Geosynthetic Clay Liners Research Articles

Hydraulic conductivity of geosynthetic clay liners to trona ash leachate: Effects of mass per unit area, bundles of fiber existence, and preydration conditions

The barrier performance of geosynthetic clay liners (GCLs) to coal combustion products (CCPs) is of primary importance. One of the CCPs leachates that has a damaging effect on hydraulic conductivity is trona ash leachate (TAL). In this study, the hydraulic conductivity of sodium GCL (Na-GCL) to TAL was investigated in terms of mass per unit area (MPUA). The hydraulic conductivity of GCLs to TAL was 2.6 × 10-6 and 7.6 × 10-7 m/s when the MPUA was 3.0 kg/m2 (Mb3) and 4.0 kg/m2 (Mb4), respectively. Dye tests conducted on these GCLs showed that flow preferentially occurred through bundles of fibers existing in the GCLs. In contrast, increasing the MPUA to 5.0 kg/m2 (Mb5) led to a decrease in the hydraulic conductivity (i.e. 4.1 × 10-11 m/s). Additional tests were performed on fiber-free GCLs to determine the role of fiber bundles. Regardless of MPUA, the fiber-free GCLs had low hydraulic conductivity (6.7 × 10-11 m/s). Prehydrating Mb3 and Mb4 with deionized water (DIW) before permeation with TAL also decreased the hydraulic conductivity. The hydraulic conductivities of prehydrated Mb3 and Mb4 were 1.6 × 10-10 and 4.8 × 10-11, respectively. Chemical analyses showed that the cation exchange reaction had a negligible influence on the hydraulic conductivity. Because TAL was a potential source of Na+ throughout the tests.

A Semi-Analytical Model of Contaminant Transport in Barrier Systems with Arbitrary Numbers of Layers

In regions with sanitary landfills, unsuitable liner designs can result in significant soil and groundwater contamination, leading to substantial environmental remediation costs. Addressing this challenge, we propose a semi-analytical model for solute transport that uses the advection–dispersion–reaction equation in a multi-layered liner system. A distinctive feature of our model is its ability to account for infiltration velocity, arbitrary numbers of layers, thin layers such as geomembranes, and mass flow. We validated our model against existing published models and applied it to a case study of a real sanitary landfill in the capital of Brazil. Through parametric analyses, we simulated contaminant transport across various layers, including the geomembrane (GM), geosynthetic clay liner (GCL), soil liner (SL), and compacted clay liner (CCL). The analyses showed the importance of choosing the most appropriate construction system based on the location and availability of materials. Considering toluene contamination, a GM molecular diffusion coefficient (DGM) greater than 10−13 m2 s−1 exhibited similar efficiency when compared with CCL (60 cm thick). In addition, the results showed that the liner system may have the same efficiency in changing SL (60 cm thick) for a GCL (1 cm thick).

Seasonal hydrology and gas transport in a composite cover on sulfide tailings

This study presents the field performance of a five-layer composite cover to mitigate acid mine drainage in legacy sulfide tailings in northern Ontario, Canada. Installed in 2008, this cover comprised sand, clay, geosynthetic clay liner, sand, and waste rock layers. To evaluate the effectiveness of the cover in reducing water and oxygen ingress, groundwater and vadose zone hydrological characterization, stable water isotope analysis, pore-gas measurements, oxygen flux calculations, and variably saturated flow modeling were conducted. The results indicate that the clay layer stayed nearly saturated in the spring, fall, and winter, but temporary desiccation occurred during the summer. Compared to uncovered tailings, the cover significantly lowered diffusive oxygen flux. In the summer, fall, and winter, the capillary barrier effect of the cover functioned effectively and inhibited percolation. Atmospheric pore-gas oxygen concentrations at one out of the three monitoring locations indicate potential cover imperfections that enabled oxygen transport into the tailings. In the spring and early summer, snowmelt infiltration resulted in percolation that compromised the capillary barrier effect, as well as lateral drainage. The resulting increase in water saturation in the cover limited oxygen transport. Despite potential cover imperfections, this composite cover reduced oxygen and water ingress a decade after installation.

