technical standards and commentaries for port and … · technical standards and commentaries for...
TRANSCRIPT
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
(3)PerformanceverificationofSRCMembers
① Thesteelandreinforcedconcrete(SRC)membersshallbedesignedagainsttheflexuralmomentandshearingforce,bytakingfullaccountofthestructuralcharacteristicsduetodifferencesinthestructuraltypeofthesteelframe.
② SRCmemberscannormallybeclassifiedasfollows,dependingonthestructuraltypeofsteelframes:
(a) Full-webtype
(b)Trusswebtype
③ Fortheflexuralmoment,thesectionstresscanbecalculatedasareinforcedconcretememberbyconvertingsteelframestoequivalentreinforcements.Whenthefixingofsteelframeendswithconcreteisinsufficientinfull-webtype,itshouldbecalculatedasacompositeoftheindependentsteelframememberandthereinforcedconcretemember.
④ Forshearingforce,ifthewebisoftrusstype,theshearstresscanbecalculatedasareinforcedconcretebyconvertingsteelframestoequivalentreinforcements.Ifitisoffull-webtype,steelframesthemselvescanresistagainsttheshearingforce,andtheycanbedulyconsideredindesign.
(4)PerformanceVerificationofPartitionWalls
Becausepartitionwallsfunctionasabearingsideoftheouterwallsandbottomslab,inperformanceverification,stabilityofthecrosssectionofthepartitionwallshouldbesecuredagainstthesectionalforcescalculatedbasedontheactionsonthesebearingsides.
(5)PerformanceVerificationofCornersandJoints
① Cornersandjointsshallbedesignedtosmoothlyandfirmlytransmitsectionforces,andtobeeasilyfabricatedandexecuted.
② Tosecuresufficientstrengthatcornersandjoints,itisdesirabletofirmlyconnectthesteelmaterialsonthetensile side to thoseof thecompressiveside. It isalsodesirable toprovideshear reinforcedsteelmaterials(haunches)againstconcretetensilestressoftheinsideofjoints.
(6)PerformanceVerificationforFatigueFailure
① Hybridcaissonsusealargenumberofweldedjointsforconnectingsteelplates,andattachingshearconnectorsandshearresistancesteel.Therefore,wherethemembersarefrequentlysubjecttorepeatedload,thefatiguestrengthinweldedpartsshouldbeexamined.
② In coastal revetments and quaywalls, the influence of repeated actions is small. However, in performanceverificationsofbreakwaters,whenthestressonmembersduetowavesasarepeatedactionchangessignificantly,examinationforfatiguefailureofthecaissonisneeded.
1.6.5 Corrosion Control
(1)Corrosioncontrolofhybridcaissonsshallbesetappropriatelyconsideringtheperformancerequirements,levelofmaintenancecontrol,constructionconditions,andotherrelevantfactors.
(2)Themaincauseofdeteriorationofhybridmembersiscorrosionofthesteelmaterials.Becausetherearecasesinwhichcorrosionofthesteelmaterialsmayresultindevelopingcracksoftheconcrete,appropriatecorrosionpreventionmeasuresshouldbetakenforsteelplatesinordertoimprovethedurabilityofthehybridmembers.Thedeteriorationcharacteristicsoftheconcreteitselfshouldbeconsideredtobethesameasthatofconventionalreinforcedconcrete.
(3)Steelmaterialsusedontheoutsideofhybridcaissonsaregenerallycoveredwithconcreteorasphaltmats.Theinsideofacaissonisisolatedfromtheexternalatmospherebymeansofconcretelids.Itisalsoincontactwithfillingsand inastaticstateandwithresidualseawater. Thus,whendesigninghybridcaissons,directcontactbetweenthesteelplatesofmembersandthemarineenvironmentisgenerallyavoided.Forcorrosioncontrol,itisusualtosetsteelplateontheinsideandconcreteontheoutsidesoastoavoiddirectcontactofsteelplatewithfreshseawater.Ifsteelplatesareindirectcontactwithseawater,corrosioncontrolshouldbeappliedsuchascoatingmethodstosplashzoneortidalzoneandcathodicprotectionmethodsinseawater.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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1.7 Armor Stones and BlocksPublic NoticePerformance Criteria of Armor Stones and Blocks
Article 28 Theperformancecriteriaofrubblestonesandconcreteblocksarmoringastructureexposedtotheactionsofwavesandwatercurrentsaswellasarmorstonesandarmorblocksofthefoundationmoundshallbesuchthattheriskofexceedingtheallowabledegreeofdamageunderthevariableactionsituation,inwhichthedominantactionsarevariablewavesandwatercurrents,isequaltoorlessthanthethresholdlevel.
[Commentary]
(1)PerformanceCriteriaofArmorStonesandBlocksThesettingsoftheperformancecriteriaanddesignsituations,excludingaccidentalsituations,forarmorstonesandblocksshallbeasshownintheAttached Table 14.
Attached Table 14 Settings for Performance Criteria and Design Situations (excluding accidental situations) for Armor Stones and Blocks
MinisterialOrdinance PublicNotice
Performancerequirements
Designsituation
Verificationitem Indexofstandardlimitvalue
Article
Paragraph
Item
Article
Paragraph
Item Situation Dominatingaction
Non-dominatingaction
7 1 – 28 1 – Serviceability Variable Variablewaves Selfweight,waterpressure
Extentofdamage Limitvalueofdamagerate,degreeofdamage,ordeformationlevel
①ExtentofdamageTheindexeswhichexpresstheextentofdamageofarmorstonesandblocksforthevariablesituationsinwhichthedominatingactionsarevariablewavesandwatercurrentsarethedamagerate,thedegreeofdamage,andthedeformationlevel. In theperformanceverificationofarmor stonesandblocks, the indexes including thedegreeofdamageandthelimitvaluethereofshallbesetappropriatelyconsideringthedesignworkinglifeoftheobjectivefacilities,theconstructionworkconditions,thetimeandcostnecessaryforrestoration,andtheconditionsofwavesandwatercurrents,etc.
[Technical Note]
1.7.1 Required Mass of Armor Stones and Blocks on Slope24),25)
(1)GeneralThe armor units for the slopes and a sloping breakwaters are placed to protect the rubble stones inside; it isnecessarytoensurethatanarmorunithasamasssufficienttobestablesothatitdoesnotscatteritself.Thisstablemass,requiredmass,cangenerallybeobtainedbyhydraulicmodeltestsorcalculationsusingappropriateequations.
(2)BasicEquationforCalculationofRequiredMassWhencalculatingtherequiredmassofrubblestonesandconcreteblockscoveringtheslopeofaslopingstructurewhichisaffectedbywaveforces,Hudson’sformulawiththestabilitynumberNS,whichisshowninthefollowingequation,maybeused.26)Inthisequation,thesymbolγisapartialfactorforitssubscript,andthesubscriptskanddshowthecharacteristicvalueanddesignvalue,respectively.ForthepartialsafetyfactorsγNS andγH intheequation,1.0maybeused.
(1.7.1)where
M :requiredmassofrubblestonesorconcreteblocks(t) ρr :densityofrubblestonesorconcreteblocks(t/m3) H :waveheightusedinstabilitycalculation(m) NS :stabilitynumberdeterminedprimarilybytheshape,slope,damagerateofthearmor,etc. Sr :specificgravityofrubblestonesorconcreteblocksrelativetowater
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
Thedesignvaluesintheequationmaybecalculatedusingthefollowingequations.
(3)DesignWaveHeightHUsedinthePerformanceVerificationHudson’sformulawasproposedbasedontheresultsofexperiments thatusedregularwaves. Whenapplyingit totheactionofactualwaveswhicharerandom,thereisthusaproblemofwhichdefinitionofwaveheightsshallbeused.However,withstructuresthataremadeofrubblestonesorconcreteblocks,thereisatendencyfordamagetooccurnotwhenonesinglewavehavingthemaximumheightH amongarandomwavetrainattacksthearmorunits,butratherfordamagetoprogressgraduallyunderthecontinuousactionofwavesofvariousheights.Consideringthisfactandpastexperiences,ithasbeendecidedtomakeitstandardtousethesignificantwaveheightofincidentwavesattheplacewheretheslopeislocatedasthewaveheightH inequation (1.7.1),becausethesignificantwaveheightisrepresentativeoftheoverallscaleofarandomwavetrain.Consequently,itisalsostandardtousethesignificantwaveheightwhenusingthegeneralizedHudson’sformula.Notehoweverthatforplaceswherethewaterdepthislessthanonehalfoftheequivalentdeepwaterwaveheight,thesignificantwaveheightatthewaterdepthequaltoonehalfoftheequivalentdeepwaterwaveheightshouldbeused.
(4)ParametersAffectingtheStabilityNumberNSAsshowninequation (1.7.1),therequiredmassofarmorstonesorconcreteblocksvarieswiththewaveheightandthedensityofthearmorunits,andalsothestabilitynumberNS.TheNS valueisacoefficientthatrepresentstheeffectsofthecharacteristicsofstructure,thoseofarmorunits,wavecharacteristicsandotherfactorsonthestability.ThemainfactorsthatinfluencetheNS valueareasfollows.
① Characteristicsofthestructure
(a) Type of structure; sloping breakwater, breakwater covered with wave-dissipating concrete blocks, andcompositebreakwater,etc.
(b)Gradientofthearmoredslope
(c) Positionofarmorunits;breakwaterhead,breakwatertrunk,positionrelativetostillwaterlevel,frontfaceandtopofslope,backface,andberm,etc.
(d)Crownheightandwidth,andshapeofsuperstructure
(e) Innerlayer;coefficientofpermeability,thickness,anddegreeofsurfaceroughness
② Characteristicsofthearmorunits
(a) Shapeofarmorunits(shapeofarmorstonesorconcreteblocks;forarmorstones,theirdiameterdistribution)
(b)Placementofarmorunits;numberoflayers,andregularlayingorrandomplacement,etc.
(c) Strengthofarmormaterial
③Wavecharacteristics
(a) Numberofwavesactingonarmorlayers
(b)Wavesteepness
(c) Formofseabed(seabedslope,whereaboutofreef,etc.)
(d)Ratioofwaveheighttowaterdepthasindicesofnon-breakingorbreakingwavecondition,breakertype,etc.
(e)Wavedirection,wavespectrum,andwavegroupcharacteristics
④ Extentofdamage(damageratio,deformationlevel,relativedamagelevel)Consequently, theNS valueusedintheperformanceverificationmustbedeterminedappropriatelybasedonhydraulicmodelexperimentsinlinewiththerespectivedesignconditions.Bycomparingtheresultsofregularwavesexperimentswiththoseofrandomwaveexperiments,27)itwasfoundthattheratiooftheheightofregularwavestothesignificantheightofrandomwavesthatgavethesamedamageratio,withintheerrorof10%,variedintherangeof1.0to2.0,dependingontheconditions.Inotherwords,therewasatendencyfortherandomwaveactiontobemoredestructivethantheactionofregularwaves.Itisthusbettertoemployrandomwavesinexperiments.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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(5)StabilityNumberNS andKDValueIn1959,Hudsonpublishedtheso-calledHudson’sformula,26)replacingthepreviousIribarren-Hudson’sformula.Hudsondevelopedequation (1.7.1)byhimselfusingKD cotαinsteadofNS.
(1.7.3)
where α :angleoftheslopefromthehorizontalline(°) KD :constantdeterminedprimarilybytheshapeofthearmorunitsandthedamageratio
TheHudson’sformulawasbasedontheresultsofawiderangeofmodelexperimentsandhasproveditselfwellinusagein-site.ThisformulausingtheKD valuehasthusbeenusedinthecalculationoftherequiredmassofarmorunitsonaslope. However,theHudson’sformulathatusesthestabilitynumberinequation (1.7.1)hasbeenusedforquiteawhileforcalculatingtherequiredmassofarmorunitsonthefoundationmoundofacompositebreakwaterasdiscussedin1.7.2 Required Mass of Armor Stones and Blocks in Composite Breakwater Foundation Mound against Waves,andisalsousedforthearmorunitsofotherstructuressuchassubmergedbreakwaters.ItisthusnowmorecommonlyusedthantheoldformulawiththeKD value. ThestabilitynumberNS canbederivedfromtheKD valueandtheangleαoftheslopefromthehorizontallinebyusingequation (1.7.3)ThereisnoproblemwiththisprocessiftheKD valueisanestablishedoneandtheslopeangleiswithinarangeofnormaldesign.However,mostoftheKD valuesobtaineduptothepresenttimehavenotsufficientlyincorporatedvariousfactorslikethecharacteristicsofthestructureandthewaves.Thus,thismethodofdetermining the stabilitynumberNS from theKD value cannotbeguaranteed toobtain economicaldesignalways.Inordertocalculatemorereasonablevaluesfortherequiredmass,itisthuspreferabletousetheresultsofexperimentsmatchedtotheconditionsinquestion,orelsetousecalculationformulas,calculationdiagrams,thatincludethevariousrelevantfactorsasdescribedbelow.
(6)VanderMeer’sFormulaforArmorStonesIn1987,vanderMeercarriedoutsystematicexperimentsconcerningthearmorstonesontheslopeofaslopingbreakwaterwithahighcrown.Heproposedthefollowingcalculationformulaforthestabilitynumber,whichcan consider not only the slopegradient, but also thewave steepness, thenumberofwaves, and thedamagelevel.28)NotehoweverthatthefollowingequationshavebeenslightlyalteredincomparisonwithvanderMeer’soriginaloneinordertomakecalculationseasier.Forexample,thewaveheightH2%forwhichtheprobabilityofexceedanceis2%hasbeenreplacedbyH1/20.
(1.7.4)
(1.7.5)
(1.7.6)
where Nsp :stabilitynumberforplungingbreakers Nssr :stabilitynumberforsurgingbreaker Ir :iribarrennumber(tanα/Som0.5)),alsocalledthesurfsimilarityparameter Som :wavesteepness(H1/3/L0) L0 :deepwaterwavelength(L0=gT1/32/2π,g=9.81m/s2) T1/3 :significantwaveperiod CH :breakingeffectcoefficient{=1.4/(H1/20/H1/3)},(=1.0innon-breakingzone) H1/3 :significantwaveheight H1/20 :highestone-twentiethwaveheight,seeFig. 1.7.1 α :angleofslopefromthehorizontalsurface(°) Dn50 :nominaldiameterofarmorstone(=(M50/ρr)1/3) M50 :50%valueofthemassdistributioncurveofanarmorstonenamelyrequiredmassofanarmor
stone P :permeabilityindexoftheinnerlayer,seeFig. 1.7.2 S :deformationlevel(S=A/Dn502),seeTable 1.7.1 A :erosionareaofcrosssection,seeFig. 1.7.3 N :numberofactingwaves
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
Thewave heightH1/20 inFig. 1.7.1 is for a point at a distance 5H1/3 from the breakwater, andH0’ is theequivalentdeepwaterwaveheight.ThedeformationlevelS isanindexthatrepresentstheamountofdeformationofthearmorstones,anditisakindofdamageratio.ItisdefinedastheresultoftheareaA erodedbywaves,seeFig. 1.7.3,beingdividedbythesquareofthenominaldiameterDn50ofthearmorstones.AsshowninTable 1.7.1,threestagesaredefinedwithregardtothedeformationlevelofthearmorstones : initial damage,intermediatedamage,andfailure.Withthestandarddesign,itiscommontousethedeformationlevelforinitialdamageforN =1000waves.However,incasewhereacertainamountofdeformationispermitted,usageofthevalueforintermediatedamagemayalsobeenvisaged.
1.4
1.3
1.3
1.2
1.2
1.3
1.2
1.4
1.4
0 0.5 1 1.5 2 2.5 3 3.5 4
H1/20/H1/3
h/H0'
H0'/L0
0.08 0.04 0.02 0.010.0050.002
Sea Bottom slope 1/100Sea Bottom slope 1/100
Sea Bottom slope 1/50Sea Bottom slope 1/50
Sea Bottom slope 1/30Sea Bottom slope 1/30
H0′: Equivalent deepwaterwave heightH0′: Equivalent deepwaterwave height
Fig. 1.7.1 Ratio of H1/20 to H1/3 (H1/20 Values are at a Distance 5H1/3 from the Breakwater)
P=0.1 P=0.4
P=0.5 P=0.6
(a) (b)
(c) (d)
Dn50A = Nominal diameter of armor stones
Dn50C = Nominal diameter of core materialDn50F = Nominal diameter of filter material
2Dn50A
2Dn50A
1.5Dn50A
2Dn50
0.5Dn50A
Dn50A/Dn50F =4.5
Dn50A/Dn50C =3.2
Dn50A/Dn50F =2Dn50F/Dn50C =4
Armor layer
Armor layer
Armor layer
Armor layer
Core
Filter layerFilter layerImpermeable
layer
No filter, no core
Fig. 1.7.2 Permeability Index P
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S.W.L
A (Area of eroded part)
Fig. 1.7.3 Erosion Area A
Table 1.7.1 Deformation Level S for Each Failure Stage for a Two-layered Armor
Slope Initialdamage Intermediatedamage Failure1:1.51:21:31:41:6
22233
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88121717
(7)FormulationforCalculatingStabilityNumberforArmorBlocksincludingWaveCharacteristicsVanderMeerhascarriedoutmodelexperimentsonseveralkindsofprecastconcreteblocks,andproposedtheformulasforcalculatingthestabilitynumberNS.29)Inaddition,otherpeoplehavealsoconductedresearchintoestablishingcalculationformulasforprecastconcreteblocks.Forexample,BurcharthandLiu30)haveproposedacalculationformula.However,itshouldbenotedthatthesearebasedontheresultsofexperimentsforaslopingbreakwaterwithahighcrown.Takahashietal.31)showedaperformanceverificationmethodofthestabilityagainstwaveactionforarmorstonesofaslopingbreakwaterusingVanderMeer’sformulaastheverificationformula,andproposedtheperformancematrixusedforperformanceverification.
(8)FormulasforCalculatingStabilityNumberforConcreteBlocksofBreakwaterCoveredwithWave-dissipatingBlocksThewave-dissipatingconcreteblockpartsofabreakwatercoveredwithwave-dissipatingblocksmayhavevariouscross-sections.Inparticular,whenallthefrontfaceofanuprightwalliscoveredbywave-dissipatingconcreteblocks,thestabilityishigherthanthatofarmorconcreteblocksofanordinaryslopingbreakwaterbecausethepermeabilityishigh.InJapan,muchresearchhasbeencarriedoutonthestabilityofbreakwaterscoveredwithwave-dissipatingconcreteblocks.Forexample,Tanimotoetal.32),Kajimaetal.33),andHanzawaetal.34)havecarriedoutsystematicresearchonthestabilityofwave-dissipatingconcreteblocks. Inaddition,Takahashietal.35)haveproposedthefollowingequationforwave-dissipatingconcreteblocksthatarerandomlyplacedinallthefrontfaceofanuprightwall.
(1.7.7)where
N0 :degreeofdamage,akindofdamageratethatrepresentstheextentofdamage:itisdefinedasthenumberofconcreteblocksthathavemovedwithinawidthDn inthedirectionofthebreakwateralignment,whereDn isthenominaldiameteroftheconcreteblocks:Dn=(M/ρr)1/3,whereM isthemassofaconcreteblock
CH :breakingeffectcoefficient;CH=1.4/(H1/20/H1/3),innon-breakingzoneCH =1. a,b :coefficientsthatdependontheshapeoftheconcreteblocksandtheslopeangle.Withdeformed
shapeblockshavingaKDvalueof8.3,itmaybeassumedthata =2.32andb =1.33,ifcotα=4/3,anda =2.32andb =1.42,ifcotα=1.5.
