Geosynthetics In Waste Containment Facilities: Recent Advances

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Geosynthetics - 7 th ICG - Delmas, Gourc & Girard (eds) 2002 Swets & Zeitlinger, Lisse ISBN 90 5809 523 1Geosynthetics in waste containment facilities: recent advancesA. BOUAZZA, Monash University, Melbourne, Victoria, AustraliaJ. G. ZORNBERG, University of Colorado, Boulder, Colorado, USAD. ADAM, Technical University of Vienna, Vienna, AustriaBouazza, A., Zornberg, J.G., and Adam, D. (2002). “Geosynthetics in Waste Containment Facilities: RecentAdvances.” State-of-the-Art keynote paper, Proceedings of the Seventh International Conference onGeosynthetics, Nice, France, September 22-27, A.A. Balkema, Vol. 2, pp. 445-510.ABSTRACT: Geosynthetics are widely used in waste containment facilities, as these facilities have used literally all types ofgeosynthetics in all identified functions (e.g., filtration, reinforcement, etc.). The inclusion of geosynthetic components is likely toexpand as manufacturers develop new and improved materials and as engineers/designers develop new analysis routines for newapplications. This paper focuses on specific advances involving the use of geosynthetics in the different components of wastecontainment facilities. In particular, this paper addresses recent advances involving the use of geosynthetics in bottom liner systems(e.g. geosynthetic clay liners, service life of geomembranes), cover systems (e.g. reinforced cover systems, exposed geomembranecovers), side slope lining systems (e.g., interface stability, steep sided walls), liquid collection systems (e.g., determination of themaximum liquid thickness, design of double slope layers), cut-off wall systems (e.g. interlocks and geomembrane performance) andremediation work (e.g. prefabricated vertical drains for methane extraction and soil flushing). Recent case histories are also providedto document the implementation of these advances in engineering practice.1 INTRODUCTIONThe protection of groundwater and surface water is now a majorconsideration in the design of waste containment facilities inmany countries. Geosynthetics play an important role in thisprotective task because of their versatility, cost-effectiveness,ease of installation, and good chracterization of their mechanicaland hydraulic properties. Furthermore they can offer a technicaladvantage in relation to traditional liner systems or othercontainment systems. The use of geomembranes as the primarywater proofing element at the Contrada Sabetta Dam, Italy(Cazzuffi 1987) and to keep an upstream clay seepage controlliner from dessicating in the Mission Dam (today TerzaghiDam), Canada (Terzaghi & Lacroix 1964)) in the late 1950’srepresent applications that have been the precursors of today’susage of geosynthetics in containment systems. Bothapplications predated the use of conventional geosynthetics bysome 20 years. Geosynthetics systems are nowadays an acceptedand well established component of the landfill industry (since atleast early 1980’s). Containment systems for landfills typicallyinclude both geosynthetics and earthen material components,(e.g., compacted clays for liners, granular media for drainagelayers, and various soils for protective and vegetative layers).The objective of this paper is to provide a review of recentadvances on the use of geosynthetics in waste containmentfacilities. Emphasis is on the advances that have taken place inthe period 1998-2002 (i.e. since the Sixth InternationalConference on Geosynthetics). The state of the art on the use ofgeosynthetics in waste containment facilities previous to thisperiod has been documented by various important sources,which have set the path for the growth of geosynthetics in thisfield (e.g. Giroud & Cazzuffi 1989; Koerner 1990; Cancelli &Cazzuffi 1994; Gourc 1994; Rowe et al. 1995; Bonaparte 1995;Gartung 1996; Daniel & Bowders 1996; Manassero et al. 1996,1998; Rowe 1998). This paper also builds on more recentreviews on the use of geosynthetics in waste containmentfacilities (e.g. Zornberg & Christopher 1999; Manassero et al.2000; Rowe 2001). The reader is referred to these sources forfurther information on factors influencing the selection ofdifferent types of geosynthetics and factors to be considered inconstruction.Focus of this paper is not on recent advances in geosyntheticmaterials, but on specific advances involving the use of thesematerials in the different components of waste containmentfacilities. Accordingly, following an overview of landfillfacilities and their regulations, this paper addresses recentadvances in bottom liner systems (e.g. hydraulic conductivityand chemical compatibility of GCLs, service life ofgeomembranes), cover systems (e.g. reinforced cover systems,exposed geomembrane covers, gas migration), side slope liningsystems (e.g., interface and internal stability through GCLs,steep sided walls), liquid collection systems (e.g., determinationof the maximum liquid thickness, design of double slope layers),cut-off wall systems (e.g. interlocks and geomembraneperformance) and soil and groundwater remediation (e.g. soilvapour/gas extraction and soil flushing systems enhanced withprefabricated vertical drains; geotextiles for permeable reactivebarriers). Recent case histories are also provided to document theimplementation of recent advances in engineering practice.445

