Geosynthetic Liners Research Articles

Brittle rupture of an aged HPDE geomembrane at local gravel indentations under simulated field conditions

ABSTRACT: The susceptibility of a 1.5 mm thick high-density polyethylene geomembrane to brittle rupture from long-term stress cracking in a simulated municipal solid waste landfill liner is examined. The geomembrane was pre-aged in a leachate at 85°C to lower the notched constant tensile load stress crack resistance of the geomembrane to about 75 h. The aged geomembrane was then used as part of a composite liner system in geosynthetic liner longevity simulators (GLLSs) with a geosynthetic clay liner and sand foundation layer below the geomembrane and a 560 g/m2 geotextile protection layer and 50 mm drainage gravel above the geomembrane. The GLLSs allow the simulation of field conditions including elevated temperatures, overburden pressure, leachate circulation, and composite liner exposure conditions. The geomembrane experienced brittle rupture on the side slopes of the local gravel indentations for temperatures between 55 and 85°C. The higher the liner temperature, the shorter the time to rupture and the higher the tensile strain at rupture. Arrhenius modelling of the test data gave an activation energy of Ea = 112 kJ/mol.

Study on Effect of Gradient of Landfill Side Slope on Tensile Force of Geosynthetic Liner

It is important to study the effect of gradient of landfill side slope on the tensile force of geosynthetic liner in order to assure adequate performance and to increase the landfill volume. In this research, for the landfill liner composed of upper protective mat, barrier sheet and bottom protective mat, finite Element Analysis, in which the gradient of modelled landfill side slope was changed from 1:2.0 to vertical, were conducted to evaluate the effect of side slope gradient on the tensile force of geosynthetic liner. In the FEM analysis, the stress-strain relationship of ash and friction stress-relative displacement relationship of joint element were modelled by hyperbola. The results of centrifugal model experiments were also used to verify the FEM analysis. As a conclusion, the tensile force of geosynthetic liner at the slope crest decreases with increasing side slope gradient from 1:2.0 to 1:0.2 and then it increases slightly as the gradient increases up to vertical.

Antioxidant depletion of HDPE geomembrane with sand protection layer

ABSTRACT: The performance of a 1.5 mm thick high-density polyethylene geomembrane (GMB) in simulated municipal solid waste landfill liners is presented. Accelerated ageing experiments were conducted in geosynthetic liner longevity simulators that allow simulation of field conditions including elevated temperatures, overburden pressure, leachate circulation and composite liner exposure conditions. A 150 mm sand protection layer was used between a gravel drainage layer and an underlying GMB liner. A comparison between the results obtained for this sand protection layer and those obtained for a 580 g/m2 geotextile protection layer is presented in terms of both antioxidant depletion and tensile strains. The antioxidant depletion stage for the GMB with the sand protection layer was predicted to be around 500 and 9 years at 20°C and 60°C, respectively. The antioxidant depletion stage with a sand protection layer was longer than that with geotextile protection by a factor of 1.6 for the same GMB, leachate and test boundary conditions. A comparison between the tensile strains induced in the GMB with sand and geotextile protection layers shows that the long-term tensile strains in the GMB with a sand protection layer were substantially lower than those for the GMB with a 580 g/m2 geotextile protection layer.

Modeling Sorption and Diffusion of Organic Sorbate in Hexadecyltrimethylammonium-Modified Clay Nanopores – A Molecular Dynamics Simulation Study

Organoclays are highly sorptive engineered materials that can be used as amendments in barrier systems or geosynthetic liners. The performance of confining and isolating the nonpolar organic contaminants by those barrier/lining systems is essentially controlled by the process of organic contaminant mass transport in nanopores of organoclays. In this article, we use molecular dynamics (MD) simulations to study the sorption and diffusion of organic sorbates in interlayers of sodium montmorillonite and hexadecyltrimethylammonium (HDTMA(+))-modified montmorillonite clays. Simulated system consisted of the clay framework, interlayer organic cation, water, and organic sorbate. Their interactions were addressed by the combined force field of ClayFF, constant-valence force field, and SPC water model. Simulation results indicated that in HDTMA coated clay nanopores, diffusion of nonpolar species benzene was slowed because they were subjected to influence of both the pore wall and the HDTMA surfactant. This suggested the nonpolar organic compound diffusion in organophilic clays can be affected by molecular size of diffusive species, clay pore size, and organic surfactant loading. Additionally, a model that connected the diffusion rate of organic compounds in the bulk organoclay matrix with macropores and nanopores was established. The impact of intercalated organic cations on the diffusion dominated mass transport of organic compounds yielded insight into the prediction of the apparent diffusion behavior of organic compounds in organic-modified clays.

