Landfill Liner Research Articles

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.

Tracking interface position of a high-speed imploding composite liner based on magnetic diffusion difference

A technique for tracking the interface position of non-metal–metal composite liners during high-speed implosion is proposed in this paper. Based on the magnetic diffusion difference between metal and non-metal, the interface position information is obtained by measuring magnetic fields in the cavity of the liner. An efficient magnetic flux estimation algorithm based on iterative magnetic diffusion simulation is also proposed to estimate the magnetic flux loss of the liner. Numerical experiments show that the estimation algorithm can reduce the relative error to less than 0.5%. The composite solid liner experimental results show that the maximum error is about 2% under imperfect experimental conditions. Detailed analysis suggests that this method can be widely applied to non-metallic sample materials (electrical conductivity is less than 103 ∼ 104 S/m). The technique provides a useful supplement to the existing interface diagnosis methods for high-speed implosion liners.

Hydraulic Conductivity Characteristics of Iron-Ore Tailings–Bentonite Mixtures Exposed to Landfill Leachate

Landfill liner materials are required to provide reliable hydraulic performance for very long times after construction, and at least for the design lifespan of the facility. To meet this objective, liner systems must retain their low hydraulic conductivity over their service lives. In this paper, we report on the durability aspects of iron-ore tailings (IOT)–bentonite mixtures in extended hydraulic conductivity experiments. The hydraulic conductivity tests were conducted on mixtures containing 20%, 25%, 30%, 35%, and 40% bentonite, compacted at 2% wet of optimum by the British standard light (BSL) effort, and permeated with municipal solid waste (MSW) landfill leachate (electrical conductivity = 25.60 mS/m, pH = 7.94) with or without prehydration for a duration of 120 days. Under these influences, permeation with leachate showed no detrimental effect on mixtures with 25% and 30% bentonite, but was rather beneficial in reducing the hydraulic conductivity (k) values of the two mixtures at the end of testing by two orders of magnitude to 4.19 × 10−8 and 9.25 × 10−9 cm/s for the prehydrated specimens and 2.4 × 10−8 and 9.9 × 10−9 cm/s for the nonprehydrated specimens. For mixtures containing 20%, 35%, and 40% bentonite, k values representing a 1.6 times decrease from the average were recorded for both the prehydrated and nonprehydrated conditions at the end of testing. Further analysis showed that prehydration had a slightly substantial effect on those specimens containing 20%, 35%, and 40% bentonite, whereas it had a minor effect, if any, on mixtures with 25% and 30% bentonite. In terms of durability, only mixtures containing 25% and 30% bentonite that consistently maintained low k values up to the end of testing are projected to be effective as liner materials in the construction of geological repositories for MSW. Regarding the hydraulic conductivity characteristics of the mixtures upon exposure to the combined effects of leachate and the elevated temperatures expected in landfill conditions, all mixtures maintained relatively good hydraulic performance, exhibiting a decrease in hydraulic conductivity with time.

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

Study on Utilization of Biopolymer in Liner

Abstract: Biogeotechnology is a branch of Geotechnical Engineering that deals with the application of biotransformation, biogrouting and mineral precipitation (MICP) to geotechnical engineering problems. Soil capping is a technology to curb the interaction between a waste body and the ground surface. A final cover system in landfill capping play a major role in intercepting rainwater infiltration and percolation of surface water into the subsurface waste dumped area. In order to minimize the water infiltration through different barrier layers such as single liner system, single composite liner system and double liner system in cover system are recommended. A single composite liner system comprises of two barrier (made up of different material), placed over one another to provide beneficial effect whereas the single and double liner system consists of same material to attain the effect. The present study deals with the action of sea weed in the form of powder (produced by the cell wall) in the layer of soil capping which intercept the rainwater intrusion in liner. The results obtained from the hydraulic conductivity of different treated soils indicate that the effect of single liner system is equivalent to single composite liner system. It has been observed that the addition of sea weed powder causes dissociation of hydroxyl groups attached to silicon in silica sheets with increase in optimum water content. Thus the addition of sea weed powder decreases the infiltration rate by clogging the soil layers.