Takahashi et al.35)have further presented amethod for calculating the cumulative degree of damage, theexpecteddegreeofdamage,overtheservicelifetime.Inthefuture,reliabilitydesignmethodsthatconsidertheexpecteddegreeofdamageisimportantasthemoreadvanceddesignmethod.Intheregionwherewavebreakingdoesnotoccur,ifthenumberofwavesis1000andthedegreeofdamageN0is0.3,thedesignmassascalculatedusingthemethodofTakahashietal.ismore-or-lessthesameasthatcalculatedusingtheexistingKD value.ThevalueofN0=0.3correspondstotheconventionallyuseddamagerateof1%.
(9) IncreaseofMassinBreakwaterHeadWavesattacktheheadofabreakwaterfromvariousdirections,andthereisagreaterriskofthearmorunitsonthe
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
topoftheslopefallingtotherearratherthanthefront.Therefore,rubblestonesorconcreteblockswhicharetobeusedattheheadofabreakwatershouldhaveamassgreaterthanthevaluegivenbyequation (1.7.1). Hudson proposed increasingmass by about 10% in the case of rubble stones and about 30% in the caseofconcreteblocks. However,becausethisisthoughttobeinsufficient, it ispreferabletouserubblestonesorconcreteblockswithamassatleast1.5timesthevaluegivenbyequation (1.7.1).Kimuraetal.36)haveshownthat,inacasewhereperpendicularincidentwavesactonthebreakwaterhead,thestablemasscanbeobtainedbyincreasingtherequiredmassofthebreakwatertrunkby1.5times.Incaseofobliqueincidenceat45º,inthebreakwaterheadontheuppersiderelativetothedirectionofincidenceofthewaves,thenecessaryminimummassisthesameasfor0ºincidence,whereas,onthelowersideofthebreakwaterhead,stabilityissecuredwiththesamemassastheinthebreakwatertrunk.
(10)SubmergedArmorUnitsSincetheactionofwavesonaslopingbreakwaterbelowwatersurfaceisweakerthanabovethewatersurface,themassofstonesorconcreteblocksmaybereducedatdepthsgreaterthan1.5H1/3belowthestillwaterlevel.
(11)CorrectionforWaveDirectionIncaseswherewavesactobliquely to thebreakwater alignment, theextent towhich the incidentwaveangleaffectsthestabilityofthearmorstoneshasnotbeeninvestigatedsufficiently.However,accordingtotheresultsofexperimentscarriedoutbyVandeKreeke,37)inwhichthewaveanglesof0º,i.e.,directionofincidenceisperpendicular to thebreakwater alignment, 30º, 45º, 60º and90º, i.e., directionof incidence isparallel to thenormallinewereadopted,thedamagerateforawavedirectionof45ºorsmallerismore-or-lessthesameasthatforawavedirectionof0º,andwhenthewavedirectionexceeds60º,thedamageratedecreases.Consideringtheseresults,whentheincidentwaveangleis45ºorless,therequiredmassshouldnotbecorrectedforwavedirection.Moreover,Christensenetal.38)haveshownthatstability increaseswhen thedirectionalspreadingofwaves islarge.
(12)StrengthofConcreteBlocksIncaseofdeformedshapeconcreteblock,itisnecessarynotonlytoensurethattheblockhasamasssufficienttobestableforthevariablesituationinrespectofwaves,butalsotoconfirmthattheblockitselfhassufficientstructuralstrength.
(13)StabilityofArmorBlocksinReefAreaIngeneral,areefrisesupatasteepslopefromtherelativelydeepsea,andformsarelativelyflatandshallowseabottom.Consequently,whenalargewaveentersatsuchareef,itbreaksaroundtheslope,andthentheregeneratedwavesafterwardpropagateoverthereefintheformofsurge.Thecharacteristicsofwavesoverareefarestronglydependentonnotonlytheincidentwaveconditionsbutalsothewaterdepthoverthereefandthedistancefromtheshoulderofthereef.Thestabilityofwave-dissipatingconcreteblockssituatedonareefalsovariesgreatlyduetothesamereasons.Thereforethecharacteristicsoverareefaremorecomplicatedthanthatingeneralcases.Thestabilityofwave-dissipatingconcreteblockssituatedonareefmustthusbeexaminedbasedeitheronmodelexperimentsmatchingtheconditionsinquestionoronfieldexperiencesforsiteshavingsimilarconditions.
(14)StabilityofWave-dissipatingBlocksonLowCrestSlopingBreakwaterForalowcrownslopingbreakwaterwithwave-dissipatingblocksandwithoutsupportingwall,itisnecessarytonotethatthewave-dissipatingblocksarounditscrownareeasilydamagedbywaves.39)Forexample,fordetachedbreakwater composedofwave-dissipatingblocks, unlike a caissonbreakwater coveredwithwave-dissipatingblocks,thereisnosupportingwallatthebackandthecrownisnothigh.Thismeansthattheconcreteblocksnearthecrowninparticularattherearareeasilydamaged,andindeedsuchcasesofblockdamagehavebeenreported.Inthecaseofadetachedbreakwater,itispointedoutthatsomekindofconcreteblocksattherearofthecrownshouldhavealargersizecomparedtotheoneatthefrontofthecrown.
(15)StabilityofBlocksonSteepSlopeSeabedIncaseswherethebottomslopeissteepandwavesbreakinaplungingwaveform,alargewaveforcemayactontheblocks,dependingontheirshapes.Therefore,appropriateexaminationshouldbecarriedout,consideringthisfact.40)
(16)High-densityBlocksTherequiredmassofblocksthataremadeofhigh-densityaggregatemayalsobedeterminedusingtheHudson’sformulawiththestabilitynumbershowninequation (1.7.1).Asshownintheequation,high-densityblockshaveahighstability,soastablearmorlayercanbemadeusingrelativelysmallblocks.41)
(17)EffectofStructuralConditionsThestabilityofwave-dissipatingblocksvariesdependingonstructuralconditionsandonthemethodofplacement,suchasregularorrandomplacementetc.Accordingtotheresultsofexperimentsunderconditionsofrandomplacementovertheentirecrosssectionandregulartwo-layerplacementonastonecore,theregularplacementwithgoodinterlockinghadremarkablyhigherstabilityinalmostallcases.32)Provided,however,thatifthelayer
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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thicknessoftheblocksisminimalandthepermeabilityofthecorematerialislow,conversely,thestabilityoftheblocksdecreasesinsomecases.42) Thestabilityofwave-dissipatingblocksisalsoaffectedbythecrownwidthandcrownheightoftheblocks.Forexample,accordingtotheresultsofanumberofexperiments,thereisatendencyofhavinggreaterstabilitywhenthecrownwidthandthecrownheightaregreater.
(18)StandardMethodofHydraulicModelTestsThe stability of concrete blocks is influenced by a very large number of factors, and so it has still not beensufficientlyelucidated. Thismeansthatwhenactuallyverifyingtheperformance, it isnecessarytocarryoutstudiesusingmodel experiments, and it is needed toprogressively accumulate the results of such tests. Thefollowingpointsshouldbenotedwhencarryingoutmodelexperiments.
① Itisstandardtocarryoutexperimentsusingrandomwaves.
② For eachparticular setof conditions, theexperiment shouldbe repeatedat least three times i.e.,with threedifferentwavetrains.However,whentestsarecarriedoutbysystematicallyvaryingthemassandotherfactorsandalargeamountofdatacanbeacquired,onerunforeachtestconditionwillbesufficient.
③ Itisstandardtostudytheactionof1000wavesintotalofthreerunsforeachwaveheightlevel.Evenforthesystematicexperiments,itisdesirabletoapplymorethan500wavesorso.
④ Forthedescriptionoftheextentofdamage,inadditiontothedamageratiowhichhasbeencommonlyusedinthepast,thedeformationlevelortherelativedamagelevelmayalsobeused.Thedeformationlevelissuitablewhenitisdifficulttocountthenumberofarmorstonesorconcreteblocksthathavemoved,whilethedegreeofdamageissuitablewhenonewishestorepresentthedamagetowave-dissipatingblocks.Thedamagerateistheratioofthenumberofdamagedarmorunitsinaninspectionareatothetotalnumberofarmorunitsinthesameinspectionarea.Theinspectionareaistakenfromtheelevationofwaverunuptowhicheverisshallower,thedepthof1.5Hbelowthestillwaterlevelortothebottomelevationofthearmorlayer,wherethewaveheightHisinverselycalculatedfromtheHudson’sformulabyinputtingthemassofarmorunits.However,forthedeformationlevelandthedegreeofdamage,thereisnoneedtodefinetheinspectionarea.Forevaluatingthedamagerate,anarmorblockisjudgedtobedamagedifithasmovedoveradistanceofmorethanabout1/2to1.0timesitsheight.
(19)KDValueProposedbyC.E.R.C.Table 1.7.2showstheKDvalueofarmorstonesproposedbytheCoastalEngineeringResearchCenter,C.E.R.C.,oftheUnitedStatesArmyCorpofEngineers.Thisvalueisproposedforthebreakwatertrunk,partsotherthanthebreakwaterhead,inthe1984EditionoftheC.E.R.C.’sShore Protection Manual.43)Inthetable,thevaluesnotinparenthesisarebasedonexperimentresultsbyregularwaves,anditisconsideredthatthosecorrespondsto5%orlessofthedamagerateduetoactionofrandomwaves.Thevaluesinparenthesesareestimatedvalues.Forexample,thevalue(1.2)forroundedrubblestoneswhicharerandomlyplacedintwo-layerunderthebreakingwaveconditionsisgivenasthevaluewhichishalfof2.4,becausetheKDvalueoftwo-layerangularrubblestonesunderthebreakingwavesconditionis1/2thatunderthenon-breakingwaveconditions. However, incaseswherethewaveheightofregularwavescorrespondstothesignificantwaveheight, thewavewhichisclosetothemaximumwaveheightofrandomwavesactscontinuouslyunderthebreakingwavecondition in the regularwaveexperiments. Therefore, the regularwaveexperimentunder thebreakingwaveconditionfallsintoanextremelyseverestateincomparisonwiththatunderthenon-breakingwaveconditions.Inrandomwavesexperiments,asdescribedpreviously,itisconsideredthatsolongasthesignificantwaveheightisastandard,asthebreakingwaveconditionsgetssevere,conversely,KDhasatendencytoincrease.Thus,atleastitisnotnecessarytoreducethevalueofKD underthebreakingwaveconditions.
Table 1.7.2 KD Value of Rubble Stones Proposed by C.E.R.C. (Breakwater Trunk)
Typeofarmor Numberoflayers Placementmethod
KDcotα
Breakingwaves Non-breakingwaves
Rubblestones(rounded) 23ormore
Random″
(1.2)(1.6)
2.4(3.2)
1.5–5.0″
Rubblestones(angular) 23ormore
″″
2.0(2.2)
4.0(4.5)
″″
()showsestimatedvalues.
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1.7.2 Required Mass of Armor Stones and Blocks in Composite Breakwater Foundation Mound against Waves
(1)GeneralTherequiredmassofarmorstonesandblockscoveringthefoundationmoundofacompositebreakwatervariesdependingonthewavecharacteristics,thewaterdepthwherethefacilityisplaced,theshapeofthefoundationmoundsuchasthickness,frontbermwidthandslopeangleetc.,andthetypeofarmorunit,theplacementmethod,andtheposition,breakwaterheadorbreakwatertrunketc.Inparticular,theeffectsofthewavecharacteristicsand the foundationmoundshapearemorepronounced than thaton thearmorstonesandblocksonaslopingbreakwater.Adequateconsiderationshouldalsobegiventotheeffectsofwaveirregularity.Accordingly,therequiredmassofarmorstonesandblocksonthefoundationmoundofcompositebreakwatershallbedeterminedbyperforminghydraulicmodelexperimentsorpropercalculationsusinganappropriateequationinreferencewiththeresultsofpastresearchandactualexperiencesinthefield.Provided,however,thatthestabilityofthearmorunitscovering thefoundationmoundofacompositebreakwater isnotnecessarilydeterminedpurelyby theirmass.Dependingonthestructureandthearrangementofthearmorunitsitmaybepossibletoachievestabilityevenwhenthearmorunitsarerelativelysmall.
(2)BasicEquationforCalculationofRequiredMassAstheequationforcalculationoftherequiredmassofarmorstonesandblocksinthefoundationmoundofacompositebreakwater,Hudson’sformulawiththestabilitynumberNS,asshowninthefollowingequation,canbeusedinthesamemanneraswitharmorstonesandblocksonslopingbreakwater.Inthisequation,thesymbolγisapartialsafetyfactorforitssubscript,andthesubscriptskanddshowthecharacteristicvalueanddesignvalue,respectively.ForthepartialsafetyfactorsγNS andγH intheequation,1.0maybeused.Thispartialsafetyfactoristhevalueincaseswherethelimitvalueofthedamagerateis1%orthelimitvalueofthedegreeofdamageis0.3.
(1.7.1)
This equationwaswidely used as the basic equation for calculating the requiredmass of the foundationmounds of uprightwalls byBrebner andDonnelly.44) In Japan, it is also calledBrebner-Donnelly’s formula.Becauseithasacertaindegreeofvalidity,evenfromatheoreticalstandpoint,itcanalsobeusedasthebasicequationforcalculatingtherequiredmassofarmorunitonthefoundationmoundofacompositebreakwater.45)Provided,however,thatthestabilitynumberNS variesnotonlywiththewaterdepth,thewavecharacteristics,theshapeofthefoundationmound,andthecharacteristicsofthearmorunits,butalsowiththepositionofplacement,breakwatertrunk,breakwaterheadetc.Therefore,itisnecessarytoassignthestabilitynumberNSappropriatelybasedonmodelexperimentscorrespondingtotheconditions.Moreover,thewaveheightusedintheperformanceverification is normally the significantwave height, and thewaves used in themodel experiments should berandomwaves.
(3)StabilityNumberforArmorStonesThestabilitynumberNS maybeobtainedusingthemethodproposedbyInagakiandKatayama,46)whichisbasedontheworkofBrebnerandDonnellyandpastdamagecaseofarmorstones.However,thefollowingformulasproposedbyTanimotoetal.45)arebasedonthecurrentvelocityinthevicinityofthefoundationmoundandallowtheincorporationofavarietyofconditions.TheseformulashavebeenextendedbyTakahashietal.47)soastoincludetheeffectsofwavedirection,andthushavehighapplicability.
(a) ExtendedTanimoto’sformulas
(1.7.8)
(1.7.9)
(1.7.10)
(1.7.11)
where h' :waterdepthatthecrownofrubblemoundfoundationexcludingthearmorlayer(m)(seeFig.
1.7.4) :inthecaseofnormalwaveincidence,thebermwidthoffoundationmoundBM (m)
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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inthecaseofobliquewaveincidence,eitherBM orB'M ,whichevergivesthelargervalueof(κ2)B(seeFig. 1.7.4)
L' :wavelengthcorrespondingtothedesignsignificantwaveperiodatthewaterdepthh' (m) αs :correctionfactorforwhenthearmorlayerishorizontal(=0.45) β :incidentwaveangle,anglebetweenthelineperpendiculartothebreakwaterfacelineandthe
wavedirection,noanglecorrectionof15ºisapplied(seeFig. 1.7.5) H1/3 :designsignificantwaveheight(m)
Thevalidityoftheaboveformulashavebeenverifiedforthebreakwatertrunkforobliquewaveincidencewithanangleofincidenceofupto60º.
Shoreward
Foot protection blocksFoot protection blocks
Armor unitsArmor units
Upr
ight
sect
ion
Rubble mound
Seaward
hh'
dBM
BM'
hC
Fig. 1.7.4 Standard Cross Section of a Composite Breakwater and Notations
Breakwater head
Breakw
ater tr
unk
β
Fig. 1.7.5 Effects of Shape of Breakwater Alignment and Effects of Wave Direction
(b)StabilityNumberWhenaCertainAmountofDamageisPermittedSudoetal.havecarriedoutstabilityexperimentsforthespecialcasesuchthatthemoundislowandnowavebreakingoccurs.TheyinvestigatedtherelationshipbetweenthenumberofwavesN andthedamagerate,andproposedthefollowingequationthatgivesthestabilitynumberNS*foranygivennumberofwavesN andanygivendamagerateDN (%).
(1.7.12)
whereNS isthestabilitynumbergivenbytheTanimoto’sformulawhenN =500andthedamagerateis1%.Intheperformanceverification,itisnecessarytotakeN =1000consideringtheprogressofdamage,whilethedamagerate3%to5%canbeallowedfora2-layerarmoring.IfN =1000andDN =5%,thenNS*=1.44NS.Thismeansthattherequiredmassdecreasestoabout1/3ofthatrequiredforN =500andDN =1%.
(4)StabilityNumberforConcreteUnitsThestabilitynumberNS forconcreteblocksvariesaccordingtotheshapeoftheblockandthemethodofplacement.Itisthusdesirabletoevaluatethestabilitynumberbymeansofhydraulicmodelexperiments.49),50)Whencarryingoutsuchexperiments,itisbesttoemployrandomwaves.
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BasedonthecalculationmethodproposedbyTanimotoetal.,45)Fujiikeetal.51)newlyintroducedreferencestability number, which is a specific value for blocks, and separating the termswhich is determined by thestructuralconditionsofthecompositebreakwateretc.,andthen,presentedthefollowingequationregardingthestabilitynumberforarmorblocksincaseswherewaveincidenceisperpendicular.
(1.7.13)
refer(1.7.9)
refer(1.7.10)
(1.7.14)
where NS0 :referencestabilitynumber A :constantdeterminedbasedonwaveforceexperiments(=0.525)
(5)ConditionsforApplicationofStabilityNumbertoFoundationMoundArmorUnitsIncaseswherethewaterdepthabovethearmorunitsonthemoundisshallow,wavebreakingoftencausesthearmor units to become unstable. Therefore, the stability number for foundationmound armor units shall beappliedonlywhenh’/H1/3>1,anditisappropriatetousethestabilitynumberforarmorunitsonaslopeofaslopestructurewhenh’/H1/3≤1.ThestabilitynumberforarmorstonesintheTanimoto’sformulashavenotbeenverifiedexperimentallyincaseswhereh’/H1/3issmall.Accordingly,whenh’/H1/3isapproximately1,itispreferabletoconfirmthestabilitynumberbyhydraulicmodelexperiments. Ontheotherhand,Matsudaetal.52)carriedoutmodelexperimentsinconnectionwitharmorblocks,includingthecaseinwhichh’/H1/3issmallandimpulsivewavesactontheblocks,andproposedamethodthatprovidesalowerlimitofthevalueofκcorrespondingtothevalueofαIinthecasewheretheimpulsivebreakingwaveforcecoefficientαIislarge.
(6)ArmorUnitsThicknessTwo-layers are generally used for armor stones. It may be acceptable to use only one layer provided thatconsiderationisgiventoexamplesofarmorunitsconstructionandexperiencesofdamagedarmorunits.Italsomaybepossibletouseonelayerbysettingtheseveredamagerateof1%forN=1000actingwavesinequation (1.7.12).Onelayerisgenerallyusedforarmorblocks.However,twolayersmayalsobeusedincaseswheretheshapeoftheblocksisfavorablefortwo-layerplacementorseaconditionsaresevere.