Modelling a geosynthetic clay liner in a centrifuge and its application to the dynamic stability of small-sized earth-fill dams

This study proposes a centrifuge modelling method for geosynthetic clay liners (GCLs). The development of such a centrifuge model has been challenging due to the complex hydraulic and mechanical behaviour of GCLs and their interface with the soil. Additionally, the proposed method was applied to the seismic stability of an earth-fill dam. Impermeable sheets were selected as the GCL model based on validation using finite element seepage analysis and similarity laws. Dynamic centrifuge model experiments were conducted on a 10-m-high embankment with a high phreatic line to visually verify the failure mechanism, as previous full-scale tests did not provide clear visualisation. A transparent plate imaging confirmed upstream translational failure of the GCL, which was installed in a staircase shape. With regard to improving the seismic resistance of the embankment, it was found that cement-stabilisation of the lower half of the water level upstream side of the GCL significantly reduced deformation.

Analytical solution for contaminant transport through a GCL-enhanced composite cutoff wall system

The geosynthetic clay liners (GCLs) have been recently shown to be effective in cutoff wall applications. Yet, its influence on contaminant transport through cutoff wall system is rarely reported. This study presents an analytical solution for the transport of organic contaminant through a composite cutoff wall system comprising a soil-bentonite wall, a GCL, and an aquifer. The analytical solution was obtained by variable separation method and verified against an existing analytical solution and a numerical solution. Parametric analysis was conducted to elucidate the effects of GCL, soil-bentonite (SB) wall thickness (Lw), aquifer thickness (La), and contaminant half-life (t1/2) on contaminant transport. The results show that by adding a GCL layer, the contaminant concentration and the maximum flux can be significantly decreased. When the GCL retardation factor increases 1 to 300, the required time to reach the maximum flux is delayed from about 62 years to 1500 years. Larger aquifer thickness sufficiently weakens the contaminant transport process. Under the same breakthrough criteria, the required thickness of SB wall decreases by about 20% when the GCL retardation factor increases from 1 to 50. The proposed analytical solution provides a useful tool for the design of the SB-GCL cutoff wall system.

JEDAN PRIMER UPOTREBE AKTIVNOG GEOKOMPOZITA ZA SANACIJU DEPONIJE

The ''Chalk landfill Bruck I/II'', a former industrial landfill is located in Austria. The landfill was filled from 1926-1981 with calcium carbide, CHC and mercury contaminated wastes. The total amount of HCH is estimated to 100-1000 t. Since 1995 different remedial actions took place as well as continuous securing measures. In 2000 the site was put on the list of contaminated sites that need remediation and got codename K20. Additional tests in 2003 gave the site highest priority level one. In 2009 decision is made to remove all stored material and treat or safely store in state-of-the-art landfill. After observation of Hexachlorobenzene in food in the area around the thermal treatment plant works were stopped. The new course of action was to secure the waste on site. The new physical safeguard measures included an innovative, multifunctional surface sealing system consisting of calcium bentonite geosynthetic clay liner, an activated carbon mat, a LDPE membrane with integrated aluminium sheet and a drainage element. This system creates a strong barrier for volatile CHC. There are soil vapor extraction pipes below and above the sealing system to ensure a monitoring. Minimal interference with existing landfill body was requirement. To enable long term stability of the whole sealing system geogrids are used. The construction work was executed in 2016.

