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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 [...]

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 [...]

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 [...]

The effect of texturing (co-extrusion using blowing agent) on the longevity of a geomembrane (GMB) when immersed in synthetic municipal solid waste leachate is investigated over a ~3 year period. Based on data at four temperatures (40, 55, 75, and 85[degrees]C), the time to antioxidant depletion of the textured portion of a 1.5 mm core thickness high-density polyethylene (HDPE) GMB is 40% (standard oxidative induction time) and 9% (high-pressure oxidative induction time) faster compared to the 1.5 mm smooth edge of the GMB. However, despite this, stress crack resistance results show that texturing may have no significant effect on the time to nominal failure for this GMB. It is also shown that HDPE GMBs made from nominally the same resin but from different production lots have different rates of stress crack resistance degradation and hence time to nominal failure; this should be considered both in landfill design and landfill construction quality assurance. Key words: geosynthetics, textured, geomembrane, municipal solid waste (MSW) landfills, antioxidant depletion, stress crack resistance, degradation, failure, physical ageing. L'effet de la texturation (co-extrusion a l'aide d'un agent gonflant) sur la longevite d'une geomembrane (GMB) lorsqu'elle est immergee dans un lixiviat synthetique de dechets solides municipaux est etudie sur une periode de ~3 ans. D'apres des donnees obtenues a quatre temperatures (40, 55, 75 et 85[degrees]C), le temps d'appauvrissement en antioxydants de la partie texturee d'un polyethylene haute densite (PEHD) GMB de 1,5 mm d'epaisseur est 40% (temps d'induction oxydatif standard) et 9% (temps d'induction oxydatif a haute pression) plus rapide que la partie lisse de 1,5 mm du GMB. Cependant, malgre cela, les resultats de la resistance a la fissuration sous contrainte montrent que la texturation peut n'avoir aucun effet significatif sur le temps jusqu'a la defaillance nominale pour ce GMB. Il est egalement demontre que les GMB PEHD fabriques a partir nominalement de la meme resine mais de lots de production differents presentent des taux differents de degradation de la resistance a la fissuration sous contrainte et donc un temps de defaillance nominal different; cela devrait etre pris en compte tant dans la conception des decharges que dans l'assurance qualite de leur construction. [Traduit par la Redaction] Mots-cles : geosynthetiques, texture, geomembrane, decharges de dechets solides municipaux (MSW), epuisement des antioxydants, resistance a la fissuration sous contrainte, degradation, defaillance, vieillissement physique., 1. Introduction The long-term efficacy of a barrier system is crucial to environmental protection offered by modern engineered municipal solid waste (MSW) landfills (Rowe et al. 2004; Rowe 2016, 2018; [...]

The leakage and the peak chloride concentration in an aquifer for a single composite liner facility is modelled for (i) a hole in a geomembrane wrinkle and (ii) a failed seam. A method using a closed-form solution to calculate leakage together with a 1 1/2-dimensional (P/2D) semi-analytic contaminant transport model is proposed, and the results compared with those obtained from two-dimensional (2D) finite element modelling (FEM). Leakage is shown to be highly dependent on the interaction between the interface transmissivity ([theta]) and hydraulic conductivity beneath the wrinkle (kb). Similar leakages arising from different combinations of transmissivity and hydraulic conductivity are shown to have significantly different impacts on an underlying aquifer. Contaminant transport modelling is needed to assess this effect for the likely range of uncertainty regarding interface transmissivity ([theta]) and hydraulic conductivity. The 2D FEM is conceptually more comprehensive; however, using conventional software only a very limited size of problem could be accurately modeled given the greatly different scales that must be modelled. In contrast, the semi-analytic 1 1/2D approach readily allowed consideration of the highly variable scales, and gave results at the down-gradient edge sufficiently similar to the 2D approach. Key words: geosynthetics, contaminant migration, landfill, interface transmissivity, composite liner. La fuite et le pic de concentration de chlorure dans un aquifere pour une seule installation de revetement composite sont modelises pour (i) un trou dans une ride de geomembrane, et (ii) un joint defectueux. Une methode utilisant une solution sous forme fermee pour calculer les fuites avec un modele de transport de contaminants semi-analytique en 1 1/2 dimensions (P/2D) est proposee, et les resultats sont compares a ceux obtenus par la modelisation par elements finis (FEM) en deux dimensions (2D). Il a ete demontre que les fuites dependent fortement de l'interaction entre la transmissivite de l'interface ([theta]) et la conductivite hydraulique sous la ride ([[kappa].sub.b]). Des fuites similaires resultant de differentes combinaisons de transmissivite et de conductivite hydraulique ont des impacts significativement differents sur un aquifere sous-jacent. Une modelisation du transport des contaminants est necessaire pour evaluer cet effet dans l'intervalle d'incertitude probable concernant la transmissivite de l'interface ([theta]) et la conductivite hydraulique. Le modele FEM 2D est conceptuellement plus complet, mais avec un logiciel conventionnel, seule une taille tres limitee de probleme pourrait etre modelisee avec precision, etant donne les tres differentes echelles a modeliser. En revanche, l'approche semi-analytique 1 1/2 D permettait aisement de prendre en compte les echelles tres variables et donnait des resultats au niveau du bord descendant suffisamment similaire a l'approche 2D. [Traduit par la Redaction] Mots-cles : geosynthetiques, migration des contaminants, decharge, transmissivite d'interface, doublure composite., 1. Introduction Geomembranes (GMBs) are often used in conjunction with a geosynthetic clay liner (GCL), a compacted clay liner (CCL) or both to form a composite liner for a wide [...]

A numerical model to estimate the tensile strains (loads) of the geomembrane liner in the waste containment facility due to waste settlement is presented. A centrifuge test of the geomembrane-lined landfill is used to validate the numerical model. The calculated surface settlement at the centre of the landfill and the geomembrane tensile strains on intermediate benches are generally in good agreement with the measured data. Parametric analyses associated with foundation shear strength as well as interface shear strength and stiffness are performed. The influence of geometric nonlinearity on the geomembrane tensile strains is also examined. The numerical analyses indicate that the maximum geomembrane tensile strain occurs at the crest of the side slope near the intermediate bench for the cases and conditions examined. The lessons learned are likely to be useful to landfill design engineers using numerical models to aid in the design of the geosynthetic liner system for the waste containment facilities. Key words: waste settlement, geomembrane tensile strain, geosynthetic liner system, waste containment facility, numerical modeling, FLAC. Un modele numerique pour estimer les deformations en traction (charges) de la geomembrane dans l'installation de confinement de dechets en raison du tassement des dechets est presente. Un essai centrifuge de l'enfouissement a paroi en geomembrane est utilise pour valider le modele numerique. Le tassement de la surface calculee au centre du site d'enfouissement et des deformations en traction sur des bancs intermediaires est generalement en bon accord avec les donnees mesurees. Les analyses parametriques associees a la resistance au cisaillement ainsi que la resistance au cisaillement et la rigidite de l'interface sont effectuees. L'influence de la non-linearite geometrique sur les deformations en traction de la geomembrane est aussi examinee. Les analyses numeriques indiquent que la deformation en traction de la geomembrane se produit a la crete de la pente laterale pres du banc intermediaire pour les cas et les conditions d'examen. Les lemons tirees sont susceptibles d'etre utiles aux ingenieurs de conception de site d'enfouissement a l'aide de modeles numeriques pour faciliter la conception du systeme de la paroi geosynthetique pour les installations de confinement de dechets. [Traduit par la Redaction] Mots-cles: tassement de dechets, deformation en traction de la geomembrane, systeme de paroi geosynthetique, installation de tassement de dechets, modelisation numerique, FLAC., 1. Introduction Modern waste containment facilities generally have a barrier system at the base of the facility to minimize the potential impacts of contaminants in the facilities on the surrounding [...]

For geosynthetic reinforced column supported embankments (GRCSE) supporting a high embankment, lateral forces associated with lateral sliding and embankment stability often govern the acceptability of a given design under serviceability conditions. Frequently, the complex soil-structure-geosynthetic interaction, the size, and the three- dimensional nature of a GRCSE necessitate the use of numerical analysis to assess embankment performance relative to serviceability criteria. However, traditional finite element method techniques used to model serviceability behaviour are limited in their ability to model the geotechnical mechanisms associated with column installation, equilibration, and group installation effects. These installation effects are examined herein based on a GRCSE field case study located in Melbourne, Australia, that has been extensively instrumented. The role that these installation effects have on the performance of the GRCSE is highlighted and the behaviour of the columns supporting the embankment is emphasized. It is shown that cracking of the unreinforced columns supporting the embankment is likely inevitable and that the reduction of lateral resistance provided by the columns should be accounted for in design. The suitability of various numerical approaches currently used in design to model the columns supporting the GRCSE, and the embankment itself, are discussed and recommendations are made. Key words: geosynthetic, field case study, column-supported embankment, installation effects. Pour les remblais colonne renforcee aux geosynthetiques (<>), soutenir un haut talus, les forces laterales associees au glissement lateral et la stabilite du remblai regissent souvent l'acceptabilite de la conception etant sous conditions de maintenance. Frequemment, l'interaction complexe sol- structure-geosynthetique, la taille et la nature tridimensionnelle d'un GRCSE necessite l'utilisation d'analyse numerique pour evaluer le rendement de remblais par rapport aux criteres de maintenance. Cependant, les techniques traditionnelles d'elements finis utilises pour modeliser le comportement de maintenance sont limitees dans leur capacite a modeliser les mecanismes geotechniques associes a l'installation de colonne, l'equilibre et les effets d'installation du groupe. Ces effets sont examines dans le present document et sont fondes sur une etude de cas sur le terrain GRCSE situe a Melbourne, en Australie, qui a ete largement instrumente. Le role que ces effets d'installation ont sur la performance de GRCSE est mis en evidence et le comportement des colonnes soutenant le talus est souligne. Il est demontre que la fissuration des murs colonnes soutenant le remblai est probablement inevitable et que la reduction de la resistance laterale fournie par les colonnes doit etre prise en compte dans la conception. La pertinence des differentes approches numeriques actuellement utilisee dans le modele de conception de colonnes soutenant le GRCSE, et le remblai lui- meme sont discutes et des recommandations sont formulees. [Traduit par la Redaction] Mots-cles: geosynthetique, etude de cas sur le terrain, remblai soutenu par colonne, effets d'installation., Introduction The design of geosynthetic reinforced column supported embankments (GRCSEs) requires the consideration of a number of limit state conditions. These typically include, but are not limited to, the following: [...]