2 LANDFILLS: AN OVERVIEW2.1 Historical perspectiveAccording to the Concise Oxford Dictionary, a landfill is definedas follows:Landfill, n.1- Waste material etc. used to landscape or reclaimareas of ground.2- The process of disposing of rubbish in this way.3- An area filled in by this process.The third definition is the operable one used for the purposesof this paper. Landfills, in various forms, have been used formany years. The first recorded regulations to control municipalwaste were implemented during the Minoan civilization, whichflourished in Crete (Greece) from 3000 to 1000 B.C.E. Solidwastes from the capital, Knossos, were placed in large pits andcovered with layers of earth at intervals (Tammemagi 1999).This basic method of landfilling has remained relativelyunchanged right up to the present day. Landfill design evolved asa series of responses to problems. Only when a problem wasidentified or reached a sufficient level of concern were correctivesteps taken. These improvements were invariably driven byregulatory requirements. In Athens (Greece), by 500 B.C.E. itwas required that garbage be disposed of at least 1.5 kilometresfrom the city walls. Each household was responsible forcollecting its own waste and taking it to the disposal site. Thefirst garbage collection service was established in the RomanEmpire. People tossed their garbage into the streets, and it wasshovelled into a horse drawn wagon by appointed garbagemanwho then took the garbage to an open pit, often centrally locatedin the community. The semi-organised system of garbagecollection lasted only as long as the Roman Empire. Asindustrialisation of nations occurred, many containment facilitieswere constructed to retain various types of raw materials and/orwaste products. Most of these containment facilities were notdesigned and almost none were lined to prevent leakage ofwastes into the surrounding environment. Until the late 1970sthere was little engineering input into landfilling practice andlittle consideration given to the impact of landfilled wastes onland and groundwater. By the end of the 1970’s, the problems inmanaging landfill sites had arisen from the contamination of soiland groundwater (with, for example, heavy metals, arsenic,pesticides, halogenated organic compounds and solvents) and thepotential risks to exposed populations. From the 1970’s throughthe 1990s landfill design philosophy moved towards theobjective of containment and isolation of wastes. This hasresulted in a major upsurge in the development of engineeredwaste disposal systems, which included extensive use ofgeosynthetics. In the United States and Europe, the evolution ofmunicipal landfill design philosophy since the 1970’s has beenrelatively simple and has involved three significant phasesthrough the 1990s and is entering a fourth phase as we enter the21st century. These phases of municipal landfill development aresummarized in Table 1. In Australia this evolutionary processhas followed the same steps with the exception that thedevelopment of policy, regulation and guidance for landfilldesign was given more attention only in the mid-1990s (Bouazza& Parker 1997). The focus in this decade is anticipated to be onmechanical and biological waste treatment, either in ground orprior to deposition, including increased use of leachaterecirculation and bioreactor technology, as owners, regulators,and engineers become more familiar with these concepts andtheir benefits with respect to decreasing long term costs andliabilities. While waste reduction and reuse efforts may diminishthe per capita quantity of waste generated in industrializednations, there is no doubt that landfills will remain an importantmethod of waste disposal for the foreseeable future due to theirsimplicity and cost-effectiveness. In this respect, geosyntheticswill certainly continue to play a key role in landfill design,construction and operation. In less developed countries, thisevolutionary process is taking place at a much slower pace sincetheir priorities are on providing housing, education and health totheir population.Table 1. Summary of municipal landfill evolution (modified from Bouazza & Kavazanjian tary landfillsHealth/nuisance, i.e odour, Daily cover, better compaction, engineered approach tofires, littercontainmentLate 1980s-early Engineeredlandfills, Ground and groundwater Engineered liners, covers, leachate and gas collection systems,1990srecyclingcontaminationincreasing regulation, financial assuranceLate 1980’s, 1990s Improved siting and Stability, gas migrationIncorporation of technical, socio-political factors into sitingcontainment,wasteprocess, development of new lining materials, new coverdiversion and re-useconcepts, increased post-closure