desiıgning with geosynthetics robert kroner

8/3/2019 designing with geosynthetics robert kroner

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Fourth EditionDesigningwithGeosyntheticsRobert M. Koerner, Ph.D., P.E.H. L. o-an Profesrorof Civil Engineering.Drexel Universityand Director, GeosynthetieResearch h t i t u t e

PRENTICE HALLUpper Saa le KNW, ew Jersey 074%


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i~.. ... .:

B

452 Designing with Geomembranes Chap.5within the moieeularStruclUre.It eventudly IeaCtS With anothcr poiymer chain. creat.ing a new free radical and eausing chain scission.he reaction generally aecelerate.once it is triggered, 8s shown in the following equations.

R. + O, -f ROO. (5.10)ROO. + RH + ROOH + R. (5.11)

whereR.= free radicalROO. = hydroperoxy free.radicalRW = polymer ChainROOH= axidired polymer chain

Antioxidation additives (aotionidants) are added to the eompound to scavengethese free adicals in order to hait, or at least to interferewith, the prac essh ese addi-tives, or s tab iers , are rpecific to each type of resin (recallTable 1.5) . h ir area is verysophkticated and quite advanced with ail the m i n manufachuersbeing involved in ameaninghiland positive way.The specificantiaxidanls that arc used ar e usuaily propn-etary (sec Hruan et al. 1301for a review of the topic).lie rcrnovalof oxygen from thegeomembrane's surface,of ourse,eliminates the caneern.Thusonce placed and COY-ered with waste or iquid, degradation by midation shauld be greatly retarded. Con-vemdy, exposed geomembranesor those covcred by nonsaturated soil will be propor-tionatciy more susceptible to the phenomeoan. It should be recognized tha t oxidationofpolym ers wili eventuay,perhaps aft er hundreds ofyears,caure degradationeven hthe absenceof other types of degradation phenornena.Thereare wo related test methods that are. used to track the amount andlor de-pletion of antioxidantrhey aie ealied oxidolivc induclion lime (OIT) tests and arcperformed with aDSC device as described in Section1.22.

Srandord OI T (ASTM D3095);he oxidation is eonducted at 35 kPa and2WT.This test app ears to misrepresent antioxidant packages containing thiosynergisaandlor hiodered amines due to th e relatively high test temperature.High Pressure 011: (ASTM D5085);he oxidation isconducted st 35W kPa and150"Chis test can be used for al1 types of antioxidant packages and is the pE.ferred test.

. . madeling... I: . .. .. Svnerilistie Effear. Ea c h of he previous degradation phenornena has been

mechanirms are acting ~imuiianeously. or example, a warte-eontainment geomem-:... , : dwribed iodividuaily and separately.Inpractice,however,it 1slikely that two Ormore. .. ..~. .:. .:. .:: ..

Sec. 5.1 Geomemhians Properties an d Test Methodr 453brane may have anaerabic leachate above t and a partially saturated le&-detectionnetwork contsining mygen below it.Thus chemical degrada$on from above and oxi-dation degradation from below wiil be acting on the liner. Additionally, elcvated tem-pcrature from ecomposing solid waste and the local stress +iuation may complicatethe situation further. Evaluation of these various phenornena is the essence of oo-membrane lifetime prediction.5.1.5 LifetimePreiction TechniquesClearly, th e long t h e rames invalved in ivaiuating individual degradation mecha-nisrns at field-relaied emperatures and stre


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454 Designing with Gsomembranes Chap. 5

1 10 1M 1m 1o.m iw,m 1.w3.m8 ' ' # * 1 ' ' 1 ' 8 , - 8 t h - ' 1 1 ' 1 - I ' , , " " t "-Filluce i'me (hr)