Two geosynthetic clay liners (GCLs) reported to have experienced significant shrinkage at other locations are examined on both a 3H:1V south-facing slope and a relatively flat base on a silty sand. The GCLs were overlapped by 300 mm with 400 g/m of supplemental bentonite and covered by a black 1.5 mm high-density polyethylene (HDPE) geomembrane to form a composite liner that was left exposed in a full-scale field test embankment for a period of almost 5 years. It is shown that despite the relatively uniform exposure conditions, shrinkage is highly variable with a maximum shrinkage of GCL A being 165 mm on the slope and 415 mm on the base while GCL B shrunk by up to 75 mm on the side slope and only up to 25 mm on the base. The dominant role played by variable overlap stick and heterogeneity to the locations where the overlaps are re-wetted are discussed. Based on this study of shrinkage and a related study of downslope erosion at the same site, it is concluded that neither GCLs A nor B should be left in exposed composite liners when they can be subjected to thermal cycles that can lead to hydration and dehydration of the GCL. Key words: geosynthetics, composite liner, geosynthetic clay liner, overlap, shrinkage. Deux doublures d'argile geosynthetique (GCL) qui ont connu un retrecissement significatif a differents endroits sont examines sur une pente orientee au sud de 3H:1V et d'une base relativement plate sur un sable limoneux. Les GCL ont ete chevauches de 300 mm avec 400 g/m de bentonite supplementaires et recouverts d'une geomembrane en polyethylene haute densite (HDPE) noire de 1,5 mm pour former une doublure composite qui a ete laissee exposee dans un talus d'essai a grande echelle pour une periode de pres de 5 annees. Il a ete demontre que, malgre les conditions d'exposition relativement uniformes, le retrecissement est tres variable avec un retrecissement maximal de la GCL de 165 mm sur la pente et de 415 mm sur la base tandis que la GCL B est retrecie jusqu'a 75 mm sur la pente laterale et seulement jusqu'a 25 mm sur la base. Le role dominant joue par l'adhesion du chevauchement variable et aleatoire aux endroits ou les chevauchements sont a nouveau en contact avec le produit est discute. Sur la base de cette etude du retrecissement et d'une etude connexe de l'erosion descendante sur le meme site, on conclut que ni les GCL A et ni B ne devraient etre laissees dans des revetements plastiques exposes lorsqu'ils peuvent etre soumis a des cycles thermiques pouvant entrainer l'hydratation et la deshydratation de la GCL. [Traduit par la Redaction] Mots-cles: geosynthetiques, doublure composite, revetement d'argile geosynthetique, chevauchement, retrecissement., Introduction Composite liners comprised of a geomembrane over a geosynthetic clay liner (GCL) are extensively used in landfills and increasingly in mining applications (Shackelford et al. 2000; Bouazza 2002; Rowe [...]

The effect of a synthetic municipal solid waste leachate on the long-term performance of dual-wedge welds in a 1.5 mm thick high-density polyethylene geomembrane (GMB) is reported based on 4 years of testing at 40, 65, 75, and 85 [degrees]C. The effect of leachate on the GMB well away from the weld, in the heat-affected zone (HAZ) beside the weld, and in the welded zone are investigated. The slowest antioxidant depletion rate was in the weld itself and the fastest rate for the HAZ adjacent to the weld. The shear break and peel break properties started to decrease after the standard oxidative induction time had depleted to residual, but before the high-pressure oxidative induction time had reached residual. Failures occured at the HAZ adjacent to weld in both the shear and peel tests. No failure of the seam itself was observed. The times to nominal failure of the GMB in the critical HAZ are predicted. The rate of degradation in the weld and sheet are compared. Key words: geosynthetics, geomembrane, welds, durability, high-density polyethylene (HDPE). L'effet d'un lixiviat de dechets solides municipaux synthetique (DSM) sur le rendement a long terme des soudures a panne double dans une geomembrane en polyethylene (GMB) a haute densite d'epaisseur de 1,5 mm est rapporte d'apres quatre annees d'essais a 40, 65, 75, et 85 [degrees]C. L'effet du lixiviat sur le DSM bien loin de la soudure, dans la zone affectee thermiquement (HAZ) a cote de la soudure, et dans la zone soudee est etudie. Le plus lent taux d'epuisement de l'antioxydant etait dans la soudure elle-meme et le taux le plus rapide pour la HAZ etait a cote de la soudure. La rupture en cisaillement et les proprietes de rupture a commence a diminuer apres l'induction oxydative standard avaient epuise au residuel, mais avant que l'induction a haute pression eut atteint la valeur residuelle. Des echecs se produisent au HAZ a cote de la soudure a la fois a l'essai de cisaillement et au deboutonnage. Aucun echec du joint meme n'a ete observe. Les heures de l'echec du DSM nominal dans la HAZ critique sont prevues. Le taux de degradation dans la soudure et la feuille est compare. [Traduit par la Redaction] Mots-cles: geosynthetique, geomembrane, soudure, durabilite, polyethylene a haute densite (PEHD)., Introduction High-density polyethylene (HDPE) geomembranes (GMBs) are used as liners for municipal solid waste (MSW) landfills to minimize leakage of both liquids and gases into the surrounding environment (Rowe et [...]

Post-construction data from an instrumented geosynthetic reinforced column supported embankment (GRCSE) on drilled displacement columns in Melbourne, Australia, show the time-dependent development of arching over the 2 year monitoring period and a strong relationship between the development of arching stresses and subsoil settlement. A ground reaction curve is adopted to describe the development of arching stresses and good agreement is found for the period observed thus far. Predictions of arching stresses and load-transfer platform behaviour are presented for the remaining design life. Four phases of arching stress development (initial, maximum, load-recovery, and creep strain phases) are shown to describe the time-dependent, and subsoil-dependent, development of arching stresses that can be expected to occur in many field embankments. Of the four phases, the load-recovery phase is the most important with respect to load-transfer platform design, as it predicts the breakdown of arching stresses in the long term due to increasing subsoil settlement. This has important implications in assessing the appropriate design stress for the geosynthetic reinforcement layers, but also the deformation of the load-transfer platform in the long term. Key words: arching, geosynthetics, load-transfer platform, column-supported embankment, field case study. Les donnees apres la construction d'une colonne renforcee de maniere geosynthetique instrumentee sur du remblai (GRCSE) soutenu sur les colonnes a deplacement fore a Melbourne, Australie, montrent l'evolution dans le temps du developpement de l'effet de voute sur la periode de surveillance de deux annees et une relation forte entre le developpement de contrainte de l'effet de voute et le tassement du sous-sol. Une courbe de reaction du terrain est adoptee pour decrire le developpement de grandes contraintes de l'effet de voute et un bon accord est trouve pour la periode observee jusqu'a present. Les predictions de contraintes de l'effet de voute et du comportement de la plate-forme de transfert de charge sont presentees pour le reste de la duree de vie theorique. Quatre phases de developpement de contraintes de l'effet de voute (la phase initiale, maximum, reprise du chargement et deformation due au fluage) sont indiquees pour decrire l'evolution de contraintes de l'effet de voute en temps, et dans le sous-sol, qui peut se produire dans de nombreux remblais. Des quatre phases, la phase de reprise de charge est la plus importante en ce qui a trait a la conception de la plate-forme de transfert de charge, car elle prevoit l'effondrement des contraintes a long terme en raison de l'augmentation du tassement du sous-sol. Ceci a des implications importantes dans l'evaluation de la contrainte admissible appropriee pour les couches de renforcement geosynthetique, mais aussi la deformation de la plate-forme de transfert de charge a long terme. [Traduit par la Redaction] Mots-cles: effet de voute, geosynthetiques, plate-forme de transfert de charge, remblai soutenu par la colonne, etude de cas sur le terrain., Introduction Ground improvement using geosynthetic reinforcement and column supported embankments (GRCSEs) is an increasingly popular design solution to support embankments for road and rail applications. A significant quantity of research [...]

Experiments conducted over a 4 year period, on a polymer-enhanced bentonite-sand mixture (PEBSM) used as cover for gold mine tailings are reported. The effect on PEBSM hydraulic conductivity (k) of subgrade porewater chemistry, subgrade water content, and confining stress are investigated. Results show that the reduction in the mole fraction of bound Na+ (ESP) and corresponding increase in k of PEBSM with time was highly dependent on the ionic strength of the subgrade porewater. When the PEBSM was in direct contact with gold mine tailings with porewater having an ionic strength of 145 mmol/L, ESP decreased from 59% to 2% and k increased from 4 x [10.sup.-11] to 6.9 x [10.sup.-9] m/s. The ESP and k values of PEBSM over tailings with 11 mmol/L porewater were 21% and 6.9 x [10.sup.-11] m/s, respectively. A 0.15 m thick foundation layer between tailings and PEBSM layer significantly lowered the reduction in ESP and increase in k with time as did a reduction in the subgrade water content. There was no effect of changing confining stress from 15 to 7.5 kPa on k values of PEBSM. The PEBSM layer acted as a good barrier to the migration of arsenic from tailings upward towards cover soil above the PEBSM layer. Key words: bentonite-sand mixture, cover, gold mine tailings, hydraulic conductivity, laboratory study. Des experiences menees sur une periode de 4 ans sur un melange de bentonite et de sable ameliore par polymere (PEBSM) utilise comme couverture pour les residus de mines d'or sont rapportees. On etudie l'effet de la conductivite hydraulique (k) de la chimie des eaux de porosite des fondations, de la teneur en eau des fondations et de la contrainte de confinement. Les resultats montrent que la reduction de la fraction molaire de [Na.sup.+] liee (ESP) et l'augmentation correspondante de k de PEBSM avec le temps dependaient fortement de la resistance ionique de l'eau interstitielle de la fondation. Lorsque le PEBSM etait en contact direct avec les residus de mine d'or avec de l'eau interstitielle ayant une resistance ionique de 145 mmol/L, l'ESP a diminue de 59 a 2%et k est passee de 4 x [10.sup.-11] a 6,9 x [10.sup.-9] m/s. Les valeurs ESP et k du PEBSM sur des residus avec 11 mmol/L d'eau interstitielle etaient de 21 % et de 6,9 x [10.sup.-11] m/s, respectivelment. Une couche de fondation de 0,15 m d'epaisseur entre les residus et la couche du PEBSM a considerablement abaisse la reduction de l'ESP et l'augmentation de k avec le temps tout comme une reduction de la teneur en eau de la fondation. Il n'y a pas eu d'effet cause par le changement de la contrainte de confinement de 15 a 7,5 kPa sur les valeurs k du PEBSM. La couche du PEBSM a agi comme une bonne barriere a la migration de l'arsenic des residus vers le haut pour couvrir le sol au-dessus de la couche de PEBSM. [Traduit par la Redaction] Mots-cles : melange de bentonite-sable, couverture, residus de mines d'or, conductivite hydraulique, etude de laboratoire., Introduction Gold mine tailings often contain total and porewater arsenic (As) concentrations higher than the maximum allowable values specified by the Canadian soil quality guidelines (12 [micro]g/g, Environment Canada 1996) [...]