Investigating the impact of flowable composite liner on the fracture strength and microleakage of large composite resin restorations of primary anterior teeth.

To investigate the effect of pre-cured and co-cured flowable composite liner on fracture strength and microleakage of primary anterior teeth with extended composite resin restorations. In the current in vitro experimental study, the crowns of 54 extracted primary canine teeth were cut 1mm above the CEJ, and a pulpectomy procedure was performed. The samples were randomly divided into three groups to restore the coronal part up to 4mm above the CEJ. In group 1, the samples were built up with Filtek Z250 packable composite resin. In group 2 (pre-cure), first, 1mm of Filtek Z350 XT flowable liner was applied to the sample, and after curing, the restoration process continued using packable composite resin. In group 3 (co-cure), the flowable composite liner was cured while the first layer of packable composite resin was applied; then, the same restorative procedure similar to the other groups was followed. The samples' cross-sectional area in the fracture strength test was calculated by AutoCAD software. Subsequently, the samples were subjected to a force in a universal testing machine. The samples related to the microleakage experiment were cut vertically, and then, the dye penetration percentage (10% methylene blue) was measured under a stereomicroscope. ANOVA was used to analyze the data. Mean fracture strength in group 2 was significantly higher than in group 1 (P = 0.016). The microleakage mean in group 3 was significantly lower than in groups 1 (P = 0.000) and 2 (P = 0.026). The flowable composite liner and its relevant separate curing increased the fracture strength of composite resin restorations. However, less microleakage was reported in the group where the liner was applied as a co-cure.

A mobile-immobile model for contaminant transport through GCL/AL composite liner: analytical solutions.

The current study focuses on developing alternative formulations (mobile-immobile model) of transient analytical modelling for organic contaminant transport in a composite of geosynthetic clay (GCL) and attenuation layer (AL) system. The Laplace transform method is adopted to derive the solution. The proposed analytical frameworks are validated by two set of benchmarks. The varied examples of organic contaminant transport in the composite liner are evaluated by the proposed solution to discuss the effects of soil properties, flow conditions, adsorption, and mass transfer in mobile and immobile zones on the overall transport of contaminants. Finally, an example case is presented to show the application prospect of the proposed model. The result demonstrated that mass transfer between mobile and immobile may increase the breakthrough time by a factor of 2. This indicates that heterogeneities of clay are a non-negligible part for the performance assessment of the liner system. Péclet number in GCL ([Formula: see text]) is used to investigate the relative importance of advection and diffusion mechanisms. Increasing [Formula: see text] from 0.1 to 1 can lead to an increase of the breakthrough time by a factor of 15. The analytical solutions presented here may also serve as the basic benchmark test tool for alternative numerical studies of contaminants transport in heterogeneous media.

Simulation study on the jet formation and penetration of aftereffect enhanced shaped charge

In order to reveal the aftereffect damage enhancement to armored targets, the jet formation of biconical Ti-Hf composite reactive liner shaped charge and the penetration behavior of steel target are studied by numerical simulation. The effects of cone angle, height ratio and standoff of biconical liner on jet formation and penetration performance were analyzed. The numerical simulation results show that the effective jet formed by the biconical Ti-Hf composite reactive liner shaped charge is more concentrated than that of the single-cone Ti liner shaped charge, and the maximum velocity in the head and the average velocity in the middle of the forerunning penetration jet are increased by about 23.5% and 13% compared with the single-cone Ti liner shaped charge. When the cone angle α=50° of Hf liner, with the increase of the cone angle β of the forerunning Ti liner, the velocity distribution of the composite reactive jet along the axial direction shows a gradual downward trend, and the maximum velocity of the following reactive projectile shows an upward trend; With the increase of the height ratio of the biconical composite reactive liner, the velocity distribution of the forerunning penetration jet along the axial direction gradually increases, and the maximum velocity of the following reactive projectile gradually decreases. When the cone angle α=50°, β=80° and the height ratio H 1:H 2=2:3 of the biconical composite reactive liner, the penetration depth increases with the increase of standoff, but when the standoff exceeds 3.0CD, its influence on the penetration depth is significantly weakened.

