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THE THIRTY-SECOND TERZAGHI LECTURE

Presented at the American Society of Civil Engineers

1996 Annual Convention

Robert M. Koerner

JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING / APRIL 2000 / 291

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INTRODUCTION OF ROBERT M. KOERNER

THIRTY-SECOND TERZAGHI LECTURER, 1996, WASHINGTON, D.C.

By Lawrence H. Roth, Fellow, ASCE

In 1936, the same year as the landmark first conference ofthe International Society of Soil Mechanics and FoundationEngineering at Cambridge, Mass., Dr. Karl Terzaghi,Hon.M.ASCE, and his fellow practitioners of the time helpedto establish the Soil Mechanics and Foundation EngineeringDivision of ASCE. In 1960 the division, soon to becomeknown as the Geotechnical Engineering Division, created thislecture series to honor Karl Terzaghi, the father of our profes-sion, by annually recognizing the contributions of one of ourpeers to the profession and to geotechnology. This year, 60years after the establishment of our division, we celebrate thecreation of a new entity, the Geo-Institute of ASCE, and wealso celebrate our thirty-second Terzaghi Lecturer, an individ-ual selected by his peers for one of the highest honors that ageotechnical engineer may achieve.

Members of the Geo-Institute, friends and family of BobKoerner, ladies and gentlemen, it is my honor and pleasure tointroduce our thirty-second Terzaghi Lecturer. In my view, thepreceding thirty-one lecturers have been recognized, andrightly so, for their immense contributions to the advancementof the technology of soil mechanics and foundation engineer-ing, for their contributions to the profession of geotechnicalengineering, and for their recognition of the importance ofgeology and natural processes, such as earthquakes and othergeologic hazards, to our field. Tonight, as will be recorded inthe literature of the Geo-Institute, we recognize a geotechnicalengineer who, like Terzaghi, is a pioneer, an individual whosevision and energy have helped the profession move beyond itsfoundation in earth materials and earth science to embracegeosynthetics as a key element of today’s geotechnology.

Professor Robert M. Koerner is the thirty-second TerzaghiLecturer of the Geo-Institute of ASCE. Like Terzaghi, BobKoerner has made major contributions to the development ofnew applications, of new systems and test methods, and ofnew design procedures, this time for man-made materials incontrast to earth materials. But, as we shall see in the lecture,Terzaghi himself anticipated the importance of geosyntheticsin the new applications he devised during the construction ofTerzaghi Dam in British Columbia.

Bob Koerner, the son of naturalized U. S. citizens fromAustria and Germany, earned his bachelor’s degree and hismaster’s degree from Drexel University. After gaining industryexperience, he earned his PhD from Duke University in 1968,and then returned to his alma mater, Drexel, to begin his ac-ademic career—a career distinguished by many activities ofnote, by research and publications, and by honors and awards.At Drexel, he is the H. L. Bowman Professor of Civil Engi-

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neering, and, since 1968, the Director of the Geosynthetic Re-search Institute, which he founded and developed into theworld’s premier research and technology transfer organizationin the field of geosynthetics.

Bob Koerner has made important contributions to our lit-erature, and excels at clearly conveying technical material,most notably in the field of geosynthetics. He has authored oredited 45 books, and has contributed chapters in 27 more. Hehas written over 500 technical papers and reports, and hasmade hundreds of presentations at short courses and technicalconferences. In recognition of his enthusiastic leadership in thefield of geosynthetics, Bob Koerner has been the recipient ofmany honors and awards, including tonight’s recognition as aTerzaghi Lecturer. An Honorary Member of ASCE, he hasearned recognition for his teaching, his research, and his con-tributions to the profession. He was the IGS/ISSMFE F. B.Mercer Lecturer and the IGS Inaugural Giroud Lecturer. Inaddition, he has received the Alan Haliburton Award and theAward of Merit and Fellow from ASTM, and the Award ofMerit in Geosynthetics Design from IGS, among many well-deserved others.

Bob Koerner is also a consummate professional, with asense of leadership and wisdom that is to be admired by usall. Several years ago, I shared a podium with him, debatingthe use of geosynthetics in the construction of new, and therepair of old dams. In our discussion, Bob quickly recognizedthat in this battle of wits he was dealing with an unarmed man,and he used his considerable charm and his art of persuasionto win the audience to his side, with his well-founded reason-ing and his sound basis in fact.

Bob Koerner has made enormous contributions to our profes-sion, which are certainly worthy of our recognition of him as thethirty-second Terzaghi Lecturer. But, tonight, we also celebratehis contributions that extended beyond his teaching, research, andwritings. Bob and his lovely wife, Paula, a naturalized U.S. cit-izen from Germany, have happily teamed for 37 years. Despitehis tendencies to overwork, and his many hours logged road-running and later, road-jogging, Bob and Paula have successfullydeveloped three new engineers for the profession, all fromDrexel: Son Michael, a chemical engineer, son George, a civilengineer, and daughter Pauline, an electrical engineer.

With great honor and pleasure, I am pleased to introducethe thirty-second Terzaghi Lecturer, Professor Robert M.Koerner, Hon.M.ASCE, who will describe ‘‘Emerging and Fu-ture Developments of Selected Geosynthetic Applications.’’Ladies and gentlemen, please join me in recognizing Bob Ko-erner, husband, father, industry leader, and esteemed colleague.

INEERING / APRIL 2000

EMERGING AND FUTURE DEVELOPMENTS OF SELECTED

GEOSYNTHETIC APPLICATIONS

By Robert M. Koerner,1 Honorary Member, ASCE

(The Thirty-Second Terzaghi Lecture)

ABSTRACT: This paper presents 17 separate applications within the current technology of geosynthetics. Theywere selected as being illustrative of the wide range of applications that can utilize geosynthetics in geotechnical,transportation, hydraulics, and geoenvironmental engineering. All are permanent and/or critical applicationswherein design by function is required, thereby necessitating the calculation of a product-specific test resultversus a site-specific design requirement. This calculation results in a factor of safety, which must be assessedaccordingly. In this regard, geosynthetics are no different from any other engineering material. This paper,however, does not go into calculation details, which are available in the literature. References are provided inthis regard. The various applications presented were selected to illustrate that both emerging developments andfuture possibilities are ongoing. This approach illustrates the dynamic nature of the field of geosynthetics, whichis both exciting and stimulating, and speaks well for future endeavors.