Antioxidant depletion from a high-density polyethylene (HDPE) geomembrane with hindered amine light stabilizers (HALS) immersed in seven different low pH solutions is examined over a 3 year period. The examined solutions had the range of pH (0.5,1.25, and 2.0) likely to encompass the pH of the leach solutions found in copper, nickel, and uranium heap leach pads. The metal concentration for these solutions is adopted from copper raffinate solutions. Additional solutions are investigated to examine the effects of field practices such as using surfactants in the leach solutions and pre-curing of the ores used to improve the metallurgical response of the ore. For the antioxidants detected by standard oxidative induction time (Std-OIT), there was a depletion to residual value of about 20% of the initial Std-OIT that varied depending on the incubation temperature and pH of the solution whereas decreasing the pH from 2 to 0.5 did not significantly affect the depletion rates of Std-OIT. The antioxidants detected by high-pressure oxidative induction time (HP-OIT) exhibited the fastest depletion in pH = 1.25 with the highest residual values followed by pH 2.0 and the slowest HP-OIT depletion was in pH = 0.5, but with the lowest residual values. Arrhenius modelling is used to predict the length of the antioxidant depletion stage for each solution based on both Std-OIT and HP-OIT. Key words: geosynthetics, geomembranes, high-density polyethylene (HDPE), hindered amine light stabilizers (HALS), antioxidant depletion, heap leach pads, mining, low pH, copper, uranium, nickel. L'epuisement des antioxydants d'une geomembrane de polyethylene a haute densite (PEHD) avec des photostabilisants d'amine a encombrement sterique (HALS--hindered amine light stabilizers) immergee dans sept solutions de differents pH faibles est examinee sur une periode de 3 ans. Les solutions examinees avaient la gamme de pH (0,5, 1,25 et 2,0), susceptible d'englober le pH a des solutions de lixiviation trouve dans les aires de lixiviation en tas de cuivre, de nickel et d'uranium. La concentration des metaux pour ces solutions est adoptee de solutions raffinats en cuivre. Des solutions supplementaires sont etudiees pour examiner les effets des pratiques de chantier telles que l'utilisation des agents de surface dans les solutions de lixiviation et la prepolymerisation des minerais utilises pour ameliorer la reaction metallurgique du minerai. Pour les antioxydants detectes par temps d'induction oxydative standard (Std-OIT), il y a un appauvrissement de la valeur residuelle d'environ 20% du Std-OIT initial, qui varie en fonction de la temperature d'incubation et du pH de la solution, alors que la diminution du pH de 2 a 0,5 n'a pas significativement affecte le taux d'epuisement de Std-OIT. Les antioxydants detectes par temps d'induction oxydative a haute pression (HP-OIT) a expose l'epuisement rapide du pH = 1,25 avec les plus hautes valeurs residuelles suivies de pH 2,0 et le plus lent appauvrissement de HP-OIT etait a un pH = 0,5, mais avec les plus faibles valeurs residuelles. La modelisation d'Arrhenius est utilisee pour predire la longueur de l'etape d'epuisement d'antioxydant pour chaque solution basee a la fois sur le Std-OIT et le HP-OIT. [Traduit par la Redaction] Mots-cles : geosynthetiques, geomembranes de polyethylene a haute densite (PEHD), photostabilisants d'amine a encombrement sterique (HALS), epuisement d'antioxydant, aires de lixiviation en tas, exploitation miniere, faible pH, cuivre, uranium, nickel., Introduction The primary technologies used to extract metals from ore are (i) milling (crushing and grinding) followed by leaching or flotation and (ii) heap leaching followed by metal extraction from [...]

The thermal conductivities of powdered and granular bentonite based needle punched geosynthetic clay liners (GCLs) were investigated at different gravimetric water contents under 25, 50, 75, and 100 kPa vertical stresses. Both types of GCLs exhibited an increase in thermal conductivity with increasing vertical stress at all water contents. The effect of vertical stresses was more pronounced for the specimens hydrated at lower gravimetric water contents and this was attributed to their high initial volumetric air content. The variability of water distribution in partially hydrated GCLs has been identified as a factor that may affect their thermal conductivity. The forms of bentonites (i.e., powder or granular) affected their thermal conductivities; however, this effect was less apparent at higher gravimetric water contents due to the reduced air content and gel formation in the bentonites. Finally, the GCL thermal conductivity calculated from the measured thermal conductivities of its various constituents (i.e geotextile and bentonite) components differed from the measured values. This was attributed to the nonuniform water distribution across the GCL specimen and change in material properties when components of GCL were disassembled. Key words: geosynthetic clay liner, thermal conductivity, vertical stress, gravimetric water content. Resume : Les conductivites thermiques des couches d'argile geosynthetiques (CAG) aiguilletees a base de bentonite en poudre et granulaire ont ete etudiees a differentes teneurs gravimetriques en eau sous des contraintes verticales de moins de 25, 50, 75 et 100 kPa. Les deux types de CAG ont montre une augmentation de la conductivite thermique avec une augmentation de la contrainte verticale a tous les contenus d'eau. L'effet des contraintes verticales a ete plus prononce pour les echantillons hydrates a une teneur en eau gravimetrique inferieure et ceci a ete attribue a leur haute teneur en air volumetrique initial. La variabilite de la distribution de l'eau dans les CAG partiellement hydrates a ete identifiee comme un facteur qui peut affecter leur conductivite thermique. Les formes des bentonites (a savoir, en poudre ou granulaire) ont affecte leur conductivite thermique; cependant, cet effet etait moins apparent a des teneurs plus elevees en eau gravimetrique en raison de la teneur en air reduite et de la formation de gel dans les bentonites. Enfin, la conductivite thermique du CAG calculee a partir de la conductivite thermique mesuree de ses differents composants constituants (a savoir, les geotextiles et la bentonite) different des valeurs mesurees. Ceci fut attribue a la distribution d'eau non uniforme a travers l'echantillon CAG et les changements dans les proprietes du materiau lorsque les composants du CAG ont ete demontes. [Traduit par la Redaction] Mots-cles : couche d'argile geosynthetique, conductivite thermique, contrainte verticale, contenu gravimetrique en eau., Introduction Composite liners have become an inseparable part of modern municipal solid waste landfills, fluid and mining waste containment facilities, and heap leach pads (Rowe 2005, 2014; Hornsey et al. [...]

A gas flow unified measurement system (UMS-G) for sequential measurement of gas diffusion and gas permeability of geosynthetic clay liners (GCLs) under applied stress conditions (2 to 20 kPa) is described. Measurements made with the UMS-G are compared with measurements made with conventional experimental devices and are found to give similar results. The UMS-G removes the need to rely on two separate systems and increases further the reliability of the gas properties' measurements. This study also shows that the gas diffusion and gas permeability reduce greatly with the increase of both gravimetric water content and apparent degree of saturation. The effect of applied stress on gas diffusion and gas permeability is found to be more pronounced at gravimetric water content greater than 60%. These findings suggest that at a nominal overburden stress of 20 kPa, the GCL used in the present investigation needs to be hydrated to 134% gravimetric water content (65% apparent degree of saturation) before gas diffusion and gas permeability drop to 5.5 x [10.sup.-11] [m.sup.2] x [s.sup.-1] and 8.0 x [10.sup.-13] m x [s.sup.-1], respectively, and to an even higher gravimetric water content (apparent degrees of saturation) at lower stress. Key words: geosynthetic clay liner, gas flow, diffusion, advection, gravimetric water content. Dans le cadre de cette etude, on decrit un systeme de mesure du flux gazeux unifie (UMS-G) afin de mesurer sequentiellement la diffusion gazeuse et la permeabilite au gaz des membranes geosynthetiques d'etancheite d'argile (GCL) soumises des conditions de contrainte (2 20 kPa). Les mesures prises au moyen de l'UMS-G sont comparees aux mesures obtenues au moyen de dispositifs experimentaux courants et il s'avere que les resultats sont semblables. En utilisant l'UMS-G, il n'est plus necessaire d'avoir deux systemes separes et la fiabilite des mesures des proprietes des gaz augmente davantage. De plus cette etude demontre que la diffusion gazeuse et la permeabilite au gaz diminuent considerablement lorsqu'a la fois la teneur en eau gravimetrique et le degre de saturation apparent augmentent. Lorsque la teneur en eau gravimetrique est superieure 60%, on constate que l'effet de la contrainte appliquee sur la diffusion gazeuse et la permeabilite au gaz est plus prononce. Ces resultats suggerent que sous une surcharge de 20 kPa, la GCL utilisee aux fins de cette investigation doit subir une hydratation jusqu'a une teneur en eau gravimetrique de 134% (degre de saturation apparent de 65%) avant que la diffusion gazeuse et la permeabilite au gaz ne baissent jusqu'a 5.5 x [10.sup.-11] [m.sup.2] x [s.sup.-1] et 8.0 x [10.sup.-13] m x [s.sup.-1], respectivement, et jusqu'a une teneur en eau gravimetrique encore plus elevee (degre de saturation apparent) a des contraintes plus faibles. [Traduit par la Redaction] Mots-cles: membrane geosynthetique d'etancheite d'argile (GCL), flux gazeux, diffusion, advection, teneur en eau gravimetrique., Introduction Evaluation of gas migration is important in engineered cover systems of waste containment facilities to prevent or minimize possible contamination of the environment following their closure due to gas [...]

