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The degradation in physical and mechanical properties of a 1.5 mm thick HDPE geomembrane immersed in seven different low pH and three high pH simulated mining solutions is examined at temperatures between 95 and 40[degrees]C for 3 years. The solutions with pH between 0.5 and 13.5 encompass solutions found in copper, nickel, uranium, gold, and silver heap leach pads. The geomembrane did not exhibit any chemical degradation during the three years of incubation in all the low-pH solutions. However, in the solutions with pH 9.5, 11.5, and 13.5, some of the geomembrane's physical and mechanical properties are shown to reach nominal failure at 95 and 85[degrees]C. While the geomembrane examined shows superior performance in the acidic environments than in the basic solutions examined, its performance in such extremely basic environments is still better than in neutral reduced municipal solid waste leachate. Using Arrhenius' modelling, the predicted times for the antioxidant depletion stage of the geomembrane examined in composite liner configuration range between 31 years in pH 13.5 to 51 years in pH 0.5 for pad liners at 50[degrees]C, exceeding a typical leaching period of the ore of around 20 years in different heap leaching operations. Key words: geosynthetics, geomembranes, HDPE, degradation, heap leach pads, mining, low pH, high pH, stress crack resistance, HALS, 1. Introduction Heap leaching is a mining process in which ores are leached with various solvents (acidic or basic) to extract valuable metals. Relative to other mineral extraction technologies, heap [...]

The stress crack resistance (SCR) and standard oxidative induction time (Std-OIT) reduction of high- density polyethylene (HDPE) geomembrane (GMB) fusion seams is examined for a 12-year old 1.5 mm HDPE GMB when welded using nine welding parameter combinations. The GMB experienced a decrease in Std-OIT from 135 to 87 min between manufacturing and welding. Welding did not significantly decrease the Std-OIT in the heat-affected zone (HAZs). In general, individual seam SCR failure times fell between the notched and unnotched sheet, with adhered squeeze-out bead seams exhibiting individual failure times closer to the notched sheet and an average time until nominal failure ([t.sub.NF]) ~21%-35% shorter than the unnotched sheet. Differences in [t.sub.NF] are attributed to residual stresses and (or) accelerated craze formation in seams with adhered squeeze-out beads. Non-adhered squeeze-out seams exhibited a slower [t.sub.NF] similar to that of the unnotched sheet, indicating a seam [t.sub.NF] less than that of the sheet may not be intrinsic to all HDPE fusion seams. High sheet temperatures at the time of welding and higher heat-applied welding parameters are thought to increase the likelihood of squeeze-out bead adherence. This paper shows that squeeze-out adherence can have a deleterious effect on seam SCR. Keywords: geosynthetics, seams, welds, ageing, long-term performance, stress crack resistance, HDPE, geomembranes, quality assurance, 1. Introduction High-density polyethylene (HDPE) geomembranes (GMBs) are used extensively as hydraulic barriers to minimize the migration of fluids such as landfill leachate, tailings fluid, chlorinated water, and many others [...]

This study demonstrates the change in porosity of permeable reactive barrier (PRB) material when it reacts with acidic flow. The laboratory column test data obtained over 9 months prove that the porosity of a granular limestone assembly decreases significantly due to bio-geochemical clogging caused by a continuous flow of acidic groundwater. The variations in pH, the pressure measurements, ion concentrations, and the results from X-ray diffraction suggest that clogging at the outlet of the column is much less than at the inlet. About 57% of the total reduction in porosity of the column is attributed to chemical clogging, while the remainder is mainly due to biological clogging. In this paper, a mathematical approach is proposed to estimate the reduction of reactive surface area based on changes in the pore volume. These proposed equations suggest that at the end of experimentation, the dissolution of calcite and bio-geochemical clogging can reduce the total surface area of limestone aggregates by more than 70%. The rigorous approach presented in this paper to determine the dominant clogging component within a granular filter at a given time is vital in estimating the longevity of a PRB and for planning its maintenance. Key words: acidic groundwater, permeable reactive barrier, biogeochemical clogging, porosity, surface area, 1. Introduction Biological and chemical clogging reduces the porosity of granular filters, obstructs the flow, and increases the hydraulic gradients in porous media (Cooke et al. 2005; McIsaac and Rowe [...]