Formation behavior of hypervelocity reactive compostite jet

A kind of hypervelocity reactive composite liner shaped charge(HRCLSC) structure is designed by combining tungsten additional liner and reactive cooper composite liner. The formation behavior of hypervelocity reactive composite jet (HRCJ) is studied by numerical simulation method. The velocity distribution and detonation wave propagation of HRCJ are compared with that of normal reactive composite jet (NRCJ), which proves that HRCJ has better formation performance. The influence of liner structure on the formation performance of HRCJ is investigated by changing the cone angle of the composite liner and the thickness of the additional liner, the results show that the cone angle of the liner has little effect on jet head velocity while the thickness of the additional liner has great effect on jet velocity. When the thickness of the additional liner is 5mm and the cone angle of the composite liner is 60°, the effective mass utilization rate of the jet is better, and the head velocity reaches maximum.

Geotechnical properties and applicability of bentonite-modified local soil as landfill and environmental sustainability liners

Geotechnical properties and applicability of bentonite-modified local soil as landfill and environmental sustainability liners

Study on jet formation and penetration behaviour of shaped charge with reactive material composite liner

The shaped charge with reactive material composite liner could not only meet the requirement of the after-effect damage behavior, but also achieve a deeper penetration capability. Based on the platform of AUTODYN-2D code, the jet formation characteristics of the reactive material-titanium liner shaped charge and its penetration behavior to multi-spaced plates were studied. Numerical simulations showed that with increasing of the detonation pressure of explosive, the tip velocity of the composite jet and its penetration capability increased, but the reactive material liner was subjected to the higher pressure and the temperature rise within the elements was larger. In addition, the influence of the standoff and the protective steel block thickness on the penetration behavior of the reactive composite jet was investigated. As the standoff increases from 0.5 CD to 3.0 CD, the penetration capacity of the composite jet increased, but the mass of reactive materials follow-in the spaced plates decreased. With increasing of the steel block thickness, the penetration capability of the reactive material-titanium jet and reactive material follow-in behavior decreased gradually.

Effect of compaction water on strength and hydraulic properties of bentonite-based liner

The abundance of pond ash and its resemblance to natural sand encourages its use as a substitute for sand in sand–bentonite (SB) liner material. Compaction water content influences the geoengineering properties of cohesive soil to a great extent. Accordingly, the compaction, strength, permeability and shrinkage characteristics of both pond ash–bentonite (PAB) and SB mixes are investigated at standard and modified Proctor compaction energies at various water contents to support the recommendation of the PAB mixture as an alternative landfill liner. At similar compaction conditions, the PAB mix exhibits higher unconfined compressive strength (UCS) and hydraulic conductivity than the SB mix. The UCS values of mixes compacted on the dry side of optimum are higher than those of mixes compacted on the wet side. Dry-side compacted mixes exhibit a reduction in hydraulic conductivity with permeation time, whereas no substantial reduction in hydraulic conductivity is noticed for wet-side compacted mixes. Furthermore, the volumetric shrinkage of both PAB and SB mixes is within the permissible value of 4%, for a wide range of water variation from the dry to the wet side of optimum. The observed mechanical properties are correlated to the shape of coarse fraction particles and the corresponding microstructural arrangements of the compacted specimens.

Experimental study on impermeability of Loess liner mixed with bentonite-HDTMA

Permeability tests are performed by using the flexible wall permeameter to study the influence of bentonite-HDTMA (hexadecyl trimethyl ammonium bromide) on the permeability performance of Loess as a lining material in the solid waste landfill. Results show, the impermeability of compacted Loess in the middle and lower reaches of the Yellow River in China does not meet the standard requirement as the landfill liner. The permeability of Loess mixed with more than 10% bentonite ratio is less than 1.0 × 10−7 cm·s−1. The permeability of Loess increases slightly after mixing a small amount of HDTMA. The impermeability of Loess mixed with some bentonite-HDTMA ratio still meet the standard requirement. The HDTMA may destroy the soil aggregate structure and increase the soil permeate channel. The SEMs show that the bentonite clay particle can fill the pores between Loess coarse particles and improve the impermeability performance of the material. The digital photos show that HDTMA can effectively resist the development of soil macro-cracks induced by wetting–drying cycles, better for liner to maintain good impermeability. On this basis, the relationship between the hydraulic conductivity of bentonite-HDTMA modified Loess and dry density is constructed. From this study, Loess can be used as a lining material for landfills, when mixed with bentonite/HDTMA at ratios of 10%/0% or 14%/2%.