The performance of four sections of a full-scale embankment constructed on soft soil is examined using a fully coupled and fully three-dimensional finite element analysis. The four sections had similar embankment loadings but different improvement options (one unimproved, one with pile-support only, one with a single layer geotextile-reinforced platform and pile-support, and one with two layers of geogrid-reinforced platform and pile-support). Like the field data, the numerical results show that the inclusion of piles decreases the settlement at the subsoil surface to 52% of that for the unimproved section, and the addition of a single layer of geotextile reinforcement J = 800 kN/m) further reduced settlement to only 31% of that of the unimproved section. The effects of geosynthetic reinforcement and multiple layers of reinforcement on the performance of the pile-supported embankment are discussed. The relative load transfer is calculated using eight existing methods and they are compared with the field measurements and numerical results. Key words: geosynthetics, reinforcement, piles, embankments, deformations, three-dimesional analysis, coupled modelling, load transfer. Les performances de quatre sections d'un remblai en talus en taille reelle construit sur un sol mou sont etudiees a l'aide d'une analyse entierement couplee et tridimensionnelle basee sur la methode des elements finis. Les quatre sections presentaient des chargements similaires, mais les solutions d'ameliorations differaient pour chacune d'elle (une section depourvue d'elements d'amelioration; une autre, soutenue uniquement par des pieux; une troisieme, soutenue par des pieux et comportant une plateforme renforcee a l'aide d'une simple couche de geotextile; et une quatrieme, soutenue par des pieux et comportant une plateforme renforcee au moyen de deux couches de geogrille). Tout comme les donnees de terrain, les resultats numeriques montrent que le tassement a la surface du sous-sol diminue sous l'effet de l'inclusion de pieux et equivaut a 52% de celui de la section non amelioree et que l'ajout d'un dispositif de renforcement constitue d'une simple couche de geotextile (J = 800 kN/m) reduit davantage le tassement, qui n'equivaut alors qu'a 31 % de celui de la section non amelioree. Le present article traite des effets du dispositif de renforcement geosynthetique et des multiples couches de ce dispositif sur les performances du remblai soutenu par des pieux. Le transfert de charge relatif est calcule a l'aide de huit methodes existantes et les resultats obtenus sont compares avec les mesures effectuees sur le terrain et avec les resultats numeriques. [Traduit par la Redaction] Mots-cles: materiaux geosynthetiques, renforcement, pieux, remblais en talus, deformations, analyse tridimensionnelle, modelisation couplee, transfert de charge., Introduction One widely adopted approach to constructing embankments over soft soils is the use of basal geosynthetic reinforcement or the combined use of basal geosynthetic reinforcement and prefabricated vertical drains [...]

Progressive kidney fibrosis contributes greatly to end-stage renal failure, and no specific treatment is available to preserve organ function. During renal fibrosis, myofibroblasts accumulate in the interstitium of the kidney, leading to massive deposition of extracellular matrix and organ dysfunction. The origin of myofibroblasts is manifold, but the contribution of an epithelial-tomesenchymal transition (EMT) undergone by renal epithelial cells during kidney fibrosis is still debated. We show that the reactivation of Snai1 (encoding snail family zinc finger 1, known as Snail1) in mouse renal epithelial cells is required for the development of fibrosis in the kidney. Damage-mediated Snai11 reactivation induces a partial EMT in tubular epithelial cells that, without directly contributing to the myofibroblast population, relays signals to the interstitium to promote myofibroblast differentiation and fibrogenesis and to sustain inflammation. We also show that Snail1-induced fibrosis can be reversed in vivo and that obstructive nephropathy can be therapeutically ameliorated in mice by targeting Snail1 expression. These results reconcile conflicting data on the role of the EMT in renal fibrosis and provide avenues for the design of novel anti-fibrotic therapies., Chronic kidney disease (CKD), the progressive deterioration of kidney function, is characterized by glomerulosclerosis (a form of kidney scarring) and tubulo-interstitial fibrosis, regardless of the initial cause of the renal [...]

The degradation of high-density polyethylene (HDPE) geomembranes exposed to the elements depends, inter alia, on the climatological conditions. This study investigates the degradation in the properties of HDPE geomembranes installed at two mine facilities after almost 16 years of exposure in a warm-hot climate and at a research site after 6 years of exposure in a mild-cold climate. Samples were exhumed at the field sites from different locations and the properties of the geomembrane were measured in the laboratory. The depletion of antioxidants detected by the standard oxidative induction time (Std- OIT) test for the geomembrane installed at the research site was faster on the slope than on the base; however, there was negligible difference in the depletion of antioxidants-stabilizers detected by the high-pressure oxidative induction time (HP-OIT) test between the slope and base. Under the field conditions described, the antioxidant depletion time for the exposed geomembrane installed at the research site (mild-cold climate) was inferred to be 20 to 54 years. The exposed HDPE geomembranes installed at the mine facilities (warm-hot climate) have reached the time of nominal failure based on their stress crack resistance. However, they have not ruptured under the exposure conditions even though the stress crack resistance has dropped to as low as 70 h at some locations. Key words: geosynthetics, field case, exposed geomembranes, high-density polyethylene (HDPE), ultraviolet (UV) index, geomembrane degradation. La degradation des geomembranes en polyethylene a haute densite (PEHD) exposees aux elements depend entre autres des conditions climatiques. Cette etude evalue la degradation des proprietes de geomembranes en PEHD installees sur deux sites miniers apres 16 ans d'exposition dans un climat chaud et sur un site de recherche 6 ans apres l'exposition dans un climat tempere-froid. Des echantillons ont ete exhumes des sites sur le terrain a plusieurs endroits et les proprietes de la geomembrane ont ete mesurees en laboratoire. L'epuisement en antioxydants, detecte ?i l'aide de l'essai du temps d'induction de l'oxydation standard (Std-OIT), de la geomembrane installee au site de recherche etait plus rapide sur la pente que sur la base, cependant il y avait une difference negligeable entre l'epuisement des antioxydants-stabilisateurs detectes par l'essai du temps d'induction de l'oxydation ti haute pression (HP-OIT) sur la pente et sur la base. Dans les conditions de terrain decrites, le temps d'epuisement des antioxydants pour la geomembrane exposee installee au site de recherche (climat tempere-froid) a ete estime a 20 a 54 ans. Les geomembranes en PEHD exposees installees sur les sites miniers (climat chaud) ont atteint leur temps nominal de rupture base sur leur resistance aux fissures de contrainte. Cependant, elles n'ont pas cede sous les conditions d'exposition meme si la resistance aux fissures de contrainte a diminue jusqu'a 70 h a certains endroits. [Traduit par la Redaction] Mots-cles: geosynthetique, cas de terrain, geomembranes exposees, polyethylene a haute densite (PEHD), indice ultra- violet (UV), degradation de geomembrane., Introduction High density polyethylene (HDPE) geomembranes (GMBs) are used as barriers to liquids and gas in many geotechnical and geoenvironmental engineering applications, such as landfills, reservoirs, lagoons, and dams (e.g., [...]

This study investigates the performance of bentonite components of geosynthetic clay liners (GCLs) when exposed to aggressive leachates using the fluid loss test and provides a possible quick method for estimating the effect of acidic conditions on hydraulic conductivity. Fluid loss generally increases with increasing acid concentrations. Hydraulic conductivity values back-calculated from the fluid loss tests ([k.sub.FL]) are compared with the values measured using a flexible-wall permeameter ([k.sub.Tri]). Generally, the predicted hydraulic conductivity values are conservative ([k.sub.FL]/[k.sub.Tri] > 1) under water and low acid concentrations (≤0.015 mol/L). However, the back-calculated hydraulic conductivity is shown to be nonconservative ([k.sub.FL]/[k.sub.Tri] < 1) at high acid concentrations (>0.125 mol/L). Key words: acid solutions, bentonite, fluid loss, geosynthetic clay liners (GCLs), hydraulic conductivity. Cette etude evalue la performance de composantes de bentonite a l'interieur de revetements d'argile et de geosynthetique (<< geosynthetic clay liners >>, GCLs) lorsqu'elles sont exposees a des lixiviats agressifs a l'aide de l'essai de perte de fluide, et offre une methode rapide pour estimer l'effet des conditions acides sur la conductivite hydraulique. La perte de fluide augmente generalement avec l'augmentation des concentrations en acide. Les valeurs de conductivite hydraulique retrocalculees a partir des essais de perte de fluide ([k.sub.FL]) sont comparees aux valeursmesurees avec un permeametre a parois flexibles ([k.sub.Tri]). Generalement, les conductivites hydrauliques predites sont conservatrices ([k.sub.FL]/[k.sub.Tri] > 1) dans des conditions submergees et des concentrations faibles d'acide ([less than or equal to]0,015 mol/L). Cependant, la conductivite hydraulique retro-calculee n'est pas conservatrice ([k.sub.FL]/[k.sub.Tri] < 1) dans des concentrations elevees d'acide (≥ 0,125 mol/L). [Traduit par la Redaction] Mots-cles : solutions acides, bentonite, revetements d'argile et de geosynthetique (GCLs), conductivite hydraulique., Introduction Geosynthetic clay liners (GCLs) containing sodium-bentonite are commonly used as hydraulic barriers due to their high swelling potential (swell index, SI > 24 mL/2 g) and low hydraulic conductivity [...]

