Hydraulic Conductivity Of Geosynthetic Clay Liners Research Articles

Hydrodynamic assessment of bentonite granule size and granule swelling on hydraulic conductivity of geosynthetic clay liners

Flow in an idealized geosynthetic clay liner (GCL) containing bentonite comprised of equisized and equispaced square granules was simulated using a hydrodynamic model to quantitatively evaluate the premise that the hydraulic conductivity of GCLs diminishes as the bentonite granules hydrate and swell into adjacent intergranular pores, creating smaller and tortuous intergranular flow paths. Predictions with the model indicate that hydraulic conductivity decreases as granules swell and intergranular pores become smaller, and that greater granule swelling during hydration is required to achieve low hydraulic conductivity when the bentonite is comprised of larger granules, or the bentonite density is lower (lower bentonite mass per unit area). Predictions made with the model indicate that intergranular pores become extremely small (<1 μm) as the hydraulic conductivity approaches 10−11 m/s. These outcomes are consistent with experimental data showing that GCLs are more permeable when hydrated and permeated with solutions that suppress swelling of the bentonite granules, and that the hydraulic conductivity of GCLs with bentonite having smaller intergranular pores (e.g., GCLs with smaller bentonite granules, more broadly graded particles, or higher bentonite density) is less sensitive to solutions that suppress swelling.

A Numerical Study of Chemical Compatibility of GCLs

A series of COMSOL numerical models were established to study the chemical compatibility of GCLs (geosynthetic clay liner). The effect of chemistry on the mesoscopic structure and the hydraulic conductivity of GCLs was investigated. The factors, including the initial mobile porosity, the swelling ratio, the pore size, and the ionic strength, were discussed as well. The mesoscopic mechanism of the physical and chemical processes of GCLs was explored by the COMSOL models. The hypothesis that the final mobile porosity and the final pore size are the key factors of the hydraulic conductivity of GCLs was proven by the simulation. Meanwhile, when the ionic strength increased from low to medium, the changes in pore size, mobile porosity, and hydraulic conductivity were obvious. However, when the ionic strength increased from medium to high, the changes of these parameters tended to be gentle, and the changes in hydraulic conductivity were not obvious. Moreover, a theoretical model considering the effect of the initial particle size, the initial mobile porosity, and the ionic strength was developed to predict the hydraulic conductivity of GCLs in a chemical solution. This theoretical model was verified by experimental data. A good agreement was obtained.

Insights into Desiccation and Self-Healing of Bentonite in Geosynthetic Clay Liners under Thermal Loads

Geosynthetic Clay Liners (GCLs) are widely used for protecting groundwater from pollution sources at the surface, including applications in which they are subject to significant thermal gradients. Hence, sodium bentonite in the GCL may undergo significant dehydration and cracking, and the GCL might fail as a result. The paper presents outcomes of a set of recent experimental and numerical investigations exploring the propensity of bentonite to desiccate and self-heal, as well as means of mitigating the effect of thermal gradients on the hydraulic conductivity of GCLs. An elasto-plastic thermo-hydro-mechanical model was found to yield reasonable predictions of experimental behaviour, except for the transient phase of pre-heating hydration. Introducing an airgap between the GCL and the heat source can reduce the extent of desiccation and its effects on hydraulic conductivity. However, the effectiveness of the solution will depend on other factors including subgrade, magnitude of thermal and mechanical loads and type of GCL.

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.

Interface transmissivity and hydraulic conductivity of GCLs below poured concrete