Experiments were conducted to quantify short-term tensile strains induced in a 1.5 mm thick high-density polyethylene geomembrane overlain by tailings. Four subgrades, a poorly graded angular to subangular gravel (GP), a well-graded angular to subangular gravel (GW), a poorly subrounded graded sand (SP), and silty sand (SM), and two nonwoven geotextiles, 450 and 1420 g/[m.sup.2], were evaluated. All the indentations in the geomembrane (GMB) were due to the subgrade, and with an adequate fraction of sand size particles in the subgrade, the tensile strains could be minimized. At 2000 kPa, the maximum tensile strain was 32% for GP, 16% for GW, 13% for SP, and no discernable indentation was observed for SM prepared at the optimum water content of 11%. For the soft SM subgrade prepared at 20% water content, only one indentation with the tensile strain of 2% was observed. At 2000 kPa, a 450 g/[m.sup.2] geotextile beneath the GMB reduced the maximum tensile strain from 32% to 23% for GP subgrade, from 16% to 8% for GW subgrade, and from 13% to 6% for SP subgrade; the 1420 g/[m.sup.2] geotextile reduced the maximum tensile strain to 14% for GP subgrade. Thus, minimal subgrade indentation induced strain and hence the possibility of a very long service life of GMB could be achieved using SM subgrade. Key words: geosynthetics, geomembrane, geotextile, tailings, geomembrane strain, 1. Introduction Tailings storage facilities (TSFs) are engineered structures constructed to impound slurry, thickened, and paste tailings resulting from mineral processing activities. With the increase in the footprint of mining [...]

Microstructure showing the involvement of the fine and coarse grains in the soil skeleton is evaluated. Incremental loading tests using a stress-dependent permeameter are conducted on the mixtures of poorly graded sand and nonplastic fines originating from tailings. The results are compared with the published data of various tailings. It is shown that increasing the fines content from 0% to 100%, the involvement of the fine and coarse components of soil skeleton can be classified into four categories: no fines involvement (40% fines). At the same consolidation stress, the void ratio, e, rapidly decreases for fines less than 30%, then almost remains constant between 30% and 50% fines, and gradually increases for fines exceeding 50%. The hydraulic conductivity, k, decreases more than 20-fold as the fines content increases from 12% to 50%, then remains constant. k is proportional to [[[e.sup.3]/(1 + e)].sub.A] and inversely proportional to [S.sup.2], where A is a factor describing the effect of particle angularity and S is the specific surface. Finally, the influence of fines content on the seepage- induced internal stability is discussed. Key words: soil skeleton, sands, silts, nonplastic fines, tailings, compressibility, hydraulic conductivity, angularity, specific surface. La microstructure montrant l'implication des grains fins et grossiers dans le squelette du sol est evaluee. Des essais de charge incrementielle a l'aide d'un permeametre dependant de la contrainte sont realises sur des melanges de sable mal calibre et de fines non plastiques provenant de residus. Les resultats sont compares aux donnees publiees de divers residus. Il est demontre qu'en augmentant la teneur en fines de 0 a 100 %, l'implication des composantes fines et grossieres du squelette du sol peut etre classee en quatre categories : aucune implication des fines ( 40 % de fines). Pour une meme contrainte de consolidation, le taux de vide, e, diminue rapidement pour les fines inferieures a 30 %, puis reste presque constant entre 30 et 50 % de fines, et augmente progressivement pour les fines superieures a 50 %. La conductivite hydraulique, k, est divisee par plus de 20 lorsque la teneur en fines passe de 12 a 50 %, puis reste constante. k est proportionnel a [[[e.sup.3]/(1 + e)].sup.A] et inversement proportionnel a [S.sup.2], ou A est un facteur decrivant l'effet de l'angularite des particules et S est la surface specifique. Enfin, l'influence de la teneur en fines sur la stabilite interne induite par le suintement est discutee. [Traduit par la Redaction] Mots-cles : squelette du sol, sables, limons, fines nonplastiques, residus, compressibilite, conductivite hydraulique, angularite, surface specifique., Introduction Compressibility and permeability are two of the most important engineering properties of soil because of their influence on rate of consolidation, settlement, seepage, and stability. These two soil parameters [...]