A test cover comprised of three different needle-punched geosynthetic clay liner (GCL) products and covered with up to1mof cover soil (gravelly sand) was built over arsenic-rich tailings at a former gold mine in Nova Scotia, Canada, to evaluate the performance of the GCLs under local climatic conditions. Of the GCLs examined, one had untreated and two had polymerenhanced natural sodium bentonite. The three GCLs each had different carriers: one with a woven geotextile, one with a scrim-reinforced nonwoven geotextile, and one with a woven geotextile laminated with a polypropylene film. At some locations, each type of GCL was placed in direct contact with the tailings. At other locations, each GCL was separated from the tailings by 0.15 m of cover soil. Samples of each GCL, tailings, and cover soil were recovered 1 and 2 years after construction. Tests show that the GCL with untreated bentonite maintained a low hydraulic conductivity ([less than or equal to]5 x [10.sup.-11] m/s) at locations where there was [greater than or equal to]0.7 m of cover soil above the GCL even though there was significant cation exchange of the sodium in the GCL with divalent cations in the tailings-soil porewater (the mole fraction of sodium (exchangeable sodium percentage (ESP)) decreased from 65% to 10%-17%). The GCL with polymer-enhanced bentonite had a lower hydraulic conductivity ([less than or equal to]3 x [10.sup.-11] m/s under ≥0.7 m of cover soil above the GCL) and experienced less cation exchange (ESP decreased to 19%-28%) than the standard GCL. The other GCL with polymer-enhanced bentonite and a carrier geotextile coated with a geofilm demonstrated the best hydraulic performance regardless of the thickness of cover soil or presence of an initially uncontaminated foundation layer. The presence of a foundation layer between the GCL and tailings impeded the migration of arsenic from the tailings into the GCLs. All GCLs were serving as an effective barrier to arsenic migration. Key words: geosynthetic clay liners, covers, gold mine tailings, cation exchange, hydraulic conductivity, arsenic, field study. Une couverture d'essai faite de trois produits differents de type recouvrement geosynthetique avec argile (GCL) poinconnes avec une aiguille, et recouverte d'un metre de sol (sable graveleux), a ete construite sur des residus riches en arsenic sur le site d'une ancienne mine d'or en Nouvelle-Ecosse, Canada, pour evaluer la performance de GCL soumis aux conditions climatiques locales. Parmi les GCL evaluees, une contient de la bentonite de sodium naturelle non traitee et deux contiennent de la bentonite de sodium naturelle renforcee d'un polymere. Les trois GCL avaient chacun un porteur different: un geotextile cousu pour le premier, un geotextile non cousu de canevas leger pour le deuxieme, et un geotextile cousu lamine d'un film de polypropylene pour le troisieme. A certains endroits, chaque type de GCL etait place en contact direct avec les residus. A d'autres endroits, chaque type de GCL etait separe des residus par 0,15 m de sol. Des echantillons de chaque GCL, de residus et de sol de couverture ont ete recuperes un an et deux ans apres la construction. Les essais demontrent que le GCL avec bentonite non traitee maintient une faible conductivite hydraulique (≤5 x [10.sup.-11] m/s) aux endroits ou il y avait ≥0,7 m de sol par-dessus le GCL, meme s'il y avait des echanges de cations significatifs entre le sodium du GCL et les cations divalents dans l'eau des pores des residus et du sol (la fraction molaire du sodium (pourcentage de sodium echangeable (ESP)) a diminue de 65 % a 10-17 %). Le GCL avec la bentonite renforcee d'un polymere avait une conductivite hydraulique plus faible ([less than or equal to]3 x [10.sup.- 11] m/s sous ≥0,7 m de sol par-dessus le GCL) et a subi moins d'echanges de cations (ESP a diminue jusqu'a 19-28 %) que le GCL standard. L'autre GCL, avec de la bentonite renforcee d'un polymere et un geotextile porteur recouvert d'un geofilm, a demontre la meilleure performance hydraulique quelque soit l'epaisseur du recouvrement ou la presence d'une couche de fondation initialement non contaminee. La presence d'une couche de fondation entre le GCL et les residus empeche la migration de l'arsenic des residus vers le GCL. Tous les GCL sont consideres comme une barriere efficace pour prevenir la migration de l'arsenic. [Traduit par la Redaction] Mots-cles : recouvrement geosynthetique avec argile, recouvrements, residus de mine d'or, exchange de cations, conductivite hydraulique, arsenic, etude de terrain., Introduction Leaching of hazardous metals and metalloids (e.g., arsenic) from waste rock and abandoned mine tailings is a significant environmental concern (Ruby et al. 1999; Kaltreider et al. 2001; Reeder [...]

A numerical model 'BioClog-2D' is used to examine the service life and clogging of leachate collection systems with granular drainage material of different grain sizes. The modelling shows that the leachate characteristics at the end of the drainage pipe are significantly different from those in the leachate entering the leachate collection system and this reduction in leachate strength corresponds to an accumulation of clog mass within the saturated drainage layer. The calculated clog mass within the saturated drainage layer is dominated by the inorganic material, which is in encouraging agreement with field-observed data. The service life of leachate collection systems is increased with an increase in the grain size of the drainage material and decreased with an increase in the length of the drainage path. The service life of the drainage layer is shown to vary from a few years to over 100 years depending on the design of the system. The results indicate that in addition to the particle size of the granular material, the infiltration rate and leachate strength history greatly affect the estimated service life of leachate collection systems. Key words: grain size, drainage path, numerical modelling, clogging, service life, leachate collection systems, landfills. Le modele numerique <> est utilise pour evaluer la duree de vie et le colmatage de systemes de collecte des lixiviats faits de materiaux de drainage granulaires de differentes tailles granulometriques. La modelisation demontre que les caracteristiques du lixiviat a la sortie du tuyau de drainage sont significativement differentes de celles du lixiviat qui entre dans le systeme de collecte du lixiviat, et cette reduction de concentration du lixiviat correspond a une accumulation de masse colmatee a l'interieur de la couche de drainage saturee. La masse colmatee calculee dans la couche de drainage saturee est dominee par la presence de matiere inorganique, ce qui correspond aux donnees observees sur le terrain. La duree de vie du systeme de collecte des lixiviats est augmentee lorsque la taille des particules du materiau drainant augmente, et diminuee lorsque la longueur du parcours de drainage augmente. La duree de vie de la couche drainante varie de quelques annees a plus de 100 ans dependamment de la conception du systeme. Les resultats indiquent qu'en plus de la granulometrie du materiau granulaire, le taux d'infiltration et l'historique de concentration du lixiviat influencent significativement la duree de vie estimee des systemes de collecte des lixiviats. [Traduit par la Redaction] Mots-cles : granulometrie, parcours de drainage, modelisation numerique, colmatage, duree de vie, systemes de collecte des lixiviats, sites d'enfouissement., Introduction The engineered barrier system at the base of a modern municipal solid waste (MSW) landfill typically includes two components (Rowe 2005): (i) a bottom liner system with low permeability [...]

A numerical model 'BioClog-2D' is used to examine the service life and clogging of leachate collection systems with granular drainage material of different grain sizes. The modelling shows that the leachate characteristics at the end of the drainage pipe are significantly different from those in the leachate entering the leachate collection system and this reduction in leachate strength corresponds to an accumulation of clog mass within the saturated drainage layer. The calculated clog mass within the saturated drainage layer is dominated by the inorganic material, which is in encouraging agreement with field-observed data. The service life of leachate collection systems is increased with an increase in the grain size of the drainage material and decreased with an increase in the length of the drainage path. The service life of the drainage layer is shown to vary from a few years to over 100 years depending on the design of the system. The results indicate that in addition to the particle size of the granular material, the infiltration rate and leachate strength history greatly affect the estimated service life of leachate collection systems. Key words: grain size, drainage path, numerical modelling, clogging, service life, leachate collection systems, landfills. Le modele numerique <> est utilise pour evaluer la duree de vie et le colmatage de systemes de collecte des lixiviats faits de materiaux de drainage granulaires de differentes tailles granulometriques. La modelisation demontre que les caracteristiques du lixiviat a la sortie du tuyau de drainage sont significativement differentes de celles du lixiviat qui entre dans le systeme de collecte du lixiviat, et cette reduction de concentration du lixiviat correspond a une accumulation de masse colmatee a l'interieur de la couche de drainage saturee. La masse colmatee calculee dans la couche de drainage saturee est dominee par la presence de matiere inorganique, ce qui correspond aux donnees observees sur le terrain. La duree de vie du systeme de collecte des lixiviats est augmentee lorsque la taille des particules du materiau drainant augmente, et diminuee lorsque la longueur du parcours de drainage augmente. La duree de vie de la couche drainante varie de quelques annees a plus de 100 ans dependamment de la conception du systeme. Les resultats indiquent qu'en plus de la granulometrie du materiau granulaire, le taux d'infiltration et l'historique de concentration du lixiviat influencent significativement la duree de vie estimee des systemes de collecte des lixiviats. [Traduit par la Redaction] Mots-cles: granulometrie, parcours de drainage, modelisation numerique, colmatage, duree de vie, systemes de collecte des lixiviats, sites d'enfouissement., Introduction The engineered barrier system at the base of a modern municipal solid waste (MSW) landfill typically includes two components (Rowe 2005): (i) a bottom liner system with low permeability [...]