(7)ArmorUnitsforBreakwaterHeadAt theheadofabreakwater,strongcurrentsoccur locallynear thecornersat theedgeof theuprightsection,meaningthatthearmorunitsbecomeliabletomove.Itisthusnecessarytoverifytheextenttowhichthemassofarmorunitsshouldbeincreasedatthebreakwaterheadbycarryingouthydraulicmodelexperiments.Ifhydraulicmodelexperimentsarenotcarriedout,itshouldincreasethemasstoatleast1.5timesthatatthebreakwatertrunk.Astheextentofthebreakwaterheadinthecaseofcaissontypebreakwater,thelengthofonecaissonmaybeusuallyadopted.ThemassofthearmorstonesatthebreakwaterheadmayalsobecalculatedusingtheextendedTanimoto’sformula.Specifically,forthebreakwaterhead,thevelocityparameterκ inequation (1.7.9)shouldberewrittenasfollows:
(1.7.15)
(1.7.16)
Notehoweverthatifthecalculatedmassturnsouttobelessthan1.5timesthatforthebreakwatertrunk,itispreferabletosetitto1.5timesthatforthebreakwatertrunk.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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(8)ArmorUnitsatHaborSideItispreferabletodecidethenecessityandrequiredmassofarmorunitsattheharborside,notonlyreferringtopastexamples,butalsoperforminghydraulicmodelexperimentsifnecessaryandconsideringthewavesattheharborside,thewaveconditionsduringconstructionworkandwaveovertoppingetc.
(9)ReductionofMassofArmorTheequationsforcalculationoftherequiredmassofarmorunitsarenormallyapplicabletothehorizontalpartsandthetopofslope.Incaseswherethemoundthicknessisminimal,armorunitsoftheentireslopehavethesamemassinmanycases.However,incaseswherethemoundisthick,themassofarmorunitsplacesontheslopeindeepwatermaybereduced.
(10)FoundationMoundArmorUnitsinBreakwatersCoveredwithWave-dissipatingBlocksInthecaseofbreakwaterscoveredwithwave-dissipatingblocks,theupliftpressureactingonthearmorandthecurrentvelocities in thevicinityof themoundare smaller than thoseofconventional compositebreakwaters.Fujiikeetal.51)carriedoutmodelexperimentsinconnectionwiththestabilitiesofboththearmorunitsoftheconventionalcompositebreakwatersandthebreakwaterscoveredwithwave-dissipatingblocks,andproposedamethodofmultiplicatingequation (1.7.9)bythecompensationrate.Namely,
(1.7.17)
where CR :breakwatershapeinfluencefactor,itmaybeused1.0forconventionalcompositebreakwaters
approximately0.4forbreakwaterscoveredwithwave-dissipatingblocks.
(11)FlexibleArmorUnitsUseofbag-typefootprotectionunitswhichconsistofsyntheticfibernetfilledwithstonesasthearmorunitsonthefoundationmoundhasvariousadvantages:largestonesarenotrequired,andmoundlevelingisnotvirtuallyneededbecausetheyhavehighflexibilityandcanadheretotheirregularseabed.Shimosakoetal.53)proposedamethodofcalculatingtherequiredmassofarmorunitsonthefoundationmoundusingbag-typefootprotectionunits,andalsoexaminedtheirdurability.
1.7.3 Required Mass of Armor Stones and Blocks against Currents
(1)GeneralTherequiredmassofrubblestonesandotherarmormaterialsforfoundationmoundstobestableagainstwatercurrentsmaybegenerallybedeterminedbyappropriatehydraulicmodelexperimentsorcalculatedusing thefollowingequation.Inthisequation,thesymbolγisapartialsafetyfactorforitssubscript,andthesubscriptskanddshowthecharacteristicvalueandthedesignvalue,respectively.
(1.7.18)
where M :stablemassofrubblestonesorotherarmormaterial(t) ρr :densityofrubblestonesorotherarmormaterial(t/m3) U :currentvelocityofwateraboverubblestonesorotherarmormaterial(m/s) g :gravitationalacceleration(m/s2) y :Isbash’sconstant,forembeddedstones,1.20;forexposedstones,0.86 Sr :specificgravityofrubblestonesorotherarmormaterialrelativetowater θ :slopeangleinaxialdirectionofwaterchannelbed(º)
Thedesignvaluesintheequationmaybecalculatedbyusingthefollowingequations.ForthepartialsafetyfactorsγU andγy,1.0maybeused.
Ud =γU Uk,yd =γy yk
ThisequationwasproposedbytheC.E.R.C.forcalculationofthemassofrubblestonesrequiredtopreventscouringbytidalcurrentsandiscalledIsbash’sformula.43)Asalsoshownintheequation,attentionshouldbegiventothefactthattherequiredmassofarmorunitsagainstcurrentsincreasesrapidlyasthecurrentvelocityincreases.Therequiredmassalsovariesdependingontheshapeanddensityofthearmorunitsetc.
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
(2)Isbash’sConstantEquation (1.7.18)wasderivedconsideringthebalanceofthedragforceoftheflowactingonasphericalobjectonaslopeandthefrictionresistanceforce.TheconstantyisIsbash’sconstant.Thevaluesof1.20and0.86forembeddedstonesandexposedstones,respectively,aregivenbyIsbash,andarealsocitedinReference54).Itshouldbenotedthat,becauseequation (1.7.18)wasobtainedconsideringthebalanceofforcesinasteadyflow,itisnecessarytouserubblestoneswithalargermassintheplacewherestrongvorticeswillbegenerated.
(3)ArmorUnitsonFoundationMoundatOpeningsofTsunamiProtectionBreakwatersIwasakietal.55)conductedexperimentson2-dimensionalsteadyflowsforthecaseinwhichdeformedconcreteblocksareusedasthearmorunitsonafoundationmoundintheopeningofthesubmergedbreakwatersoftsunamiprotectionbreakwater,andobtainedavalueof1.08forIsbash’sconstantinequation (1.7.18).Tanimotoetal.56)carriedouta3-dimensionalplaneexperimentfortheopeningofbreakwaters,clarifyingthe3-dimensionalflowstructureneartheopening,andalsorevealedtherelationshipbetweenIsbash’sconstantandthedamagerateforthecaseswherestonematerialsanddeformedconcreteblocksareusedasthearmorunits.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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1.8 Scouring and Washing-outPublic NoticePerformance Criteria Common to Structural Members
Article 22 3Incaseswheretheeffectsofscouringoftheseabedandsandoutflowontheintegrityofstructuralmembersmayimpairthestabilityofthefacilities,appropriatecountermeasuresshallbetaken.
[Commentary]
(1)ScouringandWashout(serviceability)Incaseswherescouringofthefoundationoffacilitiesconcernedandgroundandoutflowofsandfromthegroundbehindstructuresmightimpairthestabilityofthefacilities,appropriatecountermeasuresagainstscouringandcountermeasuresagainstwashoutmustbetaken,consideringthestructuraltypeoftheobjectivefacilities.
References
1) JSCE:ConcreteSpecifications,Construction,20022) Yamaji, T.: Durability evaluationmethod for port concrete structures based on the results of long-term exposure tests,
ProceedingsofAnnualConferenceofPARI,2006,pp.41-58,20063) JSCE:Trendoftestingmethods,whichwantestablishmentofchlorideiondiffusioncoefficienttestingmethodofchlorideion
ofconcreteanditsstandardization,ConcreteTechnologySeries,55,20034) Yamaji,T.,T.AoyamaandH.Hamada:Effectofexposureenvironmentandkindsofcementondurabilityofmarineconcrete,
Proceedingsofannualconferenceonconcreteengineering,Vol.23,No.2,pp.577-582,20015) Nagao,T:Reliabilitybaseddesignmethodforflexuraldesignofcaissontypebreakwaters,Jour.JSCENagao,T.:No.696/I-
58,pp,173-184,20026) Nagao,T.:StudiesontheApplicationoftheLimitStateDesignMethodtoReinforcedConcretePortStructures,Rept.of
PHRIVol.33No.4,1994,pp.69-1137) Nagao,T.:CaseStudiesonSafetyFactorsaboutSeismicStabilityfortheSlobofCaissonTypeQuaywalls,TechnicalNoteof
PHRI,TechnicalNoteofPHRI8) Moriya,Y.,M.MiyataandT.Nagao:Designmethodforbottomslabofcaissonconsideringsurfaceroughnessofrubble
mound,TechnicalNoteofNationalInstituteforLandandInfrastructureManagementNo.94,20039) NagaoT.,M.Miyata,Y.MoriyaandT.Sugano:Amethodfordesigningcaissonbottomslabsconsideringmoundunevenness.
Jour.JSCEC,Vol.62,No.2,pp.277-291,200610) Kikuchi,Y.,K.TakahashiandT.Ogura:DispersionofEarthPressureinExperimentsandEarthPressureChangeduetothe
RelativeMovementoftheNeighboringWalls,TechnicalNoteofPHRINo.811,199511) Tanimoto,K.,K.KobuneandM.Osato:WaveForcesonaCaissonWallandStressAnalysisof theWall. forPrototype
Breakwaters,TechnicalNoteofPHRINo.224,pp.25-33,197512) Shiomi,M.,H.Yamamoto,A.Tsugawa,T.KurosawaandK.Matsumoto:Damagesandcountermeasuresofbreakwatersdue
tothewaveforceincreaseatdiscontinuouspointsofwave-absorbingblocks,Proceedingsofthe41stconferenceonCoastalEng.JSCE,pp.791-795,1994
13) Miyata,M.,Y.Moriya,T.NagaoandT.Sugano:Effectsofsurfaceroughnessofrubblemoundonsectionforceofbottomslabofcaisson,(Part2),TechnicalNoteofNationalInstituteforLandandInfrastructureManagementNo.93,2003
14) Moriya,Y.,M.MiyataandT.Nagao:Designmethodforbottomslabofcaissonconsideringsurfaceroughnessofrubblemound,TechnicalNoteofNationalInstituteforLandandInfrastructureManagementNo.94,2003
15) Nishibori, T. and T. Urae : Dynamic characteristics of metal fitting for hanging of large caisson, Proceedings of 29thConferenceofJSCE,1974
16) Yokota,H.,K.Fukushima,T.AkimotoandM.Iwanami:ExaminationforRationalizingStructuralDesignofReinforcedConcreteCaissonStructures,,TechnicalNoteofPHRINo.995,2001
17) CoastalDevelopmentInstituteofTechnology:TechnicalManualforL-shapeblockwharves,200618) Takahashi, S., K. Shimosako and H. Sasaki: Experimental Study onWave Forces Acting on PerforatedWall Caisson
Breakwaters,Rept.ofPHRIVol.30No.4,pp.3-34,199119) Takahashi,S.andK.Tanimoto:UpliftForcesonaCeilingSlabofWaveDissipatingCaissonwithaPermeableFrontWall(2nd
Report)-FieldDataAnalysis-,Rept.ofPHRIVol.23No.2,198420) Tanimoto,K.,S.TakahashiandT.Murakami:UpliftForcesonaCeilingSlabofWaveDissipatingCaissonwithaPermeable
FrontWall-AnalyticalModelforCompressionofanEnclosedAirLayer-,Rept.ofPHRIVol.19No.1,pp.3-31,198021) CoastalDevelopmentInstituteofTechnology:DesignManualforHybridcaisson,199922) Yokota,H.: Study onMechanical Properties of Steel-ConcreteComposite Structures andTheirApplicability toMarine
–424–
TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
Structures,TechnicalNoteofPHRINo.750,199323) JSCE:Guidelineforperformanceverificationofhybridstructures(Draft),HybridStructureSeriesNo.11,200224) JSCEEdition:Handbookofdesignofcoastalprotectionfacilities(RevisedEdition),pp.174-176,196925) LiteraturesurveyCommittee:Deformedwaveabsorbingblocks,JournalofJSCE,Vol.49,No.4,pp.77-83,196426) R.Y.Hudson:Laboratoryinvestigationofrubble-moundbreakwater,Proc.ASCE.,Vol.85,W.W.3.,pp.93-121,195927) Kashima,R.,T.Sakakiyama,T.Shimizu,T.Sekimoto,H.KunisuandO.Kyoutani:Evaluationequationofdeformationof
waveabsorbingworksduetorandomwaves,ProceedingsofCoastalEng.JSCEVol.42,pp.795-799,199528) J.W.VanderMeer:Rockslopesandgravelbeachesunderwaveattack,Doctoralthesis,DelftUniv.ofTech.,p.152,1988 or
J.W.VanDerMeer:Stabilityofbreakwaterarmorlayer?Designformulae,CoastalEngineering,11,pp.219-239,198729) J.W.VanderMeer:Stabilityofcubes,TetrapodsandAccropode,Proc.OfBreakwater‘88,Eastbourne,UK.,pp.71-80,198830) H.F.BurcharthandZ.Liu:DesignofDolosarmourunits,Proc.Ofthe23rdInternationalConferenceonCoastalEngineering,
Venice,pp.1053-1066,199231) Takahashi S.,M.Hanzawa andK. Shimosako: Performance verification of stability of armour stones of rubble-mound
breakwatersagainstwaves,ProceedingsofCoastalEng.JSCEVol.50,pp.761-765,200332) Tanimoto,K.,Y.HaranakaK.Yamazaki:ExperimentalStudyontheStabilityofWaveDissipatingConcreteBlocksagainst
IrregularWaves,Rept.ofPHRIVol.24,No.2,pp.85-121,198533) Kashima,r.,T.Sakakiyama,T.Shimizu,T.Sekimoto,H.KunisuandO.Kyoutani:Evaluationequationofdeformationof
waveabsorbingworksduetorandomwaves,ProceedingsofCoastalEng.JSCEVol.42,pp.795-799,199534) Hanzawa,M.,H.Sato,T.Takayama,S.TakahashiandK.Tanimoto:Studyonevaluationequationforthestabilityofwave
absorbingblocks,ProceedingsofCoastalEng.JSCEVol.42,pp.886-890,199535) Takahashi,S.,M.Hanzawa,H.Sato,M.Gomyou,K.Shimosako,K.Terauchi,T.TakayamaandK.Tanimoto36) Kimura,K.,K.Kamikubo,Y.Sakamoto,Y.Mizuno,H.TakedaandM.Hayashi:Stabilityofblocksattheendofbreakwaters
armoredwithwaveabsorbingblocks,ProceedingsofCoastalEng.JSCEVol.44,pp.956-960,199737) VandeKreeke,J.:Damagefunctionofrubblemoundbreakwaters,ASCE.,JournaloftheWaterwayandHarborsDivision,
Vol.95,WW3,pp.345-354,196938) F.T.Christensen,R.C.Broberg,S.E.Sand, andP.Tryde :Behavior of rubble-moundbreakwater indirectional anduni-
directionalwaves,CoastalEng.,Vol.8,pp.265-278,198439) Soave,T.andT.Yajima:Outstandingtechnicalissuesindesigningofdetachedbreakwaters,LecturenoteofSummertraining
forHydraulicEngineering1982,(18th)CourseB,UralicCommitteeofJSCE,pp.B-5-1-B-5-24,198240) Takeda,H.,Y.Yamamoto,K.Kimura andT. Sasazima: Impactwave forces and stability ofwave absorbing blocks on
breakwatersplacedonsteepslope,ProceedingsOffshoreDevelopmentVol..11,pp.287-290、199541) CoastalDevelopmentInstituteofTechnology(CDIT):TechnicalManualforwaveabsorbingblocksoflargespecificgravity,
p.45,199542) Kubota,S., S.Kobayashi,A.Matumoto,M.HanzawaandM.Matuoka:On the effect of the layer thickness andfilling
materialsofwaveabsolvingblocksontheirstabilityagainstwaves,ProceedingsofCoastalEng.JSCEVol.49,pp,756-760,2002
43) CoastalEngineeringResearchCenter:ShoreProtectionManual,Vol.II,DepartmentofArmyCorpsofEngineering,197744) A.Brebner,D.Donnelly:Laboratorystudyofrubblefoundationsforverticalbreakwaters,Proc.8thConf.ofCoastalEngg.,
NewMexicoCity,pp.408-429,196245) Tanimoto,K.,T.Yanagisawa,T.Muranaga,K.ShibataandY.Goda:StabilityofArmorUnitsforFoundationMoundsof
CompositeBreakwatersDeterminedbyIrregularWaveTests,Rept.ofPHRIVol.21,No.3,pp.3-42,198246) Inagaki,K.andT.Katayama:Analysisofdamagetoarmorstonesofmoundsincompositebreakwaters,TechnicalNoteof
PHRINo.127,pp.1-22,197147) TakahashiS.,K.KimuraandK.Tanimoto:StabilityofArmourUnitsofCompositeBreakwaterMoundagainstOblique
Waves,Rept.ofPHRIVol.29No.2,pp.3-36,199048) Sudo,K.,K.Kimura,T.Sasajima,Y.MizunoandH.Takeda:Estimationequationofrequitedweightofarmourunitsof
rubble-moundofcompositebreakwatersconsideringtheallowabledeformation,ProceedingsofCoastalEng.JSCEVol.42,pp.896-900,1995
49) Kougami,Y.andT.Narita:On the stabilityofarmour layer,madewithwave-absorbingblocks,of rubble foundationofcomposite breakwaters, Journal of PublicWorks Research Institute (PWRI), Hokkaido Regional Development Bureau(HRDB)No.232,pp.1-13,1972
50) Kashima,R.,S.SaitouandH.Hasegawa:Requiredweightofarmourconcretecubeforrubblemoundfoundationofcompositebreakwaters,ReportoftheSecondTechnicalResearchInstituteoftheCentralResearchInstituteofElectricPowerIndustry70022,p.18,1971
51) Fujiike,T.,K.Kimura,T.Hayashiandy.Doi:Stabilityagainstwavesofarmorunitsplacedatfrontfaceofrubble-moundofwave-absorbing-block-armoredbreakwaters,ProceedingsofCoastalEng.JSCEVol.46,pp.881-885,1999
52) Matuda,S.,W.Nishikiori,A.MatumotoandM.Saitou:Estimationmethodofstableweightofarmourblocksofrubble-moundofcompositebreakwatersconsideringimpactwaveforceactions,ProceedingsofCoastalEng.JSCEVol.47,pp.896-900,2000
53) Shimosako,K.,S.Kubota,A.Matumoto,M.Hanzawa,Y.Shinomura,N.Oike,T.IketaniandS.Akiyama54) Kudou,T.:Temporaryriverclosingdikesanditsoverflow,JournalofJSCE,Vol.58No.11,pp.63-69,1973
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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55) Iwasaki,T.,A.Mano,T.NakamuraandN.Horikoshi:Experimentalstudyonfluiddynamicforceinsteadyflowactingonmoundmaterialsofsubmergedbreakwatersandprepackedbreakwaters,Proceedingsofthe31stConferenceonCoastalEng.JSCE,pp527-531,1984
56) Tanimoto,K.,K.Kimura andK.Miyazaki: Study on Stability of SubmergedDike at theOpening Section of TsunamiProtectionBreakwaters,Rept.ofPHRIVol.27No.4,pp.93-121,1988
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2 Foundations2.1 General Comments
(1)Thefoundationstructuresof theport facilitiesshallbeselectedappropriately,givingdueconsideration to theimportanceofthefacilitiesandsoilconditionsofthefoundationground.