INTRODUCTION

It should come as no surprise that the earliest user of geo-synthetics in at least two specific applications was Karl Ter-zaghi, in whose name this lecture series is celebrated. In thelate 1950s, Terzaghi made use of filter fabrics (today, geotex-tiles) as flexible forms. They were filled with a cement grout,thereby making closure between steel sheetpiling and rockabutments at the Mission Dam (now Terzaghi Dam) in BritishColumbia, Canada. During this same project, Terzaghi usedpond liners (today, geomembranes) to keep an upstream clayseepage-control liner from desiccating. This latter applicationwas arguably the forerunner of composite liners (geomem-branes placed over compacted clay liners) as routinely used inpresent waste containment applications. Both applications pre-dated conventional geosynthetics by some 20 years; see Ter-zaghi and Lacroix (1964) for details regarding this importantcase history.

With the advent of the first conference on geosynthetics inParis in 1977, the first book on the subject in 1980 (Koernerand Welsh 1980), the formation of the International Geosyn-thetics Society in 1983, and the appearance of a number ofspecialty journals, magazines, and newsletters throughout the1980s, the field has established itself in areas of geotechnical,transportation, hydraulics, and geoenvironmental engineering.Also to be noted is the fact that the various geosynthetic man-ufacturers have consistently been involved in pushing the fron-tiers of the technology. In so doing, their influence, products,and designs have been very positive and generally found tobe credible.

The 1990s have been a period where design models andperformance testing have advanced to the point where tech-nical acceptance of geosynthetics has been achieved in myriadapplications. Furthermore, a structure of the technology hasbeen established in that the various types of geosynthetics canreadily be associated with their primary function (Table 1).

Using this table as a guide, one can counterpoint specificproperties of a candidate geosynthetic material against its re-quired value to arrive at a factor of safety (FS) value, i.e.,

allowable propertyFS =

required property

The allowable property value is obtained from a stimulatedperformance test (or an index test modified by site-specific

1H. L. Bowman Prof. of Civ. Engrg., Drexel Univ., Philadelphia, PA19104.

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reduction factors), while the required property is obtained froman appropriate design model. Such models are generally mod-ifications of existing geotechnical or hydraulic models. Theentire process, generally called ‘‘design by function,’’ is wide-spread in its use and is available in Koerner (1998), amongnumerous other publications. However, as might be anticipatedwith a young technology, universally accepted values of min-imum factors of safety have not yet been established, and con-servatism in this regard is still warranted.

Regarding the current status of geosynthetics, growth is con-tinuing at a rapid pace. Fig. 1 shows this approximate growthin North America based on both quantity and sales of geosyn-thetics. Note that approximate sales in the year 1998 were $2.5billion. This attests to the fact that geosynthetics have arrivedas a viable and widely used construction material.

In developing the structure for this paper on the topic ofemerging developments and future possibilities of selectedgeosynthetic applications, there are at least two different ap-proaches. One, which is used by many in the presentation ofprofessional and academic courses, is from a geosyntheticsvantage point. In this approach, all applications are essentiallyforced into the primary function matrix shown in Table 1. Thisapproach has served the geosynthetics industry well, but thematuring of the technology suggests a somewhat different ap-proach. This second approach is to present the potential futureof geosynthetics from an applications perspective. It is thissecond approach that will be used in this paper. The particularcategories of the various geosynthetic applications describedin this paper are as follows:

• Geotechnical• Transportation• Hydraulic• Geoenvironmental

In selecting the specific applications within each category,most standard and ongoing uses of geosynthetics are well po-sitioned and are not included herein. As such, this is a clearindication of the maturing of the industry, and only selectedkey references are included. Applications were selected for thispaper on the basis that both emerging developments and futurepossibilities are likely to occur. Thus, each of the sections tofollow will briefly present the selected application topic, andthen will address both emerging developments and future pos-sibilities. The applications are placed in somewhat arbitrarycategories for the sake of segmenting the paper.

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TABLE 1. Geosynthetics vis- -vis Primary Functiona

Type of geosynthetic(1)

Primary Function

Separation(2)

Reinforcement(3)

Filtration(4)

Drainage(5)

Containment(6)

Geotextiles Yes Yes Yes Yes Noa

Geogrids Nob Yes No No NoGeonets No No No Yes NoGeomembranes Yesc Nod No No YesGeosynthetic clay liners Yesc Nod No No YesGeopipe No No No Yes NoGeocomposites a/de a/de a/de a/de a/de

aUnless impregnated by bitumen or other polymer.bUnless very large particle size soils are involved.cUsually considered to be secondary function.dUnless fabric reinforced and designed accordingly.eApplication dependent design of particular product.

FIG. 1. Growth of Geosynthetics in North America Based onQuantity and Sales

GEOTECHNICAL APPLICATIONS

This section addresses some of the major emerging exten-sions and possible future aspects of geosynthetics used in geo-technical engineering applications.

Slopes and Revetments

One of the earliest uses of geosynthetics was to steepen soilslopes and embankments as shown in Fig. 2(a). Such soilmasses can be made stable at essentially any angle by usinghorizontally placed layers of appropriately designed geogridsor geotextiles. This realization comes about by assessing thefollowing standard FS equation:

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FIG. 2. Geosynthetic Use for Steep Soil Slopes and Embank-ments

M 1 TaR OFS =

MD

where FS = factor of safety; MR = resisting moments arisingfrom soil shear strength; MD = driving moments due to deadand live loads; T = allowable strength of geosynthetics; and a= moment arm associated with the geosynthetics. Thus, morelayers (of stronger geosynthetics), at greater distances from thecenter of the assumed failure location, produce progressivelyhigher FS values. The application and its design are well es-tablished in the literature and in practice.

