Landfill Liner Research Articles

TRIBOLOGICAL PROPERTIES OF PISTON RINGS DESIGNEDFOR SLIDING AGAINST COMPOSITE MATERIALSIN LUBRICATED CONTACTS

The paper presents basic information on the production, structure and tribological properties of a compositechromium-ceramic coating deposited electrolytically on a cast-iron piston ring for a combustion enginedesigned for sliding against a composite cylinder liner. The results of comparative tests of two contacts,i.e. cast-iron GJL-250/AlMC and GJL250+Cr-Al2O3/AlMC, are described. The deposition of the Cr-Al2O3coating on the cast-iron piston ring reduces almost trifold the wear of the piston ring and about 20% thefriction resistance in the contact due to the presence of aluminium oxide particles and fibres. The reinforcingphase removed from the chromium layer polishes the chromium and composite sliding surfaces. The placesleft by the removed particles serve as depots for oil, which reduces the friction forces and minimises oilconsumption. The Al2O3 wear debris decreases the roughness of the surfaces in contact, which additionallyreduces the friction forces according to the friction hypothesis of Ernst and Merchant.

Study on the relationship between permeability coefficient and porosity, the confining and osmotic pressure of attapulgite-modified loess

This study investigated attapulgite-modified loess as an efficient and cost-effective method for creating an impermeable liner for landfills in regions with scarce clay resources. Laboratory permeability tests were conducted using a flexible wall permeameter to determine the permeability of compacted loess and attapulgite mixtures under varying osmotic conditions. The relationship between the permeability coefficient, attapulgite dosage, radial pressure, and osmotic pressure was analyzed. Nuclear magnetic resonance and scanning electron microscopy were also used to observe the microstructure of the modified loess. The results showed that attapulgite dosage significantly reduced the permeability coefficient, but the effect became limited when the content surpassed 10%. The decrease of the permeability coefficient of the modified loess is mainly due to the filling of pores between the loess by attapulgite, which makes the pore size and throat size of the modified loess smaller. The modified loess displayed a sheet structure that contributed to an increased permeability coefficient due to increased radial pressure. This study provides valuable insights into using attapulgite-modified loess as a material for landfill lining in regions with scarce clay resources.

Study on the forming characteristics of polytetrafluoroethylene/copper jet with different preparation processes

In this paper, PTFE/Cu composite material for liner is taken as the research object, and the preparation process and jet forming characteristics of PTFE/Cu composite liner are studied. The liners were prepared by extrusion molding, molded sintering and hot-pressing sintering. Due to different preparation processes, different microstructures of the liner can occur, including defects such as pores and microcracks, resulting in different strength and density of the liner, leading to differences in the forming characteristics of the jet. Therefore, the forming process of the jet was simulated by the finite element numerical simulation software. It was found that there was obvious radial expansion effect in the head of the jet, but with the increase of density, the radial expansion effect was weakened, and the jet velocity decreased gradually. The strength and densification of the shaped charge liner prepared by different processes were different. The densification of the molded sintering liner was generally better than that of the other two kinds of shaped charge liners. As a result, the velocity of the jet formed by the molded sintering liner is always the highest, with a numerical simulation velocity of 6642 m/s and an experimental velocity of 6534.7 m/s. The second is the jet of the hot-pressing sintering liner and the lowest velocity is the jet of the extrusion molding cover, with a numerical simulation velocity of 6482 m/s, while the experimental velocity is only 6397.9 m/s. The jet velocity measured by the pulse X-ray experiment was compared with the velocity of the numerical simulation, and the error was within 2.96%, which verifies the accuracy of the numerical simulation.

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.

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.

Shrinkage and Consolidation Characteristics of Chitosan-Amended Soft Soil—A Sustainable Alternate Landfill Liner Material

Kuttanad is a region that lies in the southwest part of Kerala, India, and possesses soft soil, which imposes constraints on many civil engineering applications owing to low shear strength and high compressibility. Chemical stabilizers such as cement and lime have been extensively utilized in the past to address compressibility issues. However, future civilizations will be extremely dependent on the development of sustainable materials and practices such as the use of bio-enzymes, calcite precipitation methods, and biological materials as a result of escalating environmental concerns due to carbon emissions of conventional stabilizers. One such alternative is the utilization of biopolymers. The current study investigates the effect of chitosan (biopolymer extracted from shrimp shells) in improving the consolidation and shrinkage characteristics of these soft soils. The dosages adopted are 0.5%, 1%, 2%, and 4%. One-dimensional fixed ring consolidation tests indicate that consolidation characteristics are improved upon the addition of chitosan up to an optimum dosage of 2%. The coefficient of consolidation increases up to seven times that of untreated soil, indicating the acceleration of the consolidation process by incorporating chitosan. The shrinkage potential is reduced by 11% after amendment with 4% chitosan and all the treated samples exhibit zero signs of curling. Based on the findings from consolidation and shrinkage data, carbon emission assessments are carried out for a typical landfill liner amended with an optimum dosage of chitosan. In comparison to conventional stabilizers like cement and lime, the results indicate that chitosan minimized carbon emissions by 7.325 times and 8.754 times, respectively.