use2000sImprovedwaste ?Increasing emphasis on mechanical and biological waste pretreatmenttreatment, leachate recirculation and bioreactors, “smart landfills”2.2 Landfill componentsThere are various design philosophies and landfill managementapproaches in use today (Rowe et al. 1995). One (passive) is toprovide a cover system as impermeable as possible and as soonas possible after the landfill has ceased operating, so as tominimize the generation of leachate (waste liquid). Thisapproach has the benefits of minimizing both the amount ofleachate that must be collected and treated, and the mounding ofleachate within the landfill. It also has the disadvantage ofextending the contaminating lifespan. With low infiltration, itmay take decades to centuries before the field capacity of thewaste is reached and full leachate generation to occur. Analternative philosophy (active) is to allow as much infiltration aswould practically occur. This would bring quickly the landfill tofield capacity and allow the removal of a large proportion ofcontaminants (by the leachate collection system) during theperiod when the leachate collection system is most effective andis being carefully monitored (e.g. during landfill constructionand, say, 30 years after closure). The disadvantages of thisapproach are two-fold: Firstly, larger volumes of leachate mustbe treated; this has economic consequences for the operator.Secondly, if the leachate collection system fails, a highinfiltration will result in significant leachate mounding.Geosynthetics play an important role in either case andcontribute, in both design approaches, to minimize contaminantmigration into the surrounding environment to levels that willresult in negligible impact.The liner components of confinement systems used inmodern waste disposal facilities are illustrated in Figure 1.Geosynthetics and related products have found wide applicationin the design and construction of these facilities and also inremediation projects as will be discussed later in the paper. Thisapplication has been triggered by the economical and technicaladvantages that geosynthetics can offer in relation to moretraditional materials.Referring to the three liner components (i.e. bottom, side andcover liners) of a containment system as shown in Figure 1, it ispossible to summarize their main functions as follows (see alsoManassero et al. 2000):446

BOTTOM LINERSIDE LINERMINERAL COMPONENTSPOLYMERIC COMPONENTSFilter-transition layersFilter-transition layersDrainage layersDrainage layersProtection layersDrainage pipesBarrier layersProtection layersAttenuation layer(Geological barrier)Barrier layersCOVER SYSTEMMINERAL COMPONENTSPOLYMERIC COMPONENTSMINERAL COMPONENTSPOLYMERIC COMPONENTSFilter-transition layersFilter-transition layersErosion control layer(Top soil, cobbles, vegetation layer)Erosion control layer(Bio-grid, geo-cell)Drainage layersDrainage layersBiotic (animals) barrier(Cobbles)Reinforcement elements(Geogrid, geotextiles)Protection layersDrainage pipesFrost-desiccation control layerBiotic (animals) barrierBarrier layersProtection layersDrainage layerDrainage pipesAttenuation layer(Geological barrier)Barrier layersBarrier layerDrainage layerGas collection layerBarrier layerGas collection layerFigure 1. Liner components of solid waste containment systems (from Manassero et al., 2000).x The bottom liner must reduce as much as possible theadvective and diffusive contaminant migration toward theunderlying vadose zone and/or aquifer. The performance ofthe bottom barriers is fundamentally governed by thefollowing parameters: (1) field hydraulic permittivity anddiffusivity, compatibility, sorption capacity and service life.On the other hand the performance of filters and drainagelayers are governed by the capacity to avoid clogging, whichin turn is influenced by the type of waste and landfillmanagement. Direct field observations have shown thatclogging in the liquid collection and removal system (LCRS)is reduced by increasing the seepage velocity of the leachate(Rowe 1998). Recent advances involving the use ofgeosynthetics in bottom liner systems are discussed inSection 4.x The side slope liner has the same function as the bottomliner. However, its drainage component is less demandingthan for the bottom liner due to the generally high hydraulicgradients along the side slopes. On the other hand, design ofthe side lining may be governed by stability considerationsand by the need of controlling biogas migration into thevadose zone. Recent advances involving the use ofgeosynthetics in side slope liner systems are discussed inSection 5.x The cover system has numerous functions: it must controlwater and gas movement and it should minimize odors,disease vectors and other nuisances. Cover systems are alsoused to meet erosion, aesthetic, and other post-closuredevelopment criteria. In spite of the numerous functions ofcover systems, their design criteria are often less stringentthan those used in the design of the other two linercomponents because they can be easily repaired andmonitoring