The variation in length of the longest hydraulic features (connected wrinkles) formed in an exposed black high-density polyethylene (HDPE) geomembrane liner observed at different times of the day and in different seasons over multiple years is presented for both a 3% base slope and 3H:1V side slope at the Queen's University Experimental Liner Test Site (latitude of 44°34'N and longitude 76°39'W). The longest wrinkle observed on the 0.15 ha base was about 1500 m. The longest wrinkle observed on the 0.17 ha slope was about 2000 m. The length of connected wrinkles is shown to be primarily related to solar radiation, although the soil and ambient temperature played a role in maintaining wrinkles in the afternoon as solar radiation decreased. Wrinkles of less than 20 m connected length were observed for geomembrane surface temperatures of less than 30 °C and solar radiation of less than 600 W/[m.sup.2]. Wrinkles exceeding 500 m in connected length were observed for geomembrane temperatures between about 30 and 62 °C and solar radiation between 600 and 1100 W/[m.sup.2]. The vast majority (about 85%) of wrinkle heights were between 0.04 and 0.08 m with the average wrinkle height being 0.06 m and a maximum wrinkle height of about 0.18 m. The manually measured wrinkle widths around noon (when there was the greatest number of wrinkles) ranged between about 0.20 and 0.43 m, but most of the wrinkles were between 0.23 and 0.36 m with a mean of 0.29 m (standard deviation 0.05 m). The data from this study suggest that a reasonable estimate of mean wrinkle width would be about 0.2 to 0.3 m. The size of the area constraining the geomembrane is shown to affect the connected wrinkle length. Calculations of leakage for the wrinkle lengths and widths observed are reported to be consistent with what has been reported for landfills in North America. Key words: geomembranes, wrinkles, landfills, liners, leakage. Cet article presente la variation de la longueur du parametre hydraulique le plus long (rides connectees) forme dans un revetement expose en geomembrane de polyethylene de haute densite (<< HDPE >>) noir, et observe a differents moments de la journee et durant des saisons differentes sur plusieurs annees. Le cas a l'etude comporte une pente de 3% a la base et une pente de 3H : 1V sur les cotes, et provient du site experimental de revetements de l'Universite Queen's. La plus longue ride observee sur la base de 0.15 ha avait environ 1500 m de long. La plus longue ride observee sur la pente de 0.17 ha etait d'environ 2000 m. Il est demontre que la longueur des rides connectees est reliee principalement a la radiation solaire, malgre que le sol et la temperature ambiante jouent le role du maintient des rides dans l'apres-midi lorsque la radiation solaire diminue. Des rides connectees de moins de 20 m ont ete observees lorsque la temperature a la surface de la geomembrane est inferieure a 30 °C et que la radiation solaire est inferieure a 600 W/[m.sup.2]. Des rides connectees de plus de 500 m ont ete observees lorsque la geomembrane atteint des temperatures entre 30 et 62 °C environ, et que la radiation solaire se situe entre 600 et 1100 W/[m.sup.2]. La majorite (environ 85%) des hauteurs des rides se trouve entre 0.04 et 0.08 m, avec une moyenne de 0.06 m, et une hauteur maximale d'environ 0.18 m. La largeur des rides a ete mesuree manuellement. Les resultats autour de midi (periode ou ilyale plus de rides) se situent entre 0.20 et 0.43 m environ, mais la majorite des largeurs de rides sont entre 0.23 et 0.36 m, avec une moyenne de 0.29 m (ecart type de 0.05 m). Les resultats de cette etude suggerent qu'une estimation raisonnable de la largeur moyenne d'une ride serait d'environ 0.2 a 0.3 m. La dimension de la zone qui contraint la geomembrane affecte la longueur des rides connectees. Des calculs d'ecoulement a partir des longueurs et des largeurs de rides observees correspondent bien avec les valeurs rapportees dans la litterature sur les sites d'enfouissement en Amerique du Nord. Mots-cles: geomembranes, rides, sites d'enfouissement, revetements, fuite. [Traduit par la Redaction], Introduction Even if a high-density polyethylene (HDPE) geomembrane is initially flat and in direct contact with the underlying soil (Fig. 1a), when it is exposed to solar radiation the combination [...]

A numerical model to predict biologically induced clogging of municipal solid waste leachate collection systems is described. The model simulates the accumulation of clog mass in the porous media by the growth of biomass and precipitation of minerals. In addition, the settling and deposition of suspended particles is modelled. A technique for modelling filter-separator layers between the waste and the coarse granular drainage material is described. The application of the model is illustrated for two series of laboratory mesocosm experiments: one where the waste was in direct contact with the underlying drainage layer and the second where there was a granular filter between the waste and the coarse gravel drainage layer. The modelling shows that the clogging of the gravel in the lower regions of the saturated drainage layer is estimated better by the advanced numerical model than the previously published model. In both cases, the calculated results are in encouraging agreement with the observed behaviour. It is concluded that this model has potential for use in modelling biologically induced clogging of municipal landfill leachate collection systems. Key words: porous media, multiple species, biofilm, deposition, clogging, numerical modelling, leachate collection systems, landfills. Cet article decrit un modele numerique servant a predire le colmatage induit biologiquement dans des systemes de collecte du lixiviat de dechets solides municipaux. Le modele simule l'accumulation de la masse colmatante dans le medium poreux causee par la croissance de biomasse et la precipitation de mineraux. De plus, la sedimentation et la deposition des particules en suspension sont modelisees. Une technique pour modeliser les couches du filtre-separateur entre les dechets et le materiau de drainage grossier et granulaire est decrite. L'application du modele est illustree pour deux series d'experiences mesocosme en laboratoire : une serie dans laquelle les dechets etaient en contact direct avec la couche drainante sous-jacente, et la deuxieme ou il y avait un filtre granulaire entre les dechets et la couche drainante de gravier grossier. La modelisation demontre que le colmatage du gravier dans les regions basses de la couche de drainage sature est mieux estime avec le modele numerique avance qu' avec le modele publie precedemment. Dans les deux cas, les resultats calcules correspondent bien avec le comportement observe. En conclusion, ce modele presente un potentiel d'utilisation pour la modelisation du colmatage induit biologiquement dans des systemes de collecte du lixiviat de dechets solides municipaux. Mots-cles : medium poreux, especes multiples, biofilm, deposition, colmatage, modelisation numerique, systeme de collecte du lixiviat, site d'enfouissement. [Traduit par la Redaction], Introduction Leachate collection systems (LCSs) in municipal solid waste (MSW) landfills are commonly built above a low-permeability liner. The primary design objective for the LCS is to control the leachate [...]

An existing elastoviscoplastic constitutive model is modified using concepts of the state-dependent fluidity parameters and the damage law, to incorporate the effect of soil structure and its destructuration. The model is employed to simulate the performance of a well-documented case study of the reinforced test embankment constructed over a sensitive Champlain clay deposit at Saint Alban, Quebec. The finite element calculations, using both the original (nonstructured) and modified (structured) elastoviscoplastic soil models, are compared with the observed field data from a test embankment brought to failure. The results from the structured elastoviscoplastic soil model show better agreements with the field data when compared with those analyzed using the nonstructured elastoviscoplastic soil model. The modified model captures many features of the reinforced embankment behaviour, such as vertical settlement, excess pore-water pressure responses, and reinforcement force. However, they also reveal the fact that another important characteristic of the natural clay deposit--anisotropy--needs to be considered to provide an adequate prediction of horizontal deformations. The role of geosynthetic reinforcement and its viscosity on short-term responses of the reinforced embankment examined in this study is also discussed Key words: elastoviscoplastic, strain-softening, embankment, reinforced soil, numerical modelling, time-dependent behaviour, rate-sensitive clay. Un modele constitutif elastoviscoplastique existant est modifie a l'aide de concepts provenant des parametres de fluidite dependants de l'etat et de la loi du dommage, afin d'inclure l'effet de la structure du sol et de sa destructuration. Le modele est utilise pour simuler la performance d'une etude de cas bien documentee; la digue d'essai renforcee construite sur un depot d'argile de Champlain sensible a Saint-Alban, Quebec. Les calculs par elements finis, employant autant le modele de sol elastoviscoplastique original (non-structure) que le modele modifie (structure), ont ete compares aux donnees de terrain observees sur une digue d'essai sollicitee jusqu'a rupture. Les resultats du modele structure de sol elastoviscoplastique correspondent mieux aux resultats de terrain que ceux obtenus a l' aide du modele non structure de sol elastoviscoplastique. Le modele modifie integre plusieurs caracteristiques du comportement de la digue renforcee telles que le tassement vertical, les variations de pression interstitielle excessive et la force de renforcement. Cependant, les modelisations ont identifie qu'une autre caracteristique importante du depot d'argile naturelle, soit l'anisotropie, doit etre consideree afin d'offrir une prediction adequate des deformations horizontales. Le role du renforcement par des geosynthetiques et de sa viscosite sur le comportement a court terme de la digue renforcee evaluee dans cette etude est aussi discute. Mots-cles : elastoviscoplastique, adoucissement par deformation, digue, sol renforce, modele numerique, comportement dependant du temps, argile sensible aux taux. [Traduit par la Redaction], Introduction In many parts of eastern Canada and Scandinavia, soft clay deposits are highly sensitive. For these sensitive-structured soils, during deformation plastic straining gradually breaks down interparticle bonding and results [...]

Contaminant transport through a single hole in a geomembrane (GM) that forms part of composite liner with a geosynthetic clay liner (GCL) for applied heads (0.3 and 1 m) and an applied pressure of about 100 kPa is modeled and compared with experimental results. The system was first permeated with distilled water until a steady state was reached. The permeant was then switched to an NaCl solution. The inferred interface transmissivity at steady state (after 280 days) is about 2.3 x [10.sup.-11] [m.sup.2]/s for both heads examined. After 800 days permeation with an 0.14 mol/L NaCl solution, the interface transmissivity between the geomembrane and GCL was inferred to have decreased from 2.3 x [10.sup.-11] to 1.1 x [10.sup.-11] [m.sup.2]/s for experiments with heads of both 0.3 and 1 m. Modeling of the flow and changes in the GCL hydraulic conductivity arising from interaction between the bentonite and the 0.14 mol/L NaCl permeant is shown to give excellent agreement with the observed leakage. The differences between modeling a uniform and nonuniform interface transmissivity is found to be small--with the leakage being dominated by the interface transmissivity 0.1 to 0.15 m from the hole in the GM. Typical published values for the diffusion coefficient for both the GCL and sandy soil are shown to give good predictions of effluent concentration with time and chloride distribution in the silty sand in contact with the composite liners at the end of the test. Key words: numerical modeling, leakage, composite liner, geosynthetic clay liner, advection, transport, landfill. Cet article presente la modelisation du transport de contaminants a travers un trou unique dans de la geomembrane (GM) faisant partie d'un revetement composite avec argile et geosynthetique (GCL) pour des tetes appliquees (0,3 et 1 m) et des pressions appliquees d'environ 100 kPa. Les resultats de la modelisation sont ensuite compares a des resultats experimentaux. Le systeme est d'abord infiltre avec de l'eau distillee jusqu'a ce que le regime permanent soit atteint. Ensuite, le liquide permeant est change par une solution de NaCl. La transmissivite inferee a l'interface en regime permanent (apres 280 jours) est d'environ 2,3 x [10.sup.-11] [m.sup.2]/s pour les deux tetes testees. Apres 800 jours de permeation avec une solution de 0,14 mol/L NaCl, la transmissivite de l'interface entre la geomembrane et le GCL est supposee avoir diminue de 2,3 x [10.sup.-11] [m.sup.2]/s a 1,1 x [10.sup.-11] [m.sup.2]/s pour les essais avec des tetes de 0,3 et de 1 m. La modelisation de l'ecoulement et des variations de conductivite hydraulique du GCL survenant en reponse aux interactions entre la bentonite et la solution de 0,14 mol/L NaCl demontre des correspondances excellentes avec les fuites observees. Les differences entre la modelisation d'une transmissivite a l'interface uniforme ou non uniforme s'averent etre faibles, les fuites etant dominees par la transmissivite a 0,1 m et 0,15 m du trou dans la GM. Des valeurs typiques publiees du coefficient de diffusion autant pour le GCL que pour le sol sablonneux permettent d'obtenir des bonnes predictions de la concentration a l'effluent avec le temps et de la distribution du chlorure dans le sable silteux en contact avec les revetements composites a la fin de l' essai. Mots-cles : modelisation numerique, fuite, revetement composite, revetement d'argile et geosynthetique, advection, transport, site d' enfouissement. [Traduit par la Redaction], Introduction Composite liners used at the base of modern landfills often involve a high-density polyethylene (HDPE) geomembrane (GM) over a geosynthetic clay liner (GCL). The primary role of the GCL [...]