Hydraulic conductivity and multi-scale pore structure of polymer-enhanced geosynthetic clay liners permeated with bauxite liquors

A study was conducted to investigate the multi-scale pore structure-based mechanism controlling the hydraulic conductivity of polymer-enhanced geosynthetic clay liners (GCLs) prepared by the wet-mixed method to bauxite liquors (BLS and BLA). The multi-scale pore structures were evaluated using MIP and N2GA tests quantitatively. Conventional GCL permeated with BLS had a larger flow path volume than with DI water (0.194 > 0.119 cm³/g), attributed to the bentonite swelling inhibition and the montmorillonite dissolution, leading to the higher hydraulic conductivity (3.0 × 10−7 > 2.7 × 10−11 m/s). Polymer-enhanced GCLs developed more micropores and had a smaller quantity proportion and volume of flow paths since polymer formed more micropores to clog pores, contributing to a lower hydraulic conductivity than conventional GCL to BLS. The hydraulic conductivity of polymer-enhanced GCL to BLS (ionic strength: 622.5 mM) was higher than that to BLA (156.9 mM) (2.6 × 10−9 > 6.0 × 10−12 m/s), given that the coiled or contracted polymer conformation left a smaller quantity proportion (5.54% < 6.71%) and volume (0.0002 cm3/g < 0.0035 cm3/g) of micropores.

Analytical model for contaminants transport in triple composite liners with depth-dependent adsorption process

Predictions of contaminant transport in landfill composite liners are essential to assess the risk of groundwater pollution. The amount of soil organic carbon is strongly depth-dependent, which plays a crucial role in the adsorption of organic contaminants and heavy metal ions. The one-dimensional analytical model of contaminant transport in the triple composite liner consisting of geomembrane, geosynthetic clay liner and attenuation liner is presented considering the influence of depth-dependent adsorption coefficients. A specific sigmodal function is introduced to describe the attenuation of adsorption coefficients along the depth. The solution is obtained by the Laplace transformation. The analytical model was validated by experimental and numerical results. The results of the sensitivity analysis show that depth-dependent adsorption coefficients are critical for the risk assessment of groundwater pollution. The breakthrough time of composite liners can be overestimated by a folder of 2.5 with constant adsorption coefficients. The effects of parameters related to the depth-dependent adsorption process on the long-term transport of contaminants are critical for the design of a stable and effective composite liner system The proposed solution can capture the field observed data well and is consistent with the field observation. In addition, the proposed analytical solution may serve as a benchmark for various numerical models.

Unlocking the sorption mechanism of perfluoroalkyl acids (PFAAs) on geosynthetics: Case of the geotextile components of geosynthetic clay liners

We present here an experimental investigation on the sorption of four perfluoroalkyl acids (PFAAs): namely, two perfluorocarbonic acids (PFCAs) – perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA); and two perfluorosulfonic acids – perfluorooctane sulfonate (PFOS) and, perfluorobutane sulfonic acid (PFBS) to polypropylene cover and carrier geotextiles commonly used in geosynthetic clay liners. The impacts of various operational parameters, such as sorbent mass, contact time, and initial PFAA concentration, were investigated. A bi-exponential adsorption model was observed to describe the adsorption kinetics for all PFAAs sufficiently. The model indicates two (probably physically) different types of adsorption sites involved in the PFAAs adsorption. The Freundlich and Langmuir equations well represented the adsorption isotherms. Furthermore, it was observed that PFAA sorption was strongly dependent on the end functional groups and perfluorinated carbon chain length of PFAAs. The maximum adsorption capacities for all PFAAs on geotextiles were consistent with results obtained for clay minerals, indicating that, in the absence of sufficient organic matter, sorption of PFAAs onto solids is mainly analyte and solution dependent. The results obtained and reported for the first time herein are imperative for understanding the fate and migration of PFAAs in modern geosynthetic composite liner systems.