There are at least two aspects of this application that areemerging developments. Both are associated with using lowhydraulic conductivity backfill soils. One emerging feature isthe use of needle punched nonwoven geotextiles to take ad-vantage of the inherent transmissivity characteristic of thesematerials. They can be used by themselves or, more likely,with a geogrid or a woven geotextile [Fig. 2(b)]. A compositematerial of this type is currently available from several man-ufacturers. The second emerging development is to providedrainage behind the reinforcement using geocomposite sheetdrains or geonets. Such drainage materials essentially provide


FIG. 3. Geosynthetic Use for Reinforced Walls and Bulkheads

a chimney drain connected to a drainage gallery, albeit fromgeosynthetics rather than from natural soils.

A future possibility within this application is to use the re-inforcement inclusions as carriers for activated carbon fibers,conductivity filled polymers, or metallic fibers [Fig. 2(c)]. Byso doing one can modify the fine-grained soils in the rein-forced zone via electroosmosis, ion migration, or electropho-resis. Nettleton et al. (1998) describe a number of concepts inthis regard. Such electrokinetic geosynthetics are currently inthe early investigation and trial implementation stages.

Reinforced Walls and Bulkheads

In a manner very similar to the previous application, it haslong been realized that a geosynthetic material (geotextile orgeogrid) wrapped around layers of soil backfill can providefor a vertical wall. What has progressed over the past 10 yearsis the nature of various facing systems associated with suchinternal reinforcement. The reinforcement can be a geotextile,but is currently more often a geogrid. The progression of fac-ing materials has been approximately as follows:

• Wrap-around facing• Timber facing• Welded wire mesh facing• Stacked gabions• Precast concrete (full-height) panels• Cast-in-place reinforced concrete facing• Precast concrete (individualized) units• Modular concrete blocks, currently called segmental re-

taining walls (SRWs) [Fig. 3(a)]

Based upon a recent cost survey (Koerner et al. 1998), theabove type of geosynthetic reinforced walls are the least ex-pensive of any wall type and for all wall height categories(Fig. 4).

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FIG. 4. Mean Values of Various Categories of Retaining WallCosts

Of the wall facing types listed previously, the segmentalretaining walls using dry-laid masonry blocks are most com-mon. New block systems, facing details, and anchorage sys-tems are constantly appearing (Bathurst and Simac 1994).SRWs are currently used for walls of large heights (up to 15m) to accommodate high surcharge loads (such as railroads),and are even placed adjacent to running water (creeks, streams,and rivers). SRWs perform well in areas of seismic activity(Tatsuoka et al. 1998).

Most interesting in regard to SRWs are emerging block sys-tems with openings, pouches, or planting areas within them.These openings are soil-filled and planted with vegetation thatis indigenous to the area [Fig. 3(b)]. Providing the climate isappropriate, a ‘‘live wall’’ can be created which completelyobscures the masonry facing. Gray and Sotir (1996) provideinsight into vegetated slopes and walls from an engineeringperspective.

Future possibilities in the area of reinforced wall systemscould be in the use of polymer rope, straps, or anchors tied tothe facing units, or to geosynthetic layers, and extending theminto the retained earth zone [Fig. 3(c)]. Such individual unitscan also be anchored into rock.

Base Reinforcement of Embankments

The area of base reinforcement was pioneered by the U.S.Army Corps of Engineers in the early 1970s using highstrength geotextiles (Haliburton et al. 1997). The focus ofthese projects was construction of embankment dikes over softfoundation soil where a reduction of total settlement was theultimate goal (Sprague and Koutsourais 1992). The Dutchwere also early users of the same technique for large area fills(Voskamp and Risseeuw 1987).

The emerging development on this theme is to provide re-inforcement against differential settlement. Fig. 5 shows threeconfigurations of this type (Koerner 1998). In all cases, thedesign requires the adaptation of Terzaghi’s arching theory(Giroud et al. 1990), which has been rediscovered and some-what modified (Schmertmann 1999). In this regard, the max-imum dimensions of the void creating the potential differentialsettlement is critical in the design as far as the required tensilestrength of the reinforcement is concerned.

A future possibility in this particular application could wellcome from the development of a practical field installationmethod for prestressing the reinforcement. If effective, withrespect to possible stress relaxation, such prestressing couldeliminate deformations from occurring.

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FIG. 5. Geosynthetic Use for Base Reinforcement to Preventor Minimize Differential Settlement

Concrete Dam Waterproofing

Many existing concrete dams have significant deterioration.Other than visual observation of this deterioration via spallingand exposed reinforcement, the increased seepage through thestructure is probably of greatest concern. Geomembranes,placed directly on the upstream face of the dam, are a currentapplication that provides a waterproofing barrier [Fig. 6(a)].In order to place the geomembrane against the upstream face,the reservoir is emptied and stainless steel channels are in-stalled in vertical alignment approximately 2 m apart. Geo-membranes are then used to span the channels and are fixedwith mated channels for removing slack [Fig. 6(b), after Scu-ero and Vaschetti (1996)]. The technique can be modified byfirst placing a geonet against the concrete, then placing thegeomembrane against the geonet. The purpose of the geonetis to provide drainage for reservoir leakage that bypasses thegeomembrane. Geomembranes have been used for about 15years in this application. Cazzuffi (1987) has reported earlyuses in Italy, and the method is now spreading worldwide.

The emerging development of this application is in the in-stallation area. For example, the use of divers to install thesystem while the reservoir is full or partially full has had atleast one successful field trial (J. Wilkes, CARPI USA Inc.,personal communication, 1999). Also, the use of an air bub-bling system placed at the base of the geomembrane in orderto provide for the breaking of ice at the upper surface of thereservoir is being attempted. Such ice, if sufficiently thick,could cause puncture damage to the geomembrane. Fig. 6(c)illustrates both of these emerging extensions of the applica-tions.

The geomembrane’s lifetime currently is limited due to theobvious degradation mechanisms of ultraviolet and oxidative


exposure. When coupled with high temperature, these mech-anisms can be very aggressive to most polymeric materials.The future possibility appears to be in the development ofimproved polymer formulations to provide greater service life-times than currently available under the required exposed con-ditions.