Halloysite-gold core-shell nanosystem synergistically enhances thermal conductivity and mechanical properties to optimize the wear-resistance of a pheonlic-PBO/PTFE textile composite liner

Polymer-textile liner composites have potential applications in aerospace applications for reducing the abrasion damage of moving parts during operation owing to their self-lubrication, light weight, and high loading capacity. Herein, Au nanoparticles (AuNPs) are successfully loaded into the lumen of halloysite nanotubes (HNTs) to construct an HNTs-Au peasecod core-shell nanosystem to optimize the wear resistance of phenolic resin-based poly(p-phenylene benzobisoxazole) (PBO)/polytetrafluoroethylene (PTFE) textile composites. Transmission electron microscope (TEM) characterization reveals that the AuNPs are well-dispersed inside the HNTs, with an average diameter of 6–9 nm. The anti-wear performance of the HNTs and Au-reinforced PBO/PTFE composites is evaluated using a pin-on-disk friction tester at 100 MPa. Evidently, the addition of HNTs-Au induces a 27.9% decrease in the wear rate of the composites. Possible anti-wear mechanisms are proposed based on the analyzed results of the worn surface morphology and the cross-section of the tribofilm obtained by focused ion beam transmission electron microscopy.

A novel approach to utilize recycled concrete aggregates as landfill liner

Demolition wastes are produced in huge quantity. Generally, they are used in the construction field as replacement for normal aggregate, pavement, roadways, curbs, embankment, etc. still there are plenty of quantity to be used for various purposes. Landfill is a place where huge quantity of material is required as cover to protect the ground from contamination. In this paper optimal utilization of Recycled Coarse Aggregate (RCA) as a landfill layer is explored. It was found that RCA lacks adsorbent capacity, in order to address the issue various chemicals were added to induce adsorbing capacity in the RCA. The pH observation, lucidity and color were analyzed to assess the adsorbent property of RCA. In this paper a study on various adsorbents such as activated carbon, silica gel powder, zeolite, sodium chloride, calcium sulphate, calcium chloride that induces adsorbing characteristics to RCA was studied. The pilot setup design consists of a layer of RCA, paper pulp, adsorbents and the unfiltered leachate. The setup was observed for the performance of the adsorbents when added with RCA. The study concluded that the performance of activated carbon, zeolite and sodium chloride was Congenial when compared to silica gel, calcium chloride and calcium sulphate.

Correction to: Analytical solutions to thermal gradient enhanced diffusion of organic contaminants through unsaturated composite liner: considering the existence of capillary fringe

Correction to: Analytical solutions to thermal gradient enhanced diffusion of organic contaminants through unsaturated composite liner: considering the existence of capillary fringe

Sustainable utilization of chemically depolymerized polyethylene terephthalate (PET) waste to enhance sand-bentonite clay liners