Prediction of hydraulic conductivity of sodium bentonite GCLs by machine learning approaches

Six machine learning methods (linear regression, logistic regression, extreme gradient boosting (XGBoost), support vector machine, K-nearest neighbours and artificial neural network) were used to predict/classify the hydraulic conductivity of conventional sodium bentonite (Na-B) geosynthetic clay liners (GCLs) to saline solutions or leachates. Data were collected from the literature and randomly divided into two groups – that is, 80% of the data were used to train machine learning models and the rest, 20%, were applied to evaluate model performance. Features that are known to affect the hydraulic conductivity of Na-B GCLs (e.g. mass per unit area of GCLs, monovalent and divalent cations, ionic strength (I), relative abundance of monovalent to divalent cations (RMD), swell index and effective stress) were employed to predict/classify the hydraulic conductivity of Na-B GCLs. Comparative analyses were conducted with seven subsets corresponding to the combination of different features, and the best model was determined through cross-validation. The results showed that XGBoost consistently had the best performance among all methods over all subsets of features for both regression and classification analyses. Subset 4, using the swell index, I, RMD, I 2 × RMD, monovalent cations, divalent cations, effective stress and mass per unit area as features, outperformed all other six subsets in both regression analysis (R 2 = 0.826) and classification analysis (accuracy = 0.887) in the out-of-sample tests.

Shear strength of HDPE smooth geomembrane/bentonite-polymer geosynthetic clay liner interface

This study investigated the impact of polymer elution on the interface shear strength between a smooth geomembrane (GMB) and two types of bentonite-polymer (B–P) geosynthetic clay liners (GCLs) containing linear and crosslinked polymers. Tests were also conducted with sodium bentonite (Na–B) GCLs as a control. Interface shear tests were conducted with dry, two-stage, and free hydration conditions with varying normal stresses. The results showed that under dry conditions, the displacement at peak strength and shear strength envelops of GMB/Na–B GCL and GMB/B–P GCLs were similar. However, the displacement at peak strength of GMB/B–P GCLs was higher than that of GMB/Na–B GCL under two-stage and free hydration. Meanwhile, the peak shear strength of the GMB/B–P GCLs showed a greater reduction than that of GMB/Na–B GCLs when transitioning from a dry condition to a free hydration condition at the same normal stress, particularly at higher normal stress. Loss on ignition (LOI) tests confirmed that there was a decrease in polymer loading of B–P GCLs after the shearing test, indicating polymer elution occurred during the shearing test. The result suggests that polymer elution had a significant effect on the GMB/B–P GCL interface shear strength, especially at higher normal stress.

Effect of temperature on critical strength of geosynthetic clay liner / textured geomembrane composite systems

The objective of this study was to evaluate the effect of temperature on the shear behavior and critical strength of composite systems comprising of a geosynthetic clay liner (GCL) and textured geomembrane (GMX). For this purpose, displacement-controlled internal and interface direct shear tests were performed at both room temperature (≈20 °C) and an elevated temperature of 80 °C on three GCL/GMX composite systems at normal stresses varying from 100 kPa to 2000 kPa. An increase in the test temperature resulted in peak shear strength reduction up to 45% in GCL internal shear tests and up to 46% in GCL-GMX interface shear tests. The large-displacement shear strength at the elevated temperature was also reduced by up to 32% in GCL internal shear tests and up to 48% in GCL-GMX interface shear tests.

A solution for calculating the leakage rate through GMB/CCL composite liners with long defects

Geomembranes (GMBs) of the landfill composite liners frequently contain long defects, which will form the dominant flow path in the composite liner. The significant differences between the geosynthetic clay liner (GCL) and the compacted clay liner (CCL) lead to distinct flow patterns in the defective composite liners. For GMB/CCL composite liners, the induced flow in the CCL is two-dimensional, thus the existing solution with the assumption of one-dimensional flow significantly underestimates the leakage rate with a maximum relative error of 87% when compared to the results of a 2D finite element model. A new solution for predicting the leakage rate through GMB/CCL composite liners with a long defect is proposed with a consideration of two-dimensional flow in the CCL, with relative errors of leakage rate less than 29% for the cases investigated. The proposed solution also shows a lower relative error for the wetted distance (6–23%) compared to the existing solution (49–77%) for GMB/CCL composite liner cases. The comparisons with numerical results show that the proposed analytical solution significantly reduces the underestimation of leakage rate through the defective GMB/CCL composite liner, thus can help to improve the composite liner design for landfills.