The observation of failure surfaces within column-supported embankments is critical to understanding how the embankment stresses are transferred towards the column heads. In this study, finite element simulations utilising a strain-softening constitutive model, nonlocal regularisation, and the Arbitrary Lagrangian-Eulerian formulation are used to examine these failure surfaces over various embankment geometries. This methodology offers insights into the nature of the failure mechanism, the development of a plane of equal settlement, and the influence of the subsoil settlement profile. Depending on the embankment geometry, the results indicate a punching failure, inverted general bearing failure, or a localised failure develops. The transition between punching and inverted general bearing failure is found to be closely related to the establishment of a plane of equal settlement within the embankment. The height of the plane of equal settlement and the range of failure mechanisms that develop were largely insensitive to the nature of the subsoil settlement profiles simulated. These findings have implications for the practical design of efficient embankments and the effective design of future experimental studies. Key words: soil arching, embankments, bearing failure, critical height, numerical modelling. Pour comprendre comment les contraintes du remblai sont transferees vers les tetes de colonne, il est essentiel d'observer les surfaces de rupture dans les remblais reposant sur des colonnes. La presente analyse s'appuie sur des simulations par elements finis utilisant un modele constitutif d'adoucissement des deformations, une regularisation non locale et une formulation lagrangienne-eurelienne arbitraire pour examiner ces surfaces de rupture sur diverses geometries de remblais. Les donnees recueillies par cette methodologie apportent un eclairage sur la nature du mecanisme de rupture, le developpement d'un plan de tassement egal et l'influence du profil de tassement du sous-sol. Les resultats indiquent, selon la geometrie du remblai, soit une rupture par poinconnement, soit une rupture generale inversee, soit le developpement d'une rupture localisee. On constate que le changement entre la rupture par poinconnement et la rupture generale inversee est etroitement lie a l'etablissement d'un plan de tassement egal dans le remblai. Le developpement de la hauteur du plan de tassement egal et la gamme des mecanismes de defaillance ont ete largement insensibles a la nature des profils de tassement du sous-sol simules. Les conclusions de cette etude ont des implications pour la realisation pratique de remblais efficaces et pour la conception efficace de futures etudes experimentales. [Traduit par la Redaction] Mots-cles : voute du sol, remblais, defaillance de la portance, hauteur critique, modelisation numerique., 1. Introduction Geosynthetic reinforced column-supported embankments (GRCSEs) have seen increasing research and application in the last 25 years (Almeida et al. 2007; Gallant et al. 2020; Ghosh et al. 2021; [...]

Experiments are conducted to quantify leakage through a circular geomembrane (GMB) hole using two subgrades (underliners) not meeting modern filter criteria. Test results show that a 1.9- and 5.0-fold increase in hole diameter causes a 1.8- and 6.2-fold increase in leakage, respectively, whereas a 2-fold increase in GMB thickness results in an approximate 10% decrease in leakage. For a constant hydrostatic effective stress, a 2- and 3-fold increase in water head above the GMB leads to a 1.8- and 2.5-fold increase in leakage, respectively. Higher leakage arising from the intrusion of subgrade materials through the hole is quantified. A numerical model, considering the localized concentration of head loss around the hole and the consequent heterogeneity in hydraulic conductivity due to the seepage force, is presented. The percent of head loss within the hole and from the hole to any position above the GMB is independent of loading conditions and only influenced by the GMB thickness and hole diameter. Finally, empirical equations for predicting leakage through a circular GMB hole in tailings storage applications are proposed. Compared with published equations that do not consider consolidation induced heterogeneity in hydraulic conductivity, the proposed equation (which does consider these factors) gives a more accurate prediction for the cases examined. Key words: geosynthetics, geomembrane, hole, leakage, seepage force, tailings. Des essais sont menes dans le but de quantifier les fuites a travers un trou circulaire de geomembrane (GMB) en utilisant deux sous-couches (<>) ne repondant pas aux criteres modernes de filtration. Une augmentation de 1,9 et 5,0 fois du diametre du trou entraine une augmentation de 1,8 et 6,2 fois des fuites, respectivement, alors qu'une augmentation de 2 fois de l'epaisseur de la GMB entraine une diminution d'environ 10 % des fuites. En ce qui concerne la contrainte hydrostatique effective constante, une multiplication par 2 et 3 de la hauteur d'eau au-dessus de la GMB entraine une multiplication par 1,8 et 2,5 des fuites, respectivement. Le taux de fuite plus eleve resultant de l'intrusion de materiaux de la sous-couche a travers le trou est quantifie. Nous presentons un modele numerique envisageant la concentration localisee de la perte de charge autour du trou et l'heterogeneite consequente de la conductivite hydraulique due a la force d'infiltration. La proportion de perte de charge a l'interieur du trou et entre le trou et toute position au-dessus du GMB est independante des conditions de charge et n'est influencee que par l'epaisseur du GMB et le diametre du trou. Finalement, des equations empiriques pour predire les fuites a travers un trou GMB circulaire dans les applications de stockage de residus sont proposees. Par rapport aux equations publiees qui ne tiennent pas compte de l'heterogeneite de la conductivite hydraulique induite par la consolidation, l'equation proposee (qui tient compte de ces facteurs) donne une prediction plus precise pour les cas examines. [Traduit par la Redaction] Mots-cles: geosynthetiques, geomembrane, trou, fuite, force d'infiltration, residus., 1. Introduction Geomembranes (GMBs) have proven to be excellent seepage barriers for modern municipal solid waste (MSW) landfills, where the GMB is generally overlain by a high permeable layer and [...]