of their performances is simpler. Accordingly,many advances are expected in the near future regarding thedesign of cover systems. Recent advances involving the useof geosynthetics in cover systems are discussed in Section 7.In addition to the three liner system components,geosynthetics have gained significant use in two additionalcomponents in waste containment systems, namely, the liquidcollection systems and cut-off wall systems:x The liquid collection systems are used for liquid collectionin association with cover liners, for leachate collection layersin association with bottom liners, and as leakage detectionand collection layers in the case of double liners. Gascollection systems have also been designed usinggeosynthetics. Recent advances involving the use ofgeosynthetics in liquid collection systems are presented inSection 6.x Cut-off wall systems are being designed increasinglymaking use of geosynthetics. This is particularly the case forclosure projects of old sites that have been constructedwithout stringent bottom liner systems or for hazardous wastecontainment. The advantages of these systems have beenfully recognized, the trend is to design them as highlyengineered structures where aspects like chemicalcompatibility, diffusion, defects, etc. are taken into account toevaluate their global performance. Recent advances involvingthe use of geosynthetics in cut-off walls are presented inSection 8.Application of existing geosynthetics materials to newapplications, e.g., prefabricated vertical drain remediation,systems is a good indicator of their immense potential inremediation work, this aspect is dicussed in section 9.2.3 Geosynthetics in landfillsThere are numerous types of geosynthetics, which can be used inwaste containment applications and each has a specific function.Functions can include:x Separation: the material is placed between two dissimilarmaterials so that the integrity and functioning of bothmaterials can be maintained or improved,x Reinforcement: the material provides tensile strength inmaterials or systems that lacks sufficient tensile capacity,x Filtration: the material allows flow across its plane whileretaining the fine particles on its upstream side,x Drainage: the material transmits flow within the plane oftheir structure,x Hydraulic/Gas Barrier: the material is relatively imperviousand its sole function is to contain liquids or gasses, and447

x Protection: the material provides a cushion above (or below)geomembranes in order to prevent damage by puncturesduring placement of overlying materials.The individual types of geosynthetics are given in Table 2. Insome cases, a geosynthetic may serve multiple functions (e.g., ageocomposite layer that serves as a drainage means and aprotection layer for an underlying geomembrane).Table 2. Types and functions of various geosynthetics. main function; secondary functionFunctionGeosynthetic typesSeparationDrainageFiltrationReinforcementNon woven geotextileWoven geotextileGeogridsGeomembranesGeocellsGeosynthetic clay linersGeocompositesGeonetGeopipe1 asphalt-saturated geotextiles Landfills employ geosynthetics to varying degrees depending onthe designer and the applicable regulatory requirements. In thisrespect Geogrids can be used to reinforce slopes beneath thewaste as well as for veneer reinforcement of the cover soilsabove geomembranes (Zornberg et al. 2001). A growing areafor geosynthetic reinforcement materials is in vertical andhorizontal expansions of landfills (Stulgis et al. 1995). Here thegeogrids or high strength geotextiles are used as support systemsfor geomembranes placed above them in resisting differentialsettlement of the underlying waste. Reinforcing is also used inliner sections located above potential subsidence zones (Gabr etal. 1994). Geonets are unitized sets of parallel ribs positioned inlayers such that liquid can be transmitted within their openspaces. Their primary function is in-plane drainage. There arebasically two designs on the market, biplanar and tri-planargeonets. The tri-planar geonets are a more recent development,which resist vertical compression under load and allow larger inplane flows (Banks & Zhao 1997). Because of their openstructure, geonets must be protected from becoming clogged bysoil or adjacent material. In all cases, geonets are used withgeotextiles or geomembranes on one or both of their planarsurfaces. Geomembranes are relatively impermeable sheets ofpolymeric formulations used as a barrier to liquids and/orvapors. The most common types of geomembranes are highdensity polyethylene (HDPE), very flexible polyethylene(VFPE), polyvinyl chloride (PVC), and reinforcedchlorosulfonated polyethylene (CSPE-R), although there areother types available (Koerner 1991). Polypropylene (PP) is anexam

to document the implementation of these advances in engineering practice. Bouazza, A., Zornberg, J.G., and Adam, D. (2002). Geosynthetics in Waste Containment Facilities: Recent Advances. State-of-the-Art keynote paper, Proceedings of

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