Pore Scale Simulation of Rheology Properties on Residence Time of Polymer Hydrogel and Hydraulic Conductivity of Bentonite Polymer Composite Geosynthetic Clay Liners

Flow in an idealized bentonite polymer composite geosynthetic clay liner (BPC-GCL) containing bentonite comprising two idealized circular granules was simulated using a COMSOL hydrodynamic model. The effect of the polymer rheology properties, including viscosity, surface tension, and contact angle, on the hydraulic conductivity of BPC-GCLs was investigated. The results showed that the hydraulic conductivity of BPC-GCLs significantly decreased by 2–4 orders of magnitude with polymer loadings of 3.3%, 6.5%, and 9.8% compared to conventional geosynthetic clay liners (GCLs). The polymer rheology properties are critical to the residence time and the hydraulic conductivity of BPC-GCLs. The residence time increases with the viscosity, surface tension, and contact angle of polymer hydrogel. In the overall study, the hydraulic conductivities increased significantly from 2.80 × 10−9 m/s to 1.40 × 10−7 m/s when the residence time was insufficient. When the viscosity of the polymer hydrogel is 5000 Pa∙s, 1 × 104 Pa∙s, and 1 × 105 Pa∙s, the residence time of the polymer hydrogel in the domain of BPC-GCLs is 14 min, 23 min, and 169 min, respectively. When the surface tension of the polymer hydrogel is 0 N/m, 0.01 N/m, and 0.02 N/m, the residence time of the polymer hydrogel in the domain of BPC-GCLs is 9 min, 17 min, and 23 min, respectively. When the contact angle between the polymer hydrogel and the NaB granules is 30° to 60°, the residence time of the polymer hydrogel in the domain of BPC-GCLs is 9 min and 33 min. These few minutes can approximate the actual passage of several days in physical time. When the viscosity, the surface tension, and the contact angle are higher than 1 × 106 Pa∙s, 0.03 N/m, and 60°, the residence time of the polymer hydrogel in the domain of BPC-GCLs tends to be very long, which means that a very low hydraulic conductivity of BPC-GCLs can be maintained in the very long term. This research unveils a nuanced and profound correlation between the rheological properties of the polymer hydrogel and the resulting hydraulic conductivity. This discovery enhances the understanding of the potential to tailor hydrogel characteristics for BPC-GCLs. The advanced model developed in this study also lays the groundwork for constructing a more realistic model that considers irregular geometries, interconnected pores, and diverse polymer distributions within the pore spaces.

Some black cotton soils of Ghana; A potential for use in geosynthetic clay liners

Black cotton soils contain the clay mineral montmorillonite which is the property of bentonite that makes it useful in geosynthetic clay liners. These soils occur in large quantities in Ghana. Importation of geosynthetic clay liners which contain bentonite as the major barrier material is expensive and a local alternative will have positive economic repercussions. The hydraulic conductivity of black cotton soils from Dowhenya, Prampram, and Tsopoli all in the Accra plains of Ghana were sandwiched between two geotextiles, tested, and compared to commercial bentonite. The results of the swell index test were 7.0mL/2g, 7.0mL/2g, 5.0mL/2g, and 30mL/2g for Dowhenya, Prampram, Tsopoli, and commercial bentonite respectively. The water content results obtained were 12.20%, 10.13%, 10.83%, and 17.48% for Dowhenya, Prampram, Tsopoli, and commercial bentonite respectively. The particle size distribution test results indicated that clay fractions are 83.4%, 71.3%, 72.9%, and 95.0% for Dowhenya, Prampram, Tsopoli, and commercial bentonite respectively. pH results determined are 7.86, 7.82, 7.90, and 10.24 for Dowhenya, Prampram, Tsopoli, and commercial bentonite respectively. The permeability of Dowhenya, Prampram, and Tsopoli black cotton soils was determined to be 1.03 X 10-9cm/s, 7.61 X 10-9cm/s, 2.04 X 10-9cm/s and these compare well to the commercial bentonite permeability value of 2.08 X 10-9cm/s tested under the same conditions. Based on the results, black cotton soils from these areas can be used as a potential substitute for commercial bentonite in geosynthetic clay liners.