Earth Dam Waterproofing

The application of geomembranes, and potentially geosyn-thetic clay liners, on the upstream face of earth and earth/rockdams is an ongoing application [Fig. 7(a)]. The geomembranemust obviously be protected against puncture and be suitablyanchored, but these considerations are within the state-of-the-practice (Sembenelli and Rodriguez 1996).

This same type of approach has recently emerged in thegeomembrane waterproofing of a roller compacted concretedam [Fig. 7(b), after Gannett-Fleming Consultants Inc. (per-sonal communication, 1999)]. In this case, the geomembraneand an underlying geotextile were factory-attached to concretepanels that were placed incrementally as the dam was con-structed. The panels were joined in the field using geomem-brane cap strips. The technique essentially eliminates possiblehorizontal seepage flow, which can arise with incremental con-struction methods consisting of individual layers or lifts ofmaterials.

The future possibility for geomembranes in the waterproof-ing of earth (and earth/rock dams) will probably focus on theretrofitting of existing dams [Fig. 7(c)]. Utilizing a bentoniteslurry supported trench excavation through the embankment(and foundation if necessary), the geomembrane is placedagainst the upstream face of the trench. Sheets, rolls, or panelsof geomembranes can possibly be used in the same manner ascurrently practiced with vertical walls to contain seepage fromlandfills (Koerner and Guglielmetti 1995). The backfill usedto displace the slurry can be carefully selected to provide animpervious layer in its own right. Thus, the resulting backfilledtrench can consist of a composite liner, albeit one that is ver-tical instead of being oriented in the usual horizontal or sideslope orientation.

Tunnel Waterproofing

The use of waterproofing geomembranes placed in advanceof liner plates or permanent concreting in tunnels is an on-going practice [Fig. 8(a)]. When coupled with a thick, needle-punched nonwoven geotextile, and a drainage outlet at the toeof the geotextile, a complete seepage control system is avail-able (Frobel 1988). Most rock tunnels utilizing the New Aus-tria Tunneling Method (NATM) use this waterproofing tech-nique.

The deployment of the geomembrane and underlying geo-textile, however, is somewhat difficult. The geosynthetics sagfrom their temporary roof anchors and are prone to damageduring placement of the permanent lining. For this reason, theemerging development will probably focus on installation.Contractors and installers are working with deployment sys-tems whereby the geosynthetic materials are placed concurrentwith the final liner system [Fig. 8(b)]. It should be noted thatthe geotextile and geomembrane might be placed immediatelypreceding the permanent liner when concrete slip lining is thetechnique that is used.

A future possibility in this application is felt to be in de-veloping polymer formulations to provide extremely long ser-vice lifetimes. Service lifetimes well in excess of 100 yearsrequire the materials involved to resist the relatively harsh am-bient tunnel environment. At the same time, such formulationscannot impede progress of the work, thus both installation andserviceability are paramount.


FIG. 6. Geosynthetic Use for Concrete, or Masonry, Dam Waterproofing

FIG. 7. Geosynthetic Use for Earth, Earth-Rock, and RollerCompacted Concrete Dam Waterproofing

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FIG. 8. Geosynthetic Use for Tunnel Waterproofing


TRANSPORTATION APPLICATIONS

This section addresses some of the major emerging exten-sions and possible future aspects of geosynthetics used intransportation engineering applications.

Geosynthetic Modified Roadways

There are a number of approaches toward using polymericmaterials in roadway cross sections that invariably have astheir goal better performance, longer service lifetime, or acombination of both features. Fig. 9(a) illustrates the varioustarget areas for geotextiles and/or geogrids. The functions ofthe geosynthetics illustrated are as follows:

• Geotextiles as separators and/or reinforcement betweensoil subgrade and base course

• Geogrids as reinforcement between soil subgrade and basecourse

• Geogrids as lateral reinforcement (containment) withinthe base course

All three of the above approaches are ongoing applications,which are appropriately marketed by many manufacturers.

Some emerging developments are the use of continuous fil-aments within the base course as it is placed. Leflaive andLiausu (1986) have pioneered a technique using high tenacitypolyester filaments, which are continuously placed within thesoil matrix during construction. In a somewhat similar manner,microgrids could be mixed with the pavement (asphalt or con-crete) as it is placed. McGown et al. (1985) have performed

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laboratory experiments with this material and field trials havebeen conducted. Perhaps the greatest success to date, however,has been with discrete fibers, typically polypropylene, dis-persed throughout the stone base course. Gregory and Chill(1998) have developed this application area [Fig. 9(b)].

Regarding future possibilities, one might be able to treatpotholes in the soil subgrade with geosynthetics as seen in Fig.9(c). D’Andrea and Sage (1989) have performed tests that firstdeploy a wick drain in the center of the hole. They line thevoid with a needle-punched nonwoven geotextile and finallybackfill the hole with a fiber reinforced soil. The techniqueshows promise and awaits field trials.

Trenchless Pipe Remediation

Along with an aging infrastructure in the urban environmentis the deterioration of the associated lifeline systems. Suchpipelines vary in size from 100 to 3,000 mm, and vary in typeacross the entirety of construction materials that have beenused for hundreds of years. In situ remediation, via trenchlesstechnology, is an ongoing and rapidly growing industry thatutilizes polymeric materials almost exclusively [Fig. 10(a)].Numerous references are available on the subject (Jeyapalan1985; Jeyapalan and Jeyapalan 1995). Table 2 gives an over-view of the various methods used for pipeline remediation andrehabilitation.

Since all of these remediation methods decrease the size ofthe existing pipe, the emerging development is to use an ex-pandable ram under great pressure to laterally burst the hostpipe, thereby enlarging its diameter [Fig. 10(b)]. This burstingaction is immediately followed by the insertion of a new pipe

FIG. 9. Geosynthetic Use for Roadway Pavement Systems

NEERING / APRIL 2000

FIG. 10. Geosynthetic Use for Pipeline Remediation

or lining in a manner that the original pipe capacity is notdecreased. In some cases the diameter may even be increased.A number of pipe bursting methods are available (Jeyapalanet al. 1995).

One ongoing difficulty of trenchless pipe remediation andrehabilitation is the making of connections to laterals such thata leak-free joint is realized. In the future, this difficulty willpossibly be addressed by using remote entry cutting systems,which not only drill through the newly formed (or placed)pipe, but are followed by some type of robot that remotelymakes the actual connection [Fig. 10(c)].