The factors that may affect short-term leakage through composite liners are examined. It is shown that the leakage through composite liners is only a very small fraction of that expected for either a geomembrane (GM) or clay liner (CL) alone. However, the calculated leakage through holes in a GM in direct contact with a clay liner is typically substantially smaller than that actually observed in the field. It is shown that calculated leakage taking account of typical connected wrinkle lengths observed in the field explains the observed field leakage through composite liners. Provided that care is taken to avoid excessive connected wrinkle lengths, the leakage through composite liners is very small compared to a typical GM or CL alone. It is shown that the leakage through composite liners with a geosynthetic clay liner (GCL) is typically much less than for composite liners with a compacted clay liner (CCL). Finally, factors that will affect long-term leakage through composite liners are discussed. It is concluded that composite liners have performed extremely well in field applications for a couple of decades and that recent research both helps understand why they have worked so well and provides new insight into issues that need to be considered to ensure excellent long- term liner performance of composite liners--especially for applications where the liner temperature can exceed about 35°C. Key words: leakage, composite liner, geosynthetic clay liner, geomembrane, landfill, municipal solid waste, lagoons. Les facteurs qui peuvent influencer a court terme les fuites a travers les etancheites composites sont examines. On demontre que les fuites a travers ce type d'etancheite sont moindres que celles anticipees pour une geomembrane (GM) ou une couche d'argile (CA) seule. Toutefois, les fuites calculees pour les defauts dans une GM mise en contact direct avec une CA sont typiquement beaucoup plus petites que celles observees sur le terrain. On montre que la contribution des fuites calculee en tenant compte de la longueur typique de plis raccordes entre eux explique l' ampleur des fuites observees sur le terrain pour de telles etancheites composites (GM et CA). Lorsque l'on reduit la presence de longueurs excessives de plis raccordes, les fuites a travers les etancheites composites peuvent s'averer tres faibles lorsque comparees a celles des GM ou CA utilizees seules. Il est aussi demontre que les fuites a travers les etancheites composites comportant un geosynthetique bentonique (GSB) sont typiquement bien moindres que pour les etancheites composites avec une couche d'argile compactee (CAC). Finalement, on discute des facteurs qui affectent les fuites a long terme a travers les etancheites composites. Les travaux montrent que ces etancheites composites se sont tres bien comportes sur le terrain depuis deux decennies, et que les recherches recentes aident a comprendre les raisons qui expliquent ces bonnes performances. Les etudes fournissent aussi une nouvelle perception des aspects qui doivent etre consideres pour assurer une excellente performance a long terme des etancheites composites, particulierement dans le cas ou la temperature peut exceder 35°C. Mots-cles : fuites, etancheites composites, geosynthetique bentonique, geomembrane, site d'enfouissement, dechets solides municipaux, lagons., Introduction Composite liners are comprised of a geomembrane (GM) over a clay liner. Typically the clay liner (CL) will be either a compacted clay liner (CCL) or a geosynthetic clay [...]

The diffusive properties of two coextruded geomembranes, one with a polyamide inner core and the other with an ethylene vinyl-alcohol (EVOH) inner core, and a standard 0.53-mm (20-mil) linear low-density polyethylene (LLDPE) geomembrane were examined. Diffusion and sorption laboratory tests were performed to estimate the parameters controlling diffusive migration, including the partitioning, diffusion, and permeation coefficients of the geomembrane in both the aqueous and vapor phases. Results indicate a significant reduction in mass flux through the coextruded geomembranes compared to conventional LLDPE. The EVOH coextruded geomembrane had the lowest permeation coefficients ([P.sub.g]) with a range of (2-6) x [10.sup.-12] [m.sup.2] [s.sup.- 1] for diffusion from the aqueous phase. These values for EVOH are upper bounds and the actual values may be lower than as stated. The polyamide (nylon) coextruded geomembrane had higher values than for EVOH, with a [P.sub.g] range of (0.7-2.2) x [10.sup.-11] [m.sup.2] [s.sup.-1] from the aqueous phase. The highest permeation coefficients were for the standard 20-mil LLDPE, which ranged from (0.6-1.1) x [10.sup.-10] [m.sup.2] [s.sup.-1]. Thus the permeation coefficient for LLDPE was about one order of magnitude greater than for the nylon coextruded and at least two orders of magnitudes higher than for the EVOH coextruded geomembrane. Both coextruded geomembranes showed decreased [P.sub.g] values and therefore improved diffusive resistance to volatile organic compounds over traditional 0.56-mm PVC geomembranes. The EVOH geomembrane showed a 5-12-fold decrease in [P.sub.g] in comparison to a 2.0-mm high density polyethylene geomembrane. DOI: 10.1061/(ASCE)GT.1943-5606.0000345 CE Database subject headings: Geomembranes; Diffusion; Permeability; Organic compounds; Barriers. Author keywords: Geomembranes; Diffusion; Permeability; Volatile organic chemicals; Barriers.

In 1993, over 100 years after the completion of the original St. Clair Tunnel and its approach cuts, work commenced on the new St. Clair Tunnel. The new tunnel used the existing approaches, but required additional excavation to widen and deepen the original cuts. In Sarnia, the new work initiated unusual deep-seated deformations on the south slope of the approach. Effective stress finite element analysis (FEA), using an elliptical cap soil model coupled with Biot consolidation theory, was used to model the 1993 construction, but initial predictions were unable to capture the trend of deformations noted in the field. Naturally occurring gases are frequently encountered near the base of the overburden in the Sarnia area and this phenomenon was observed during drilling investigations in the Sarnia approach cut. Including the effects of the presence of exsolved natural gases in fine-grained soils subjected to unloading in the FEA results in substantially better predictions in the trend of deformations on the slopes of the approach cut. Key words: natural gases, excavation, slope deformation, St. Clair clay plain, finite element analysis. En 1993, plus de 100 ans apres la fin du tunnel original de St. Clair el ses coupes d'approche, le travail a debute stir le nouveau tunnel de St. Clair. Le nouveau tunnel a employe les approches existantes mais a exige l'excavalion additionnelle pour elargir et approfondir les coupes d'original. A Sarnia, le nouveau travail a lance des deformations peu communes situees en profondeur sur la pente du sud de l'approche. L'analyse par elements finis (<< FEA >>) en contrainte effective utilisant un modele elliptique de sol couple a la theorie de consolidation de Biot est employee pour modeliser la construction de 1993 mais les previsions initiales ne peu vent pas prendre en compte la tendance des deformations observers sur le chantier. Des gaz naturels sont frequemment produits pres de la base des terrains de recouvrement dans la region de Sarnia et ce phenomene a ete observe pendant les investigations par forage dans la coupe d'approche de Sarnia. L'inclusion des effets de la presence des gaz naturels ex-resolus dans les sols granuleux fins soumis au dechargement dans le FEA a donne des previsions sensiblement meilleures de la tendance des deformations sur les pentes de la coupe d'approche. Mots-cles : gaz naturels, excavation, deformations de la pente, plaine d'argile de St. Clair, analyse par elements finis., Introduction The St. Clair Tunnel project consists of two railway tunnels, approximately 1800 m in length running parallel to each other beneath the St. Clair River from Sarnia, Ontario, Canada, [...]

A method to control the increase in landfill liner temperature due to the heat generated by the waste is examined. The design involves installation of an array of cooling pipes beneath the waste. The feasibility of this system for cooling the liner was examined by performing a series of analyses for conditions based on the Tokyo Port Landfill. The results suggest that the introduction of a cooling system can substantially reduce liner temperature and consequently significantly increase the service life of a high- density polyethylene (HDPE) geomembrane liner in an engineered barrier system. The effects of pipe layout, pipe spacing, and coolant flow rate are examined. It is shown that a periodic pipe layout is the most efficient. Liner temperature decreases with increased coolant transfer flow rate DOI: 10.1061/(ASCE)EE.1943-7870.0000212 CE Database subject headings: Landfills; Liners; Service life; Temperature effects; Cooling; Japan. Author keywords: Landfills; Liners; Service life; Temperature effects; Cooling.

Accelerated aging tests to evaluate the depletion of antioxidants from a high density polyethylene geomembrane are described. The effects of temperature, high pressure, and continuous leachate circulation on the aging of geomembranes in composite liner systems are examined. The antioxidant depletion rates (0.05, 0.19, and 0.41 [month.sup.-1] at 55, 70, and 85[degrees]C, respectively) obtained for the simulated landfill liner at 250 kPa vertical pressure are consistently lower than that obtained from traditional leachate immersion tests on the same geomembrane (0.12, 0.39, and 1.1 [month.sup.-1] at 55, 70, and 85[degrees]C). This difference leads to a substantial increase in antioxidant depletion times at a typical landfill liner temperature (35[degrees]C) with 40 years predicted based on the data from the landfill liner simulators tests, compared to 15 years predicted for the same geomembrane based on leachate immersion tests. In these tests, the crystallinity and tensile yield strain of the geomembrane increased in the early stages of aging and then remained relatively constant over the testing period. There was no significant change in other geomembrane properties within the testing period. DOI: 10.1061/(ASCE)GT.1943-5606.0000302 CE Database subject headings: Durability; Geomembranes; Landfills; Liners; Service life; Temperature; Solid wastes; Oxidation. Author keywords: Durability; Geomembranes; Landfills; Liners; Service life; Temperature; HDPE; Municipal solid waste.