ABSTRACT: The performance of four geosynthetic clay liners (GCLs) used as a hydraulic barrier below concrete-lined sewage treatment lagoons was examined based on a series of laboratory tests aimed at measuring: (i) the lateral flow of synthetic wastewater through the interface between each GCL product and a 0.1 m thick cast-in-place concrete above the GCL over a 14-month period and, from this data, calculating the concrete/GCL interface transmissivity (θ); and (ii) the hydraulic conductivity (k) of the GCLs below poured concrete when exposed to (iia) synthetic wastewater under isothermal conditions, or (iib) a series of wet–dry and/or cool–heat cycles for up to 12 months. The four GCLs have either sodium or polymer-enhanced sodium bentonite, and either granular or powdered bentonite. When the wastewater head above the GCL was 1.0 m (stress on concrete, σ = 10 kPa), θ for the GCL with granular sodium bentonite was 4 × 10−11 m2/s. For the same GCL, when the head increased to 2.5 m (σ = 25 kPa), the value of θ was reduced by about one order of magnitude to 2 × 10−12 m2/s. For the GCL which has polymer-enhanced granular bentonite, the value of θ was similar to (and possibly lower than) that for the GCL with untreated granular bentonite. For the GCL with powdered bentonite and cover geotextile impregnated with 1280 g/m2 of bentonite, the values of θ were 2 × 10−12 and 4 × 10−13 m2/s at 1.0 and 2.5 m head, respectively. With a reduction in the amount of the impregnated powdered bentonite in the cover geotextile to 840 g/m2, θ was 1 to 9 × 10−12 m2/s. The lowest k (3.2 × 10−11 m/s) for a GCL below concrete and exposed to wastewater under isothermal conditions was measured for the GCL with polymer-enhanced granular bentonite, whereas the highest value of k (1.9 × 10−10 m/s) was for the GCL with standard granular bentonite. Under 0.5 m head and 3 kPa stress, the k of the GCL below concrete and exposed to wet–dry cycles was 1.2–2.6 times the k of the GCL exposed to wastewater under isothermal conditions. Analytical calculations for the leakage through concrete/GCL liners for the four GCLs showed that the leakage was below the allowable limits specified by the Australian, British, and American standards.

Geosynthetic Clay Liner Permeated with Acid Rock Drainage:The Role of Iron in Arsenic Immobilization

=Geosynthetic Clay Liners(GCLs) have the potential to immobilize cations present in solution. Due to this, GCLs have been considered suitable materials not only in landfill bottom liners, but also in rock containments eith the potential of acid rock drainage(ARD) generation.However,the bentonite inside GCLs dose not have affinity towards anions such as aresenic, which is one of the toxic components present in ARDs. Based on the authors' previous research on swelling, sorption, and hydraulic conductivity of GCL against ARD, through discussion on the role of Fe in As immobiliation was done in this paper.Swelling test showed that the presence of metals, especially a high concentration of Fe(4500 mg/L approximately) due to its high concentration, negatively impact the swelling of bentonite by increaing the hydraulic conductivity value. The hydraulic conductivity remained low during the test duration but was one order of magnitude higher in the ARD permeation case(5.0×10-10 m/s)than in the water permeation case(1.4×10-11 m/s)。Single metal sorption tests showed that Fe was sorbed by the betonite while As was As sorption.Considering that GCLs do not retain As, but Fe does, an additional Fe layer could be placed in the bottom liner system in order to immobilize it. However, if the ARD contains high Fe concentration, this additional layer would not be neccessary as the Fe in solution will prevent As mitigation.

Relative Abundance of Monovalent and Divalent Cations and the Impact of Desiccation on Geosynthetic Clay Liners

Laboratory experiments were conducted on a geosynthetic clay liner (GCL) containing Na–bentonite to determine how the swell index and hydraulic conductivity of GCLs are affected by wet-dry cycling with solutions having different relative abundance of monovalent and multivalent cations. Relative abundance of monovalent and multivalent cations was characterized by the RMD of the test solution, which is defined as the ratio of the total molarity of monovalent cations to the square root of the total molarity of multivalent cations at a given ionic strength. RMD was found to control the final swell index, relative abundance of monovalent and divalent cations in the final exchange complex, and the final hydraulic conductivity of bentonite exposed to wet-dry cycling. Ionic strength affects the number of wet-dry cycles required for a change in hydraulic conductivity to occur and the rate of change in swell index. Large increases in hydraulic conductivity and loss of swelling capacity occurred for solutions having...

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.

Hydraulic conductivity of compacted clay liners permeated with inorganic salt solutions

Due to their low permeability, geosynthetic clay liners (GCLs) and compacted clay liners (CCLs) are the main materials used in waste disposal landfills. The hydraulic conductivity of GCLs and CCLs is closely related to the chemistry of the permeant fluid. In this study, the effect on the hydraulic conductivity of clays of five different inorganic salt solutions as permeant fluid was experimentally investigated. For this purpose, NaCl, NH(4)Cl, KCl, CaCl(2), and FeCl( 3) inorganic salt solutions were used at concentrations of 0.01, 0.10, 0.25, 0.50, 0.75 and 1 M. Laboratory hydraulic conductivity tests were conducted on low plasticity (CL) and high plasticity (CH) compacted raw clays. The change in electrical conductivity and pH values of the clay samples with inorganic salt solutions were also determined. The experimental test results indicated that the effect of inorganic salt solutions on CL clay was different from that on CH clay. The hydraulic conductivity was found to increase for CH clay when the salt concentrations increased whereas when the salt concentrations were increased, the hydraulic conductivity decreased for the CL clay.