Egurc5.E Schcmalicplofof im c o f l~ i lur c v s r r v a plpr ho o pr ~r e r r lo r bunI te r i~in& ofunnotshedMDPEpipe.n i e ate process method (RPM)s then used to predict B faure crime et somctemperature other than the high temperatures tested, that is, at a lower (field-related)temperaturc?his method is based on an absolutereaction rate theory and i s expiained

in [32].].nie relationships behveen the failure t h e nd stressare erpressed in the formofone of thefoliowing equations:

log t,= A,T-' + AIT-'- " (5.12)log rI= A +AIT-' + A2T-'P (5.13)l ag r ,=Ao+AiT'+Az lagP (5.14)log 1 = A, + AIT-' + A,T-' log P (5.15)

where1,= time o failure,T = temperature,LT = tellsilestress,P = iat emd pipe pressure pmpoItional10 the hoop stress io the pipeA, andA, = uinstanwand

h e application ofRPM equires a minimum of two expeRmental aure enmes at dif-ferent elevated temperahires. generaily above 40DC.Tnc quation that yieldr the bestuinelation to these curyes is then used in th e prediction procedure for a rerponsecurve at a field-related temperature (e,g,, 10 to 25DC).'Jbo eparate exirapolatiom aferequired,one or he ductilerespense and one for he bnttle response.lhree epresen-tative points are chosen on the ductile regions of the tw o experimentai C U N ~ .One

455ec. 5.1cume v dl be selected fortwo points,and he ather,for lhe remainingpoint.niesedataare substituted into the chosen equation 10 abtain the prediclionequationfor the duc-tile respanse of the c w e t the desired (iawer) temperature. The process is now re-peatedforlhepredicted bnttlerespnse-eat thesamedesired 1emperanircThein-terseetion of thse wo lines d e h a he transition time.Figure 5.16 shows two experimentd failure C U N ~ S hat Were conducted at tem-perahiresof80'CandM)"Calongwithhepiedicted curyesatZO"C.?h~intersection6fthe linear portions of the 2 0 T represents the anticipated time for transition inthe HDPE pipi from a ductile to a briftle behavior of the matenal. For pipe design,however, the intersection of the desired semice lifetime, say 50 years, with the bnttlew e a s hefocalpoint.Afactor ofsafely is thenplaced onthisvalue,forcnampie,notethat it irlowered inFigure5.16.Thisdalue of stresli isUSed as a limiiingvalue for thein-

Geornembrane PropenieS and Test Methods

temal pressure in the pipe.Rate Process Melhod IRPMI for Geomembranes. A simiiarRPM method

10 thst jurt described for HDPE pipes ean be applied to HDPE geomembranerlhemajor difierence i s the method of strcssing the material.n i e geomembrane tests areperformedwbg a notchedeonrtantload test (NCTL) ( l e c aUSe c t i onI1 .3 ) .~ gur e.17shows ypical eaperimental cwes at 50'C and 40C,which are very similar to the be-havior of MDPEpipe. Here distinct ductiie and bnttle regions ca n be seen dong witha clcarly defuied transition time.


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oesigning wifh Geornembranes Chap. 5458

n 1Seo. 5.1 GeomembranePropenieSand Test Methods 459

(b) AnhaniUrplot forha-iepmperty


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460 Deaigning with Geornembrane

Solution: ~ f w r nverting fromcentigrade o kclvin

= 6083

0Chap.5

If th e 93-c reacfion e k a 3W haun 10 mrnplete. the comparable 20C reactionwili ukcrzVc=6083(300)

= 1.825,WO hr= 7-08 yr

mur the predicted ime forthis particvlar poiymer toreach 50% of ls o r i g i d sirmgtha i2 0 ~ c i s ~ p p ~ o ~ a t c l y mearrit~predicledlifcfimeforstugeC

rn elatively long section on properlies and test methodr has, hopefully, ervedlustrate the wedth of lest melhodr availahlc for the charactenvtion and d e m Wu-riderations of geamembranes Many of the estabikhed tests and siandardized tesL