Experimental results from physical testing are reported to examine the thickness and hydraulic performance of three geosynthetic clay liners (GCLs) overlying a geonet when subjected to vertical stresses (e.g., as may be found in a secondary leachate collection layer or hydraulic control layer in solid waste landfills). The GCL was found to intrude into the underlying geonet and the effects of GCL type and water content, temperature, applied pressure, and test duration on the final GCL thickness are examined. The results are consistent with GCL deformation from the beneficial consolidation of bentonite as opposed to lateral extrusion of bentonite. Results from fixed ring flow tests suggest that the indentations in the GCL caused by intrusion into the underlying geonet do not appear to negatively impact the hydraulic performance (permittivity or resistance to internal erosion) of the particular GCLs tested for the conditions examined. The flow capacity of the geonet in these tests was found to depend not only on the amount of GCL intrusion but also on the orientation of the geonet relative to the flow direction. DOI: 10.1061/(ASCE)GT.1943-5606.0000247 CE Database subject headings: Clay liners; Linings; Landfills; Geosynthetics. Author keywords: Geosynthetic clay liners; Lining, landfills.

The results of an accelerated aging test program to evaluate the effect of thickness on the depletion of antioxidants from high-density polyethylene (HDPE) geomembranes and subsequent degradation of the physical properties are reported. Three commercially available HDPE geomembranes having nominal thicknesses of 1.5, 2.0, and 2.5 mm were examined. The geomembranes were immersed in a synthetic leachate at 85, 70, 55, and 22[degrees]C and tested for oxidative induction time, crystallinity, melt index (MI), tensile properties, and stress-crack resistance. The antioxidant depletion rate for the 1.5 mm geomembrane was faster than for the 2.0 and 2.5 mm geomembranes. Antioxidant depletion time was predicted at representative landfill temperatures of 20-60[degrees]C using Arrhenius modeling and was found to increase with geomembrane thickness for the three geomembranes examined. Based on the results of crystallinity, MI, and stress-crack resistance, the degradation of the geomembrane was slowest for the thickest geomembrane. These results suggest that a thicker geomembrane may have a longer service life (other things being equal). DOI: 10.1061/(ASCE)GT.1943-5606.0000207 CE Database subject headings: Geomembranes; Aging; Landfill; Polyethylene; Oxidation. Author keywords: Geomembrane; Aging; Antioxidant depletion; HDPE; Landfill.

Epithelial-mesenchymal transition (EMT) is required for mesodermal differentiation during development. The zinc-finger transcription factor, Snail1, can trigger EMT and is sufficient to transcriptionally reprogram epithelial cells toward a mesenchymal phenotype during neoplasia and fibrosis. Whether Snail1 also regulates the behavior of terminally differentiated mesenchymal cells remains unexplored. Using a Snail conditional knockout model, we now identify Snail1 as a regulator of normal mesenchymal cell function. Snail1 expression in normal fibroblasts can be induced by agonists known to promote proliferation and invasion in vivo. When challenged within a tissue-like, three-dimensional extracellular matrix, Snail1-deficient fibroblasts exhibit global alterations in gene expression, which include defects in membrane type-1 matrix metalloproteinase (MT1-MMP)-dependent invasive activity. Snail1-deficient fibroblasts explanted atop the live chick chorioallantoic membrane lack tissue-invasive potential and fail to induce angiogenesis. These findings establish key functions for the EMT regulator Snail1 after terminal differentiation of mesenchymal cells.

Abstract: A two-dimensional fluid flow and reactive transport model, BioClog, created to predict clogging in landfill leachate collection systems is used to calculate the clogging of gravel and treatment of [...]

A 2D model for predicting clogging of a landfill leachate collection system and subsequent leachate surface position (mounding) is described. A transient finite element fluid flow model is combined with a reactive, multiple-species finite element transport model. The transport model considers biological growth and biodegradation, precipitation, and particle attachment and detachment. It uses a geometrical relationship to establish porosity from the computed thickness of the accumulated clog matter and a relationship between the porosity and hydraulic conductivity of elements in the system. The model represents the flow path within the drainage layer in profile. An iterative method is used to solve for the new hydraulic heads, surface and internal nodal positions, and redistributed clog properties (clog quantity, porosity, hydraulic conductivity) for each element and for each time step. The porosity (and consequently hydraulic conductivity) of the media can therefore change spatially and temporally. The mesh is regenerated automatically each time step (including the addition or subtraction of nodes) taking into account allowable element aspect ratios, the interfaces between differing hydrostratigraphic layers, and static point sources and openings. An integrated alternate solution for very thin mounds is included. The application of the model is demonstrated using a hypothetical field case. Key words: clogging, landfills, leachate collection systems, modelling, biofilms, mineral precipitation. On decrit un modele a deux dimensions pour predire le colmatage de systemes de collecte du lixiviat d'un enfouissement sanitaire et la position subsequente du lixiviat en surface (formation de monticules). On a combine un ecoulement de fluide transitoire en elements finis avec un modele reactif de transport de multiples especes en elements finis. Le modele de transport prend en consideration la croissance biologique et la biodegradation, la precipitation, et l'attachement et le detachement des particules. Il utilise une relation geometrique pour etablir la porosite en partant de l'epaisseur calculee de la matiere colmatee accumulee, et une relation entre la porosite et la conductivite hydraulique des elements du systeme. Le modele represente le cheminement de l'ecoulement a l'interieur de la couche de drainage dans le profil. On utilise une methode d'iteration pour resoudre pour les nouvelles charges hydrauliques, surface et positions nodales internes, et les proprietes de colmatage redistribuees (quantite de colmatage, porosite, conductivite hydraulique) pour chaque element, et chaque etape dans le temps. La porosite (et consequemment la conductivite hydraulique) des media peut en consequence changer dans l'espace et dans le temps. Le grillage est regenere automatiquement a chaque etape dans le temps (incluant l'addition la ou la soustraction de noeuds) prenant en compte les rapports d'elements d'aspect admissibles, les interfaces entre differentes couches hydrostratigraphiques, et le point statique des sources et des ouvertures. On inclut une solution integree alternee pour chacun des monticules tres minces. On demontre l'application du modele au moyen d'un cas hypothetique sur le terrain. Mots-cles : colmatage, sites d'enfouissements, systemes de collecte de lixiviat, modelisation, biofilms, precipitation minerale. [Traduit par la Redaction], Introduction The leakage through landfill barrier systems has received considerable interest with most of the focus having been on the performance of the composite liner (Rowe and Brachman 2004; Rowe [...]

Abstract: The results of an experimental investigation into the clogging of unsaturated, uniformly graded 50 mm gravel permeated with municipal solid waste landfill leachate are reported. The flow of leachate [...]

Laboratory-accelerated aging experiments conducted to examine the depletion of antioxidant from a geomembrane (GM) underlain by a geosynthetic clay liner (GCL) are described. Three different 'protection' layers between the GM and overlying gravel and leachate are examined: (1) A traditional nonwoven geotextile (GT); (2) a GT-GCL; and (3) a GT-sand-GT layer. The GT-GCL protection layer gives an antioxidant depletion rate 0.59 to 0.66 times slower than the GT layer alone. The GT-sand-GT layer gives depletion rates 0.72-0.75 times that of the conventional GT alone. Based on Arrhenius modeling, the time required for depletion of antioxidants at 35[degrees]C is estimated to be 65 years for a GM with a GT-GCL protection layer, 50 years for a GT-sand-GT layer, and 40 years for a conventional GT protection layer. These times are all significantly greater than the depletion time for GM immersed in leachate (10 years) for the geomembrane tested. CE Database subject headings: Durability; Geomembranes; Landfills; Liners; Service life; Temperature.

Abstract: A numerical model called BioClog is used to backcalculate biological activity rate constants using measured values of water quality and clog chemical characteristics from well-controlled laboratory column experiments that [...]

The results of two series of accelerated aging tests are reported. Both series of tests were conducted at temperatures of 85, 70, 55, and 26[degrees]C over a period of about 3 years. In the simulated liner series, the top of the geomembrane was covered with a geotextile (protection) layer that was exposed to simulated municipal solid waste (MSW) landfill leachate while the bottom of the geomembrane was in contact with a hydrated geosynthetic clay liner. In the immersion series, the geomembrane was immersed in the simulated MSW leachate, and hence, both sides were exposed to leachate. The results from oxidative induction time tests indicate that the antioxidant depletion is about 2.2-4.8 times faster for the leachate immersed geomembrane than for geomembrane in a composite liner. The higher rates are attributed to the higher extraction of antioxidants from two sides of the geomembrane immersed in leachate. The measured antioxidant depletion rates are extrapolated to a range of temperatures (0-60[degrees]C) using Arrhenius modeling. At a liner temperature of 35[degrees]C, the calculated time for the depletion of antioxidants is about 40 years for a geomembrane in a composite liner compared to 10 years if it is simply immersed in leachate. These tests suggest that to obtain realistic estimates of geomembrane service life one needs data from tests that simulate the expected field conditions and that prediction based on immersion tests may underestimate the service life. DOI: 10.1061/(ASCE)1090-0241(2008)134:1(68) CE Database subject headings: Geomembranes; Durability; Liners; Landfills; Service life; Temperature; Composite materials.

A variety of tissue lineages can be differentiated from pluripotent stem cells by mimicking embryonic development through stepwise exposure to morphogens, or by conversion of one differentiated cell type into another by enforced expression of master transcription factors. Here, to yield functional human haematopoietic stem cells, we perform morphogen-directed differentiation of human pluripotent stem cells into haemogenic endothelium followed by screening of 26 candidate haematopoietic stem-cell-specifying transcription factors for their capacity to promote multi-lineage haematopoietic engraftment in mouse hosts. We recover seven transcription factors (ERG, HOXA5, HOXA9, HOXA10, LCOR, RUNX1 and SPI1) that are sufficient to convert haemogenic endothelium into haematopoietic stem and progenitor cells that engraft myeloid, B and T cells in primary and secondary mouse recipients. Our combined approach of morphogen-driven differentiation and transcription-factor-mediated cell fate conversion produces haematopoietic stem and progenitor cells from pluripotent stem cells and holds promise for modelling haematopoietic disease in humanized mice and for therapeutic strategies in genetic blood disorders., Author(s): Ryohichi Sugimura [1, 2, 3, 4]; Deepak Kumar Jha [1, 2, 3, 4]; Areum Han [1, 2]; Clara Soria-Valles [1, 2, 3, 4]; Edroaldo Lummertz da Rocha [1, 2, [...]

Abstract: A combination of data from laboratory tests and modelling is reported for both coarse gravel (19-38 mm) and two types of tire shred permeated with municipal solid waste leachate. [...]