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.

Modeling the Salinity Effect on the Water Retention Curve of Geosynthetic Clay Liner (GCL) on the Drying Path.

The water retention curve (WRC) of a geosynthetic clay liner (GCL) is influenced by the presence of exchangeable cations in the leachate during changes in water content in a landfill construction. This research aims to investigate the impact of salinity on the WRC of GCL. To measure the WRC of GCL under different sodium chloride (NaCl) concentrations on the drying path, a chilled-mirror dew-point device capable of controlling the GCL's volume was employed. Additionally, the dry state microstructure of the GCL was examined using electron microscopy. The test outcomes indicate that GCL hydrated with higher salinity has greater suction at the same water content during drying. This influence can be attributed to changes in salinity and the precipitation of NaCl crystals within the bentonite when water evaporates, which in turn affects the bentonite's microstructure and leads to increased matric suction. By introducing the Fredlund and Xing model and parameter relationship, it is possible to predict the WRC of GCL under salinity effects after measuring the WRC under different salinity conditions on the drying path.

Modelling migration of ammonium ion through landfill bottom barriers subjected to elevated temperature and dry-wet cycles, a case study in southern Hanoi, Vietnam

Geosynthetic clay liners and compacted clay liners are common bottom barriers in landfills. One of the important steps in barrier design is to evaluate the effectiveness of the bottom barrier system in practical conditions based on modelling contaminant migration. This study simulates the migration of ammonium ions through proposed bottom barriers for design under consideration of the southern Hanoi area’s temperature and geohydrology conditions, then evaluates potential impacts on normalized ammonium concentration in groundwater. Proposed bottom barriers include geosynthetic clay liner and compacted clay liner constituting from local soils. The results indicated the reclamation of locally natural soils and geosynthetic clay liner (GCL) placement was approximately 5.2 and 13.4 times more effective in slowing ammonium migration than natural soil, respectively. Compacted clay liner of natural soils exhibited few impacts from elevated temperature. However, being sensitive to an elevated temperature at 50°C, the barrier performance of GCL caused the peak normalized ammonium concentration in groundwater to be 4.2 times higher than normal conditions. Notably, normalized ammonium concentration in groundwater increased 29 times when the geosynthetic clay liner was exposed to 2 dry-wet cycles with ammonium solution. These results provided useful references for designers and engineers to consider in selecting barrier materials in the new landfill.

Study on the Permeability of GCL Materials in Coupled Environment

As a new-type anti-seepage material, Geosynthetic Clay Liner (hereinafter referred to as GCL) has been applied in various anti-seepage projects and achieved good benefits. Based on different salt solution types, concentrations, dry-wet, and freeze-thaw cycles, this paper designs a permeability test of GCL after aging, and the result shows that: (1) under the influencing factors of single salt solution, there is a threshold concentration of 0.15 mol/L, which means that the increase rate of GCL permeability coefficient suffers a significant decrease above this concentration. (2) With fewer numbers (<4 ) of dry-wet cycles the GCL permeability coefficient shows faster growth and then returns gradually to stability. (3) Compared with dry-wet and freeze-thaw environments, cation concentration and valence have a more prominent inhibition effect on the anti-seepage property of GCL. The research results can provide data reference and reasonable advice for the deterioration of various indicators of GCL material and its service life in corresponding projects in saline soil areas.

Numerical investigation of the effect of geosynthetic clay liner chemical incompatibility on flow and contaminant transport through a defective composite liner

Numerical investigation of the effect of geosynthetic clay liner chemical incompatibility on flow and contaminant transport through a defective composite liner