Sec. 5.2 SuwivabilityRequiiements 461methods have comcby way of the plastics and mbber industries for nongeotcchoical-reiated uses.This is lortunale,for it givesa base orreference plane ta Work Imm.How-ever,formanysomeva~ationisequired before theycan beused in helow-poundcon-smction. Still others demand completely new tests and test melhads. Instandards-selting indiutes the world over there is an awarenessof the problems andvibrant sctivily to develop such es1 methods and procedurer Until they areavailable,however,wemustactoninhiitionsnddevelopmethodslhat model therequireddesigninformationas closeiy as possible. Many of the tests and information premted in thissection arc done in that light.It shauld alro be obvious that the camplexity of the testshave progressed from the quite simple th ic he s test onsmooth geomemhranes IO lhevery eompiex degradation tests. Indeed, a very wide range of test methods areavailsble.FiaUy, a rath er lengthy discussion of durability and aging gives insight into thepotential service letime of geomembraner In a buried environment, the liictimespromise to be very long-for example,with stageA ofEgure 5.19a beiog 200 years,stageB being 20 y e m and stage C being hundreds of years, the HDPEgeomembrmek i ng evaiuated promises to far outlastolher engineeringmalerialshwmparable sit-uations. In my expenence with geosyntheticsover the past 20 y e a s my original wn-dusion WBI that geosynthetici were easy to place but wouldn't iast very long: this hassbifted dramalically towhere 1 Sense that geosynthetics have ertremely long servicelifemes, but 1have very ma l wncerns as Io the proper ioslallation of geosyntheticrClearly, the geosynthetic material must survive its initiai placement ii these long pre-dictcd lifetimes a m to bc achievcd.

5.2 URVNABILITY REQUIREMENTSFor any of he design mct hd s presented in thi chapter 10 hinction properly, t k nec-essary that the geomembrane suvive thepackaging, lraosportation, handling, and in-staUationdemandsthatareplacedonit.niisaspect f designcannot be takenlighllyorasumed simply to take care of itselEYet there s a decided problem in fomulating ageneraiized sunivsbiiity design for every sppliuitian, since each siiuation k unipue.Someof the major vwiables aectinga given situat ion are the fdowing:

Storageat themaoufac turbg facility* Handling at the mmufachxbg fadityTransportation from thefaetary tq the constructionsite- OfBoadhgat the site* Storagewnditions a1 theaite* Temperatureertremes at the site- Subgrade conditionsal he site

* Deployment at the approximate location- Movementinto he finalSeamidg ocation...?..~ ~ . ..a - l ka tme nt at the site duringseaming


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Fourth EditionDesigningwithGeosyntheticsRobert M. Koerner, Ph.D., P.E.H. L. Bowman Professor of Civil Engineering,Drexel Universityand Director, GeosyntheticResearch Institute

PRENTICE HALLUpper Saddle River, New Jersey 07458


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45 2 Designing with Geornernbran es Chap. 5within the molecular structure . It eventually reacts with anothe r polymer Chain, creat-ing a new free radical and causing Chain scission.The reaction generally acceleratesonce it is triggered, as shown in the following equations.

Re + O2+ ROO. (5.10)ROO. + RH + ROOH + R. (5.11)

whereR. = free radicalROO. = hydroperoxy free radicalRH = polymer ChainROOH = oxidized polym er Chain

Antioxidation additives (antioxidants) are added to the compound to scavengethese free radicals in order to halt, or at least to interfere with, the procesS.These addi-tives, or stabil izers, are specific to each type of resin (recall Table 1.5).This area is verysophisticated and quite advanced with all the resin manufacturers being involved in ameaningful and positive way.The specific antioxidants hat are used are usually propri-etary (see Hsuan e t al. [30] for a review of the top ic).The removal of oxygen from thegeomembrane's surface, of course, eliminates the concern.Thus once placed and cov-ered with waste or liquid, degradatio n by oxidation should be greatly retarded. Con-versely, exposed geomembranes or th ose covered by nonsaturated soi1 will be propor-tionately more susceptible to t he phenomenon. It should be recognized that oxidationof polymers will eventual ly,perhaps a fter hundreds of years, cause degrada tion even inthe absence of other types of degradation phenomena .