Leakage through a 10 mm diameter circular hole in a geomembrane beneath fine-grained tailings is examined for a range of pore pressures and effective stresses. Leakage was measured in an experiment with coupled physical and hydraulic conditions to simulate the effective stresses and flow conditions near the hole. The leakage rate was as little as 0.16 L/day with 200 kPa pore pressure (10-30 kPa effective stresses) and increased only to 0.46 L/day with 800 kPa pore pressure (200 kPa effective stress). See page analysis of the experiment and local measurements of permeability from small samples extracted after the experiment indicate that the tailings hydraulic conductivity controlling flow was 3-6 * [10.sup.-9] m/s. Only a subtle decrease in hydraulic conductivity (less than 2 times) near the hole was found. No evidence of see page-induced migration of fines within the tailings was found. Calculations with the parameters deduced from the experiment show that leakage from a tailings storage facilities containing fine-grained tailings can be limited to 1-2 L/ha/day with a geomembrane liner, even when containing up to five 10 mm diameter holes per hectare, as opposed to an unlined facility with 3 to 4 orders of magnitude more leakage. Key words: geomembrane, leakage, tailings, physical modelling. Cette etude examine les fuites a travers un trou circulaire de 10 mm de diametre dans une geomembrane sous des residus a grain fin pour une gamme de pressions interstitielles et de contraintes effectives. On a mesure les fuites dans une experience avec des conditions physiques et hydrauliques couplees pour simuler les contraintes effectives et les conditions d'ecoulement pres du trou. Le taux de fuite n'etait que de 0,16 L/jour avec une pression interstitielle de 200 kPa (contraintes effectives de 10-30 kPa) et n'augmentait que de 0,46 L/jour avec une pression interstitielle de 800 kPa (contrainte effective de 200 kPa). L'analyse des suintements de l'experience et les mesures locales de permeabilite a partir de petits echantillons extraits a la suite de l'experience indiquent que la conductivite hydraulique des residus controlant l'ecoulement etait de 3-6 * [10.sup.-9] m/s. On a constate seulement une subtile diminution de la conductivite hydraulique (moins de 2 fois) pres du trou. Rien n'indique une migration des fines dans les residus induite par le suintement. Les simulations effectuees au moyen des parametres deduits de l'experience montrent que les fuites d'une installation de stockage de residus contenant des residus a grain fin peuvent etre limitees a 1-2 L/ha/jour avec une geomembrane, meme en presence de cinq trous de 10 mm de diametre par hectare, contrairement a une installation sans revetement qui presente des fuites de 3 a 4 ordres de grandeur plus importantes. [Traduit par la Redaction] Mots-cles: geomembrane, fuite, residus, modelisation physique., Introduction Geomembranes are increasingly being used to line the bottom of tailings storage facilities to reduce the amount of flow from the tailings to the surrounding environment (McLeod 2016). The [...]