(2)Whenthestabilityofthefoundationstructuresseemstobeanobstacle,countermeasuressuchaspilefoundationorsoilimprovement,etc.shallbeappliedasnecessary.
(3)When the foundation ground is soft, excessive settlement or deformationmay arise owing to the lack of thebearingcapacity.Whenthefoundationgroundconsistsofloosesandysoil,liquefactionduetoactionofgroundmotioncausesthestructurefailureorsignificantlydamageitsfunctions.Insuchcases,thestressinsubsoilbytheweightofstructuresneedstobereducedorthefoundationgroundshouldbeimproved.
(4)Forthestabilityoffoundations,2.2 Shallow Spread Foundations,and2.3 Deep Foundations,or3 Stability of Slopes canbeusedasreference.Forsettlementoffoundations,2.5 Settlement of Foundations,andforliquefactiondue to actionofgroundmotion, Part II,Chapter 6 Ground Liquefaction canbeusedas reference. For theperformance verification of pile foundations,2.4 Pile Foundations can be used as reference. In caseswhereit isnecessary toconduct theperformanceverification forgroundmotion, theverificationshallbeperformedcorrespondingtothecharacteristicsoftherespectivefoundations.
(5)MethodsofReducingGroundStressThefollowingaremethodsofreducinggroundstressduetotheweightofstructures.
①Reductionoftheweightofthestructureitself
②Expansionoftheareaofthebottomofthestructure
③UseofapilefoundationShearstressduetothefacilitiesmaybereducedbythecounterweightmethod.
(6)MethodofSoilImprovementFormethodofsoilimprovement,4 Soil Improvement Methods canbeusedasreference.
2.2 Shallow Spread Foundations2.2.1 General
(1)Whentheembedmentdepthofthefoundationislessthantheminimumwidthofthefoundation,thefoundationmaygenerallybeexaminedasashallowspreadfoundation.
(2)Ingeneral,thebearingcapacityofafoundationisthesumofthebottombearingcapacityandthesideresistanceofthefoundation.Bottombearingcapacityisdeterminedbythevalueofthepressureappliedtothefoundationbottom considered necessary to cause plastic flow in the ground. The side resistance of a foundation is thefrictionalresistanceorthecohesionresistanceactingbetweenthesidesofthefoundationandthesurroundingsoil.Althoughconsiderableresearchhasbeendoneonthebottombearingcapacityoffoundations,relativelylittleresearchhasbeendoneonsideresistance.Iftheembedmentdepthofthefoundationislessthantheminimumwidthofthefoundation,inthecaseofso-calledshallowspreadfoundations,themagnitudeofthesideresistancewillbesmallincomparisonwiththatofthebottombearingcapacity.Therefore,itisnotnecessarytoconsiderthesideresistanceinsuchcases.
(3)Whenaneccentricandinclinedactionactsonthefoundation,2.2.5 Bearing Capacity for Eccentric and Inclined Actions canbeusedasreference.
2.2.2 Bearing Capacity of Foundations on Sandy Ground
(1)Thefollowingequationcanbeusedtocalculatethedesignvalueofthebearingcapacityofthefoundationsonsandyground.Inthiscase,appropriatevaluescorrespondingtothecharacteristicsofthefacilitiescanbeadoptedasthepartialfactors.Ingeneral,0.4orlesscanbeconsideredanappropriatepartialfactorγR.
(2.2.1)where
qd :designvalueoffoundationbearingcapacityconsideringbuoyancyofsubmergedpart(kN/m2) γR :partialfactorforbearingcapacityofsandyground
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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β :shapefactoroffoundation,seeTable 2.2.1ρ1dg :designvalueofunitweightofsoilofgroundbelowfoundationbottomorunitweightinwater,
ifsubmerged(kN/m3) B :minimumwidthoffoundation(m)
Nrd,Nqd :designvaluesobtainedbymultiplyingpartialfactorsγNqandγNγ bythecharacteristicvaluesofthebearingcapacityfactorNqkandNγk(seeFig. 2.2.1),1)respectively.Thecharacteristicvaluesofthebearingcapacityfactorareexpressedbythefollowingequations.
(Prandtl’ssolution)
(Meyerhof’ssolution)
ρ2dg :designvalueofunitweightofsoilofgroundabovefoundationbottom,orunitweightinwater,ifsubmerged(kN/m3)
D :embedmentdepthoffoundationinground(m)
(2)Whentheactionsonthefoundationincrease,first,settlementofthefoundationoccursinproportiontotheactions.However,whentheactionsreachacertainvalue,settlementincreasessuddenlyandshearfailureofthegroundoccurs.Theintensityoftheloadrequiredtocausethisshearfailurewhichisobtainedbydividingtheloadbythecontactareaiscalledtheultimatebearingcapacityofthefoundation.ThebearingcapacityofthefoundationcanbecalculatedbymultiplyingtheultimatebearingcapacityobtainedfromthebearingcapacityformulabythepartialfactorγR.
Table 2.2.1 Shape Factors
Shapeoffoundation Continuous Square Round Rectangularβ 1 0.8 0.6 1–0.2(B/L)
B: lengthofshortsideofrectangle,L:lengthoflongsideofrectangle
1
10
100
0 10 20 30 40 50
Nqk Nγk
Cha
ract
eris
tic v
alue
s of b
earin
g ca
paci
ty fa
ctor
t Nqk
and
Nγk
φφCharacteristic value of angle of shear resistance k (º)
Fig. 2.2.1 Relationship between Bearing Capacity Factors Nrk and Nqk and Angle of Shear Resistance φk
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
2.2.3 Bearing Capacity of Foundations on Cohesive Soil Ground
(1) Incalculationsofthedesignvaluesforfoundationsofcohesivesoilgroundincaseswheretheundrainedshearstrength increases linearlywithdepth, the following equation canbeused. In this case, an appropriate valuecorrespondingtothecharacteristicsofthefacilitiesshallbeselectedforthepartialfactorγR.
(2.2.2)
where qd :designvalueoffoundationbearingcapacityconsideringbuoyancyofsubmergedpart(kN/m2) γR :partialfactorforbearingcapacityofcohesivesoilground Nc0d :designvalueofbearingcapacityfactorforcontinuousfoundation n :shapefactoroffoundation,seeFig. 2.2.2 B :minimumwidthoffoundation(m) L :lengthoffoundation c0d :designvalueofundrainedshearstrengthofcohesivesoilatbottomoffoundation(kN/m2) ρ2dg :designvalueofunitweightofsoilofgroundabovefoundationbottom,orunitweightinwater,
ifsubmerged(kN/m3) D :embedmentdepthoffoundationinground(m)
(2)Astheundrainedshearstrengthofcohesivesoilgroundinportareasusuallyincreaseslinearlywithdepth,thebearing capacity of foundation should be calculated by the equation that takes account of the effect of shearstrengthincrease.
(3)Equation for Calculating Design Value of Bearing Capacity of Cohesive Soil Ground Considering StrengthIncreaseinDepthDirection ThedesignvalueNc0dofthebearingcapacityfactorinequation (2.2.2)canbecalculatedusingFig. 2.2.2.Here,kisthestrengthincreaserateinthedepthdirection.Ifthesurfacestrengthisassumedtobec0,thestrengthatdepthzisexpressedbyc0+kz.AsthepartialfactorforthebearingcapacityγR,anappropriatevalueof0.66orlesscanbeusedgenerally,butincaseswherethereisapossibilitythatslightsettlementordeformationofthegroundmayremarkablyimpairthefunctionsofsuperstructure,asinthecaseofcranefoundations,avalueofnomorethan0.4shallbeused.
12
10
8
6
4
4
2
20
00
1 3 5
0.05
0.10
0.30
0.25
0.20
0.15 n
n
kkB/c0k
Nc0k
Nc0k
z
c0
kz
Load intensity
B
Fig. 2.2.2 Relationship of Bearing Capacity factor Ncok of Cohesive Soil Ground in which Strength Increases in Depth Direction and Shape Factor n
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(4)PracticalEquationforCalculatingDesignValueofBearingCapacityBasedonthebearingcapacityfactorsshowninFig. 2.2.2,thedesignvalueofthebearingcapacityoffoundationsincaseofcontinuousfoundationscanbecalculatedusingthepracticalequationshowninequation (2.2.3)intherangewherekkB/c0k≤4.Thesymbolsusedarethesameasinequation(2.2.2).
(provided,however,thatkkB/c0k≤4) (2.2.3)
2.2.4 Bearing Capacity of Multi-layered Ground
(1)Examinationofstabilityforthebearingcapacitywhenthefoundationgroundhasamulti-layeredstructurecanbeperformedbycircularslipfailureanalysis.Assumingtheoverburdenpressureabovethelevelofthefoundationbottomasthesurcharge,circularslipfailureanalysisisperformedbythemodifiedFelleniusmethodforanarcpassingthroughtheedgeofthefoundation,asshowninFig. 2.2.3.AsthepartialfactorγRfortheanalysismethod,0.66orlesscanbeusedgenerally,butincaseswheresettlementwillhavealargeeffectonthefunctionsofthefacilitieslikecrane,itispreferabletouseavalueofnomorethan0.4.
Soil layer 1
Soil layer 2
Soil layer 3
Soil layer 4
B
Fig. 2.2.3 Calculation of Bearing Capacity of Multi-layered Ground by Circular Slip Failure Analysis
(2)IfthecohesivesoillayerthicknessH issignificantlylessthanthesmallestwidthofthefoundationB (i.e.,H <0.5B),apunchingshearfailure,inwhichthecohesivesoillayerissqueezedoutbetweenthesurchargeplaneandthebottomofcohesivesoillayer,isliabletooccur.Thebearingcapacityagainstthiskindofsqueezed-outfailurecanbecalculatedbythefollowingequation4)
(2.2.4)
where qd :design value of bearing capacity of foundation considering the buoyancy of the submerged
part(kN/m2) B :smallestwidthoffoundation(m) H :thicknessofcohesivesoillayer(m) cud :designvalueofmeanundrainedshearstrengthinlayerofthicknessH(kN/m2) ρ2dg :designvalueofunitweightofsoilabovetheleveloffoundationbottomorunitweightinwater,
ifsubmerged(kN/m3) γR :partialfactorforbearingcapacity D :embeddeddepthoffoundation(m)
2.2.5 Bearing Capacity for Eccentric and Inclined Actions
(1)Examinationofthebearingcapacityforeccentricandinclinedactionsactingonthefoundationgroundofgravity-typestructurescanbeperformedbycircularslipfailureanalysiswiththesimplifiedBishopmethodusingthefollowing equation. In this equation, the symbol γ is the partial factor for its subscript, and the subscripts k anddindicatethecharacteristicvalueanddesignvalue,respectively.Inthiscase,thepartialfactorshallbeanappropriatevaluecorrespondingtothecharacteristicsofthefacilities.Itisnecessarytosetthestrengthconstantoftheground,theformsoftheactions,andotherfactorsappropriatelyconsideringthestructuralcharacteristicsofthefacilities.
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
(2.2.5)
where R :radiusofincircularslipfailure(m) cd :incaseofcohesivesoilground,designvalueofundrainedshearstrength,andincaseofsandy
ground,designvalueofapparentcohesionindrainedcondition(kN/m2) W’d :designvalueofeffectiveweighttodiscretesegmentperunitoflength,submergesunitweightif
submerged(kN/m) qd :designvalueofverticalactionfromtopofdiscretesegment(kN/m) θ :angleofbottomofdiscretesegmenttohorizontal(º) φd :incaseofcohesivesoilground,thevalueshallbe0,andincaseofsandyground,designvalue
ofangleofshearresistanceindrainedcondition(º) Wd :designvalueoftotalweightofdiscretesegmentperunitoflength,namelytotalweightofsoil
andwater(kN/m) PHd :designvalueofhorizontalactiononlumpsofearthincircularslipfailure(kN/m) a :armlengthfromthecenterofcircularslipfailureatpositionofactionofanexternalactionH S :widthofdiscretesegment(m) γFf :partialfactorforanalysismethod
Basedonequation (2.2.5),γFf iscalculated,andstabilityisverifiedbytheverificationparameterFf≥1.Thedesignvaluesintheequationcanbecalculatedbythefollowingequations.Provided,however,thatincaseswherepartialfactorsaregivenbystructuraltype,thepartialfactorforthepartconcernedshallbeused.Inothercaseswherepartialfactorsarenotparticularlydesignated,thevalueofthepartialfactorγcanbesetat1.00.
cd =γc ck,W'd =γW' W'k,qd =γq qk,φd =tan–1(γtanφ tanφk),PHd =γPH PHk (2.2.6)
(2)Ingravity-typequaywallsandgravity-typebreakwaters,actionsduetoselfweight,earthpressure,waveforce,andgroundmotionshallbeconsidered.However,theresultantoftheseactionsisnormallybotheccentricandinclined.Therefore,examinationforeccentricandinclinedactionsisnecessaryinexaminationof thebearingcapacityoffoundations.Here,eccentricandinclinedactionmeansanactionwithaninclinationratioequaltoorgreaterthan0.1.
(3)Because normal gravity-type structures are two-layered structureswith a rubblemound layer on foundationground,anexaminationmethodwhichadequately reflects this feature isnecessary.The fact thatcircular slipfailure calculations by theBishopmethod, simplifiedBishopmethod, accurately express stability for bearingcapacity has been confirmed in a series of research results, including laboratorymodel experiments, in-situloadingexperiments,andanalysisoftheexistingbreakwatersandquaywalls,andthismethodisthereforeusedasageneralmethod.5)
(4)AnalysisofBearingCapacitybyCircularSlipFailureAnalysisbasedontheBishopMethodAnalysisthroughcircularslipfailureanalysisbasedontheBishopmethodismoreprecisethantheanalysisbasedon themodifiedFelleniusmethod,exceptwhenaverticalactionexertsonhorizontally layeredsandyground.Therefore,thecircularslipfailureanalysisbytheBishopmethodisappliedundertheconditionthateccentricandinclinedactionsexertact.AsshowninFig. 2.2.4 (a),thestartpointoftheslipsurfaceissetsymmetricalabouttheactingpointofresultantloadtooneofthefoundationedgesthatisclosertotheloadactingpoint.Inthiscase,theverticalactionexertingontherubblemoundisconvertedintouniformlydistributedloadactingonthewidthbetweenforetoeofthebottomandthestartpointoftheslipsurfaceasindicatedinFig. 2.2.4 (b) and(c).Thehorizontalforceisassumedtoactatthebottomofstructure.Whencalculatingthebearingcapacityduringanearthquake,seismicforceisassumednottoactontherubblemoundandtheground.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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(a) (b) (c)
b' b'b'
b'b' b' b'
b'
2b' 2b'
ee
q q
p1 p1p2
B Bb
R R
When subgrade reaction has a trapezoidal distribution; q=
q=p1b4 b'
(p1+p2) 4 b'-
-
B
When subgrade reaction has a triangular distribution;
Combined force of load
Rubblemound
Subsoil
Fig. 2.2.4 Analysis of Bearing Capacity for Eccentric and Inclined Actions
(5)VerificationParameterandPartialFactors
①Theverificationparameter isexpressedby the ratioof theslidingmomentdue toactionsand theweightofearthandtheresistantmomentduetoshearresistance(see3.2.1 Stability Analysis by Circular Slip Failure Surface).Asgeneralvaluesofthepartialfactorsfortheanalysismethod,thevaluesshowninTable 2.2.2canbeused.Provided,however,thatincaseswherepartialfactorsareindicatedbystructuraltype,thepartialfactorforthepartconcernedshallbeused.
②Regardingactionsonbreakwatersduetogroundmotion,fewexamplesofdamageareavailable,andthedegreeofdamage is also small.As the reasons for this, inmanycasesactionsdue togroundmotionarebasicallyequalintheharbordirectionandtheouterseadirection,andlargedisplacementdoesnotoccurduetotheshortdurationoftheaction.Accordingly,examinationofthebearingcapacityduetoactionsofgroundmotionmaybeomittedinthecaseofordinarybreakwaters.Provided,however,thatdetailedexaminationbydynamicanalysisisdesirableforbreakwaterswherestabilityduetoactionsofgroundmotionmaybeaseriousproblem.
Table 2.2.2 Standard Values of Partial Factor γFf in Analysis Method for Bearing Capacity for Eccentric and Inclined Actions (Bishop Method)
Quaywalls Breakwaters
Permanentsituation ≤0.83 –
VariablesituationforLevel1earthquakegroundmotion ≤1.00 –
Variablesituationforwaves – ≤1.00
Note)Incasepartialfactorsareindicatedbystructuraltype,thepartialfactorforthepartconcernedshallbeused.
(6)StrengthParametersforMoundMaterialsandFoundationGround
①MoundmaterialsModelandfieldexperimentsonbearingcapacitysubject toeccentricandinclinedactionshaveverifiedthathigh precision results can be obtained by conducting circular slip failure analyses based on the simplifiedBishopmethod,applyingthestrengthparametersobtainedbytriaxialcompressiontests5).Large-scaletriaxialcompressiontestresultsofcrushedstonehaveconfirmedthatthestrengthparametersoflargediameterparticlesareapproximatelyequaltothoseobtainedfromsimilargrainedmaterialswiththesameuniformitycoefficient6).Therefore,triaxialcompressiontestsusingsampleswithsimilargrainedmaterialsarepreferablyconductedinordertoestimatethestrengthparametersofrubblesaccurately.Ifthestrengthtestsarenotconducted,thevaluesofcohesioncD =20kN/m2andshearingresistanceangleφD =35ºareappliedasthestandardstrengthparametersforrubblesgenerallyusedinportconstructionworks. The above standard values have been determined as safe side values based on the results of large-scaletriaxialcompressiontestsofcrushedstones.Thevalueshavebeenprovenappropriatefromtheanalysisresultsofthebearingcapacityoftheexistingbreakwatersandquaywalls.ItshouldbenotedthatcohesioncD =20kN/m2asastrengthparameteristheapparentcohesion,takingaccountofvariationsoftheshearresistanceangle
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
φDofcrushedstonesundervariableconfiningpressures.Fig. 2.2.5 showstheresultsoftriaxialcompressiontestsonvarioustypesofcrushedstonesandrubbles5).Itshowsthatastheconfiningpressureincreases,φDdecreasesduetoparticlecrushing.ThesolidlineinthefigurerepresentsthevalueundertheassumptionthattheapparentcohesioniscD =20kN/m2andtheshearfrictionangleisφD=35º.Here,thedependencyofφDontheconfiningpressureiswelldescribedbytakingtheapparentcohesionintoaccount.Thesestandardvaluescanbeappliedonlytothestonematerialwithanunconfinedcompressivestrengthinthemotherrockof30MN/m2ormore.Ifweakstoneswiththecompressivestrengthofthemotherrockoflessthan30MN/m2areusedasapartofthemound,thestrengthparameterswillbearoundcD=20kN/m2andφD =30º7).