There are two related test methods that are used to track the amount a ndor de-pletion of antioxidants. They a re called oxidutive induction time (OIT) tests and areperformed with a DSC device as described in Section 1.2.2.

Sfandard OIT (ASTM D3895);The oxidation is conducted at 35 kPa and 200C.This test appears to misrepresent antioxidant packages containing thiosynergistsan dor hindered amines due to the relatively high test temperature.High Pressure OIT (ASTM D5885);The oxidation is conducted at 3500 kPa and150C. This test can be u sed fo r al1 types of antioxidant packag es and is the pr eferred test.By conducting a series of simulated incubations at elevated temperatures, 011

testing can be conducted on retrieved specimens o monitor the antioxidant depletiorrate. As will be seen in Section 5.1.5, this leads to lifetime prediction via Arrheniu:modeling.

Synergistic Effects. Each of the previous degradation phenomena has beeldescribed individually and separately. In practice, however, t is likely that two or mortmechani sms are actin g simultaneou sly. For example, a waste-containment geomem

Sec. 5.1 Geomemb rane Properties and Test Methods 453brane may have anaerobic leachate above it and a partially saturated leak-detectionnetwork containing oxygen below it. Thus chemical degradation from above and oxi-dation degradation from below will be acting on the liner. Additionally, elevated tem-perature rom decomposing solid waste and the local stress situation may complicatethe situatio n further. Evaluation of these various phenomena is the essence of geo-membrane lifetime prediction.5.1.5 Lifetime PredictionTechniquesClearly, the long time frames involved in evaluating individual degradation mecha-nisms at field-relat ed emperatures and stresses, compounded by synergisticeffects,arenot providing answers regarding geomembrane behavior fast enough for the decision-making practices of today.Thus accelerated testing, either by high stress, elevated tem-peratures andlor aggressive iquids, s very compelling.As will be seen, ai l of the meth-ods use these ways of accelerat ing the test , time-temperatur e superposition being offundamental importance.

Stress-Limit Testing. Focusing almost exclusively on HD PE pipe for naturalgas transmission,many institution s are active in various aspects of plastic pipe researchand development. Stress-limit testing in the plastic pipes has proceeded to a pointwhere there are generally accepted testing methods and standards. ASTM D1598 de-scribes a standard experimental procedure and ASTM D2837 gives guidance on the in-terpretation of the results of the D1598 test method.

In these experiments, ong pieces of unnotched pipe are capped and placed in aconstant temperature environment; a room temp erature of 23C is usually used. Thepipes are placed under various intemal pressures, which mobilize different values ofhoop stress in the pipe walls. The pipes are rnonitored until failur e occurs, which is in-dicated by a sudden loss of pressure. Then the va lues of hoop stre ss are plotted versusfailure times on a log-log scale (see Figure 5.15).If the graph is reasonably linear, astraight line is extrapolated to the desired, or design, lifetime, which is often 18 hoursor 11.4 years.The stress at this failure time multiplied by an appropriate factor is calledthe hydrostutic design basis stress.Whiie this is of interest for pipelines, he stress stateof geomembranes is essentially unknown and is extremely difficult o model.Thus thetechnique is not of direct value for geomembrane design. It leads, however, to the nextmethod.

Rate Process Meth od (RPM) for Pipes. Research at the Gas Institute of TheNetherlan ds (Wolters [31]), uses the metho d of pipe aging that is most prevalen t in Eu-rope. The experiments are again performed using long pieces of unnotched pipe thatare capped, but now they are placed in various constant-temperature environments.Soas to accelerate the process, elevated temperature baths up to 80C are used.The pipesare intemally pressurized so that hoop stress occurs in the pipe walls. The pipes aremonitored untii failure occurs, esulting in sudden lossof pressure. Ibodistinct types offailures are foun d ductile and brittle.The faiiure times corresponding to each appliedpressure are recorded. A response curve is presented by plotting hoop stress againstfailure t h e on a log-log scale.


