Damage Repair and Safety of Norwegian Concrete Dams.docx
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Damage Repair and Safety of Norwegian Concrete Dams.docx
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DamageRepairandSafetyofNorwegianConcreteDams
SurveyaboutDamage,RepairandSafetyofNorwegianConcreteDams
V.Jensen
SINTEFCivilandEnvironmentalEngineering,CementandConcrete,Trondheim,Norway
ABSTRACT:
ThepaperpresentresultsandassessmentsfromasurveycarriedoutbySINTEFin1998.AquestionnairewasmailedtoallVTApersonsinNorwayandanswersfrom287concretedams(432includingcombinationdams),equalto27%ofallmaintypesofconcretedamsunderpublicsupervisioninNorway,werereceived.89damsaresocalled“largedams”higherthan15meter.ThesurveyshowsthatthemajorityofdamownersfollowrequirementsandrecommendationbyNVE.Mostconcretedamscontainfewdamagesofvarioustypeswithoutanyconsequentforthefunctionandsafety.However,damagescategorizedasmanyoccurinupto5%ofthedams,whichmightinfluencesafetyandreliabilityinashortorlongtimespan.Surprisinglymanyconcretedamswererepaired(44%)orwillberepairedinthenearfuture(40%)and10%ofexistingrepairhasbeenrepairedmorethanonetime.Largedamsaregenerallymoredamagedthansmallerdamsanditlookslikedamsconstructedaround1950to1960aremoredamagedthanotherperiods.
1FIELDINVESTIGATIONSOFNORWEGIANCONCRETEDAMS
Alreadyinthe1920sconsiderabledamagewasrecordedonsomeofthedamswhichwereinoperatingatthattime.In1925theNorwegianEngineersAssociationappointedacommitteeinordertohavetheconditionofthedamsinvestigated.Theresultsoftheseinvestigationswerepublishedina251-pagereport-Halvorsenetal.(1930).Theconclusionofthereportwasthatthewater'scorrosivecharacterandthecomparativelysevereclimatewereassumedtobethemainfactorscausingthedamage.Insomedamsleachingofcalciumhadtotallydisintegratedtheconcreteintogravel.Inafewcasesahighcontentofhumusinthesandandorganicmatterinpercolatingwaterhaddisintegratedtheconcrete.Generallytheuseofaleanconcreteandinhomogeneouspoorconcretequalityhadincreasedthedeteriorationoftheconcrete.Toreducethedamageinconstructionofnewdamsitwasrecommendedtouseimperviousconcrete,freeofcracks.Inlaterdamconstructionsimperviousconcretewasobtainedbysubstantiallyincreasingthecementcontentintheconcrete.
AlaterdaminvestigationappointedbyICOLD(InternationalCommitteeOnLargeDams)132damswereinvestigatedduringtheperiod1962to1968,butafinalreportwasneverpublished.AccordingtoHeggstad&Myhren(1967)somedamageduetofreezingandpercolationofwaterwasrecorded,buttheslenderreinforcedambursen-archdamsweregenerallyinbetterconditionthangravitydamsbuiltatthesametime.Severedamagewasmostlyfoundonolderdams,normallycausedbylocalerrorsorweakspotsduringtheconstructionthework.Inambursendamscomprehensivecracksandfissureswereobservedindamplatesevendilatationjointshadbeenused.Inconcretewherecrushedrockhadbeenusedwithcrushedrockaggregatesadistinctlylowercrackingtendencyoccurredcomparedtoconcretewherenaturalsandshadbeenused.Thelowercrackingtendencyinconcretewherecrushedrockshadbeenusedwasattributedtoincreasedbondbetweentheaggregatesandthecementpaste.OfalltheAmbursendamsandthereinforcedarchdamsbuiltduringthelast10years,thereareonlytwowhicharecompletelyfreeoffissures,andforthesedamsboththefineandthecoarseaggregateweremadeexclusivelyofcrushedgranite.Damsbuiltaround1955containgenerallymoreinitialcracksandfissuresthandamsbuiltearlier.
AthirdnationaldaminvestigationappointedbytheNorwegianWaterResourcesandEnergy
Administration(NVE)wascarriedoutintheperiod1988-1990.Here55damswereinspected.AfinalreportwaspublishedbyGautefall(1990),whichconcludedthatfrost-thawdeteriorationwasthemostfrequentcauseofdamage.Generally,concretedamagesinNorwegiandamswereinsignificantaccordingtothedamsbearingandfunctioncapacities.Howeverabout50%ofthedamsweremapcrackedandrecommendedforafurtherphase2investigationforAlkaliAggregateReaction.Increasedcrackinginslenderreinforceddamsbuiltaround1960comparedtoolderdams,wasobservedhere,too,anditwasrecommendedthatthesedamsweresupervisedinthefuture.
FieldinvestigationsinSouthernNorway,generallyforAlkaliAggregateReaction,carriedoutintheperiod1989to1992byJensen(1993)alsorevealsanincreasedcrackingtendencyofconcreteroadbridgesandconcretedamsbuiltinthemid1950s.