50
45
40
35
30
25
50
100 200 400 800 1400
cD=20kN/m2, D=35゜Test values
Lateral pressureσ3 (kN/m2)
φφD(°)
φφ
Fig. 2.2.5 Relationship between φD and Lateral Confining Pressure σ3 and Apparent Cohesion
②FoundationgroundFoundationssubjecttoeccentricandinclinedactionsoftencauseshallowsurfaceslipfailure.Inthesecases,itisimportanttoevaluatethestrengthnearthesurfaceoffoundationground.Ifthefoundationgroundissandy,thestrengthcoefficientφD isusuallyestimatedfromN-value.Theestimationformulasemployedup tonowhavetendedtounderestimateφDincaseofshallowsandygrounds.Thisisbecausenocorrectionhasbeenmaderegardingtheeffectivesurchargepressurein-situ. Fig. 2.2.6 collates the results of triaxial compression tests on undisturbed sand in Japan and presents acomparative studyof the formulasproposed in thepast.Evenwhen theN-valuesare less than10, shearingresistance angles of around 40º have been obtained. Inmany cases, the bearing capacity for eccentric andinclinedactionsisimportantontheperformanceverificationwhichisnotunderthepermanentsituationbutunderdynamicexternalforcessuchaswaveandseismicforces.Inadditiontotheaboveandbasedontheresultsofbearingcapacityanalysisofthestructuresdamagedinthepast,thevaluesgivenbelowareappliedasthestandardvaluesofφD infoundationground.
SandygroundwithN-valueoflessthan10: φD=40ºSandygroundwithN-valueof10ormore: φD=45º
Ifthegroundconsistsofcohesivesoil,thestrengthmaybedeterminedbythemethodindicatedinPart II, Chapter 3, 2.3.3 Shear Characteristics.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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50
40
301 2 5 10 20 50 100 200 500N-value
Range according to Meyerhof
D(°
)
Triaxial testresults
φφ
D= 20N + 15 according to Osakiφφ
Fig. 2.2.6 Relationship Between N-value and φD Obtained by Triaxial Tests of Undisturbed Sand Samples
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
2.3 Deep Foundations2.3.1 General
(1)When thepenetrationdepthof a foundation isgreater than theminimumwidthof the foundation, it shallbeexaminedasadeepfoundation.MeansofdistinguishingthedeepfoundationsdescribedherefrompilefoundationsincludethemethodofjudgingwhetherβL(L:embedmentlengthofpile)≦1ornot,basedoncalculationsbythemethodproposedbyY.L.Chan,see 2.4.5 Static Maximum Lateral Resistance of Piles.
(2)Foundationsofthetypedescribedin(1)generallyincludethewell,pneumaticcaissonandcontinuousundergroundwall.Forpilefoundations,see2.4 Pile Foundations.
(3)Deepfoundationssupportthesuperstructurestablybytransmittingtheactionduetotheheavysuperstructurethroughtheweakupperstratatothestronglowerstrata.Accordingly,itcannormallybeconsideredthatverticalforce is supported by the frictional resistance at the side surfaces of the foundation and the vertical bearingcapacityatthebottom,andthehorizontalforceissupportedbythepassiveresistanceoftheground.
2.3.2 Characteristic Value of Vertical Bearing Capacity
(1)Thecharacteristicvalueoftheverticalbearingcapacityofadeepfoundationshallbesettakingintoaccountthesoilconditions,thestructuraltype,andthemethodofconstruction.
(2)Generally,theverticalbearingcapacityofadeepfoundationcanbedeterminedfromthebearingcapacityofthefoundationbottomand theresistanceof thefoundationsides,asshowninequation (2.3.1).However, incaseswheretheamountofdisplacementand/ordeformationofthefacilitiesmaybeaproblem,thedeformationofdeepfoundationsshouldbeestimatedbyassumingthegroundbehavesasaspring.
(2.3.1)where
quk :characteristicvalueofverticalbearingcapacityofdeepfoundation(kN/m2) qu1k :characteristicvalueofbearingcapacityoffoundationbottom(kN/m2) see2.2.2 Bearing Capacity of Foundations on Sandy Ground,2.2.3 Bearing Capacity of
Foundations on Cohesive Soil Ground qu2k :characteristicvalueofbearingcapacityduetoresistanceoffoundationsides(kN/m2)
(3)The design value of the vertical bearing capacity of deep foundations shall consider a safetymargin in thecharacteristic value of the vertical bearing capacity, as in equation (2.3.2). The characteristic value of thefoundation bottom bearing capacity determined as described in2.2.2 Bearing Capacity of Foundations on Sandy Groundand2.2.3 Bearing Capacity of Foundations on Cohesive Soil Ground,andthepartialfactorγa,whichisusedincaseswherethecharacteristicvalueoftheverticalbearingcapacityisdeterminedusingequation (2.3.3)andequation(2.3.5),asshowninthefollowing,cangenerallybesetat0.4orlessforimportantfacilitiesand0.66orlessforotherfacilities.
(2.3.2)where
qud :designvalueofverticalbearingcapacityofdeepfoundation(kN/m2) quk :characteristicvalueofverticalbearingcapacityofdeepfoundation(kN/m2)
(4)Cautionisrequiredconcerningtheresistanceofthesidesofdeepfoundations,astherearecasesinwhichthesurroundinggroundmaybedisturbedbyconstructionand,asaresult,adequatebearingcapacitybysideresistancecannotbeexpected,dependingonthestructuraltypeandmethodofconstruction.
① Thecharacteristicvalueofthebearingcapacityduetothefrictionalresistanceofthefoundationsidesinsandygroundcanbecalculatedbyequation (2.3.3).
(2.3.3)where
Kak :characteristicvalueofcoefficientofactiveearthpressure(δ=0º),seePart II,Chapter 5, 1 Earth Pressure
γ2k :characteristicvalueofunitweightofsoilaboveleveloffoundationbottom,orsubmergedunitweightifsubmerged(kN/m3)
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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D :penetrationdepthoffoundation(m) μk :characteristic value of coefficient of friction between foundation sides and sandy soil,
øk : characteristicvalueofshearresistanceangle(º) B :widthoffoundation(m) L :lengthoffoundation(m)
qu2kinequation(2.3.3),isobtainedbydividingthetotalfrictionresistancebythebottomareaoffoundation.Thetotalfrictionresistanceiscalculatedastheproductofthemeansidefrictionstrength f multiplyingwiththepenetrationdepthD andthetotalcontactsurfaceareabetweenthesandysoilandfoundationsides.Equation(2.3.4)isgenerallyusedtocalculatethemeansidefrictionstrength f correspondingtothepenetrationdepthD.
(2.3.4) Thefrictionanglebetweenthefoundationsidesandsandysoilshouldnotbegreaterthantheshearresistanceangleofsoilφ,anditmaybetakenas(2/3)φforthecasebetweenconcreteandsandysoil.
②Thecharacteristicvalueofbearingcapacityduetothecohesiveresistanceofthefoundationsidesincohesivesoilgroundcanbecalculatedbyequation(2.3.5).
(2.3.5)where
cak :characteristicvalueofmeanadhesion(meanvalueinembeddedpart)(kN/m2)
Dc :penetrationdepthoffoundationbelowgroundwaterlevel(m) B :widthoffoundation(m) L :lengthoffoundation(m)
In caseof deep foundations in cohesive soil ground, there is generally a possibility of drying shrinkageduringsummerinthesoilabovethegroundwaterlevel;therefore,thissoilisnotconsideredtobeaneffectivecontact surface.Accordingly, themeanadhesionca inequation (2.3.5) shouldbe themeanadhesion in theeffectivecontactpart. Aspracticalvaluesofmeanadhesionincohesivesoil,thevaluesinTable 2.3.1canbeusedasreference.
Table 2.3.1 Relationship between Unconfined Compression Strength and Mean Adhesion of Cohesive Soil (kN/m2)
Classofgroundatfoundationside qu caSoftcohesivesoil 20–50 –*)
Mediumcohesivesoil 50–100 6–12Hardcohesivesoil 100–200 12–25Extremelyhardcohesivesoil 200–400 25–30Consolidatedcohesivesoil >400 >30
*Note)withsoftcohesivesoil,sideresistanceshouldnotbeconsidered.
(5)ConsiderationofNegativeSkinFrictionIncaseswherethedeepfoundationpenetratesthroughtheconsolidablegroundandreachesthebearinglayer,itisnecessarytoexaminenegativeskinfrictionactingonthebody.Asthemethodofexaminationinthiscase,2.4.3 [9] Examination of Negative Skin Friction canbeusedasreference.
2.3.3 Horizontal Resistance Force of Deep Foundations
(1)Thecharacteristicvalueofthelateralbearingcapacityofadeepfoundationshallbedeterminedasappropriatetakingintoaccountsoilconditions,structuralcharacteristics,andthemethodofconstruction.
(2)Thelateralbearingcapacityofadeepfoundationisgovernedbythehorizontalsubgradereactionofthefoundationsidesandtheverticalsubgradereactionatthebottomoffoundation.
(3)Thecharacteristicvalueofthehorizontalresistanceforceofdeepfoundationscanbedeterminedfromthepassiveearthpressureandultimatebearingcapacity.
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
(4)Thedesignvalueof thehorizontal resistance forceofdeep foundationsshould includea safetymargin in thecharacteristicvalue,asinthefollowingequation.Whenthecharacteristicvalueofthehorizontalresistanceforceofadeepfoundation isobtainedbythemethodpresentedbelow, thepartial factorsshowninTable 2.3.2cangenerallybeused.
(2.3.6)where
Fud :designvalueofhorizontalresistanceforceofdeepfoundation(kN/m2) Fuk :characteristicvalueofhorizontalresistanceforceofdeepfoundation(kN/m2) γa :partialfactor
Table 2.3.2 Partial Factor γa
Resistanceforcebypassiveearthpressure ResistanceforcebyverticalbearingcapacityImportantfacilities 0.66 0.40Otherfacilities 0.90 0.66
(5)CalculationMethodforPerformanceVerification
①Whenaresultantforceatabottomoffoundationactsinsidethecore,namelytheeccentricityoftotalresultantforceactingatthebottomoffoundationiswithinone-sixthofthefoundationwidthfromthecentralaxisofthefoundation,themaximumhorizontalsubgradereactionp1andmaximumverticalsubgradereactionq1canbeestimatedbyassumingthedistributionsofhorizontalandverticalsubgradereactionareassumedasinFig. 2.3.1.
Fig. 2.3.1 When Resultant Force is inside the Core
② AssumptionontheDistributionofSubgradeReactionThedistributionofhorizontal subgrade reaction shown inFig. 2.3.1 maybe assumedasbeing aquadraticparabolawiththesubgradereactionof0atthegroundsurface.Thisassumptionisequivalenttotherelationshipbetweenthedisplacementy andthesubgradereactionp ofequation(2.3.7)whenthefoundationrotatesasarigidbody.
(2.3.7)where
p :subgradereaction(kN/m2) k :rateofincreaseincoefficientofhorizontalsubgradereactionwithdepth(kN/m4) x :depth(m) y :horizontaldisplacementatdepthx(m)
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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Whenalineardistributionisassumedforverticalsubgradereactionandaresultantforceactingatthebottomoffoundationisinsidethecore,thedistributionoftheverticalsubgradereactionbecomestrapezoidalasshowninFig. 2.3.1.
③ Conditionswhenverticalresultantisinthecoreandcharacteristicvalueforhorizontalresistanceforceinsuchcases Theconditionsforthecaseinwhichtheverticalresultantatthebottomisinthecoreareexpressedasinequation (2.3.8).
(2.3.8)
Themaximumhorizontalsubgradereactionp1(kN/m2)andthemaximumverticalsubgradereactionq1(kN/m2)inthiscaseareobtainedbyequations (2.3.9) and(2.3.10),respectively.
(2.3.9)
(2.3.10)
Whendeterminingthehorizontalresistanceforceofdeepfoundations,thevaluesofp1andq1obtainedbyequations(2.3.9) and(2.3.10)mustsatisfyequations(2.3.11)and(2.3.12),respectively.
(2.3.11)
(2.3.12)where
l :penetrationdepth(m) 2b :maximumwidthperpendiculartohorizontalforce(m) 2a :maximumlength(m) A :bottomarea(m2) P0 :horizontalforceactingonstructureabovegroundsurface(kN) M0 :momentduetoP0atgroundsurface(kN・m) N0 :verticalforceactingatgroundlevel(kN) k :horizontalseismiccoefficient K' :K'=K2/K1 K1 :rateofincreaseincoefficientofverticalsubgradereaction(kN/m4) K2 :rateofincreaseincoefficientofhorizontalsubgradereaction(kN/m4),seeequation (2.3.7) w1 :selfweightofdeepfoundationperunitofdepth(kN/m) α :constantdeterminedbybottomshape (α=1.0 for rectangular shapeandα=0.588 for round
shape) ppk :characteristicvalueofpassiveearthpressureatdepthh (m)(kN/m2),seePart II, Chapter 5,
1 Earth Pressure.Provided,howeverthathisgivenbyequation (2.3.19).
(2.3.13)
qud :designvalueofverticalbearingcapacityatbottomlevel(kN/m2),seeequation (2.3.2) γa :partialfactorforhorizontalresistanceforce
④WhenVerticalResultantForceattheBottomisoutsidetheCore12)Whentheverticalresultantforceactingatthebaseoffoundationisnotinsidethecore,atriangulardistributionofvertical subgrade reaction is assumedas shown inFig. 2.3.2 12).When thevertical subgrade reaction isexpressed as qd (kN/m2), themaximum subgrade reaction p1(kN/m2) in the front ground is obtained fromequation(2.3.14).
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
(2.3.14)
Thevalueofp1calculatedbyequation(2.3.14)shouldsatisfyequation(2.3.11).Inthiscase,h isobtainedbyequation(2.3.12).
(2.3.15)
where h :depthatwhichhorizontalsubgradereactionbecomesmaximum(m),seeFig. 2.3.2 W :selfweightoffoundation(kN) e :eccentricdistance(m)
Thedistancee isdefinedasshowninFig. 2.3.2.Whenthefoundationbottomisrectangularwiththelengthof2a (m)andthewidthof2b (m),thevalueofe iscalculatedbyequation(2.3.16).
(2.3.16)
In thecaseofaroundfoundationbottom, thecalculationmaybemadebyreplacing itwitharectangularfoundationbottomhavinglength2a andwidth2b definedbyequation(2.3.17).
(2.3.17)
where D :diameterofcircle(m)
Inthisway,thehorizontalbearingcapacitycanbeestimatedatasafersidebyapproximately10%.However,thissubstitutionshouldbeappliedonthebasisoftheappropriatejudgement,byreferringtoreference12).
N0
P0M0
kWW
2a
p
qud
qd
1
e
l
Fig. 2.3.2 When Resultant Force is Not Inside the Core
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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2.4 Pile Foundations2.4.1 General
(1)DefinitionofPileFoundationPilefoundationmeansafoundationwhichsupportssuperstructuresbymeansofasinglepileormultiplepiles,orafoundationwhichtransfersactionsonthefacilitiesorthefoundationtothegroundbymeansofsinglepilesormultiplepiles,evenwhennofacilitiesexistabovethepiles.
(2)DefinitionofPilePilemeans a columnar structural elementwhich is provided underground in order to transfer actions on thefacilitiesorthefoundationtotheground.
2.4.2 Fundamentals of Performance Verification of Piles
(1)Theloadsreceivedbypilesasaresultofactionsarecomplex.However,ingeneral,thecomponentsoftheloadsacting on a pile consist of the axial load component and the lateral load component, and verification can beperformedbasedonthepileresistanceperformancewithrespecttotheloadsintheserespectivedirections.
(2)Dependingonthetypesofsuperstructuressupportedbythepilefoundationandthetypesofloadsactingonthepiles,therearecasesinwhichisnecessarytoperformanalysisbythecomponentcouplingmethod,treatingthesuperstructureandpilefoundationascomponents.
2.4.3 Static Maximum Axial Pushing Resistance of Pile Foundations
[1] General
(1)The design value of the axial bearing resistance of pile foundations comprising vertical piles is generallydeterminedbasedonthemaximumaxialbearingresistanceduetotheresistanceofthegroundtoverticalsinglepilesasastandardvalueintakingconsiderationofthefollowingitems.
① Safetymarginfordisplacementintheaxialdirectionbasedongroundfailureanddeformationoftheground② Compressivestressofpilematerial③ Joints④ Slendernessratioofpiles⑤ Actionaspilegroup⑥ Negativeskinfriction⑦ Settlementofpilehead
(2)Theabove (1)describes thegeneralprinciple fordetermining theaxialbearing resistanceofpile foundationscomprisingverticalpiles.Inordertodeterminetheaxialbearingresistanceofapilefoundation,first,thestaticmaximumaxial bearing resistance due to the resistance of the ground is determined, and a safetymargin isconsideredonthis.Then,theaboveitems(a)to(g)areexamined,andthemaximumaxialbearingresistanceisreducedasnecessary.Theresultobtainedinthismanneristhedesignvalueoftheaxialbearingresistanceofthepileswhichshouldbeusedinperformanceverificationofthepilefoundation.
(3)Whenconsideringtheaxialbearingresistancecharacteristicsofasinglepilebasedontheresistanceoftheground,theaxialcompressiveloadP0actingonthepileheadofthesinglepileissupportedbytheendresistanceRpandtheshaftresistanceRfofthepile,andcanbeexpressedasinequation (2.4.1).
(2.4.1)where
Rt :axialbearingresistanceofsinglepile
(4)CharacteristicValueofAxialBearingResistanceofSinglePileDuetoResistanceofGround
① Typicalcharacteristicvaluesfortheaxialbearingresistanceofsinglepilesincludethefollowing.
(a) Second limit resistance:Resistance equivalent to the load at themaximum bearing resistance in a staticloadingtest.Provided,however,thatthedisplacementoftheendofthepileshallbewithinarangeofnomorethan10%oftheenddiameter.Thestaticmaximumaxialbearingresistancegivenbyappropriatecalculationsshallbeequivalenttothis.
(b)Firstlimitresistance:ResistanceequivalenttotheloadataclearbreakpointappearinginthelogP–logScurveinthestaticcompressiveloadingtest.PrepresentsloadattheheadandSmeanssettlementvalueattheheadofapile.
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(c) Verticalspringconstantofpilehead:Slopeofthesecantofthepileheadloaddisplacementcurveinthestaticcompressiveloadingtest.
(5)SettingofDesignValueofAxialBearingResistanceofaSinglePileBasedonResistanceofGround
① Asafetymarginshallbeprovidedinthesecondlimitresistance.Thefollowingequationsareusedinthissafetymargin.Provided,however,thatγintheequationisthepartialfactorforitssubscript,andthesubscriptskanddindicatethecharacteristicvalueandthedesignvalue,respectively.
(2.4.2) (2.4.3)
where Rp :bearingresistanceoftheendofpile Rf :shaftresistanceofpileduringcompressiveloading
Incaseswhereonlythebearingresistanceofthepileheadcanbeobtainedintheloadingtest,andasafetymargincanbedeterminedfromthebearingresistanceofthepilehead,thefollowingequationcanbeused.
(2.4.4)where
Rt :axialbearingresistanceofsinglepile
ThestandardvaluesofthepartialfactorsγRiforthepileendresistance,theshaftresistance,andtheaxialbearingresistanceofpilesshallbeasshowninTable 2.4.1–Table 2.4.3.Provided,thatincaseswherepartialfactorsaredeterminedseparatelybycodecalibrations,etc.,inthedesignsystem.Thesubscriptirepresentsp,f,ort.