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454 Designing with Geomembr anes Chap.5

Houn Failure PointsAt least 31ooO

Figure5.15ingof unnotched MDPE pipe.Schematic plot of time of failure versus pipe hoop stress for burst test-

The rate process method (RF'M) is then used to predict a failure curve at sometemperature other than the high temperatures tested, that is, at a lower (field-related)temperature.This method is based on an absolute reaction rate theory and is explainedin [32].The relationships between the failure time and stress are expressed in the formof one of the following equations:

(5.12)(5.13)(5.14)(5.15)

log t, = AoT-' + AIT-'ulog r, = A. + AIT-' + AJ-lPlog r = A,, +AIT-' + A2 og Plog t, = A0 +AIT-' + A2T-I log P

wheretf= time to failure,T = temperature,u = te nd e stress,P = interna1 pipe pressure proportio nal to the hoo p stress in the pipe.A, and Al = constants, and

The application of RPM requires a minimum of two experimental failure curves at dif-ferent elevated temperatures, generally above 40C. The equation that yields the bestcorrelation to these curves is then used in the prediction procedure for a responsecurve at a field-related temperature (e.g., 10 to 25"C).Two separate extrapolations arerequired, one for the ductile response and one for the bnt tle response. Three represen-tative points are chosen on the ductile regions of the two experimental curves. One

455ec. 5.1curvewili be selected for two points, and the other, for the remaining point. These dataare substituted into the chosen equation to obtain the prediction equation for the duc-tile response of the curve at the desired (lower) temperature. The process is now re-peated forthe predicted brittle response curve at the same desired temperature.The in-tersection of these two lines defines the transition time.

Figure 5.16 shows two experimental failure curves that were conducted at tem-peratures of 80C and 60C along with the predic ted curves at 20"C.The inte rsection ofthe linear portions of the 20C curve represents the anticipated t h e or transition inthe HD PE pipe from a ductile to a brittle behavior of the matenal. For pipe design,however, the int ersection of th e desired service lifetime, Say 50 years, with the brittlecurve as the focal point.A factor of safety is then placed on this value, for example,notethat i t is lowered in Figure 5.16.This valueof stress is used as a iimitin g value for thein-ternal pressure in the pipe.

Geomembrane Properties and Test Methods

Rate Process Method (RPM) for Geomembranes. A similar RPM methodto that just descnbed for HDPE pipes can be applied to HDPE geomembranes.Themajor difference is the method of stressing the material. The geomembrane test s areperformed using a notched constant load test (NCTL) (recall Section 5.1.3). Figure 5.17shows typical expenmental curves at 50C and 40"C, which are very s i m i l a r to the be-havior of MDPE pipe. Here distinct ductile and britt le regions can be seen along witha clearly defined transition time.

'Ooc\ uctileII

50yrlog timeFigure 5.16 Burst test data for unnotched MDPE pipein tap water.The intersec-tion of the ductile portion of the 20C ine and50years has been lowered by the a ppropriate factor of safety.


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Designing with Geornembranes Chap. 5456

1 I l l I l ~ 1 ~ ' ' ' " 1 ' 1 ' ' " 1 1 1 1 1 I 1 1 1 1 1 1 110 1M) 1wo0.1 1Failure time ( h r )

Figure 5.17 Notched constant load tests on HDPE geomembrane samples im-mersed in 10%Igepal/90% tap water Solution.In order to use these elevated tempera ture curves to obtain the transition time

for a realistic temperature of a geomembrane beneath solid-wasteor liquid impound-ments (e.g., 20 to 25"C), only Eqs. (5.14) or (5.15) can be used, due to the data beingDiotted in a log-log scale. How the curves are shifted to the site-specific ower temper-ature is explainedin detail in [32].

The process of predicting lifetime can now follow that outlined in Figure 5.16.Adesign lifetime can be assumed and a percent allowable stress can be determined.Con-versely, a maximum allowable desig n stress can b e given from which the unknown life-time can be determined. Work is ongoing using this approach.