Erosion Control of Systems

By any quantification method, the loss of soil by water and/or wind erosion is enormous. Such erosion not only negativelyaffects land and farm use, it represents a major water pollutionsource since the eroded soil particles eventually end up in alocal water system. In order to control, limit, or altogether

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FIG. 11. Geosynthetic Use for Erosion Control and AvalancheControl Systems

avoid soil erosion, a number of geosynthetic-related erosioncontrol materials are available [Fig. 11(a)]. Table 3 gives acategorization of the various materials.

The emerging development of erosion control materialscould be in using long rods, pins, or nails so as to reinforcepotentially weak (or extremely steep) soil slopes [Fig. 11(b)].With reinforcement rods, one has a juxtaposition of erosioncontrol materials at the soil surface and soil nailing at depth.The technique, called ‘‘anchored spider netting,’’ has beenproposed by Koerner (1984) and evaluated in the laboratoryby Ghiassian et al. (1996).

A future possibility for the control of gravity-induced move-ments of surface materials may be in the control of snow av-alanches (K. R. Massarsch, personal communication, 1990).Using a geosynthetic net (either a high strength geotextile orgeogrid), anchored at the upper surfaces, a stabilizing force

TABLE 2. Trenchless Pipe Remediation and Rehabilitation Methods Utilizing Geosynthetics and/or Polymeric Materials (Koernerand Koerner 1996)

Method(1)

Typical pipe diameter(mm)(2)

Flow bypass required(3)

Reduction in flow capacity(4)

Availability of methods(5)

Coatings >1,200 Sometimes Minor EnormousSlip linings 100–900 No Large LimitedCured-in-place pipe (CIPP) 100–600 Sometimes Nominal ManyFold and formed pipe (FFP) 100–300 Sometimes Nominal LimitedIn situ liners >1,200 No Slight Many


TABLE 3. Geosynthetic Erosion Control Materials (Theisen 1992)

Temporary Erosion and RevegetationMaterials (TERMs)

(1)

Permanent Erosion and Revegetation Materials (PERMs)

Biotechnical related(2)

Hard armor related(3)

Straw, hay, and hydraulic mulches UV-stabilized fiber roving systems (FRSs) Geocellular containment systems (GCSs)Tackifiers and soil stabilizers Erosion control revegetation mats (ECRMs) Fabric formed revetments (FFRs)Hydraulic mulch geofibers Turf reinforcement mats (TRMs) Vegetated concrete block systemsErosion control meshes and nets (ECMNs) Discrete length geofibers Concrete block systemsErosion control blankets (ECBs) Vegetated geocellular containment systems (GCSs) Stone riprapFiber roving systems (FRSs) — Gabions

can be created [Fig. 11(c)]. Obviously, the proper location ofthe nets is critical, but reasonable avalanche location predic-tion methods are currently available. However, work is clearlyneeded in estimating the stresses on the nets, the proper an-chorage materials and deployment, and the sensing of over-loads for extreme weather events.

HYDRAULIC APPLICATIONS

This section addresses some of the major emerging exten-sions and possible future aspects of geosynthetics used in hy-draulics engineering applications.

Canal Liners

One of the earliest uses of geomembranes was to line canalsfor the purpose of seepage control. The work was pioneeredby the U.S. Bureau of Reclamation, which has had field trialsongoing since the 1950s (Morrison and Starbuck 1984). Theagency has progressed through a number of liner systems andcurrently use geomembranes to line essentially all of its canals.Many other countries do likewise. However, the geomem-branes are always covered—with soil in less populated areas,and with concrete in urban areas. As seen in Fig. 12(a), thetechnique is straightforward, with only a minimal anchortrench or batten strip connection as the geomembrane edgescome out of the canal flow zone.

The emerging development in this application is to line thecanal while water (or other liquid) is flowing in it. A trialsection has been constructed that places a geomembrane, geo-textile, and high-early strength concrete in rapid succession[Fig. 12(b)]. As the protective shield progressively moves for-ward, the concrete achieves its initial set, which is sufficientfor initial stability. The concrete then hardens with time. Thetechnique is essentially a variation of slip-form paving. Comeret al. (1996) describe field trials of this type, which also in-clude the forming of longitudinal steps along the paved sideslopes to serve as animal escape ladders. This technique ap-pears to be particularly significant when lining or relining ca-nals that have no alternative alignment, or that carry hazardousliquids in industrial locations.

With the soil or concrete covering serving as a necessaryprotection layer, it seems as though a future possibility wouldbe to have a sufficiently rugged geomembrane to function inan exposed manner with no covering of any kind. Thick, tex-tured geomembranes are being evaluated in a Bureau of Rec-lamation project in Deschutes, Idaho, with mixed results (Swi-hart 1994). The project, however, has at least 20 different trialsections that are being evaluated over a 10-year period. Resultsfrom this type of exploratory project, coupled with benefit/costevaluations, will be most revealing.

Geotextile Tubes for Erosion Control

Geotextile tubes made from high-strength fabrics are agrowing technology to provide for both oceanfront and inlanderosion control [Figs. 13(a and b)]. Tubes of up to 3 m in


FIG. 12. Geosynthetic Use for Canal Liners

diameter are available in either a woven (longitudinallyseamed in the field), or a knitted (without seams) format(Leshchinsky and Leshchinsky 1996). There is no length lim-itation as far as the tube itself is concerned with the exceptionsof handlability and filling. Filling is usually accomplished byhydraulically pumping a sand fill slurry, which flows from thepoint of entry. Entry locations are at relatively close, typically10 m, centers due to the frictional drag of the slurry againstthe fabric’s inner surface. The main tubes often have a smallerdiameter subsidiary tube attached to them (on their upstreamside), which acts as an anchor in resisting lateral pressures.Also, it is generally necessary to cover tubes with a thin layerof soil to protect them from ultraviolet degradation and van-dalism/accidents. This is particularly troublesome from amaintenance standpoint when storms occur, or when the tubesare trafficked and the cover soil is displaced.