Table 2.4.1 Standard Values of Partial Factors for Shaft Resistance
Designsituation γRi:PartialfactorVariablesituationforloadactingduetoshipberthing 0.40Variablesituationforloadactingduetoshiptraction 0.40VariablesituationforLevel1earthquakegroundmotion 0.66Variablesituationforloadduringcraneoperation 0.40Variablesituationforloadactingduetowaves 0.66
Table 2.4.2 Standard Values of Partial factors for Pile End Resistance
Designsituation γRi:PartialfactorVariablesituationforloadactingduetoshipberthing 0.40Variablesituationforloadactingduetoshiptraction 0.40VariablesituationforLevel1earthquakegroundmotion 0.66(0.50)Variablesituationforloadduringcraneoperation 0.40Variablesituationforloadactingduetowaves 0.66(0.50)
Incasetheendofthepileremainsinanincompletebearingstratumwhichappearstobeunsafe,thefiguresinparenthesesshallbeused.
Table 2.4.3 Standard Values of Partial Factors for Total Resistance
Designsituation γRi:PartialfactorEndBearingpile* Frictionpile*
Variablesituationforloadactingduetoshipberthing 0.40 0.40Variablesituationforloadactingduetoshiptraction 0.40 0.40VariablesituationforLevel1earthquakegroundmotion 0.66 0.50Variablesituationforloadduringcraneoperation 0.40 0.40Variablesituationforloadactingduetowaves 0.66 0.50
*)Endbearingpilesandfrictionpilesshallbeasclassificationprovidedin(10).
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(6)Basedoninformationfortheperformanceverificationsofnormalportfacilities,theuseofthepartialfactorslistedabovemaygiveconservativeresults.
(7)Becausetheaxialbearingresistanceofpilesisstronglyaffectedbytheconstructionmethod,itisnecessarytocarryoutconstructioninadvancewithtestpilesandcollectinformationfortheverificationbyvarioustypesofexamination.Dependingontheresultsobtainedwiththetestpiles,itmaybenecessarytochangethedimensionsofthepilesortheconstructionmethod.
(8) Amongtheaxialresistancefactorsofacertainpile,whentheendresistanceofthepileRpisgoverning,thepileiscalledtheendbearingpile,andwhentheshaftresistanceRfisgoverning,itiscalledthefrictionpile.Accordingtothisdefinition,apilebecomesabearingpileorafrictionpiledependingonloadconditionssuchasthemagnitudeof the load, loadingvelocity, loadingduration, etc. Therefore, thedistinctionbetween endbearingpiles andfrictionpilescannotbeconsideredabsolute.Althoughthefollowingdefinitionslackstrictness,here,apilewhichpasses through soft ground andwhose end reaches bedrock or some other bearing stratum is called the endbearingpile,andapilewhoseendstopsinacomparativelysoftlayer,andnotahardlayerthatcouldparticularlybeconsideredabearingstratum,iscalledthefrictionpile.
(9) Ingeneral,whenapilepenetratestoaso-calledbearingstratumsuchasbedrock,ordensesandyground,axialresistanceislargerandsettlementissmallerthanwhenapileonlypenetratestoanintermediatelayer.Whenapilepenetratestoaso-calledbearingstratum,thepileitselfrarelysettles,evenwhenthesoftlayerssurroundingthepileundergoconsolidationsettlement.Therefore,negativeskinfrictionactsonthepile,applyingadownwardload,andtheamountofsettlementdiffersintheheadofthepileandthesurroundingground.Asthesephenomenacauseavarietyofproblems,cautionshouldbenecessary.Althoughthesedefectsareslightinpileswhichonlypenetratetointermediatelayers,settlementduetoconsolidationofthegroundunderthepilecontinues,andasaresult,thereisadangerofunevensettlement.
(10)Thepartialfactorfortheserviceabilitylimitisappliedtoultimatefailurephenomenaoftheground.Whenthedesignerdesirestoavoidyieldingoftheground,theuseofthefirstlimitresistanceisconceivable.ThePartialfactorinthiscasecanbesetatavalueontheorderof0.5.
(11)Incasepermanentdeformationofthegroundisexpectedtoremainafteranearthquake,separateexaminationisnecessary.Furthermore,becausetherearecasesinwhichtheshearstrengthofthesoilisremarkablyreducedbytheactionofgroundmotion,cautionisnecessary.Forexample,whensensitivecohesivesoilisaffectedbyviolentmotion,lossofstrengthisconceivable,andfrompastexamplesofearthquakedamage,ithasbeenpointedoutthatliquefactionmayoccurinloosesandylayersasaresultoftheactionofgroundmotion,causingalargedecreaseintheresistanceofpiles.Accordingly,withfrictionpiles,whichareeasilyaffectedbyphenomenaofthistype,duecautionisnecessaryinsettingthepartialfactors.
(12)Pile group means a group of piles in which the piles are mutually affected by pile axial resistance anddisplacement.
[2] Static Maximum Axial Resistance of Single Piles due to Resistance of Ground
(1)Thestaticmaximumaxialresistanceofsinglepilescanbeobtainedbyverticalloadingtestsorcalculationbystaticbearingcapacityformulasafteranappropriatesoilinvestigation.
(2)Asmethodsofestimatingthestaticmaximumaxialresistanceofsinglepilesfromtheresistanceoftheground,thefollowingareconceivable:
① Estimationbyloadingtests② Estimationbystaticbearingcapacityformulas③ Estimationfromtheexistingdata
(3)Itispreferabletoestimatethestaticmaximumaxialresistanceofsinglepilesfromtheresistanceofthegroundbyconductingaxialloadingtests.Determiningthecharacteristicvalueofthestaticmaximumaxialresistancebythismethodandthenconductingtheperformanceverificationisthemostrationalmethod.Inthiscase,thesoilconditionsmaydifferatthelocationwheretheloadingtestisconductedandatthesitewheretheactualpilesaretobedriven.Therefore,itisnecessarytoevaluatetheresultsofloadingtestswithcautionwithregardtotheirrelationshiptosoilconditions,basedonasoundunderstandingofthesoilconditionsatthelocationwheretheloadingtestisconducted.
(4)Itmaybedifficulttoconductloadingtestspriortotheperformanceverificationduetocircumstancesrelatedtotheconstructionperiodorcost.Insuchcases,estimationofthestaticmaximumaxialresistancedependingonthefailureofthegroundbystaticbearingcapacityformulastakingaccountoftheresultsofsoilinvestigationispermissible. Evenwhenestimating the staticmaximumaxial resistancebymethodsother than theabove-mentioned (2)(a), and conducting the performance verification by setting the axial resistance of piles based
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
thereon,theappropriatenessofthepileaxialresistanceusedintheperformanceverificationshouldbeconfirmedbyconductingloadingtestsattheinitialstageofconstruction.
[3] Estimation of Static Maximum Axial Resistance from Loading Tests
(1)Whenthesecondlimitresistancecanbeconfirmedfromtheload-settlementcurve,thecharacteristicvalueforstaticmaximumaxialresistancecanbesetbasedonthatvalue.Whenitisnotpossibletoconfirmthesecondlimitresistancefromtheload-settlementcurve,itispermissibletoconfirmthefirstlimitresistanceandusethatvalueasthecharacteristicvalue,ortoestimatethesecondlimitresistancefromthefirstlimitresistance.Itisalsopermissibletoobtaintheverticalspringcoefficientofthepileheadbasedontheload-settlementcurveatthepilehead.
(2)EffectofNegativeSkinFrictionWhenapilepassesthroughsoftground,thereisadangerthatthedirectionofskinfrictionmaybereversedduetoconsolidationofthesoftground,thisphenomenoniscallednegativeskinfriction.Insuchcases,itisnecessarytoconductteststoappropriatelyevaluatethepileendresistance.
(3)Load-totalSettlementCurveObtainedbyStaticLoadingTestAload-totalsettlementcurveobtainedbyastaticloadingtestisshownschematicallyinFig. 2.4.1.Thecurve,whichisinitiallygentle,showspronouncedbreakpoints,andthesettlementofthepileheadbecomesremarkable,eventhoughthereisnoincreaseintheload.
A
B
P1 P2P3
Load
Tota
l set
tlem
ent
Fig. 2.4.1 Yield Load and Ultimate Load
(4)CaseinwhichtheSecondLimitResistanceisnotObtainedDirectlybyLoadingTestAlthoughthereisnoproblemifthesecondlimitresistancecanbeobtainedbyaloadingtest,inmanycases,itisnotpossibletoapplyasufficientlylargeloadtoconfirmthesecondlimitresistanceduetoconstraintsrelatedtothetestequipment.Insuchcases,thesecondlimitresistancecanbeassumedbymultiplyingthefirstlimitresistanceobtainedbyaloadingtestby1.2.ThisjudgmentisbasedontheresultsofresearchbyYamakataandNagai14)onsteelpipepilesandstatisticalstudiesbyKitajimaetal.15)Whenthefirstlimitresistancealsocannotbeobtainedinloadingtests,thesecondlimitresistanceshouldbeassumedtobe1.2timesthemaximumloadinthetest,oramethodofsettingthedesignvalueofthepileaxialresistancewhichdoesnotdependonthesecondlimitresistanceshouldbeexamined.Ineithercase,aconditionwhichassumesthatthepileaxialresistanceestimatedinthiswaywillbelargerthanthepileaxialresistancethatcanactuallybeexpectedisrequired.
(5)AlternativeLoadingTestMethodsforStaticLoadingTest
① Therapidloadtest17)isaloadingtestwhichshallbeperformedinlessthan1second.Testequipmentcapableofapplyingalargeinstantaneousloadisnecessary;however,becausevariousinnovationshaveeliminatedtheneedforreactionpiles,thetestcanbeperformedmoreeasilythanthestaticloadingtest.
② Theendloadingtestisamethodinwhichajackisinstallednearthebottomendofthepile,andthepilebodyispushedupwhilepushingthebottomendofthepile.Thismethodenablesseparatemeasurementofthepileendresistanceandpileshaftresistance.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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③ Thedynamicloadingtest18)isatypeofloadingtestwhichemploysanordinarypiledriver.Asafeatureofthistestmethod,changesovertimeintheelasticstrainanddisplacementofthepileheadaremeasured.Inthistest,therearelimitstotheresistancewhichcanbeobtained,dependingonthemagnitudeofthepile-drivingenergy.Therefore,whentheaxialresistancewhichistobeestimatedislarge,asinlongorlarge-diameterpiles,inmanycasesitisnotappliedasamethodfordirectestimationofthesecondlimitresistance.Itcanbeusedtoestimatetherelationshipbetweenstaticresistanceanddrivingstopcontrolduringconstruction.
[4] Estimation of Static Maximum Axial Resistance by Static Resistance Formulas
(1)Whenestimatingstaticmaximumaxialresistanceusingstaticresistanceformulas,attentionmustbepaidtothesoilconditions,pileconditions,constructionmethods,andlimitsofapplicabilityofthestaticresistanceformulas.
(2)Thestaticmaximumaxialresistanceobtainedbystaticresistanceformulasmaybeconsideredtobeequivalenttothesecondlimitresistance.
(3)Whenusingstaticresistanceformulas,itisnecessarytoconsiderdifferencesinconstructionmethods.
① Pilesdrivenbyhammerdrivingmethoda)
(a)Whenemployingstaticresistanceformulasusingtheresultsofstandardpenetrationtestresultsandundrainedshearstrengthofground
i) Endresistanceofapile
a) Equation(2.4.5)canbeusedinestimatingendresistanceofapilewhenthebearingstratumissandyground.
(2.4.5)where
RPk :characteristicvalueofendresistanceofapilebystaticresistanceformula(kN) Ap :effectiveareaofendofpile(m2).Indeterminingtheeffectiveareaofanopen-endedpile,itis
necessarytoconsiderthedegreeofclosureoftheendofthepile. N :Nvalueofgroundaroundpileend
Provided,however,Niscalculatedbyequation(2.4.6).
(2.4.6)where
N1 :N-valueatendofpile(N1≤50)
N2 :meanN-valueinrangeabovetheendofpiletodistanceof4B (N2 ≤50) B :diameterorwidthofpile(m)
Inequation (2.4.5),thecoefficientoftheequationproposedbyMeyerhofbasedonthecorrelationbetweenthestaticpenetrationtestandthestandardpenetrationtestinsandygroundwasmodifiedtoconformtorealconditions. InestimatingtheultimatepileendresistanceofpilessupportedbygroundwithanN-valueof50ormore,cautionisnecessary,asN-valuesitselfisnotreliablewhenitismeasuredlargerthan50,andfurthermore,theapplicabilityofequation (2.4.5)initscurrentformtohardgroundofthiskindhasnotbeenadequatelyconfirmed.
b)Inestimationofthepointresistanceofpileswhenthepointofthepilepenetratesclayeyground,equation(2.4.7)canbeused.
(2.4.7)where
cp :undrainedshearstrengthatpositionoftheendofapile(kN/m2)
Thebearingcapacitycoefficientoftheendresistanceofapileincohesivesoilgroundshowninequation(2.4.7)wasobtainedbythesamemethodasthebearingcapacityoffoundationsoncohesivesoilgroundin2.2 Shallow Spread Foundations.Becausethecross-sectionalshapeofordinarypileshaspointsymmetry,B/L=1.0,andBk/cp <0.1.Basedonthesefacts,thebearingcapacitycoefficientNc offoundationsisobtainedfromFig. 2.2.2, see2.2.3 Bearing Capacity of Foundations on Cohesive Soil Ground. Therefore, thebearingcapacitycoefficientoftheendofthepileis6.Accordingly,theendresistanceRpofthepilecanbeshownas6cpAp.
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
As the undrained shear strength used here, the undrained shear strength cu obtained in the unconfinedcompressiontestwascommonlyuseduptothepresent.
ii) PileshaftresistancePileshaftresistancemaybeobtainedasthesumoftheproductsobtainedbymultiplyingtheaveragestrengthofskinfrictionperunitofareaineachlayerwithwhichthepileisincontact.Namely,equation(2.4.8)canbeused.
(2.4.8)where
Rfk :characteristicvalueofpileshaftresistance(kN)
rfki :averagestrengthofskinfrictionperunitofareaini-th layer(kN/m2)
Asi :circumferentialareaofpileincontactwithgroundini-thlayer(=lengthofoutercircumferenceUsxthicknessoflayerl)(m2)
Forsandyground,equation (2.4.9)canbeused.
(2.4.9)where
N :meanN-valueofi-thlayer
Forcohesivesoilground,equation(2.4.10)canbeused.
(2.4.10)where
:meanadhesionofpileini-thlayer(kN/m2)
Here,thevalueoftheadhesionofthepilemaybeobtainedasfollows.incase c ≤100kN/m2;ca=cincase c >100kN/m2;ca=100kN/m2 (2.4.11)
However,becausetheoreticalproblems24)ariseinobtainingtheadhesionofpilesfromtheundrainedshearstrengthcoftheground,thevalueofadhesionshouldbeexamined,payingdueattentiontothecharacteristicsofthegroundandconditionsofthepiles.
(b)Methodofestimatingtheendresistanceofpileswhichremaininsandygroundfrombearingcapacitytheory
i) ExpansionofbearingcapacitytheoryofshallowspreadfoundationsIftheshearresistanceangleofthebearingstratumisknown,theendresistanceofthepilecanbeestimatedasanexpansionofthebearingcapacitytheoryforshallowspreadfoundations.Here,thefollowingmethodisintroducedasanexample.Theendresistanceofthepileisobtainedusingequation (2.4.12).
(2.4.12)where
Nq :bearingcapacitycoefficientproposedbyBerezantzev,seeFig. 2.4.2σ’v0 :effectiveoverburdenpressureattheendofpile(kN/m2)
WhenNq is tobeobtainedfromFig. 2.4.2, it isnecessary toobtain theshear resistanceangle. Whenobtainingtheshearresistanceangle,equation(2.3.21)inPart II, Chapter 3, 2.3.4 Interpretation Methods for N Valuescanbeused.Whentheshearresistanceangleistobeobtainedbyatriaxialcompressiontest,itisnecessarytoconsiderthefactthattheshearresistanceangleisreducedasaresultofconfiningpressure.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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0
50
100
150
20 25 30 35 40 45
Shear resistance angle (º)
Bea
ring
capa
city
coe
ffic
ient
Nq
Fig. 2.4.2 Bearing Capacity Coefficient proposed by Berezantzev
ii) VoidexpantiontheoryThefailuremodewhentheareaaroundtheendofthepilefailsduetocompressiveforceisconsideredtobeoneinwhichaplasticregionformsattheoutsideofasphericalrigidregionaroundtheendofthepileandisinbalancewithanelasticregionatitsouterside.25)Thistheoryiscalledthevoidexpantiontheory. End resistance of a pile according to the void expantion theory can be shown by the followingequations.26),27)
(2.4.13)
where qp :endresistanceofapileperunitarea(kN/m2) Irr :correctedrigidityindex Ir :rigidityindexφcv’ :shearresistanceangleinlimitcondition;assumesφcv′=30+Δφ1+Δφ2.thevaluesofΔφ1andΔφ2
shallbeasshowninTable 2.4.4. Δav :coefficientdefiningcompressibilityofground.Δav =50(Ir)−1.8 G :shearrigidity.MaybeobtainedasG=7000N0.72(kN/m2).NistheN-valuearoundtheendof
thepile.
Table 2.4.4 ∆φ1; ∆φ2 of Sand and Gravel
(Dependsonparticleshape) ∆φ1(°) (Uniformitycoefficient) ∆φ2(°)Round 0 Uniform(Uc<2) 0
Somewhatangular 2 Moderateparticlesizedistribution(2<Uc<6) 2Angular 4 Goodparticlesizedistribution(6<Uc) 4
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0 5 10 15 20 25 30
0
20
40
60
80
Measured300NVoid Expantion theory
End bearing capacity of pile per unit area (MN/m2)
Dep
th a
t the
end
of p
ile, GL
(m)
Pile diameter ≤1000mm
Fig. 2.4.3 Comparison of Measured End Bearing Capacity of Pile and Results of Calculation by Void Expantion Theory
Fig. 2.4.3showstheresultsofacomparisonofthemeasuredendbearingcapacityofpileandtheresultsofanestimationofendbearingcapacitybytheexpandedvoidtheoryassumingφcv′=34.
② Thevibratorypiledrivingmethod,vibro-hammermethod,isincreasinglybeingusedfordrivingpilesbecauseofthecapacityincreaseofpile-drivingmachineryinrecentyears.Astheprinciplesofthismethoddifferfromthoseofpiledrivingbyhammer,thebearingcapacityshouldbecarefullyestimated.Whenusingthismethod,thegroundshouldbecompactedbythemethodofhammerpiledrivinginsteadofvibratorypiledrivinginthecourseoffinaldriving,orverticalloadingtestsshouldbeconductedtoconfirmthecharacteristicsofbearingcapacityofthegroundinquestion.
③ Inrecentyears,theuseofpileinstallationmethodbyinnerexcavationinsteadofpiledrivingbyhammerhasbeenincreasinginportandharborconstructionworks.Insuchcases,thecharacteristicsofthebearingcapacityofpilesinquestionshouldbeconfirmedbyverticalloadingtests.
(4) EffectiveAreasofPileEnd
① Evenifthereisnoshoeonthepileend,theendbearingareaofsteelpilescanbeconsideredclosed,asshownbytheshadedareasinFig. 2.4.4.Inthiscase,theouteredgeoftheclosedareaistakenastheperimeter.Thisisbasedonthefollowingprinciple.SoilenterstheinteriorofsteelpipesorthespacebetweentheflangesofH-shapedsteelduringthepiledrivinguntiltheinternalfrictionbetweenthesoilandthesurfaceofsteelpilebecomesequaltotheendresistanceofpile.Thisbalancepreventssoilfromenteringtothepilesandhasthesameeffectasthecasewhentheopenendsectionisclosed.Butcompleteclosurecannotbeexpectedinthecaseoflarge-diameterpiles.Insuchcasesthepluggingratioshouldbeexamined.
