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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.

Experimental data is presented for leakage through slits, square, and rectangular geomembrane defects overlain by silty sand tailings and underlain by a well-graded gravel. The rectangular GMB defects have a range of widths, B , lengths, L , and aspect ratios (L / B), and ratios of defect length to thickness of tailings above the geomembrane (L / T). A blade cut slit (or simulated stress crack) widens to an extent dependant on the subgrade and stress level. For L= 100 mm, increasing B (0.15 < B / L ≤ 1) from 1.6 (slit) to 100 mm (square), decreases the leakage from about twice to essentially the same as that for a circular hole of equal area. The ratio (h 1 / H) of head loss within the hole, h 1 , relative to the total head loss, H , is independent of loading conditions and constant for any particular hole shape (B / L), area (B ∙ L), and relative depth (L / T). A semi-empirical general solution is developed for a rectangle within the range of 0 ≤ B / L ≤ 1 with the solution converging to that for a strip for B / L → 0 and to a circle for B / L → 1. The solution gives calculated leakage in encouraging agreement with the experimental data. • Investigates the factors affecting leakage through a rectangular hole in a geomembrane overlain by tailings. • Studies how hole geometry affects leakage. • Provides a semi-empirical general solution for predicting leakage through quasi circular, rectangular, and strip (L » B) holes. • Investigates the physical and hydraulic response of a blade cut slit with flat and uneven ground conditions. [ABSTRACT FROM AUTHOR]

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. [...]

Ten flow cells, called mesocosms, are used to investigate the effect of different gravel sizes (38 and 19 mm) and operating conditions on clogging of leachate collection systems. These mesocosms simulated in real time and real scale the two-dimensional leachate flow conditions representative of a section of a continuous 300-mm-thick gravel drainage blanket adjacent to a leachate collection pipe in a primary leachate collection system. The tests were terminated after 6-12 years of operation. In some mesocosms the full 300 mm of gravel was saturated. In others, the leachate level was initially set at 100 mm and the upper 200 mm were unsaturated. Although the flow through all mesocosms was similar, the clogging in the fully saturated gravel was substantially more than in the partially saturated gravel. After 6 years of operation, typically, less than 10% of the initial pore space was filled with clog material in the unsaturated gravel. For the saturated zone, 45% of the initial pore space was filled with clog material in the fully saturated design as compared to only 31% in the partially saturated design. The 38 mm gravel performed much better than the 19 mm gravel. For example, it maintained a hydraulic conductivity that was higher than the 19 mm gravel even after operating for twice as long. Up to four mesocosms were placed in series, with the effluent from one mesocosm being the influent for another. The reduction in mass loading within the first mesocosm reduced the amount of clogging within the mesocosm later in series. There was a clear progression of decreasing amounts of initial pore space filled with clog material in the last mesocosm in series, and most of the clogging was due to the vertically percolating leachate. CE Database subject headings: Municipal wastes; Landfills; Hydraulic conductivity; Service life; Biofilm; Calcium carbonate; Drainage; Clogging.

Needle-punched geosynthetic clay liner (GCL) specimens subjected to 0, 5, and 12 freeze-thaw cycles in the laboratory, and GCL specimens recovered from a composite barrier wall in the Canadian Arctic after 1 and 3 years were examined to assess the hydraulic conductivity/permeability with respect to both deionized deaired water and Jet A-1. The GCL specimens recovered from the field after 3 years had a hydraulic conductivity with respect to water that was approximately 30% less than that of the GCL specimens subjected to 12 initial freeze-thaw cycles in the laboratory, suggesting that the laboratory conditions are more severe than field conditions. The combined effects of both the freeze-thaw cycles and Jet A-1 permeation increased the permeability. This increase is attributed to the creation of macropores in the GCL due to freezing and to an expansion of free-pore space due to contraction of the double layer caused by permeation of Jet A-1. Although there was an increase in permeability due to the combined effect of freeze-thaw and permeation by Jet A-1, the effect was relatively small and the results suggest that the GCL continued to exhibit good performance as a hydraulic barrier when subject to extreme climatic conditions and hydrocarbons both in the laboratory and in the field. DOI: 10.1061/(ASCE)1090-0241(2006)132:12(1526) CE Database subject headings: Geosynthetics: Hydraulic conductivity; Freeze-thaw; Permeability: Pore water: Bentonite: Hydrocarbons.

Abstract: This paper reports the results obtained after 6 years operation of nine mesocosm experiments that simulate the 50 cm of the drainage layer closest to the leachate collection pipe [...]

The diffusion and sorption characteristics of a geosynthetic clay liner (GCL) are examined for a group of volatile aromatic hydrocarbons: benzene, toluene, ethylbenzene, m&p-xylene, and o-xylene (BTEX) at two different temperatures. It is shown that geotextile component of a GCL contributes to the sorption of hydrocarbons by the GCL. While the partitioning coefficients of the BTEX compounds have the order m&p-xylene [approximately equal to] ethylbenzene>o-xylene>toluene>benzene, the diffusion coefficients have the order benzene>toluene>ethylbenzene>m&p-xylene [approximately equal to] o-xylene. The reduction in diffusion and sorption coefficients with decreasing temperature have opposite effects in terms of the rate of contaminant movement through a GCL. However, it is shown that the decrease in transport due to a reduced diffusion coefficient dominates and mass transport is reduced at lower temperature. DOI: 10.1061/(ASCE) 1090-0241 (2005) 131:10(1211) CE Database subject headings: Geosynthetics; Hydrocarbons; Diffusion; Sorption; Temperature; Clay liners; Benzene.

