal facilities where they hydrate from the subsoil and eventually from a hydraulic head on geomembranes (GMs) defects. Predicting hydration behavior of GCLs requires knowledge of the water-retention properties of the GCL along wetting paths. Given that GCLs could be subjected to different ranges of vertical stresses that are induced by the weight of the supported waste, the confining stress could affect water-retention properties of GCLs and should be investigated. To do so, a laboratory methodology to establish the water-retention curves (WRCs) of needlepunched GCLs under stress was undertaken. Various constant vertical stresses corresponding to different weights of the supported waste were applied to GCL specimens placed in controlled-suction oedometers. Suction values were selected so as to mimic a wetting path from the initial dry state to zero suction. Suction was controlled by using controlled suction techniques with controlled humidity imposed by a saturated saline solutions and using the osmotic technique with polyethylene glycol (PEG) solutions. Measurements were undertaken on oedometer systems as to apply confining stresses and have been complemented by standard saturated oedometer swelling tests. The data obtained confirm that increasing the stress on to the GCL results in less, albeit faster, water uptake, which could emphasize on recommendations about rapidly covering GCLs after they are placed at the bottom of a waste disposal facilities. Finally, the potential validity of the state-surface concept, which was developed in unsaturated soil mechanics, is discussed using van Guenuchten's and Fredlund and Xing's equations for water retention curves.

Quantification of diffusion of phenolic compounds in virgin GCL and in GCL after contact with a synthetic leachate

To quantify the diffusion coefficients of p-cresol, 2,4-dimethylphenol (2,4-DMP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-DCP), 2,3,5,6-tetrachlorophenol (2,3,5,6-TeCP), and pentachlorophenol (PCP), in-laboratory tests were conducted of diffusion through a needle-punched geosynthetic clay liner (GCL) containing natural sodium bentonite. The diffusion coefficient was qualified for the virgin GCL and for GCL that had undergone cation exchange after being exposed to a synthetic leachate. The goal of the experiment was to see if an increase in the hydraulic conductivity generated by cation exchange in a GCL would lead to significant increases in the diffusion coefficients of phenolic compounds. For all pollutants studied at a given bulk-GCL void ratio close to 3.0, the results reveal an increase in the diffusion coefficient for transit through the GCL exposed to the synthetic leachate. The increase in the diffusion coefficient due to synthetic-leachate permeation ranged from a maximum factor of 5.0 for 4-CP to a minimum factor of 1.3 for 2,3,5,6-TeCP and PCP. For virgin GCL specimens, the chemical properties of the compounds studied did not influence the diffusion coefficient. However, for the GCL specimens exposed to the synthetic leachate, the diffusion coefficient increased with the aqueous solubility and decreased with log Kow and the molecular weight.

Flow rate measurement in undamaged multicomponent geosynthetic clay liners

ABSTRACT: The objective of the paper is the presentation of a test method to quantify advective flow rates through multicomponent geosynthetic clay liners (GCLs). A procedure was developed, combining measuring devices from EN 14150 for flow rate measurement through geomembranes and a rigid wall permeameter from NF P 84-705 aiming at measuring the flow rates through GCLs. Multicomponent GCLs by structure fall between geomembranes and GCLs. The resulting testing device allows measurement of very small variations of volume with time while applying constant hydraulic pressures. The pressure difference applied on both sides of the multicomponent GCL specimens varied between 25 kPa and 100 kPa, the latter value being equal to that applied across geomembranes in EN 14150, except in one case where the multicomponent liner had a light coating. In this case hydraulic heads of 0.3 and 0.6 m were applied. Four different multicomponent GCLs were tested, from three different manufacturers, in order to determine the ability of the testing equipment to quantify the flow rate through multicomponent GCLs. The flow rate measurement was performed after a hydration phase under a very low hydraulic head and a 10 kPa normal load on the specimens in accordance with NF P 84-705. Details are given of the experimental conditions that might lead to the development of a standard for the measurement of flow rates through multicomponent GCLs. Results obtained tend to show that flow rates are one order of magnitude larger than those usually measured for virgin geomembranes, that is 10–5 m3/(m2 d), except for one of the multicomponent GCLs for which the light coating resulted in larger flow rates, measured with hydraulic heads of 0.3 and 0.6 m. In this case values consistent with previous values from the literature in the range 1.4 × 10–11 m/s to 2.2 × 10–11 m/s were obtained.

Anisotropy and directional shrinkage of geosynthetic clay liners

ABSTRACT: Results are reported from laboratory experiments to examine the potential shrinkage of two different geosynthetic clay liners (GCLs) when subject to repeated wetting and drying cycles. One GCL had a scrim-reinforced nonwoven carrier geotextile (denoted as GCL2) and the other had a nonwoven carrier geotextile (GCL4). Tests were conducted with both restrained and unrestrained GCL specimens of the same size as well as restrained specimens with different specimen sizes and length-to-width aspect ratios. For unrestrained specimens, there was no apparent difference between shrinkage in the transverse and longitudinal directions for GCL2, whereas GCL4 tended to shrink more in the longitudinal direction. There was only a small difference between restrained and unrestrained tests, with the restrained specimens giving a maximum strain about 1.1 times higher than the unrestrained for GCL4. There was no clear effect of the specimen size on the measured shrinkage. For restrained specimens, shrinkage increased with increasing aspect ratio up to an aspect ratio of approximately 5. The dry mass per unit area of the product was found not to affect shrinkage when the mass per unit area was evenly distributed. However, specimens with an uneven bentonite distribution (typically those with a low mass per unit area) can have areas of little to no bentonite content, and these specimens experienced much higher shrinkage than other specimens. A high degree of variability between specimens for apparently similar test conditions was observed. Even more noteworthy is the fact that the maximum shrinkage observed in these tests (14.4%) was well below the maximum of 23% observed by previous investigators using the same methodology and nominally the same product. This shows the difference that can occur between different rolls of nominally the same product.