Hoechst Multiparameter Approach. The Hoechst research laboratory inGermany has been act ive in the long-term testing of polyethylene pipe since the 1950sThey have also applied their expertise and experience to the long-term behavior ofHDPE geomembranes (Koch et al. [33]). The Hoechst long-term testing for a geo-membrane sh eet consists of th e following procedure:

1. Perform a modified burst testing of pipe (of the same material as the geomem-brane) with additional longitudinal stress to produce an isotropic biaxial stressstate. Note that the site-specific iquid should be used.

2. Assume a given subsidence strain-versus-time profile.3. Measure the stress relaxation curves in shee ts hat have bee n stressed biaxially atstrain values encountered in field.~4. Use Steps2 and 3 to predict the stress as a function of time.5. See how these maximum stresses compare with the stress-lifetime curves deter-mined in the normal constant stress-lifetime pipe measurements of Step l . m e

457constant stress-lifetime curves are modified (as in the norma l pipe testing) to ac-commodate the effects of various chernica ls and for seams.6. Use the variable stress curves to predict failure from the constant stress-lifetimecurves if linear degradation is assumed.

Sec. 5.1 Geomembrane Properties and Test Methods

This approach should certainly be considered seriously. One of the main impedi-ments to its viability is that pipe may have different stress conditions than geomem-branes. Furt hem ore, he residual stresses could be quite different. Other studies of arelat ed nature can be found in Hesse11 and John [34] and Gaube et al. [35].

Elevated Temperature and Arrhenius Modeling. Using an experimentalchamber, as shown in Figure 5.18, Mitchell and S panner [36] have superimposed com-pressive stress,chemical exposure, elevated temperature, and long testing time into asingle experimental device. At th e Geosynthetic Research nstitute, twenty of thesecolumns have been constructed with five each at 85, 75,65 , and 55C constant temper-ature s (see Figure 5.18). Each is und er a normal stress of 260 kPa and is under 300mmof liquid head on its upper surface. The subgrade sand is dry and vented to t he atmos-phere.The test coupons are 1.5mm thick HDPE geomembranes.

Coupons are removed periodically and evaluated for changes in numerous phys-ical, mechanical, and chemical test properties.The anticipated behavior is shown in Fig-ure 5.19a; however, at this t h e , oniy the A and B stages have been quantified.

For stageA, the antioxidant depletion t h e , he KDPE geomembrane selected re-sults in approximately 200 years (Hs uan and Ko emer [37]). On the basis of exhumedHDPE milk containers at th e bottom of a landfiil, the measured induction time(stage B) is from 20 to 30 years.Thus in a buried environment there is a t h e pan of ap-proximately 220 years with essentiallyno engineering-property degradation.This leadsdirectly to stage C.Deciding on a maximum property change to establish stage C (e.g.,a 50% reduction or half-life at each tempe ratur e) allows the plotting of another curve(see Figure 5.19b).This graph is inverse temperature versus reaction rate (actually theinverse time from Figure 5.19a) and is called the Arrhenius cunie The slope of the lineis the activation energy divided by the gas constant.

We can now extrapolate graphically to a lower site-specific temperature, as s h o wby the dashed line on Figure 5.19b, or extend the curve analytically. Examples 5.4 and5.5 illustrate how this is accompli shed, using litera ture values for the activation energy(see [38] for additional details).The essential equation for the extrapolation is

where

E,,,IR = dope of Arrhenius plot,T-test = incubated (high) temperature, andT-site = site-specific (lower) temperature.

(5.16)


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Designing with Geornembranes Chap. 5458

Perforated steel loading plate

t- eomembrane sample

1Load

Figure 5.18 Incubation unit for accelerated aging and photograph of a number Ofsimilar units used at the Geosynthetic Research Institute.Example 5.4

Using expenmental data fromMartin and Gardner [39] for the half-Me of the tendestrength of a PBT plastic, the E J R value is -12,800 K. Determine the estimated life,eX-trapolating from he 93C actual incubation tem perature (which took 300 hours tO Corn-plete) to a site-specific temp erature of 20C. t

Sec. 5.1 Geomembrane Properi ies an d Test Method 459

B = induction time

I II I I I 1 1I I 1 1 1 1I 1 V V V VO

10 t5 t 5 t65 t55Aging Tm e (log scaie)

(a) Incubated property behavior

i emperature (11%)

(b) Arrhenius plot for half-fe property

Figure5.W Arrhenius modeling for lifetime prediction via elevated temperaturea@%.