Model tests on interaction between soil and geosynthetics subjected to localized subsidence in landfills

In a landfill, excessive tensile strains or failure of the liner system due to localized subsidence underneath the geosynthetic liner, is a concern in design and operation of the landfill. The localized subsidence can be commonly withstood by reinforcements such as geogrids. A total of nine model tests were carried out to study the influence of soil arching in overburden sandy soil on the geosynthetics and the interaction between the soil and the geosynthetics. The localized subsidence was modeled by a strip trapdoor under the geosynthetic reinforcements. The reinforcement includes several layers of polyvinylchlorid (PVC) membrane or both PVC membrane and a compacted clay layer. Test results show that the vertical soil pressure acting on the geosynthetics within the subsidence zone is strongly related to the deflection of the geosynthetics. The soil pressure acting on the deflected geosynthetics will decrease to a minimum value with respect to its deflection if the final deflection is large enough, and this minimum value is almost independent of the overburden height. Otherwise, the deflection of geosynthetics cannot result in a full degree of soil arching, and the soil pressure within the subsidence zone increases with the increase of overburden height. Deflections and strains of the geosynthetics obviously decrease with the increase of their tensile stiffness. The presence of a compacted clay layer buffer can therefore reduce both deflections and strains of the geosynthetics. Finally, a composite liner structure is recommended for landfills to withstand the localized subsidences.

A performance-based method for calculating the design thickness of compacted clay liners exposed to high strength leachate under simulated landfill conditions

Compacted clay liners (CCLs) when feasible, are preferred to composite geosynthetic liners. The thickness of CCLs is typically prescribed by each country's environmental protection regulations. However, considering the fact that construction of CCLs represents a significant portion of overall landfill construction costs; a performance based design of liner thickness would be preferable to 'one size fits all' prescriptive standards. In this study researchers analyzed the hydraulic behaviour of a compacted clayey soil in three laboratory pilot scale columns exposed to high strength leachate under simulated landfill conditions. The temperature of the simulated CCL at the surface was maintained at 40 ± 2 °C and a vertical pressure of 250 kPa was applied to the soil through a gravel layer on top of the 50 cm thick CCL where high strength fresh leachate was circulated at heads of 15 and 30 cm simulating the flow over the CCL. Inverse modelling using HYDRUS-1D indicated that the hydraulic conductivity after 180 days was decreased about three orders of magnitude in comparison with the values measured prior to the experiment. A number of scenarios of different leachate heads and persistence time were considered and saturation depth of the CCL was predicted through modelling. Under a typical leachate head of 30 cm, the saturation depth was predicted to be less than 60 cm for a persistence time of 3 years. This approach can be generalized to estimate an effective thickness of a CCL instead of using prescribed values, which may be conservatively overdesigned and thus unduly costly.

Feedback and guidelines for geomembrane lining systems of mountain reservoirs in France

Mountain reservoirs are hydraulic structures in mountains, used in ski resorts to store water, generally for producing artificial snow; there are about 120 of them in France. Despite their modest volumes (5000–400,000 m 3) and dam heights of between 5 and 20 m, these structures do induce potentially high risks, due to their location in mountain at altitudes of between 1200 and 3000 m. These reservoirs are very often made watertight artificially by geomembrane. A survey conducted on about 70 of these reservoirs provided considerable information on their pathologies, incidents and even accidents and served as a basis for writing a set of guidelines for studying, designing, constructing, monitoring and rehabilitating. The paper is divided into two parts; the first based on an analysis of the 32 best documented structures is a feedback of water-tightness quality of Geosynthetic Liner Systems (GLS) at high altitudes; the second based on the guidelines above-mentioned, concerns the construction choices and behaviour of GLS at high altitudes. In particular, the guide advises using a cover layer in most cases to protect the geomembrane, and paying particular attention to the support layers and to drainage under the geomembrane.