Three hundred and twenty-four data points on the saturated hydraulic conductivity (k) of various hard rock mine tailings are collected from previous publications. The applicability of existing empirical equations for hard rock mine tailings is assessed based on this database collected. Results show that with a greater exponent of d10, the correlation between the measured and predicted k is greatly improved. An empirically modified version of the Kozeny–Carman equation is then proposed for predicting the saturated k of tailings and compared with the database. The proposed equation gives the best fit with a varying exponent greater than 2 for d10. Finally, the impact of particle shape on k is discussed. [ABSTRACT FROM AUTHOR]

The UK sixth carbon budget has recommended domestic biomass supply should increase to meet growing demand, planting a minimum of 30,000 hectares of perennial energy crops a year by 2035, with a view to establishing 700,000 hectares by 2050 to meet the requirements of the balanced net zero pathway. Miscanthus is a key biomass crop to scale up domestic biomass production in the United Kingdom. A cohesive land management strategy, based on robust evidence, will be required to ensure upscaling of miscanthus cultivation maximizes the environmental and economic benefits and minimizes undesirable consequences. This review examines research into available land areas, environmental impacts, barriers to uptake, and the challenges, benefits, and trade‐offs required to upscale miscanthus production on arable land and grassland in the United Kingdom. Expansion of perennial biomass crops has been considered best restricted to marginal land, less suited to food production. The review identifies a trade‐off between avoiding competition with food production and a risk of encroaching on areas containing high‐biodiversity or high‐carbon stocks, such as semi‐natural grasslands. If areas of land suitable for food production are needed to produce the biomass required for emission reduction, the review indicates there are multiple strategies for miscanthus to complement long‐term food security rather than compete with it. On arable land, a miscanthus rotation with a cycle length of 10–20 years can be employed as fallow period for fields experiencing yield decline, soil fatigue, or persistent weed problems. On improved grassland areas, miscanthus presents an option for diversification, flood mitigation, and water quality improvement. Strategies need to be developed to integrate miscanthus into farming systems in a way that is profitable, sensitive to local demand, climate, and geography, and complements rather than competes with food production by increasing overall farm profitability and resilience. [ABSTRACT FROM AUTHOR]

The long-term performance of geomembranes with 12 different resin-antioxidant master-batch combinations, including eight high-density polyethylene (HDPE), three linear low-density polyethylene (LLDPE), and one blended polyolefin (BPO) base resins, is investigated. Results are reported for immersion tests in chlorinated water (0.5 ppm) for 35 months at 85[degrees]C. The degradation trends show that the choice of resin type played a key role in the longevity of the geomembranes but also that some hindered amine light stabilizer (HALS) packages contributed to better resistance to degradation in chlorinated water. The results show that the specific antioxidant package is more important than the initial oxidative induction time (OIT) in terms of long-term performance. Finally, it is shown that while increased thickness may be beneficial, a more resistant resin or antioxidant-stabilizer package can be more effective than increasing thickness in improving geomembrane performance in chlorinated water. The conclusion regarding the beneficial role of HALS is specific to chlorinated water and generally is not true in other cases of submerged or buried geomembranes. Key words: geosynthetics, geomembranes, chlorinated water, oxidative degradation, high-density polyethylene (HDPE), low-density polyethylene (LLDPE), blended polyolefin, ageing, antioxidants. La performance a long terme des geomembranes avec 12 combinaisons differentes de resine et d'antioxydant, dont huit polyethylenes a haut densite (PEHD), trois polyethylenes lineaires a basse densite (PEBDL) et une resine de base de polyolefine melangee (BPO), est etudiee. Les resultats sont rapportes pour des tests d'immersion dans de l'eau chloree (0,5 ppm) pendant 35 mois a 85[grados]C. Les tendances de la degradation montrent que le choix du type de resine a joue un role cle dans la longevite des geomembranes mais aussi que certains ensembles de stabilisants a la lumiere aux amines encombrantes (HALS) ont contribue a une meilleure resistance a la degradation dans l'eau chloree. Les resultats montrent que le paquet specifique d'antioxydants est plus important que le temps d'induction oxydative initial (TIO) en termes de performance a long terme. Enfin, il est demontre que si l'augmentation de l'epaisseur peut etre benefique, une resine plus resistante ou un ensemble antioxydant-stabilisant peut etre plus efficace que l'augmentation de l'epaisseur pour ameliorer les performances de la geomembrane dans l'eau chloree. La conclusion concernant le role benefique des ESLA est specifique a l'eau chloree et n'est generalement pas vraie dans les autres cas de geomembranes submergees ou enterrees. [Traduit par la Redaction] Mots-cles : geosynthetiques, geomembranes, eau chloree, degradation oxydative, polyethylene a haute densite (PEHD), polyethylene lineaire a basse densite (PEBDL), polyolefine melangee, vieillissement, antioxydants., 1. Introduction Geotechnical and geoenvironmental engineers frequently use polyethylene (PE) geomembranes (GMBs) in applications including landfills, brine ponds, mining facilities, stormwater ponds, and potable water reservoirs for containment of liquids [...]