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a460 Designing with Geornernbran es Chap. 5

Solution: After converting from centigrade to kelvin

'ZOT= e -A]= 6083

If the 93C reaction takes 300 hours to complete, the comparable 20C reaction will takpr200c= 6083(300)

= 1,825,000 hr= 208 yr

n i u s the predicted time for this particular polymer to reach 50% of its original strength at20C is approximately 200 years, its predicted lifetime for stage C.

Example 5.5Using Undenvriters Laboratory Standard [40] data for HDPE cable shieldmg, the &IRvalue is -14,000 K.This comes from the half-lifeof impact streng th tests. One of the hi&temperature tests was at196OCand it took 1000hours t o obtain th ese data.W hat is the Meexpectancy of this material at 9O"C?Solution.After converting from centigrade to kelvin

= e - R 196t273 m + mrWC

= 6104If the 196C reaction takes 1000hours to complete, the comparable 90Creaction will take

rwc = 6104(1000)= 6,104,000 r= 697yr

Thus he predicted time for this particular polymer to reach 50% of its onginal impactstrength at 90C is approxirnately 700 years, its predicted lifetime for stage C.

5.1.6 SurnmaryThis relatively long section on properties and test methods has, hopefully, served 10il-lustrate the wealth of test methods available for the characterization and design con-siderations of geomembranes. Many of the established tests and standardized test

461ec. 5.2 SurvivabilityRequirementsmethods have come by way of the plastics and rubber industries for nongeotechnical-related uses. This is fortunate, for it gives a base or reference plane to work from. How-ever, for many some variation is required before they can be used in below-ground con-struction. Stili others demand completely new tests and test methods. Instandards-setting institutes the world over there is an awareness of the problems andvibrant activity to develop such test methods and procedures. Until they are available,however, we must act on intuit ion and develop methods that mode1 the requi red designinformat ion as closely as possible. Many of the t ests and informat ion presented in thissection are done in that light. It should also be obvious that the complexity of the testshave progressed from the quite simple thickness test on smooth geomembranes to thevery complex degradation tests. Indeed, a very wide range of test meth ods areavaiiable.

Finaily, a rather lengthy discussion of durability and aging gives insight into thepotential service lifetime of geomembranes. In a buned environment, the lifetimespromise to be very long-for example , with stage A of Figure 5.19a being 200 years,stage B being 20years and stage C being hundreds of years, the HD PE geomembranebeing evaluated promises to far outlast other engineering materials in comparable sit-uations. In my experience with geosynthetics over the past 20 years, my original con-clusion was that geosyn thetics were easy to place but wouldn't la st very long; this hasshifted dramatically to where 1 sense that geosynthetics have extremely long serviceietimes but 1have very real concerns as to the proper installa tion of geosynth eticsClearly, the geosynthetic matenal must survive its initial placement if these long pre-dicted lifetimes are to be achieved.

5.2 SURVlVABlLlTY REQUIREMENTSFor any of the design methods presented in this chapter to function properly, t is nec-essary that the geomembrane survive the packaging, transportation, handling, and in-stallation demands that are placed on it.This aspectof design cannot be taken lightly orassumed simply to take care of itself. Yet there is a decid ed problem in formula ting ageneralized survivability design for every application, since each situation is unique.Some of the major variables affecting a given situation are the following:

Storage at the manufacturing facilityHa nd li g at the manufacturing facilityTransportation from the factory to the construction siteOffloading at the siteStorage conditions at the siteTemperature extremes at the siteSubgrade conditions at the siteDeployment at the approximate locationMovement into the &al seaming ocationTreatment at the site during seaming

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desiıgning with geosynthetics robert kroner