Polyethene terephthalate (PET) waste poses major environmental harm which can be minimized by reusing it in clay soil stabilization. In general, various polymers are known to reduce hydraulic conductivity and increase the shear strength of clays. However, the application of the effect of a chemically depolymerized form of PET, i.e., Bis (2-Hydroxyethyl) terephthalate (BHET) has not been performed as an additive in Compacted Clay Liners (CCLs) for landfills. This research focuses on the effect of the air curing period (1 and 28 days) on the hydromechanical behavior of BHET-treated SBM (0, 1, 2, 3, and 4 % by dry weight). Results from One Dimensional Consolidation tests showed that an increase in BHET content reduced both compressibility and hydraulic conductivity of SBM due to pore clogging mechanism of swollen BHET hydrogel, however, hydraulic conductivity reduced over 28 days of curing due to loss in re-swelling availability of the hydrogel, thereby allowing less tortuous paths to flow. Results from Consolidated-Drained Direct Shear tests showed that for 1 and 28-days curing, BHET treatment to SBM increased the cohesion (c’) due to strong polymer interparticle bridging, however, polymer coating over the sand grains causes a reduction in its surface roughness to decrease the frictional angle (ϕ'). SEM (Scanning Electron Microscopy) and EDX (Energy-dispersive X-ray spectroscopy) analysis on BHET-treated specimens support the flocculation of bentonite, polymer bridging of sand and clay-sand polymer links. A significant Pb2+ removal capacity was also observed with BHET-treated SBM from the batch tests. FTIR (Fourier Transform Infrared Spectroscopy) analysis on batch sorption specimens confirms the role of the carbonyl groups (C = O) and hydroxyl groups (OH) present in the BHET structure indicating the possibility to adsorb Pb2+. The findings of the study suggested that a mechanism of interaction exists between sand-bentonite and BHET polymer and it can be adopted in CCLs design.

Transport of heavy metal contaminants in a composite liner under non-isothermal condition

A mathematical model for the transport of heavy metal contaminants (HMCs) in a triple-layer composite liner with defective geomembrane under the non-isothermal condition is developed in this study, where the GMB/GCL/CCL (geomembrane, geosynthetic clay liner and compacted clay liner) composite liner is adopted as an example and the Langmuir adsorption model is incorporated. The proposed model is solved by the finite difference approach, and its correctness is validated by comparison with the experimental results, an existing analytical solution and another numerical method. Later, the transport behaviours of HMCs are explored with the established model. Compared with the isothermal condition, the non-isothermal condition enlarges the transport flux, but also reduces the concentration of HMCs. The relative concentration based on the Langmuir adsorption model is higher than that based on the linear adsorption model, which is related to the decrease of the retardation factor under the Langmuir adsorption model. Furthermore, the parametric study shows that when the leachate head ht is between 1.0 and 3.0 m, the defined breakthrough time tb increases by about 1.57 a with the increase of GCL thickness lg by 1 cm, and the tb increases by about 9.07 a with the increase of CCL thickness lc by 0.1 m.

Effect of retardation and capillarity on organic contaminant diffusion through an unsaturated composite liner: An analytical approach

AbstractIn unsaturated composite liners, the heterogeneous distribution of water content and capillarity are common phenomena with remarkable influence on the transport parameters. This study presents an analytical solution to assess the effect of unsaturation‐dependent retardation and capillarity on the organic contaminant diffusion through an unsaturated composite liner. The solution is obtained by the generalized integral transform technique and is verified against other analytical and numerical solutions. Particular attention is paid to the potential errors in predicting organic contaminant transport caused by unsaturation‐independent retardation factor assumption. The results show that neglecting saturation‐dependent retardation may cause considerable errors. The considerations of capillary fringe and degradation also have significant effects on the errors. In addition, a simplified solution based on a new averaged retardation factor is proposed and its performance is evaluated.

Durability of two bituminous geomembranes (BGMs) with different thicknesses in MSW synthetic leachate

The effect of thickness (4.8 and 4.1 mm) on the degradation of two bituminous geomembranes (BGMs), when immersed in a synthetic leachate is investigated over a period of 33 months. Based on the data collected at four different temperatures (20, 40, 55, 70 °C), it is shown that the 4.1 mm has slightly faster degradation than the 4.8 mm thick BGM. Due to the reduced conditions of the examined leachate, the degradation in the chemical and rheological properties of the bitumen coat was relatively lower than in air and water immersion. However, the presence of a surfactant in the leachate increased the degradation of the polymeric back film and the reinforcement layer responsible for the mechanical properties of the BGM. The time to nominal failure of the two BGMs is predicted at a typical range of landfill liner temperatures using Arrhenius modelling. The predictions at temperatures >20 °C suggest that the examined BGMs may not be suitable for the containment of solid wastes containing surfactants due to the fast degradation in their mechanical properties.