Fig. 2.4.4 End Bearing Area of Steel Piles
② PluggingratioThemechanismoftheendresistanceofopenendedpilesiscomposedofthesumoftheendresistanceofthesubstantialpartoftheendofthepileandtheskinfrictionoftheinnersurfaceofthepileasshowninFig. 2.4.5.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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Theresistancefromtheinnersurfaceofthepileisconsideredtobedeterminedfromthedirectstressactiononthecircumferenceandtheinnercircularareaofthepile.Becausethepilecross-sectionalareaisproportionaltothesquareofitsdiameteranditscircumferenceisproportionaltoitsdiameter,asthediameterofapilebecomeslarger,theconceptthatthetotalcross-sectionalareaofthepileiseffectiveforresistancelosesvalidity.Inpilesofthis type,amongtheresistanceswhichareconceivableduetoclosureofthepileend,onlysomefractioncanbeexpectedtofunctionastheendresistance.Thatfractioniscalledthepluggingeffectratio.Thesizeofthepluggingeffectratioisaffectedbythediameterorwidthofthepile,thepenetrationdepthofthepile,thepropertiesoftheground,theconstructionmethod,andcannotbedeterminedsimplybythediameterorwidthofthepilealone.
Pu
Rp Rp
t
RfRf Rf
d
Pu : actionsRf : outer skin friction of pileRp : resistance attributable to wall thickness of pile end in open-ended pileRf : resistance due to plugged soild : ile diameter
Fig. 2.4.5 Schematic Diagram of Plugging Effect Ratio
③ Differentfrompluggingeffectratio,thepluggingratioreferstotheratiooftheendresistancethatcanactuallybeexpectedtotheendresistanceobtainedbystaticresistanceformulas.Frompastdata,thepluggingratiocanbeconsideredtobe100%whenthediameterofsteelpipepilesislessthan60cmorH-shapedsteelpileswhichshortsidewidthislessthan40cm.Numeroustheoreticalcalculationmethods30),31),32),33),34),35)andresultsoflaboratoryexperiments36),37)havebeenpresentedasmethodsofestimatingthepluggingeffectratiowhichconsiderthevariousfactorsmentionedaboveforpileswithlargerdiametersorwidths.Therearealsoexamplesofstudybyactuallyconductingpileloadingtests.However,inadditiontothefactthatthepluggingeffectratiovariesgreatlydependingonthepropertiesoftheground,theconstructionmethod,andotherfactors,thestateofpluggingofactualpilesdiffersdependingonthepenetrationdepth,includingthestressintheground,makingitdifficulttoobtaintheratiobytheoreticalcalculation.
④ TheJapanAssociationofSteelPipePilescollectedexamplesofmeasurementsof thepluggingratio.38)Fig. 2.4.6shows databasedthereontogetherwithadditionalnewdata.Thenewdataaddedhereareforpileswithdiametersof1100mmto2000mm. According to thesedata, thepluggingratio for thecasewhereequation(2.4.5)isconsideredtoexpresstheendresistanceforcompletepluggingisintherangeof30-140%.Inanycase,itappearsthatthereisvirtuallynocorrelationbetweentheembeddedlengthratiointhebearingstratumandthepluggingratio.Provided,however,thatthereisclearlyadifferenceinthepluggingratioinsteelpipepileswithdiametersoflessthan1000mmandthosewithdiametersgreaterthan1000mm.Cautionisparticularlynecessarywhenusinglargediametersteelpipepileswithdiameterslargerthan1000mm.Fig. 2.4.7showstheresultswhenthex-axisindicatesthepilediameter.Inspiteofsomedispersioninthedata,thepilediameterhasalargeeffectonthepluggingratio,ascanbeunderstoodbycomparisonwithFig. 2.4.6. Thepluggingratioisaffectedbyconstructionmethodsandsoilcondition,thereforeitisnecessarytograspthepluggingratioinactualconstructionworksandbycarryingouttheloadingtests.
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
0
0.5
1
1.5
0 2 4 6 8 10 12
OD ≤ 650mmOD 700~900mmOD ≥ 1000mm
penetration length ratio in bearing stratum L/D
*
* ) Thin stratum bearing pile
End
resi
stan
ce o
f pile
bas
ed o
n lo
adin
g te
st /
(300NAp
)
Fig. 2.4.6 Plugging Effect of Open Ended Piles (effect of embedded length ratio in bearing stratum)
0
0.5
1
1.5
0.5 1 1.5 2
Mea
sure
d va
lue
/ (30
0NAp
)
Pile diameter (m)
Fig. 2.4.7 Plugging Effect of Open Ended Piles (effect of pile diameter)
(5) BearingCapacityofSoftRockWhenpilesaresupportedonsoftrockorhardclay,thebearingcapacitymaybecalculatedbyequation(2.4.5).Ifunconfinedcompressivestrengthqu (kN/m2)hasbeenmeasuredbyundisturbedsoilsamples,equation(2.4.14)mayalternativelybeused.
(2.4.14)
Further,thevalueofqu shouldbereducedto1/2or1/3ofthemeasurementvaluesdependingontheconditionsofcrackingintheground.Inanyevent,however,thevalueofqu shouldnotexceed2×104kN/m2.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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DN
DN
N=2 N=4 N=9
N ; Division Number
[5] Examination of Compressive Stress of Pile Material
Whendeterminingtheaxialresistanceofpiles,itisnecessarytoconsidersafetywithrespecttofailureofthepilematerial.
[6] Decrease of Bearing Capacity due to Joints
(1) Ifitisnecessarytosplicepiles,thesplicingworkshallbeexecutedunderappropriatesupervisionandreliabilityofjointsofsplicedpileshallbeconfirmedbyappropriateinspection.
(2)Ifjointsaresufficientlyreliable,itmaynotbenecessarytodecreasetheaxialbearingcapacityduetojoints.
(3)Whensplicedpilesareused,thejointssometimesbecometheweakpointsinthepile.Therefore,itisnecessarytoadequatelyexaminethestructuralreliabilityofthejoints.Ifthestructuralreliabilityofthejointsisinadequate,itisnecessarytoreducetheaxialresistance,inconsiderationoftheeffectofthejointonthebearingcapacityofthepilefoundationasawhole.
(4)In-sitecircularweldingbysemi-automaticmethodsisgenerallyemployedforthesplicingofsteelpipepilesusedinthefieldofportandharborconstructionworks.Whensuchhighlyreliablejointingmethodsareappliedunderappropriatesupervisionandthereliabilityofthejointshasbeenconfirmedbyinspection,itisnotnecessarytodecreasetheaxialbearingcapacity.
(5)Forothermattersrelatedtothestructuresofjoints,2.4.6[4] Joints of pilesofpilescanbeusedasreference.
[7] Decrease of Bearing Capacity due to Slenderness Ratio
(1)Forpileswithaverylargeratiooflengthtodiameter,theaxialbearingcapacityofpilesneedstobedecreasedinconsiderationoftheaccuracyofinstallation,unlessthesafetyofbearingcapacityisconfirmedbyloadingtests.
(2)This provision takes account of the fact that the inclination of piles during installation reduces their bearingcapacity.Ifloadingtestsareconductedonfoundationpiles,theultimatebearingcapacitycanbedetermined,accountingforthedecreaseofbearingcapacityduetoinstallationaccuracy.Therefore,inthiscasethedecreaseduetotheslendernessratiomaynotnecessarilybetakenintoaccount.
(3)When decreasing the bearing capacity due to the slenderness of piles, the following valuesmay be used asreferences:
① Exceptforsteelpipepiles
(2.4.15)
② Forsteelpiles
(2.4.16)
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
where α :rateofreduction(%) :pilelength(m) d :pilediameter(m)
[8] Bearing Capacity of Pile Groups
(1)Whenagroupofpilesareexaminedasapilegroup,thebearingcapacityofpilegroupmaybestudiedasasingleanddeepfoundationformedwiththeenvelopesurfacesurroundingtheoutermostpilesinthegroupofpiles.
(2)TerzaghiandPeckstatethatafailureofapilegroupfoundationdoesnotmeanthefailureoftheindividualpilesbutfailureasasingleblock,45),46)basedontheprinciplethatthesoilandpilesinsidethehatchedareainFig. 2.4.8 workasasingleunitwhentheintervalsbetweenthepilesaresmall.Theaxialresistanceofapilegroupwhenconsideredinthismannerisexpressedbyequation(2.4.17).
(2.4.17)
where Rgud :designvalueofaxialresistanceofpilegroupassingleblock(kN) qdk :staticmaximumaxialresistance(characteristicvalue)whenbottomofblockisassumedtobe
foundationloadplaneaccordingtoTerzghi’sequation(kN/m2) γq :partialfactorforbottombearingcapacity(bearingcapacityoffoundationonsandygroundand
bearingcapacityoffoundationoncohesivesoilgroundin2.2 Shallow Spread Foundations) Ag :bottomareaofpilegroup(m2) U :perimeterlengthofpilegroup(m) L :penetrationlengthofpiles(m)
sk :meanshearstrengthofsoilincontactwithpiles(characteristicvalue)(kN/m2) γs :partialfactorforskinfriction(see2.4.3[1] General)
Theaxialresistanceperpileisshownbyequation(2.4.18).
(2.4.18)where
Rad :designvalueofaxialresistanceperpileagainstfailureasablock(kN) γ’2 :meanunitweightofwholeblockincludingpilesandsoil(kN/m3);belowgroundwaterlevel,the
meanunitweightiscalculatedconsideringbuoyancy,andabovegroundwaterlevel,usingthewetunitweight.
n :numberofpilesinpilegroup
Inthecaseofcohesivesoil,equation (2.4.18) isreplacedbyequation(2.4.19),wherec isundrainedshearstrengthandγ’2 ≒γ2 (γ2:meanunitweightofsoilabovetheendofthepile).
(2.4.19)
where B :shortsidewidthofpilegroup(block)(m) B1 :longsidewidthofpilegroup(block)(m) γa :partialfactor(see2.2.3 Bearing Capacity of Foundations on Cohesive Soil Ground)
As the axial resistance of each pilewhen used as a pile group, it is necessary to use the smaller of theaxialresistanceofthesinglepilesortheresistanceagainstblockfailuregivenbyequation (2.4.18)or(2.4.19),respectively.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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Perimeter length U
sL
Fig. 2.4.8 Pile Group Foundation
[9] Examination of Negative Skin Friction
(1) If bearing piles penetrate through a soil layer that is susceptible to consolidation, it is necessary to considernegativeskinfrictionwhencalculatingtheallowableaxialbearingcapacityofpiles.
(2)Whenapilepenetratesthroughacohesivesoftlayertoreachabearingstratum,thefrictionforcefromthesoftlayeractsupwardsandbearsapartoftheloadactingonthepilehead.Whenthecohesivesoftlayerisconsolidated,thepileitselfissupportedbythebearingstratumandhardlysettles,thedirectionofthefrictionforceisreversed,asshowninFig. 2.4.9.Thefrictionforceonthepilecircumferencenowceasestoresisttheloadactingonthepilehead,butinsteadturnsintoaloaddownwardsandplacesalargeburdenontheendofthepile.Thisfrictionforceactingdownwardsonthepilecircumferenceiscalledthenegativeskinfrictionornegativefriction.
(a) (b)
Weak layer
Bearing stratum
Consolidationsettlement
Neg
ativ
e sk
in fr
ictio
n
Posi
tive
skin
fric
tion
Fig. 2.4.9 Negative Skin Friction
(3)Althoughtheactualvalueofnegativeskinfrictionisnotwellknownyet,themaximumvaluemaybeobtainedfromequation(2.4.20).
(2.4.20)
where Rnf,maxk : characteristicvalueofnegativeskinfrictionforsinglepile(maximumvalue)(kN)
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
φ : circumferenceofpiles(perimeterofclosedareainthecaseofH-shapedsteelpiles)(m) L2 : lengthofpilesintheconsolidatinglayer(m)
fs : meanskinfrictionintensityintheconsolidatinglayer(kN/m2)
(4)Intheabove, fs incohesivesoilgroundissometimestakenatqu/2.Ifasandlayerislocatedbetweenconsolidatinglayers,orifasandlayerliesontopofconsolidatinglayer,thethicknessofthesandlayershouldbeincludedinL2.Theskinfrictioninthesandlayerissometimestakenintoaccountfor sf .Thecharacteristicvalueofnegativeskinfrictioninsuchcasesisshownbyequation(2.4.21).
(2.4.21)
where Ls2 : thicknessofsandlayerincludedinL2(m) Lc : thicknessofcohesivesoillayerincludedinL2(m)
Ls2+Lc=L2
Ns2 : meanSPT-N-valueofthesandlayerofthicknessLs2 qu : meanunconfinedcompressivestrengthofcohesivesoillayerofthicknessLc (kN/m2)
(5)Inpilegroups,thecharacteristicvalueofnegativeskinfrictionmaybecalculatedbyobtainingthenegativeskinfrictionassumingallofthepilesformasingleanddeepfoundation,anddividingtheresultbythenumberofpilestoobtainthenegativeskinfrictionperpile.(seeFig. 2.4.10).
(2.4.22)where
Rnf, maxk : characteristicvalueofnegativeskinfrictionforpilegroup(kN) U : perimeterlengthofgroupofpilesactingaspilegroup(m) H : depthfromgroundleveltobottomofconsolidationlayer(m) s : meanshearstrengthofsoilinrangeofH inFig. 2.4.10 (kN/m2) Ag : bottomareaofgroupofpilesactingaspilegroup(m2) γ : meanunitweightofsoilinrangeofL2inFig. 2.4.10 (kN/m3) n : numberofpilesingroupofpilesactingaspilegroup
Equations (2.4.20) to(2.4.22)givetheconceivablemaximumvaluefornegativeskinfriction. Theactualvalueofnegativeskinfrictionisconsideredtobegovernedbytheamountofconsolidationsettlementandthespeed of consolidation, the creep characteristics of the soft layers and the deformation characteristics of thebearingstratum.
Con
solid
atio
n la
yer
H L2
Fig. 2.4.10 Skin Friction of Pile Group
(6)Thedesignvalueofnegativeskinfrictioncanbecalculatedbythefollowingequation,usingthecharacteristicvalueofnegativeskinfriction.
(2.4.23)where
γnf : partialfactorfornegativeskinfriction(normally,1.0canbeused)
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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(7)VerificationWhencalculatingtheaxialbearingcapacityofpiles,manyuncertaintiesexistastohowtheinfluenceofnegativeskin friction should be considered. However, at the present stage,when negative skin friction is adequatelyconsidered, onemethodassumes safetywhen it is confirmed that the force transmitted to the endof thepilepossessesadequatesafetyagainstfailureofthegroundatthepileendandcompressivefailureofthepilematerialcrosssection.Thatis,whenthedesignvalueoftheaxialbearingcapacityintheserviceabilitylimitstateisRad,inadditiontosecuringtherequiredsafetyagainstordinaryloads,Radsatisfiesequations (2.4.24)and(2.4.25).
(2.4.24)
(2.4.25)where
Rad : designvalueofaxialbearingcapacity(serviceabilitylimitstate)(kN) Rpk : characteristicvalueofendresistanceofpile(secondlimitresistance)(kN)
Rnf,maxd : designvalueofmaximumnegativeskinfriction(kN) (smallerofvaluesforsinglepileorpilegroup) σfk : characteristicvalueofcompressiveyieldstressofpile(kN/m2) Ae : effectivecross-sectionalareaofpile(m2) γRp : partialfactorforendresistanceofpile(generally,0.8canbeused) γσf : partialfactorforcompressiveyieldstressofpile(generally,1.0canbeused)
ThecharacteristicvalueforendresistanceofpileRpk canbecalculatedusingequation (2.4.5). Whenthepilepenetratesintothebearingstratum,thecircumferenceresistanceofthatsectionshallbeincludedinthepileendbearingcapacity.Inthiscase,thecharacteristicvalueofendresistancecanbecalculatedusingthefollowingequation(seeFig. 2.4.11).
(2.4.26)where
Rpk : characteristicvalueofendbearingcapacityofpile(ultimatevalue)(kN) N : N-valueofgroundattheendofpile Ap : areaoftheendofpile(m2)
Ls1=L1 : lengthofpilepenetratesintobearingstratum(sandyground)(m) Ns1 : meanN-valueforzoneLs1 φ : circumferenceofpile(m)
L2
L1=Ls1 Bearing ground
Fig. 2.4.11 End Bearing Capacity
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
[10] Examination of Pile Settlement
Theaxialbearingcapacityofpileshallbedeterminedinsuchawaythatanestimatedsettlementofpileheaddoesnotexceedtheallowablesettlementdeterminedforsuperstructures.
2.4.4 Static Maximum Pulling Resistance of Pile Foundations
[1] General
(1)Thedesignvalueofthepullingresistanceoffoundationpilesmustbedeterminedconsideringthefollowingitems,usingthestaticmaximumpullingresistanceofasinglepileduetofailureofthegroundasastandard.
① Tensilestressofpilematerial② Effectofpilejoints③ Loadonpilegroupduetoactions④ Upwarddisplacementofpilesbypulling
(2)Thedesignvalueofthepullingresistanceofpilescanbeobtainedasfollows.First,thecharacteristicvalueofthestaticmaximumpullingresistanceofasinglepileisobtainedbasedonfailureofthegroundandaddingsafetymargin.Thedesignvalueofthepullingresistanceofthepileisthendeterminedconsideringthestressofthepilematerial,actionsofjoints,thepilegroupanddisplacement..
(3)Thecharacteristicvaluesofthepullingresistanceofpilesareasfollows;
① ThefirstlimitresistanceThefirstlimitresistanceistheloadwhentheshearingstressgeneratedinthepilecircumferenceorthesoilsurroundingthepilebypullingofthepileaffectssubstantiallytheentirelengthofthepileandyieldingbegins.WhenaloadingtestisperformedandthelogP–logScurveisdrawn,theclearbreakpointwhichappearsonthecurveshallbeconsideredasthefirstlimitresistance.
② ThesecondlimitresistanceThesecondlimitresistanceis theresistancewhenthepullingresistanceof thepilecircumferenceshowsitsmaximumvalue.Ifthemaximumresistanceisunclear,thesecondlimitresistanceshallbetheloadwhenthedisplacementoftheendofthepilereaches10%ofthediameterorwidthofthepileend.Theresistanceobtainedusingstaticbearingcapacityformulasmaybeconsideredequivalenttothisresistance.
Maximum pulling force
Pulling force
Dea
dwei
ght
Dis
plac
emen
t
Fig. 2.4.12 Pulling Resistance of Piles
(4)SettingofDesignValueofPullingResistanceofSinglePile
(a)Asafetymarginshallbetakeninthesecondlimitresistance.Asthemethod,thefollowingequationcanbeused.
(2.4.27)where
γR : partialfactor
ThestandardvalueofpartialfactorscanbeasshowninTable 2.4.5.Table 2.4.5 Standard Values of Partial Factors for Total Resistance
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
–455–
Designsituation γR:PartialfactorVariablesituationforloadactingduetoshipberthing 0.33Variablesituationforloadactingduetoshiptraction 0.33VariablesituationforLevel1earthquakegroundmotion 0.40Variablesituationforloadduringcraneoperation 0.33Variablesituationforloadactingduetowaves 0.40
(5)Incaseswherethereappearstobeapossibilityofliquefactionofsandylayersduringanearthquake,itisnecessarytodeterminepullingresistancegivingdueconsiderationtothisfact.