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.

Study on the Equation of State and Jet Forming of 3D-Printed PLA and PLA-Cu Materials.

In order to improve the research and development efficiency and quality of low-density liners in production and scientific research development, PLA and PLA-Cu composite liners were prepared based on 3D-printing technology. In this paper, the relationship between the shock wave velocity D and the particle velocity u of PLA and PLA-Cu materials was tested by a one-stage light gas gun experiment device, and then the Grüneisen equation of state parameters of the two materials was obtained by fitting. The forming process of the two jets was numerically simulated by using the equation of state. When combined with the pulsed X-ray shooting results of the jets, it was found that the jets of the two materials showed obvious characteristics of "expansion particle flow", and the head of the PLA jet had a gasification phenomenon. The length of the PLA jet at 20 μs in the numerical simulation was 127.2 mm, and the average length of the PLA jet at 20 μs in the pulsed X-ray shooting experiment was 100.45 mm. The length of the PLA jet gasification part accounted for about 21% of the total length of the jet. The average velocity of the head of the PLA jet is 7798.35 m/s, and the average velocity of the head of the PLA-Cu jet is 8104.25 m/s. In this paper, 3D-printing technology is used to prepare the liner for the first time, aiming to open up a new preparation technology and provide a new material selection for low-density material liners.

Analytical solutions for contaminant transport through a GMB/CCL composite liner system considering effective porosity and thermodiffusion

This study presents analytical solutions for one-dimensional contaminant transport through a saturated double-layer composite liner system consisting of a geomembrane (GMB) and a compacted clay liner (CCL), considering the effects of CCL effective porosity, GMB defects, and thermodiffusion. The solutions provide temperature distribution at steady state and contaminant concentration distribution and total contaminant mass flux for transient-state condition. The heat transfer algorithm of the solutions accounts for advection, conduction, and thermal mechanical dispersion, while the solute transport algorithm of the solutions accounts for molecular diffusion, advection, mechanical dispersion, sorption, and thermodiffusion. The proposed solutions are validated against experimental data and verified against numerical solution. Using the proposed solutions, a series of parametric studies is conducted and the results indicate that neglecting the effect of thermodiffusion can underestimate the contaminant outflow rate at the bottom of the GMB/CCL liner by 6.9%∼130%. Depending on conditions, the effect of thermodiffusion on contaminant transport through the GMB/CCL liner decreases with increasing leachate head, increasing length of GMB wrinkle, and increasing number of GMB defects. CCL effective porosity also has a significant impact on contaminant transport through the GMB/CCL liner system, and neglecting this effect can substantially overestimate the contaminant outflow rate.

Utilization of organoclay amended bentonite for hydraulic barrier applications under adverse electrolyte environment

Inorganic ions such as sodium and calcium are often found in industrial leachates, municipal solid waste leachates and deep geological repositories, which can significantly impact the geotechnical properties of hydraulic barrier materials. Researchers have suggested the utilization of organoclays as landfill liner amendments, especially when the liner is in contact with organic contaminants. This study focuses on the impact of inorganic salts (NaCl and CaCl2) on the geotechnical properties, such as consistency limits, swelling, and hydraulic conductivity of organoclay-amended bentonite (BOC) liners. Different concentrations of salt solutions (0, 0.1 N and 1 N) were selected for the execution of Atterberg limits, free swell tests, and oedometer tests. The surface charge characteristics of bentonite and organoclay were attained with the aid of zeta potential measurements. The variation in the surface topographies of soil samples at different electrolyte conditions was analyzed with the help of scanning electron microscope images. The addition of organoclays significantly reduced bentonite's swelling characteristics and liquid limit due to the unique hydrophobic and organophilic attributes of organoclay but increased the hydraulic conductivity. However, the influence of inorganic salts on the geotechnical parameters of organoclay-amended bentonites showed less variance than that of bentonite. Also, no soil samples exceeded the limiting hydraulic conductivity criteria required for landfill liners, i.e. 1 × 10−9 m/s. Hence, organoclay-amended bentonites could potentially be utilized for hydraulic barrier applications even in an electrolytic environment without compromising the hydraulic conductivity criteria.