The influence of co-disposal of municipal solid waste (MSW) and incinerator ash used as daily cover on the clogging of leachate collection systems (LCSs) from landfills is examined. The 'BioClog' model is used to simulate the fate and transport of the nine leachate constituents most responsible for clogging the LCSs as they move through the porous media. It then calculates the thicknesses of five films that attach to the porous media and the effect of this clog mass-volume on the porosity and hydraulic conductivity of the granular material. Then it models the consequent growth in the leachate mound with increasing clog mass over time until the service life of the LCS is reached. The modeling shows that the concentrated source of leachable minerals in the incinerator ash accelerates the clogging rate and reduces the service life of the LCSs compared to inert daily cover. If an LCS is not designed to accommodate these higher concentrations of cations in the influent leachate during the landfill operating period, the ash can significantly reduce the LCS service life. Means of extending LCS service life are discussed. A practical technique is also utilized to estimate the service life of LCSs with conservative and reasonable agreement with BioClog. Key words: co-disposal, municipal solid waste, incinerator ash, clogging, service life, leachate collection systems, landfills. L'influence de la co-disposition des dechets solides municipaux (DSM) et des cendres d'incineration utilisees comme couverture quotidienne sur l'encrassement des systemes de collecte des lixiviats (SCL) des decharges est examinee. Le modele << BioClog >> est utilise pour simuler le devenir et le transport des neuf constituants du lixiviat les plus responsables de l'encrassement des SCL lorsqu'ils se deplacent dans le milieu poreux. Il calcule ensuite les epaisseurs de cinq films qui s'attachent au milieu poreux et l'effet de cette masse-volume de colmatage sur la porosite et la conductivite hydraulique du materiau granulaire. Il modelise ensuite la croissance consequente du depot de lixiviat avec l'augmentation de la masse du colmatage au fil du temps jusqu'a ce que la duree de vie du SCL soit atteinte. La modelisation montre que la source concentree de mineraux lixiviables dans les cendres de l'incinerateur accelere le taux de colmatage et reduit la duree de vie des SCL par rapport a une couverture quotidienne inerte. Si un SCL n'est pas concu pour recevoir ces concentrations plus elevees de cations dans le lixiviat influent pendant la periode d'exploitation de la decharge, les cendres peuvent reduire considerablement la duree de vie du SCL. Les moyens de prolonger la duree de vie des SCL sont discutes. Une technique pratique est egalement utilisee pour estimer la duree de vie des SCL en concordance raisonnable et juste avec BioClog. Mots-cles: co-disposition, dechets solides municipaux, cendres d'incineration, colmatage, duree de vie, systemes de collecte des lixiviats, decharges., 1. Introduction Even after applying waste management strategies such as reducing, reusing, and recycling waste in many countries, landfills are still the primary endpoints for municipal and industrial solid waste [...]

Low-permeability liners are required at the base of municipal solid waste (MSW) landfills to minimize leachate leakage and contaminant migration into groundwater. This paper uses a two-dimensional coupled groundwater flow and contaminant transport model to examine the performance of three types of low-permeability liners specified by the current Chinese landfill standard: (1) a compacted clay liner (CCL), (2) a geomembrane (GMB) overlying a CCL, and (3) a GMB overlying a geosynthetic clay liner (GCL) on a CCL. The model simulates leachate leaking and contaminant migrating over the entire base of the landfill for the CCL and through the holed GMB wrinkles for the GMB composite liners. The performance of each type of low-permeability liners was evaluated and compared in terms of leakage rate and peak impact of chloride on the aquifer. Based on liner cases and conditions examined in this paper, the results show that the three types of low-permeability liners are not equivalent for minimizing the leakage rate and chloride impact on the aquifer. The GMB + GCL + CCL performs the best among the three low-permeability liners, and is effective for limiting the peak chloride impact on the aquifer below the acceptable level in drinking water. [ABSTRACT FROM AUTHOR]