As far as an emerging development of the technique is con-cerned, a rugged, high-strength fabric that can perform in anexposed condition for 206 years is actively being pursued. Thiscould well be a composite fabric, which would also add to fieldruggedness. This latter issue is necessary for certain fill mate-rials such as coarse, angular gravel and limestone shells.

A future possibility of geotextile tubes could be in devel-oping an inner tube surface with a low friction value. In thisway, the transport distance of the sand slurry will be extendedover the current practice, which is limited by the relativelyhigh friction surface of woven geotextiles. Yet, a simple lowfriction coating is not acceptable in itself because of the block-


FIG. 13. Geotextile Use as Tubes for Erosion Control

age of the fabric’s permeability, which prevents the water inthe slurry from draining through the geotextile. Thus, the idealcoating (or the fabric itself) is a low friction and porous sur-face. This situation requires considerable innovation on thepart of the textile engineer/manufacturer. The fabric’s porosityis also significant in dewatering contaminated sludges, whichis also a future possibility in this application.

Geotextile Containers for Soil Disposal

Geotextile containers are limited length tubes (e.g., less than15 m long) used for the containment, transportation, and dep-osition of dredged sediment from rivers, harbors, and deltas.Fig. 14(a) illustrates the type of bottom-dump barge that iscurrently used. Placed within the barge is a high-strength geo-textile that is soil filled, and then sewn together to make thefinal seal. When transported to the disposal site, the bottom ofthe barge is opened, and the entire soil-filled container dropsto the bottom of the water. Fowler (1995) describes the pro-cess, which is rapidly being accepted by many river, harbor,and port authorities.

As an emerging development of the process just described,one can envision the possibility of stacking an array of con-tainers as shown in Fig. 14(b). Additional disposal area canbe created on the upstream side of the containers. It is evenconceivable that matched sets of stacked containers can bearranged such that the enclosed dredged soil (particularly if itis contaminated) can be sealed. The sealing can possibly beaccomplished using a geotextile mattress that is grout filled,as is done regularly on land. It is quite possible to do this ina submerged environment as well.

As a future possibility of the technique, one can conceptu-alize the construction of an underwater structure, even a hab-itat, as shown in Fig. 14(c). The superstructure, however,leaves much to be investigated! The sketch is meant to stim-ulate thought, not so much for its immediate practicality.

Aquaculture Liners

The geomembrane lining of a pond for the growing andharvesting of shellfish and other types of aquaculture is quite

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straightforward and practiced on a routine basis. The name‘‘pond liners’’ owes itself to this type of early application ofgeomembranes. What is unique is the scale to which this ac-tivity can be taken. Fig. 15 shows thousands of aquacultureponds (each 2 ha in size) for shrimp farming. It is an ongoingand ever-increasing technology.

An emerging development of the commonly used geomem-branes for this application is a rugged protective surface thatcan resist damage during operations or maintenance. Sincesafety for the workforce due to slipperiness is also an issue,the geomembrane of choice might well be a thick (e.g., >2.5mm), textured, polyolefin geomembrane.

The future possibility of the technology could also be witha modified formulation of the geomembrane. Additives can beincluded into the formulation for the purpose of nutrition, de-contamination, oxygenation, etc. By calculating the properamount and type of additives, diffusion release over time canbe estimated in a manner similar to other polymer situations,such as biocides, which are added to shower curtains to pre-vent microorganisms from growing.

GEOENVIRONMENTAL APPLICATIONS

This section addresses some of the major emerging exten-sions and possible future aspects of geosynthetics used ingeoenvironmental applications.

Landfill Liner Systems

Landfill liner systems using geomembranes were essentiallyregulated into widespread use in 1982 by the U.S. Environ-mental Protection Agency. Since that time, a genesis has oc-curred in that (1) double liners with leak detection capability;(2) composite liners (geomembranes with underlying claysoils); and (3) geosynthetic clay liners have replaced all orpart of the compacted clay soils, leading to the current situa-tion as appears in Fig. 16(a). These containment systems haveindeed proven themselves to be extremely efficient in protect-ing the subsurface environment. Table 4 illustrates the ex-


FIG. 14. Geotextile Use as Containers for Dredged Soil Dis-posal

tremely low leakage rates that are associated with double linersystems having leak detection capability.

Indeed, it is with double liner systems where the greatestenvironmental security can be achieved. Currently, 100% ofhazardous and 24% of municipal solid waste landfills in theUnited States require double lined systems. Worldwide, 58%of hazardous and 14% of municipal solid waste landfills re-quire double liner systems (Koerner and Koerner 1999).

While such liner systems clearly provide for long-term con-tainment [e.g., for high density polyethylene geomembranes,the time for half-life is in the hundreds of years (Hsuan andKoerner 1998)], they are not perpetual in their durability. Theconcept of leachate recycling is fortunate in this regard andrepresents an emerging development of landfill technology. Asillustrated in Fig. 16(b), the extracted leachate is reintroducedinto the waste mass for the purpose of accelerated degradationand enhanced gas generation (Pohland 1996). A conferencehas been dedicated to the subject, and at least 30 landfills inthe United States, and many more worldwide, practice thetechnique. The goal is to degrade the waste in a time framefar shorter than would occur in a landfill where leachate iswithdrawn on demand and treated accordingly. A variation inthis theme is aerobic degradation that introduces air along withthe leachate. Time for degradation is further accelerated, butwithout the production of gas.

A future possibility is landfill mining coupled with leachaterecycling. The leachate can be injected via a variety of geo-synthetic drainage systems, e.g., prefabricated vertial drains.


FIG. 15. Geomembrane Use for Aquaculture Ponds forShrimp Farming

The concept is to have a perpetual landfill where no new landarea is required for a constant stream of waste disposal vol-ume. The concept is shown in Fig. 16(c). By sequentially fill-ing cell after cell, and using accelerated degradation via leach-ate recycling (anaerobic or aerobic), the originally placedwaste (e.g., waste placed in cell ‘‘A’’) can be timed so as tobe capable of being mined before this specific landfill cell isneeded. The mined waste can be periodically used for fertil-izer, mulch, or other beneficial use. This practice should allowfor the liner system to be inspected, remediated, and possiblyreplaced. The situation perpetuates itself, creating an endlesscycle. It is a provocative concept and one that is being inves-tigated in areas where land is at a premium.