Controlling strain in geosynthetic liner systems used in vertically expanded landfills

According to relevant new regulations in China, a composite liner system involving geosynthetic materials must be installed at the bottom of an expanded landfill. The deformation and integrity of the composite liner under a variety of factors are important issue to be considered in the design of a landfill expansion. In this paper, we investigate the strain distribution in geosynthetic materials within the composite liner system of expanded landfills, including strains in geosynthetic materials resulting from overall settlement and lateral movement of landfills, localized subsidence in landfills, and differential settlement around gas venting wells. The allowable strains of geosynthetic materials are discussed based on the results of tensile tests, and the corresponding design criteria for composite liner systems are proposed. Meanwhile, practical measures allowing strain control in geosynthetic materials used in landfill engineering are proposed.

Pemanfaatan Limbah Padat (fly ash) untuk Mencegah Cemaran Mikrobiologis dan Kimiawi Sampah Kota pada Ekosistem Rawa

The research on the utilization of solid waste (fly ash) has been conducted to avoid the further effect of microbial and of the municipality solid waste in the wetland ecosystem. The purpose of this research is to utilize the fly ash, the solid waste of the PLTU industry, as protective layer (geosynthetic liners/GCls) at waste disposal areas in order to avoid microbial and chemical pollution to the environment. During the research, ponds with 6x6x4 m in size was added with GCLs (layer of 30 sacs of fly ash 25 kg/sac at each 2 meters of pile waste) and a control pond. The result shows that fly ash with the composition of SiO2(42,92 %) and AlO2 (29,45%) can be utilized as a protective layer (geosynthetic liners), because after 3 weeks it can minimize the contamination of bacteria (total decrease of coliform bacteria > 50%) to the environment, and also reduce some toxic compound, especially heavy metal such as Pb (30,1%) and Cu (43,54%), and the content of nitrate (32,1%). Hence fly ash has economic and ecological values as a protection layer at the solid waste disposal area to avoid the environmental contamination of bacteria's and chemicals.

Geomechanics of Landfills—Innovative Technology for Liners

Cracks in clayey landfill liner, which cannot be closed up upon re-wetting, affect the long-term performance of a landfill. In this paper, the mixture bentonite-zeolite (BEZ) is presented as a potential liner material due to its plastic properties. Also, it may fulfill an existing demand, in developing countries, for liners that are cost-effective, natural and in compliance with environmental regulations. Traditional liners have shortcomings: (i) clayey soil is suitable for liners if the temperature and moisture fluctuations are not high; otherwise, they may form cracks; (ii) geomembranes, considered as the best alternatives for liners, are out of reach of most underdeveloped countries for their high price, and do not last more than 4 years; (iii) the interface of a CGL (clay geosynthetic liner) is susceptible to sliding. In the studies performed, the low volumetric shrinkage of the BEZ indicates that it is not affected by moisture content fluctuations, and its hydraulic conductivity in the order of 10 −10 cm/s meets regulatory agency requirements. Also, its inherent chemical properties (specially clinoptilolite zeolite) and its natural selectivity indicates that it will adsorb heavy metals such as Pb 2+ , Zn 2+ , Cd 2+ , Ni 2+ ,Fe 2+ , and Mn 2+ that may be present in leachate. Therefore, BEZ is a potential innovative material for liners in landfills.

Finite element study on direct shear tests for multi-layered geosynthetic liners

Multi-layered geosynthetic liners are used widely in waste landfills. The shear stress mobilized at the top interface will be transmitted from the top to the bottom layer through frictional resistance on the interfaces between materials. It is important to understand fully the behavior of multi-layered geosynthetic liners subject to shear stress. In this study, direct shear tests with four layers were first simulated using a two-dimensional plane strain finite element model (FEM). The FEM code can consider the strain-softening behavior of the interfaces using a hyperbolic model. Next, the validity of the FEM calculations was verified by comparing the calculated results with the mechanical test results. Finally, FEM parametric analyses were performed in which the length of the specimen, the stiffness of the third layer and the thickness of the geomembrane were varied to investigate how these factors affect the tensile force in the second layer and the distribution of shear stress between materials.