Mono-dispersed AuNPs decorated enlarged halloysite nanotubes to encapsulate [HMIm][NTf2] microcapsules for improving the wear resistance of composites

In this study, a microcapsule, with gold nanoparticles dispersed on enlarged halloysite nanotube (HNTs) was prepared for encapsulating ionic liquid 1-hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide ([HMIm][NTf2]). The thermal conductivity and mechanical properties of the PBO/PTFE fabric/phenolic resin composite liner improved after incorporating [HMIm][NTf2]@HNTs/Au microcapsules. Pin-on-disk wear tests (55 MPa and 0.8 m/s for 120 min) demonstrated that the wear rate decreased from 9.4 × 10−15 m3 /(N⋅m) to 3.9 × 10−15 m3 /(N⋅m) when the filler content up to 2.0 wt% was added to a pure composites. This was attributed to a 40 nm adaptive tribofilm constructed on the counterpart surface due to filler.

Development of Composite Ablative Liners for Solid Rocket Motor Flex Nozzles

Solid Rocket Motor generates high thrust by accelerating high pressure gases to supersonic velocities in convergent divergent nozzle, thus converting pressure energy to kinetic energy of propulsion. As exhaust gas from chamber is of high temperature, the structural steel members of nozzle should be protected from hot gases by highly erosion resistant thermal liners. For this purpose, ablative composite liners made up of Phenolic resin matrix based combined with reinforcement material like carbon fabric is extensively used [1]. Divergent being largest component and contributes more to nozzle weight, the thickness of liner should be as least as possible at the same time; it should be more erosion resistant. The erosion resistant due to hot gases can be increased by fabricating the liner in such a way that the flame only touches the edge of the composite ply of liner and liner has more density. This can be achieved by tape winding of composite prepreg tapes at Zero degrees on tapered metal mandrel using tape winding machine followed by Autoclave curing [2]. This paper gives the details of prepreg, Tape winding, Autoclave Curing and NDT of ablative liner.

Comparative Assessment of Single- and Double-Interface Shear Tests of MSW Landfill Liners Using Large Direct Shear Equipment

Geosynthetics form an integral part of engineered municipal solid waste (MSW) landfill lining systems, as they provide cost saving and technical benefits. Their introduction in lining systems, however, has presented new potential interfaces for shear failure especially on bases and on side slopes of engineered MSW landfills. In the laboratory, interface shear strength parameters used in slope designs of landfill lining systems are determined through single-interface testing configurations as per ASTM D5321-20 and D6243-20 standards. However, single-interface testing configurations do not provide a clear understanding of shear strength transfers among the lining components and does not aid in pin-pointing the interface facilitating failure especially when a multi-layered lining system has been proposed. Multi-interface testing configurations present an alternative that may address such limitations. But there is minimum information available on this type of testing as it is not stipulated in any official laboratory testing standard. This study was conducted to provide an understanding of the potential use of multi-interface testing configurations of MSW landfill liners, through identifying similarities and dissimilarities to the single-interface testing configurations. These interface tests were conducted on geosynthetics and geomaterials from a proposed lining system of a new landfill cell in South Africa.

Breakthrough time assessment of liner system for MSW landfills with high leachate heads

This paper presents a design method for liner systems of municipal solid waste (MSW) landfills with high leachate heads based on the breakthrough time of an indicative contaminant (Chloride). The performance of liner systems with varying thicknesses of compacted clay liner and attenuation layer was assessed. The single composite liner consisting of a geomembrane and a 0.75-thickness compacted clay liner can meet the 50-year breakthrough time requirement of the liner system for cases with the thickness of the attenuation layer >3 m and the average height of waste HD < 60 m. The double liner system consisting of two geomembranes with one single 0.3 m-thickness compacted clay liner, as proposed in the Chinese landfill standards, cannot meet the 50-year breakthrough time requirement of the liner system, especially for large-scale landfills (e.g. HD > 60 m). The double composite liner with two composite liners consisting of a geomembrane and a 0.3 m-thickness compacted clay liner can be used for a landfill with an average height of over 60 m. Different liner systems for other cases with different average design heights of waste and the thickness of the attenuation layer were proposed. They can be easily used for MSW landfills with high leachate heads.

Field observed GCL panel shrinkage for five GCLs in composite liners

Field observed shrinkage was quantified and compared for one geosynthetic clay liner (GCL) type left covered only by a black geomembrane, a white geomembrane, and 0.3 m of gravel cover. Shrinkage is reported for up to 28 months field exposure of an additional four GCLs beneath a black geomembrane. All GCLs were needle-punched geotextile encased: one containing fine granular bentonite, two with powdered bentonite, one with polymer amended granular bentonite, and one multicomponent GCL with a film coating installed film up. All the GCLs examined have the potential to shrink with the magnitude of the shrinkage primarily dependent on the thermal/moisture cycles to which it is subjected and the degree of adhesion between panel overlaps. It is shown that the panel overlap adhesion can be highly variable and this is primarily attributed to condensation of water vapour below geomembrane wrinkles during daily thermal cycles. With a an initial GCL overlap of 300 mm, the shrinkage observed over 28 months left ≥32% of the original overlap; however, if the overlap had been only 150 mm, then gaps or ineffective seams would have occurred for several GCLs. Guidance regarding mitigating GCL panel shrinkage is provided.