Landfill Closure Systems

Closely related to the liner systems beneath the waste massin a landfill are the cover systems placed above the waste.Such systems usually consist of a composite barrier (i.e., geo-membrane over a geosynthetic clay liner, or compacted clayliner), with a drainage system placed above and a gas collec-


FIG. 16. Geosynthetic Use for Landfill Liner Systems

tion system placed below [Fig. 17(a)]. Such final closure sys-tems are constructed above recently filled landfills as well asabove abandoned waste dumps, which are arguably the mostenvironmentally challenging (Koerner and Daniel 1997).

The emerging development of final closures (which is prac-ticed at many large landfills) has to do with landfill gas cap-ture, collection, and the conversion into energy [Fig. 17(b)].The energy is used to power utilities at the site and the balanceis then sold to the local power authority. Collection of theuprising gases can be achieved using a gas collection systemdirectly beneath the cover barrier, or from wells penetratingdeep into the waste mass.

As far as a future possibility for final covers of large land-fills, many worthwhile land use possibilities exist. Some ofthem that have appeared in the literature are as follows:

• Jogging and biking trails• Sport and athletic fields• Golf courses• Storage areas and light industry• Visual artworks

The latter possible use is illustrated in Fig. 17(c) (Pinyan1987).

Vertical Barriers for Abandoned Dumps

Due to the often unknown extent and nature of abandonedwaste dumps, the usual environmental strategy is to leave thewaste material in place and contain it with a vertical barrier.While most vertical barriers consist of soil-filled trenches, theplacement of a geomembrane on the upstream side of thetrench provides added environmental protection. By backfill-ing the remaining trench with a low permeability backfill (e.g.,soil/bentonite, soil/fly ash, etc.), a composite barrier is formed[Fig. 18(a)]. Placement of the geomembrane, in roll or panelform, is accomplished by numerous installation techniques(Thomas and Koerner 1996).

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TABLE 4. Leakage Rates from Leak Detection Systems ofDouble-Lined Landfills (Othman et al. 1997)

Parameter(1)

Life cyclestage 1

(2)

Life cyclestage 2

(3)

Life cyclestage 3

(4)

(a) Type I (GM-Sand)

Average flow 380 170 64Minimum flow 7.6 0.0 0.2Maximum flow 2,140 1,480 240Number of ‘‘points’’ 30 32 8Number of landfills 11 11 4

(b) Type II (GM-GN)

Average flow 90 100 NDMinimum flow 4.8 1.4 NDMaximum flow 370 360 NDNumber of ‘‘points’’ 7 11 NDNumber of landfills 4 6 ND

(c) Type III (GM/CCL-Sand)

Average flow 210 140 64Minimum flow 1.2 22 0.0Maximum flow 1,180 660 270Number of ‘‘points’’ 31 41 15Number of landfills 11 11 4

(d ) Type IV (GM/CCL-GN)

Average flow 170 83 65Minimum flow 0.0 0.0 0.0Maximum flow 690 500 130Number of ‘‘points’’ 21 27 12Number of landfills 6 9 3

(e) Type V (GM/CCL-Sand)

Average flow 130 22 0.3Minimum flow 0.0 0.0 0.0Maximum flow 970 280 0.9Number of ‘‘points’’ 19 19 4Number of landfills 3 3 1

( f ) Type VI (GN/GCL-GN)

Average flow 6.5 2.6 NDMinimum flow 0.0 0.0 NDMaximum flow 34 9.0 NDNumber of ‘‘points’’ 6 4 NDNumber of landfills 2 2 ND

Note: Stage 1 = initial life; stage 2 = active life; stage 3 = postclosure;‘‘points’’ = measuring points (i.e., outlets of single or multiple cells); ND= no data; CCL = compacted clay liner; GCL = geosynthetic clay liner;GM = geomembrane; GN = geonet. All flow rates are in liters/hectare-day (lphad).

The emerging development of vertical barriers is to pur-posely leave a slot or gate open in the geomembrane wall asshown in Fig. 18(a). The concentrated leachate flow emergesfrom this opening, where it can be biologically or chemicallytreated (Blowes et al. 1995). Conceivably, throughlike con-duits can be formed to allow for a predetermined retentiontime of the escaping leachate so that complete treatment canbe effected.

The future possibility of this technology is likely to be avertical double wall system with leak detection capability. Var-ious options are possible as shown in Fig. 18(c)—one with ageonet as leak detection, the other with sand as leak detection.The latter case is similar to the Vienna double wall system thathas been advanced by Brandl (1990).

Bottom Liners for Abandoned Dumps

With the capability of constructing both covers and verticalside walls of abandoned waste sites as just described, one isleft with the dilemma of in situ construction of a bottom liner[Fig. 19(a)]. This situation is particularly exasperating sincedrilling into unknown sites is problematic with respect to the


FIG. 17. Geosynthetic Use for Landfill Closure Systems

FIG. 18. Geomembrane Use for Vertical Barriers of Aban-doned Dumps

depth and lateral extent of the waste as well as the possibilityof acquifer cross-contamination. When vertical walls cannotreadily reach an aquiclude, depths can be enormous, which isan obvious economic drawback. At present, there is no existing


FIG. 19. Geosynthetic (and Grouting) for Bottom Liner ofAbandoned Dumps

method to install a secure bottom beneath an existing wastemass.

Emerging developments, however, are illustrated in Fig.19(b). One option is jet grouting beneath the waste mass. Theproblem is that one must drill through the unknown waste,which can have negative implications. An alternative schemeis to use directional drilling from the sides of the waste massto install a bottom liner. Continuity of the bottom in bothcases, however, appears to be contentious.