Protective effect of overlying geosynthetic on geomembrane liner observed from landfill field tests and inclined board laboratory experiments

Geosynthetic liner systems are generally installed in landfill sites to prevent toxic leachate from escaping into the adjoining environment by utilizing their impervious characteristics. Therefore, it is important to protect the geomembrane from being damaged or destroyed during all phases of landfilling, namely landfill construction, waste tipping and landfill closure. This paper presents firstly the observed performance of a geomembrane liner from a landfill site where the geomembrane liner was installed on the slopes of a Korean landfill; and secondly the results of an inclined board laboratory test. Two types of experiments were conducted to identify the protecting effect of the overlaying geosynthetic on the geomembrane liners. At a testing landfill site, the slope consisted of three different sub-inclines and two 2-m-wide intermediate levels. The sub-inclines were each 8 m in vertical height and their angle of inclination was 1: 1.5 (vertical: horizontal). The reported observations were made for a time period of approximately 1 year, until the landfill was filled with wastes to the top of the uppermost slope. In addition, inclined board laboratory tests were carried out. During the inclined board test, a base table is inclined slowly and steadily until the block located on the base table starts to slide, when the tension and displacements of two geosynthetics, namely the geomembrane liner and protecting geotextile, are measured. In conclusion, test results showed that the down-drag force generated by waste accumulation and sliding of upper material was to a large extent dissipated through the elongation of the protecting geosynthetic overlying the geomembrane and thus was not transferred to the geomembrane. Unless the protecting geosynthetic undergoes structural failure, this stress relaxation phenomenon continues to occur so that the magnitude of tensile force to be applied on the geomembrane remains marginal.

Use of the inclined plane test in measuring geosynthetic interface friction relationship

The inclined plane test is commonly used when studying the stability of sloping geosynthetic liner systems under conditions of low normal stress. Emphasis is placed on analysis of the initial sliding phase in a standard test, prior to reaching the non-stabilised sliding phase, which is generally disregarded by designers. Comparative tests for two different geomembrane materials reveal that it is possible to clearly distinguish different interface behaviours under field conditions. Subsequently, two new test procedures using the inclined plane device are proposed: a creep test that could lead to reconsidering the significance of the threshold angle of friction, ϕgg, determined from a standard inclined plane test; and an abrasion test that could be used when studying geosynthetic slope stability in the field, in order to take into account the geosynthetic laying conditions.

Use of the inclined plane test in measuring geosynthetic interface friction relationship

The inclined plane test is commonly used when studying the stability of sloping geosynthetic liner systems under conditions of low normal stress. Emphasis is placed on analysis of the initial sliding phase in a standard test, prior to reaching the non-stabilised sliding phase, which is generally disregarded by designers. Comparative tests for two different geomembrane materials reveal that it is possible to clearly distinguish different interface behaviours under field conditions. Subsequently, two new test procedures using the inclined plane device are proposed: a creep test that could lead to reconsidering the significance of the threshold angle of friction, ϕgg, determined from a standard inclined plane test; and an abrasion test that could be used when studying geosynthetic slope stability in the field, in order to take into account the geosynthetic laying conditions.

Shear Displacement Dependent Strength of Municipal Solid Waste and Its Major Constituent

Abstract A limited amount of data exist on the shear strength properties of municipal solid waste. Similar to the soil strength parameters, the data on wastes are reported in terms of a cohesion intercept and an angle of internal friction. Most often the strength parameters reported are for the maximum values mobilized in laboratory testing. Recent state-of-the-art review papers on the topic have summarized the available strength data and noted that large shear displacements are required to mobilize peak shear strength parameters. In comparison, other components of a landfill system such as mineral and geosynthetic liners mobilize peak strengths at much smaller shear displacements. There are, therefore, shear displacement incompatibility issues that need to be resolved. In this paper the shear strength data from the direct shear tests performed on municipal solid waste samples and its major constituent (paper) are presented as a function of shear displacement. Results of a limited number of simple shear tests performed on municipal waste samples are also presented and compared with the data from direct shear testing.