2BACKGROUND
TheNorwegianWaterResourcesandEnergyAdministration(NVE)requiresinspectionprogramsandroutinesforallNorwegiandamstructuresNVE(1990).In1993NVEintroducedrequirementforcompetentandqualifiedpersonnelresponsibleforthesafetyofeachdamstructure,inNorwegiancalled“vassdragstekniskansvarlig”(VTA).TheVTA-personhastobecivilengineer,musthaveminimum3yearsexperience,followtechnicalcoursesandhavegoodknowledgeaboutthesafetyandconditionofthedamsheisresponsiblefor,NVE1993a.BecauseofthetechnicalknowledgeofVTA-personsitwasreasonabletoprepareaquestionnairewithquestionsaboutsafety,damagesandthegeneralconditionofthedams.Questionsweremostlycategorizedasyes/no,none,few,manyordon’tknow.ThecompetenceoftheVTApersonwasapreconditionforthesurveyofNorwegiandamspresentedinthispaper.Theaimswiththesurveyaretoobtaininformationaboutsafety,damages,inspectionroutinesandrepair.Theenquirydealswithconcretedams,embankmentdams(filldams)andhydropowerplants,butonlyresultsfromconcretedamsarepresentedhere.However,resultsfromembankmentdamsarepresentedbyanotherpaperinthisconferencebySkoglund(2001).
3THEQUESTIONS
ThequestionnairewasmailedtoallregisteredVTApersonsinNorwayin1998accordingtoalist
fromNVE,alltogether222persons.Questionsrelatedtoconcretedamswereofthefollowingtypes:
?
Owner,name,age,dimensions,useandlocation
?
InspectionroutinesaccordingtoNVE’srequirements
?
Damagesanddeteriorationprocesses
?
Repair,existingandplannedtobecarriedout
?
Safetyandrebuilding,nowandinthefuture
ThelastfilledinquestionnairefromdamswasreceivedinMay1998.Aprofessionalcompany,NORFAKTA,washiredtopunchdataintoadatabase.ThisworkwasconcludedinJune1998.Jensen&Skoglund(2000)reportresultsandassessmentsfromtheenquiryasanonymoustablesandfigures,whichcannotberecordedtoanyspecificdamstructure.
4RESULTS
Thesurveyreceivedanswersfrom461damsclassifiedasmaintypes,whereas287wereconcretedams,seeTable1
Table1.Maintypeofdams
Typeofdam:
NumberPercent
Concretedam28754
Filldam*9518
Filldamwithconcretedam7915
Total461100
*Notpresentedinthepaper
Embankmentdams,e.g.rockfilldamsandearthfilldamsarenotpresentedinthepaperasmentionedearlier.Thetotalnumberofconcretedamsintheenquiryishigherthan287,namely432becausecombinationdamseg.filldamwithsmallerconcretedamisincludedtoo,seefigure1.
25020015010050
0
179
122
95
36
GravitydamPlatedamArchdamOtherdams
Figure1.Typeofconcretedamsintheenquiry
19001910192019301940195019601970198019902000
40
80706050
30
20100
Firstbuildingperiod
Figure2.Concretedamsrelatedtofirstbuildingperiod
Figure3dealswithinspectionroutines.Notethatonly6damsdonothaveaninspectionprogramme.
328
6
0
250
200
150
100
50
350
300
27
YesUnderplanningNo
Figure3.Inspectionprogramisestablished
Figure4showsthefrequencyofperiodicallyinspections(left)andmaininspections(right).
01-2a3-4a>4a01-33-6>6
yearyearyearyearsyearsyears
350300250
200
150
100
5021
0
304
8261633
280
25
Figure4.Periodically-(left)andmaininspections(right)
Table2givesanswers(percent)ofdamagesinthewholedamstructure.Notethatupto4%to5%ofthedamshavemanycrackandmapcracking.
Table2.Damagesinthewholedam
Few
Many
Don’tknow
Typeofdamage
Dams
(%)
(%)
(%)
Horizontalcrack
346
48
5
2
Verticalcrack
343
52
4
2
Waterleakage
348
31
1
2
Mapcracking
337
32
4
4
Delaminating
346
45
2
2
Freereinforcement
341
23
1
1
Erosion
342
30
1
2
Deformation
340
12
2
2
Leaching/efflorescence
343
46
3
4
Corrosion(rust)
335
22
0
4
Castingdefect
338
42
3
2
Otherdamage
79
8
1
4
Table3showsdamagesinjoints.Notethat4%ofthedamshavesealingmaterialsqueezedoutfromthejointsand2%havereducedjointswidth.
Table3.Damageinjoints.
Typeofdamage
Few
Many
Don’tknow
Dams
(%)
(%)
(%)
Squeezedjointmaterial
311
20
4
3
Reducedjointwidth
312
13
2
6
Waterleakage
317
24
1
3
Movement/crushing
314
12
0
5
Reducedgroundcontact
308
3
0
10
Table4dealswithproblemsunderwaterlevelandproblemsrelatedtogatesinthespillway.Notethat16%answer“yes”foroccurrenceofdamagesbelowwaterleveland4%to8%forproblemswiththegate.
Table4.Damageunderwaterlevelandongates
Typeofdamage
Yes
No
Don’tknow
Dams
(%)
(%)
(%)
Damagebelowwaterlevel
307
16
52
31*
Lockingofgate
267
4
92
4
Reducedfreewayofgate
257
8
91
6
Otherproblemswithgate
114
6
87
7
*Notinvestigated
Table5dealswithdamagesondamplates/archesandifdamageshaveincreasedduringthelastyears.Notethat36%ofthedamshavedamagesrelatedtodamplatesandarchand6%to7%haveobservedincreasingdelaminatingandcrackingduringthelastyears.
Tab
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