With respect to a future possibility, one could consider avariation of long-wall mining to install a continuous geomem-brane floor beneath the waste mass [Fig. 19(c)]. A proposal ofthis type has been presented to the U.S. Bureau of Mines (Gabr1996). The technique would place a geomembrane, conceiv-ably a composite geomembrane/geosynthetic clay liner, andeither allow the overlying mass to collapse behind it, or tosupport the roof with geotextile tubes. Of course, such a floorsystem when coupled with vertical walls and a cover wouldentirely encapsulate the waste mass, which is the desirable endproduct. Such techniques illustrate the extent that geosyntheticbarrier systems, both geomembranes and geosynthetic clay lin-ers, can go to assure environmental safety and security of aparticular abandoned waste site.

SUMMARY AND CONCLUSIONS

Seventeen different applications involving geosyntheticshave been presented in this paper. They are somewhat arbi-trarily subdivided into geotechnical, transportation, hydraulics,and geoenvironmental categories. A very brief background ofeach topic was offered, followed by the most important emerg-ing developments, as well as future possibilities. Table 5 is asummary of the 17 topics in this regard. Clearly, other appli-cations could have been presented, or those that were pre-sented could have been addressed in a somewhat different


TABLE 5. Applications Addressed in This Paper along with Emerging Developments and Future Possibilities

Category(1)

Topic description(2)

Emerging development(3)

Future possibilities(4)

Geotechnical Soil slope reinforcement Composite geosynthetics to provide inter-nal drainage

Electrokinetic geosynthetics to modify backfillsoils in situ

Walls and bulkheads New facing systems, particularly thosewith vegetative growth, i.e., ‘‘live-walls’’

Polymer rope, straps, or anchors for unique sitesituations

Base reinforcement over voids Resist differential settlement Prestress the reinforcement to eliminate all de-formation

Concrete dam waterproofing Underwater installation and bubbling sys-tems for ice breakers

Improved polymer formulations to resist harshexposed conditions

Earth dam waterproofing Extension into roller compacted concretedams

Remediation of existing dam embankmentsand foundations

Tunnel waterproofing Simultaneous installation along with per-manent liner system

Improved polymer formulations to provide ex-tremely long service life

Transportation Geosynthetic modified roadways Fiber reinforcement and microgrids Pothole repair using geosynthetic drainage ma-terials

Trenchless pipe remediation Pipe bursting to increase diameter of hostpipe

Remote entry and robotic controlled connec-tions

Erosion control systems Reinforced geosynthetics and soil nailingfor slope stabilization

Avalanche control nets

Hydraulics Canal liners Lining of canals under flowing water Improved polymer formulations to resist ex-posed conditions

Geotextile tubes for erosion control Rugged (high strength) fabrics to resistvandalism and ultraviolet resistance

Low friction, pervious, inner liners to accom-modate long flow lengths

Geotextile containers for soil disposal Stacked containers for development of un-derwater structures

Formation of underwater habitats

Aquiculture liners Development of protective surface for rug-gedness during maintenance

Diffusion released cleaning agents within thepolymer formulation

Geoenvironmental Landfill liner systems Leachate recycling Landfill miningLandfill closure systems Gas capture and utilization for power gen-

erationSocially responsive and worthwhile final uses

Vertical barriers for abandoned dumps Creation of a gate for focused release ofleachate for subsequent treatment

Utilizing double barrier systems with leak de-tection

Bottom barriers for abandoned dumps Directional drilling or jet grouting Longwall mining installation methods

manner. However, those selected are felt to embody the es-sence of the continually growing field of geosynthetics.

At this point in time, it is suggested that geosynthetics arebona fide engineering materials and properly belong in the listof traditional materials that civil engineers take for granted.Obviously, every material (soil, concrete, steel, timber) has itsown unique characteristics. Geosynthetics are no different inthis regard. However, there is a large body of knowledge avail-able addressing geosynthetics that presents detailed character-istics of the various types of geosynthetics and of their per-formance to date.

Upon presenting this set of 17 applications addressing var-ious aspects of civil engineering, it is hoped that the readergains appreciation that geosynthetics can be (and are being)used for permanent and critical structures. The applicationswere particularly selected to emphasize this point. Designmodels and testing methods are available for design by func-tion to conclude with a reliable FS for an acceptable end prod-uct. While the subject of geosynthetics per se is usually nottaught in engineering colleges and universities as a separatetopic, geosynthetics are often integrated into course workwhere appropriate. In so doing, they can be presented as acounterpoint to traditional materials. In general, this counter-point will often favor the use of geosynthetics.

Some 20 years ago, when the writer began to work in geo-synthetics, two pervading opinions were often expressed, bothof which seemed reasonable at the time. One was that geo-synthetics would not have adequate service lifetimes, and theother was that they were obviously easy to place in the field.We now see that these two topics were indeed critical issues,but that the conclusions have been completely reversed. Wenow find that geosynthetics (when properly formulated andcovered in a timely manner) will last hundreds of years, but

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their field placement and backfilling are completely unforgiv-ing.

In this regard, a major focus in the future must be the properfield installation of geosynthetics with the requisite qualitycontrol and quality assurance. The lead of the U.S. Environ-mental Protection Agency in setting technical guidance forquality control and quality assurance for the currently targetedgeoenvironmental applications should be spread to geotechn-ical, transportation, and hydraulic applications as well (Danieland Koerner 1993).

Properly installed, geosynthetics present to the civil engi-neer a powerful tool to solve a myriad of problems.

ACKNOWLEDGMENTS

The writer is grateful to the executive committee of the GeotechnicalEngineering Division of ASCE for the privilege of presenting this 32ndTerzaghi Lecture. Thanks are also extended for the ongoing efforts andinteractions of his colleagues Drs. Grace Hsuan, George Koerner, and Te-Yang Soong. Dr. Soong was particularly helpful in drawing all of thefigures in this paper.

The financial sponsorship of the consortium of organizations that fundthe Geosynthetic Institute is obviously important to its continuing efforts.This sponsorship is critical to ongoing efforts and is sincerely appreciated.

APPENDIX. REFERENCES

The writer delivered the oral version of this paper at the ASCENational Convention in Washington, D.C., in October 1996. Inpreparing the written version, the writer has taken the libertyof citing several new references that have been published sincethe lecture was delivered. All of these new references supportand reinforce the examples cited in the oral lecture to illustrateemerging and future applications for geosynthetics.


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