Diffusion of volatile organic compounds (VOCs) through elastomeric bituminous geomembranes (BGMs)

Diffusion of volatile organic compounds (VOCs) through a 4.1 mm elastomeric bituminous geomembrane (BGM) is investigated using a dilute aqueous solution of four aromatic hydrocarbons: benzene, toluene, ethylbenzene, and xylenes (BTEX). Due to the very different diffusion characteristics of the BGM components, double-compartment diffusion experiments are separately conducted on the bituminous and non-bituminous components of the BGM to assess their diffusion parameters. A two-layer computer model is developed to obtain the diffusion parameters of the BGM that correlates with the 890-day laboratory diffusion test data obtained for the multicomponent BGM and allows the modelling of transient diffusion. Using contaminant transport modelling, the BGMs performance as a diffusive barrier for different applications is evaluated and compared to different polymeric geomembranes (GMBs). It is shown that using BGM as part of the cover system for a hydrocarbon-contaminated soil landfill or as a vapour barrier below concrete building foundations can decrease the BTEX mass flux through the cover system and the peak concentration of contaminant in the indoor air compared to monolayer polymeric GMBs. It is also predicted to reduce the impact on the aquifer when modelled as a part of the composite liner without holes for a hypothetical solid waste landfill.

Geomembrane leaks detection and leakage correlation factor analysis of composite liner systems for fifty-five (55) solid waste landfills in China

In composite liner system (CLS), there are little field data on the number, size, and shape of geomembrane (GMB) holes, which are the key parameters to identify and evaluate the volume of leachate leakage from landfills. In this paper, in-situ detection of GMB holes in composite liner systems of 55 solid waste landfills in China was conducted by electrical leak location (ELL) method, and the following conclusions were drawn. The holes frequency, equivalent radius, and theoretical leakage volume of double-layer systems are lower than those of single-layer systems under the same geotextile (GT) density by 28.2%, 51.4%, and more than 60%, respectively. As the thickness of GMB increases, the holes frequency, equivalent radius and theoretical leakage volume reduce observably. Regarding protecting GMB, the density of geotextiles should not be less than 600 g/m2. Through the analysis of various correlation factors, the thickness of geomembrane is an important parameter affecting the amount of leakage. This study will provide a reference for analyzing the data of field investigation, which would provide constructive suggestions for the composite liner system.

Effect Of Different Curing Times Of Composite Resin And Glass Ionomer Liner Use On The Pulpal Temperature

Aim: The present study was performed to measure intrapulpal temperature when photoirradiation of composite resin and glass ionomer liner at different curing times.
 Material and Methods: Thermocouple (TC) was placed in the intrapulpal space of an extracted human mandibular premolar which had a ClassV cavity preparation (1.5mm dentin thickness remaining on the buccal surface), and restored with composite resin" a bulk fill "and with LED unit " a high-intensity " at different photoirradiation times (10, 20. & 40sec). A temperature increase was obtained during photo-irradiation.
 Result: The Rise in intrapulpal temperature was associated with an increase in photo-irradiation times and significant in each study groups (p<0.05).
 Conclusion: intrapulpal temperature increase was attributed to photo-irradiation's time of composite resin. However, temperature's increase during polymerization were below the critical value.

Simulating the Hydraulic and Volume Change Behavior of Compacted Highly Expansive Soil under Potential Field Stress and Seasonal Climatic Variation

A sustainable design of some engineering applications, such as earth dam cores, landfill liners, clay barriers, and radioactive waste disposal systems, that utilize compacted expansive soils requires simulation for probable field conditions. This study investigated the hydraulic and volume change (H-VC) behaviors of highly expansive compacted soils in Al-Qatif city under different seasonal climatic variations for a wide range of stress conditions, aiming for more economical and rational design and practices. The extent of the effect of the start cycle condition of the cyclic wetting and drying (W/D) process on the examined properties is examined, as well. Two testing series of the cyclic W/D process, representing the probable seasonal climatic variations, were executed for varied axial stress conditions. The H-VC behaviors of expansive soils are affected by the simulated seasonal variation (i.e., cyclic W/D process), with the first cycle of W/D being the most effective cycle and an elastic state being attained by the third to fourth cycle. Swell fatigue is noted for both testing series, and this is attributed to the initial placement condition. Analysis of results recommends exposure of the compacted expansive soil layers in the field to drying after compaction to reduce their equilibrium wetting potential. As a consequence of the noted shrinkage accumulation, a reduction tendency of saturated hydraulic conductivity (ksat) with repeated W/D cycles is reported for both series under all the stress states applied. Finally, it is recommended for clay barrier projects to be submerged once compacted to obtain barriers with the lowest values of hydraulic conductivity.