Dynamic Response Analysis Procedure for Landfills with Geosynthetic Liners

The dynamic response of geosynthetic interfaces commonly encountered in municipal solid waste landfills were investigated using a shaking table facility. The force-slip relationships for the tested interfaces showed almost rigid and then plastic deformation where the maximum shear force transmitted through the interface increases slightly with increasing slip. The force-slip relationships were modeled with equivalent stiffness and damping ratios. These equivalent parameters were established as a function of slip displacements to account for the nonlinear behavior of the interfaces. Using the equivalent stiffness and damping, the dynamic properties of an equivalent soil layer were established such that the dynamic response of the equivalent soil layer is similar to that of the geosynthetic interface it represents. The purpose of this representation was to allow the modeling of geosynthetic interfaces in wave propagation analysis, such as SHAKE analysis. The properties of the equivalent soil layer were validated by comparing the measured dynamic response of a rigid block placed on geosynthetics with that computed using the SHAKE program and the properties of the equivalent soil layer developed. A procedure for analysis of the dynamic response of landfills with geosynthetic liners is proposed.

Performance of Solid Waste Landfills in Earthquakes

Interpretation and analysis of observational data on the performance of solid waste landfills during earthquakes is the most reliable source of information on the seismic response of solid waste landfills. The data from several major California earthquakes indicate that the general performance of landfills during earthquakes is from good to excellent. None of the landfills on which observational data is available experienced major earthquake-induced damage. Recorded strong ground motion data indicate that amplification of both peak and spectral accelerations can occur at the top of a landfill. This, combined with the fact that only a limited number of landfills with geosynthetic liners and no landfill with a geosynthetic cover have been subjected to strong ground motions, indicate that attention to detail is warranted in the design of modern, geosynthetic-lined and/or covered landfills in areas of high seismicity.

Interface Friction Properties of Multi-layered Geosynthetics

Multi-layered geosynthetic liner is often used in landfill. In a design practice, it is very important to know shearing behavior of each geosynthetics on side slope of the landfill. In this paper, new shearing test device which has two shearing interfaces was developed, where shearing force was applied to the upper-layer and tensile forces induced in middle and lower-layer were measured respectively through load-cell. 10 cases of test were performed varying two interfaces friction, normal force and rigidity of second layer.Consequently, it was founded that(1) Tensile force induced in the middle-layer increase with increasing of rigidity of the middle-layer and with decreasing of normal stress given on the interface.(2) Tensile force can mobilize even when the interface friction between upper and middle-layer is smaller than the one between middle and lower-layer. This demands a revision of Koerner's method relating to stress transmission among geosynthetics.

Interface Shear‐Strength Properties of Roughened HDPE

It is generally perceived that roughened high‐density polyethylene (HDPE) has superior interface frictional properties, when in contact with any type of granular material, compared to smooth HDPE. Large‐scale direct shear interface test results are presented that indicate that this is not always the case and that the shear strength of finer‐grained materials may be better mobilized by the currently available roughened HDPE than by coarser‐grained materials. Based upon a limited number of tests, there appears to be a direct relation between soil composition, depth of texturing, and the amount of shear strength mobilized during shearing. This study indicates that the ratio of D80 of the granular material to the height of texturing (htext) of the roughened HDPE may be used to determine how much of a materials shear strength may be mobilized at the interface. The results of this testing suggest the importance of testing all interfaces when performing analysis and design for geosynthetic liners and covers.

Hyperbolic expression for soil-geosynthetic or geosynthetic-geosynthetic interface shear strength

The shear strength at a soil-geosynthetic or geosynthetic-geosynthetic interface is an essential parameter of slope stability analyses for cases where the potential slip surface runs along a geosynthetic. A linear relationship between the interface shear strength and the stress normal to the interface is generally considered. Using a linear relationship may lead to significant errors on the factor of safety of the slope, especially in cases where normal stresses are small, such as geosynthetic liner systems covered with thin layers of soil, or cases where the normal stresses vary considerably along the potential failure surface, such as geosynthetic liner systems covered with piles of waste or ore. An equation is proposed to represent a non-linear relationship consistent with interface shear strength values obtained in laboratory shear box tests.