Geosynthetic materials such as geomembranes and geosynthetic clay liners (GCLs) are frequently used in composite liners for municipal solid waste landfills. Heat generated within such facilities due to decomposition of organic material within the waste creates thermal gradients that have the potential to cause desiccation of the mineral component of GCLs, with potential impacts on long-term performance. This paper presents the results of an experimental investigation into the potential for moisture redistribution in and around GCLs forming part of a composite liner system when subjected to thermal gradients. Large-scale laboratory testing was performed using two different subsoils and GCL materials, with emphasis placed on the spatial and temporal variation of temperature and water content within and beneath the GCLs. The influence of key initial and boundary conditions such as the applied temperature gradient, initial GCL and subsoil water content, and the type of GCL is discussed, as well as the implications of the findings for long-term GCL performance. Recommendations are made regarding aspects of the design and operation of landfill facilities likely to reduce the potential for desiccation. CE Database subject headings: Clay liners; Geosynthetics; Desiccation; Thermal gradient; Landfills; Laboratory tests.

The clogging of tire shreds and gravel is based on four column tests permeated with landfill leachate for up to 2 years. Two different types of tire shred (G shred: 100 mm x 50 mm x 10 mm; and P shred: 125 mm x 40 mm x 10 mm with many exposed wires) and a uniformly graded 38 mm gravel were examined. The compressibility of the G and P shreds at 150 kPa were reported to be 48 and 44%, respectively while the initial hydraulic conductivities were 0.007 and 0.02 m/s, respectively (compared to 0.8 m/s for the gravel). The gravel maintained a hydraulic conductivity greater than [10.sup.-5] m/s for about three times longer than a similar thickness of compressed (at 150 kPa) tire shreds. The tests were conducted at an accelerated flow rate of 0.4 [m.sup.3]/[m.sup.2]/day. At termination of the rubber shred columns after about 1 year the hydraulic conductivity at the influent end of the columns had dropped to between [10.sup.-7] and [10.sup.-8] m/s. At termination of the gravel columns after 2 years the corresponding range was [10.sup.-6]-[10.sup.-7] m/s. The clog was predominantly calcium carbonate, with calcium making up 29-34% of the total clog material. Aluminum, zinc, iron, and copper leached from the P and G shreds when exposed to typical municipal solid waste leachate, however they were not detected in the effluent leachate. The highest concentration of metals was found in the P-shred clog and this is attributed to the greater abundance of exposed steel in these shreds. It is inferred that gravel should continue to be used in critical zones where there is a high mass loading. The results suggest that an increased thickness of compressed tire shred may be used to give a service life similar to that of a given thickness of gravel in noncritical zones. CE Database subject headings: Tires; Municipal wastes; Landfills; Leachates; Clogging; Hydraulic conductivity; Gravel.

The relative improvement of the diffusive barrier function of high density polyethylene (HDPE) geomembranes to volatile organic compounds (VOCs) when subjected to surface fluorination is experimentally examined. The surface fluorination consisted of applying elemental fluorine, which exchanged with hydrogen along polymer chains at the surface of a polyolefin substrate. Sorption and diffusion tests were performed on both traditional 'untreated' and 'fluorinated' 1.5 mm HDPE geomembranes using dilute aqueous organic contaminants commonly found in municipal solid waste leachate. The partitioning coefficient is shown to remain essential the same after the surface fluorination; however, the surface fluorination resulted in a reduction in both the diffusion and the permeation coefficients by factors ranging between 1.5 and 4.5, depending on the hydrocarbon examined. Modeling of VOC diffusion through a geomembrane/compacted clay composite liner indicated that contaminant impacts were about 1.7-2.9 times lower when a fluorinated geomembrane is used. To achieve the same level of protection as provided by the fluorinated geomembrane underlain by 0.60 m of compacted clay, one would need an additional 0.4-0.9 m of compacted clay in conjunction with a conventional (untreated) geomembrane. The importance of the thickness of the treated layer is highlighted. CE Database subject headings: Geomembranes; Diffusion; Sorption; Volatile organic chemicals; Fluoridation.

A common failure mode for landfills is clogging of the leachate-collection system. The reduction in hydraulic conductivity associated with clogging causes a buildup of leachate head on the underlying liner, potentially increasing advective contaminant transport from the landfill and contaminating adjacent groundwater. In this paper, the biogeochemical model CCBATCH is used to link a primary cause of leachate collection system failure--CaC[O.sub.3(s) precipitation--to anaerobic degradation of volatile fatty acids (VFAs) in column reactors used to study the clogging phenomena. One key to applying CCBATCH correctly was dividing the VFA conversion into two steps: conversion of propionate to acetate, carbonic acid, and methane; and acetate conversion to methane and carbonic acid. The primary driver for CaC[O.sub.3(s)] precipitation in the columns was acetate fermentation to C[H.sub.4] and [H.sub.2]C[O.sub.3], which increased the total carbonate concentration in the leachate and shifted the acid/base control to a weaker acid system, which caused an increase in solution pH. A second key to proper modeling was adding C[O.sub.2(g)] gas transfer to CCBATCH. The modeling results indicate that the kinetics of C[O.sub.2(g)] gas transfer was a key control over leachate chemistry once acetate fermentation was nearly complete. These results suggest that the best approach for the long-term control of CaC[O.sub.3(s)] clogging may be to enhance C[O.sub.2(g) gas transfer from the leachate while buffeting the leachate pH to near neutral. Taken together, these actions should decrease the yield of CaC[O.sub.3(s)] precipitated per mass of acetate removed. DOI: 10.1061/(ASCE)0733-9372(2003) 129:8(723) CE Database subject headings: Calcium carbonate; Acids; Clogging; Methane; Leachates; Landfills.