Leakage and erosion of a soluble subgrade overlain by a geomembrane with a 70-mm-long slit defect is examined. The subgrade (gypsum) solubility and its rate of dissolution from a solid state in contact with various solutions are investigated. In the absence of flow, the rate of dissolution is negligible. However, when there is flow there is dissolution, and if the flow is high enough, erosion. Erosion greatly increases fluid migration. The presence of an interface between the subgrade and a dissimilar material (e.g. a geomembrane) facilitates flow, dissolution, and erosion as the interface becomes an ever increasing preferential flow path, leading to a much greater leakage and erosion feature. The findings from this study highlight the risk of having a soluble subgrade below a single geomembrane used alone and exposed for the containment of liquids. [ABSTRACT FROM AUTHOR]

The paper develops an analytical model based on the force equilibrium for the design of steep slope geosynthetic liner systems to overcome downdrag loads from waste settlement. This analytical model calculates the required tensile stiffness for a high strength/stiffness geotextile (HS-GTX) reinforcement over the GMB to limit the maximum HS-GTX tensile strain to 5% and the maximum GMB strain to 4% on the side slope. The numerical model illustrates the need for reducing the GMB tensile strains for a single GMB liner on a steep landfill slope and confirms that the use of a HS-GTX over the GMB is able to limit the maximum HS-GTX and GMB tensile strains to the acceptable strain levels. The analytical model developed in this paper is a practical tool for preliminary design to limit tensile strains of the HS-GTX and GMB in a steep slope geosynthetic liner system. [ABSTRACT FROM AUTHOR]

An approach for selecting a high-density polyethylene (HDPE) geomembrane (GMB) for a long design life is described and illustrated for five 2 mm thick textured GMBs when immersed in a simulated municipal solid waste leachate (L3) and two simulated leachates representative of low-level radioactive waste leachates (L7 and L9) for 9-16 months at a range of temperatures. Although made from the same nominal resin, substantial differences are reported in both the initial properties and the rate of antioxidant depletion for the five GMBs. At an expected operating liner temperature of 10 [degrees]C and immersed in L3, the projected time to antioxidant depletion for the five GMBs ranges from 125 to over 2000 years. The antioxidant depletion in leachates L7 and L9 were similar or slower than in leachate L3. There was no evidence of traditional thermal-oxidative degradation reported over the 9-16 months of monitoring; however, there was a significant reduction in stress crack resistance due to physical ageing ranging between 30% and 70% of the initial value. Two GMBs are considered highly likely to have service life well in excess of the required design life of 550 years. It is suggested that the proposed approach could be adopted for selecting GMBs for other projects that require a long design life. Keywords: geomembrane (GMB), antioxidant depletion, stress crack resistance, service-life, textured GMBs, white GMBs, low level radioactive waste, design approach. Une approche pour selectionner un polyethylene haute densite (PEHD) geomembrane (GMB) pour une longue duree de vie utile est decrite et illustree pour cinq GMB textures de 2 mm d'epaisseur lorsqu'ils sont immerges dans un lixiviat de dechets solides municipaux simule (L3) et deux lixiviats simules representatifs des lixiviats de dechets radioactifs de faible activite (L7 et L9) pendant 9-16 mois a une gamme de temperatures. Bien qu'elles soient fabriquees a partir de la meme resine nominale, des differences substantielles sont signalees tant dans les proprietes initiales que dans le taux d'epuisement des antioxydants pour les cinq GMBs. A une temperature de fonctionnement prevue de 10 [degrees]C et immergee dans la solution L3, la duree prevue de l'epuisement des antioxydants pour les cinq GMBs varie de 125 a plus de 2000 ans. La depletion des antioxydants dans les lixiviats L7 et L9 etait similaire ou plus lente que dans le lixiviat L3. Aucun signe de degradation traditionnelle par oxydation thermique n'a ete signale au cours des 9 a 16 mois de surveillance. Cependant, il y a eu une reduction significative de la resistance a la fissuration sous contrainte due au vieillissement physique comprise entre 30 et 70 % de la valeur initiale. Deux GMB sont consideres comme ayant une duree de vie bien superieure a la duree de vie theorique requise de 550 ans. Il est suggere que l'approche proposee pourrait etre adoptee pour la selection des GMB pour d'autres projets necessitant une longue duree de vie theorique. [Traduit par la Redaction] Mots-cles : geomembrane (GMB), epuisement des antioxydants, resistance a la fissuration sous tension, duree de vie, GMB textures, GMB blancs, dechets faiblement radioactifs, approche de conception., 1. Introduction International best practice is to select a radioactive waste disposal facility based on the level of waste hazard and an engineered near-surface disposal facility is currently considered as [...]