(6)Becausetheselfweightofthepilecanbeexpectedtoactreliablyaspullingresistancetogetherwiththeweightofthesoilinthepile,apartialfactorof1.0maybeusedforthis.Accordingly,itisrationaltocalculatethedesignvalueofthepullingresistanceduetofailureofthegroundfromthecharacteristicvalueofpullingresistanceduetofailureofthegroundasfollows.Provided,however,thatwhentheselfweightofthepileiscomparativelysmall,thisprocessisnormallyomitted.Whenthediameterofthepileisexcessivelylarge,itisconsideredthatthesoilfilledinthepileisnotnecessarilyliftedwiththepile,butseparatesandfallsdown.
① whenmaximumpullingresistanceisobtainedbypullingtest
(2.4.28)
② whenmaximumpullingresistanceisobtainedbystaticbearingcapacityformula
(2.4.29)where
Rad : designvalueofallowablepullingresistanceofpile(kN) Wpk : characteristicvalueofselfweightofpilewithbuoyancysubtracted(kN) Rut1k : characteristicvalueofmaximumpullingresistanceofpilebypullingtest(kN) Rut2k : characteristicvalueofmaximumpullingresistanceofpilebystaticbearingcapacityformula (kN) γ : Partialfactorcorrespondingtosubscript
[2] Static Maximum Pulling Resistance of Single Pile
(1) Itispreferabletoobtainthemaximumpullingresistanceofasinglepileonthebasisoftheresultsofpullingtests.
(2)Unlikeaxialbearingcapacity,therearefewcomparativedataforpullingresistance,andindirectestimationsmayinvolvesomerisk.Thusconductofpullingtestsispreferabletodeterminethemaximumpullingresistanceofasinglepile.However,inthecaseofrelativelysoftcohesivesoil,skinfrictionduringdrivingofapileisconsideredto be virtually the same as that during pulling of piles. Therefore, themaximumpulling resistancemay beestimatedfromtheresultsofloadingtests(pushingdirection)andstaticbearingcapacityequations.
(3)Estimationofthemaximumpullingresistancebystaticbearingcapacityformulasmayfollowtheexplanationgivenin2.4.3[4]. Estimation of Static Maximum Axial Resistance by Static Resistance Formulas.However,theendbearingcapacityshallbeignored.Thus,forpilesdrivenbyhammer,thefollowingequationsmaybeused.
① Sandyground
(2.4.30)
② Cohesivesoilground
(2.4.31)where
Rutk : characteristicvalueofthemaximumpullingresistanceofpile(kN) N : meanN-valuefortotalpenetrationlengthofpile As : totalcircumferenceareaofpile(m2)
ca : meanadhesionfortotalpenetrationlengthofpile(kN/m2)
(4)Incaseswherethestaticmaximumpullingresistanceofapileistobeestimatedusingastaticbearingcapacityformula,examinationissometimesperformedusingTerzaghi’sequation,whichisshowninequation (2.4.32).
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
Inthiscase,anappropriatevalueshallbeadopted,basedoncomparisonofthevaluescalculatedusingequation (2.4.30)and equation (2.4.31)andthevaluecalculatedusingTerzaghi’sequation.
(2.4.32)
(2.4.33)where
Rutk : characteristicvalueofthestaticmaximumpullingresistanceofpile(kN) Rfk : characteristicvalueofskinfrictionofpile(kN) φ : circumferenceofpile(m) L : penetrationdepthofpile(m)
fsk : characteristicvalueofaveragestrengthofskinfriction(kN/m2)
caik : characteristicvalueofadhesionbetweensoilandpileini-thlayer(kN/m2) Ksk : characteristicvalueofcoefficientofhorizontalearthpressureactingonpile qik : characteristicvalueofmeaneffectiveoverburdenpressureini-thlayer(kN/m2) μk : characteristicvalueofcoefficientoffrictionbetweenpileandsoil li : thicknessofi-thlayer(m)
For ca and μ, see 2.4.3[4] Estimation of Static Maximum Axial Resistance by Static Resistance Formulas. ThevalueofthecoefficientofhorizontalearthpressureKs isconsideredtobesmallerthaninthecaseofpushing. Ingeneral,avaluebetween0.3and0.7,whichisclose to thecoefficientofearthpressureatrest, isfrequentlyused.
[3] Items to be Considered when Calculating Design Value of Pulling Resistance of Piles
(1)Whendeterminingthepullingresistanceofpiles,itisnecessarytoconsiderthefollowingitems.
① Theresistanceusedinverificationofthepullingresistanceofpilesshouldbenomorethantheproductoftheresistanceofthepilematerialandtheeffectivecross-sectionalareaofthepile.
② Insplicedpiles,thepullingresistanceofthepilebelowthejointisgenerallyignored.Provided,however,thatwhenhigh-qualityjointscanbeusedinsteelpiles,thepullingresistanceofthelowerpilecanbeconsideredwithintherangeofthetensilestrengthofthejointafterconfirmingthereliabilityofthejoint.
③ Incaseofapilegroup,itisnecessarytoexaminethepullingresistanceasasingleblocksurroundedwiththeenvelopesurfaceoftheoutermostpilesinthegroupofpilesthatactasapilegroup.
④Whendetermining the pulling resistance of piles, it is necessary to consider the limit value of the upwarddisplacementofpileheadsbypullingdeterminedbythesuperstructure.
(2)TensileStrengthofPileMaterialsThedesignvalueof thepullingresistanceofpiles is limited to the tensilestrengthof thepilematerials. Themethodofexaminationcanconformto2.4.3[5] Examination of Compressive Stress of Pile Materials.
2.4.5 Static Maximum Lateral Resistance of Piles
[1] General
(1)The staticmaximum lateral resistance of a single pile shall be determined as appropriate on the basis of thebehaviorofthepilewhenitissubjecttolateralforces.
(2)Thecharacteristicvalueofthestaticmaximumlateralresistanceofapilemustbedeterminedsoastosatisfythefollowingtwoconditions:
① Thepilematerialshallnotfailduetostressgeneratedinthepilebody.Especiallythepilematerialshallnotfailduetobendingstressgeneratedinthepilebody.
② Thedisplacement in lateraldirectionand inclinationof thepileheadshallnotexceed the limitvalueof thedisplacementdeterminedbythesuperstructure.
(3)PenetrationLengthofPilesThelengthofpenetratedpartofpilethatyieldseffectiveresistanceagainstexternalforcesiscalledtheeffectivelength.Pilesarecalledlongpileswhenthepenetratedlengthislongerthantheireffectivelength.Pilesarecalled
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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shortpileswhenthepenetratedlengthisshorterthantheireffectivelength.
(4)PilesSubjecttoLateralActionsTheresistancewhichapileperformswhensubjectedtoactionsinthelateraldirection(actionsinthehorizontalornear-horizontaldirection)iscalledthelateralresistanceofthepile,andmaybecategorizedinthethreebasicformsshowninFig. 2.4.13.63)
(a) Theresistanceof thepile is limited to the lateraldirection,andresistance in theverticaldirectiondoesnotappear.Thisisthesimplestformoflateralresistanceandisfrequentlycalledthelateralresistanceofapileinthenarrowsense.
(b)Somepartoftheresistanceofthepileiscomposedofaxialresistance.However,becausethesharesoftheloadbornebylateralresistanceandaxialresistancearedeterminedalmostentirelybytheinclinationangleofthepiles,resistancemaybedividedintolateralresistanceandaxialresistanceandexaminedseparately.
(c) Coupledpilesarethoseinwhichtwoormorepileswithdifferingaxialdirectionsarecombined.ThesimplestformofcoupledpilesisshowninFig. 2.4.13. Incoupledpiles,mostoftheactionissupportedbytheaxialresistanceoftherespectivepiles.Therefore,whenthefreelengthofthepilesislong,thelateralresistanceisnormallyignoredandonlytheaxialresistanceisconsideredinestimatingresistance.Withcoupledpiles,itisquitedifficulttocalculatethepileheaddisplacement.Sofar,anumberofmethodshavebeenproposed,64),65)butnonecanyetbecalledadequate (see2.4.5[6] Lateral Bearing Capacity of Coupled Piles). However,becausethedisplacementofcoupledpilesisfarsmallerthanthatofsinglepiles,displacementrarelybecomesaproblem.
12
TT TTL
TA T2
TA2
TL1
TA1
TL TA
(a) When one vertical pile is subject to lateral force
(b) When one batter pile is subject to lateral force
(c) When coupled piles are subject to lateral force
Fig. 2.4.13 Piles Subject to Lateral Force
[2] Estimation of Behavior of Piles
(1)Thebehaviorofasinglepilewhichissubjecttolateralforcecanbeestimatedbyeitherofthefollowingmethodsorbyacombinationthereof.
①Methodsusingloadingtests
② Analyticalmethods
[3] Estimation of Behavior of a Single Pile by Loading Tests
(1)Whenloadingtestsareplannedtoestimatebehaviorofasinglepilesubject to lateralforce, it isnecessary toconsidersufficientlythedifferencesinthepileandloadconditionsbetweenthoseofactualstructuresandloadingtests.
(2)LoadingtestresultsandcharacteristicvalueanddesignvalueoflateralresistanceWhenloadingtestsareconductedunderthesameconditionsasthoseinactualfacilities,thecharacteristicvalue
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
ofthestaticmaximumlateralresistancemaybeobtainedfromtheloadingtestresultsbythefollowingmethod. The load-pile head displacement curve in lateral loading tests generally shows a curved form from thebeginningoftheloading.Therefore,withtheexceptionofshortpiles,aclearyieldloadorultimateloadnormallycannotbeobtained. Asexplainedpreviously in [1] General, this isbecauseonlygradual small-scale failureoccursinthegroundwithlongpenetrationlengths,andoverallfailureofthegrounddoesnotoccur.Therefore,theload-pileheaddisplacementcurveisnotusedtoobtaintheyieldloadortheultimateload,buttoconfirmthepileheaddisplacementitself.Inotherwords,thefundamentalconceptoftheperformanceverificationofpilessubjecttolateralforceisdeterminationofthelimitvalueofthedisplacementofthepileheadanddesignsoasnottoexceedthatlimitvalue. Furthermore, the bending stress corresponding to the resistance obtained in this manner must also beconsidered.Hence,itisnecessarytoensurethatfailureassociatedwiththebendingstressofthepilematerial(seePart II, Chapter 11, 2.2 Characteristic Values of Steel)doesnotoccurwhentheexpectedloadacts.Tocalculatetheallowablelateralbearingcapacityofshortpiles,overturningofpilesmustbeconsidered,inadditiontothepileheaddisplacementandbendingstressmentionedalready.Whentheoverturningloadcannotbeascertained,themaximumtestloadmaybeusedinsteadoftheoverturningload.
[4] Estimation of Pile Behavior using Analytical Methods
(1)Whenestimatingbehaviorofasinglepilesubjecttolateralforcebyusinganalyticalmethods,itispreferabletoanalyzethepileasabeamisplacedonanelasticfoundation.
(2)Methodsofanalyticallyestimatingthebehaviorofasinglepilesubjecttolateralforceasabeamisplacedonanelasticfoundation include therelativelysimpleChang’smethodswellas thePHRI(PortandHarborResearchInstitute,nameischangedtoPARI)method.68)
(3)BasicEquationforBeamonElasticFoundationEquation(2.4.34)isthebasicequationforanalyticallyestimatingbehaviorofapileasabeamplacedonanelasticfoundation.
(2.4.34)where
EI : flexuralrigidityofpile(kN・m2) x : depthfromgroundlevel(m) y : displacementofpileatdepthx (m) P : subgradereactionperunitlengthofpileatdepthx (kN/m) p : subgradereactionperunitareaofpileatdepthx (kN/m2) B : pilewidth(m)
AnalyticalmethodsdifferdependingonhowthesubgradereactionPisconsideredin equation(2.4.34).Ifthegroundisconsideredsimplyasalinearelasticbody,Porpisalinearfunctionofdisplacementofpiley.
(2.4.35)or
(2.4.36)where
Es : modulusofelasticityofground(kN/m2) kCH : coefficientoflateralsubgradereaction(kN/m3)
There ismuch discussion concerning the characteristics of themodulus of elasticityEs, but the simplestconceptisthatEs=kCHB=constant,asproposedbyChang.69)Shinohara,Kubo,andHayashiproposed thePHRImethodasananalyticalmethodconsidering thenonlinearelastic behavior of the ground.70), 71) Thismethod can describe the behavior of actual pilesmore accuratelythanothermethods.ThePHRImethodusesequation(2.4.41)todescribetherelationshipbetweenthesubgradereactionandthepiledisplacement.
(2.4.37)where
k :constantoflateralresistanceofground(kN/m3.5orkN/m2.5) m :index1or0
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
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(4)PHRIMethod
① CharacteristicsofthePHRImethodIn thePHRImethod, theground isclassified into theS typeand theC type. Therelationshipbetween thesubgrade reaction and the pile displacement for each ground is assumedby equation (2.4.38) and (2.4.39),respectively.
(a) S-typeground
(2.4.38)
(b)C-typeground
(2.4.39)where
ks : constantoflateralresistanceinS-typeground(kN/m3.5) kc : constantoflateralresistanceinC-typeground(kN/m2.5)
The identificationofS-typeorC-typegroundand the estimationofks andkc arebasedon the results ofloadingtestsandsoilinvestigation. InthePHRImethod,thenonlinearrelationshipsbetweenp andy areintroducedasgivenbyequations(2.4.38)and(2.4.39)toreflecttheactualstateofsubgradereaction.Therefore,thesolutionsunderindividualconditionswouldremainunattainablewithouthelpofnumericalcalculation,andtheprincipleofsuperpositioncouldnotbeapplied.Theresultsofmanyfull-scaletestshaveconfirmedthatthismethodreflectsthebehaviorofpilesmoreaccuratelythantheconventionalmethods.Itiscommentedherethatforpilestobehaveaslongpiles,theymustbeatleastaslongas1.5 m1( m1:depthofthefirstzeropointofflexuralmomentinthePHRImethod).64)
② ConstantsoflateralresistanceofthegroundThetwogroundtypesinthePHRImethodaredefinedasfollows;
(a) S-typeground
1) Relationshipbetweenp-y isexpressedasp=ksxy0.5 refer(2.4.38)
2) N-valuebythestandardpenetrationtestincreasesinproportiontothedepth.
3) Actualexamples:sandygroundwithuniformdensity,andnormallyconsolidatedcohesivesoilground.
(b)C-typeground
1) Relationshipbetweenp-y isexpressedasp=kcy0.5 refer(2.4.39)
2) N-valuebythestandardpenetrationtestisconstantregardlessofdepth.
3) Actual examples: sandy ground with compacted surface, and heavily-overconsolidated cohesive soilground. ArelationshipshowninFig. 2.4.14existsbetweentherateofincreaseintheN-valuepermeterofdepthinS-typegroundN andthelateralresistanceofpilesks.72)IncaseswherethedistributionoftheN-valueinthedepthdirectiondoesnotbecome0atthegroundsurface, N canbedeterminedfromtheaverage inclinationof theN-valueplotting through thezeropointat thesurface. InC-typeground,arelationshipofthetypeshowninFig. 2.4.15existsbetweentheN-valueitselfandkc.68),73)Thus,aroughestimateofksorkccanbemadefromthedistributionoftheN-value
.
–460–
TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
104
103
102
101 100
11
1412
107
1539
8 2
13
64
1
5
N-value
ks
(kN
/m3.
5 )
1. ALTON.ILLINOIS (FEAGIN)2. WINFIELD.MONTANA (GLESER)3. PORT HUENEME (MASON)4.5. Hakkenbori No.1, No.26. Ibaragigawa (GOTO)7. Osaka National Railways (BEPPU)8.9. Tobata No.6, No.910. Tobata K-I (PHRI)11. Tobata K-II (PHRI)12. Tobata L-II (PHRI)13. Kurihama model experiment14. Shin-Kasai Bridge (TATEISHI)15. Yamanoshita (IGUCHI)
Fig. 2.4.14 Relationship between N-value and ks
1. Tobata K-I (TTRI)2. Tobata K-III (TTRI)3. Tobata K-IV (TTRI)4. Tobata L-II (TTRI)5. Tobata L-IV (TTRI)6. Hakkenbori No.17. Hakkenbori No.28. Osaka National Railways9. Yahata Seitetsu No.610. Yahata Seitetsu No.911. Tobata preliminary test-1 (TTRI)-112. Tobata preliminary test-2 (TTRI)-213. Wagner (Callif.) No.1514. Wagner (Callif.) No.2515. Wagner-1 (Alaska)-116. Wagner-1 (Alaska)-217. Tokyo National Railways b18. Tokyo National Railways A419. Tokyo National Railways B
1
2
3
4
5
67
8
9
9
10 11
12
1314
15
16
1718
103
102
104
1 10 100N-value
kc
(kN
/m2.
5 )
Fig. 2.4.15 Relationship between N-value and kc
③ EstimationoflateralresistanceconstantsbyloadingtestsEstimationsofthelateralresistanceconstantsbyusingtheN-valuecanonlyprovideapproximatevalues.Itispreferabletoconductloadingteststoobtainmoreaccuratevalues.Theconstantsks andkc aredeterminedfromthegroundconditionsalone,andareunaffectedbyotherconditionsunlikeEs inChang’sequation.Therefore,ifks orkc canbeobtainedbyaloadingtest,thosevaluescanbeappliedtootherconditionsaswell.
④ Effectivelength Foracertainpiletofunctionasalongpile,itspenetrationlengthmustbegreaterthanitseffectivelength.Basedontheresultsofmodeltestswithshortpiles,ShinoharaandKubofoundthat thelowerpartofapileisconsideredtobefixedcompletelyinthegroundwhenthepenetrationlengthexceeds1.5 m1,andthereforeproposedusing1.5 m1aseffectivelength.77)Actually,ifthepenetrationlengthexceeds1.5 m1,thebehaviorofthepilewillnotdiffersubstantiallyfromthatofalongpile.However,astheminimumpenetrationlengthoflong
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
–461–
piles,1.5 m1shouldbeused,consideringtheeffectsofsoilfatigueorcreep. Itshouldalsobenotedthatthevalueof m1increasesasthestiffnessofthepileincreasesanddecreasesasthelateralresistanceofthegroundincreases.However,thevalueof m1isvirtuallyunaffectedbytheloadingheightandpileheadfixingconditions. Furthermore, m1alsohas thecharacterof increasinggradually as loadingincreases.
⑤ EffectofpilewidthTherearetwowaysinconsideringtheeffectofpilewidth.ThefirstistoconsiderthatthepilewidthB hasnoeffectontherelationshipbetweenthesubgradereactionp perunitareaandthedisplacementy.Thesecond,asproposedbyTerzaghi,istoassumethatthevalueofp correspondingtoagiveny valueisinverselyproportionaltoB.Shinohara,Kubo78)andSawaguchi79)conductedmodelexperimentsontherelationshipbetweentheks valueinsandygroundandB.TheresultsareshowninFig. 2.4.16.ItseemstoshowacombinationofthetwotheoriesmentionedaboveandindicatesthatthefirsttheoryiseffectiveifthepilewidthB issufficientlylarge.Onthebasisoftheseresults,itwasdecidednottoconsidertheeffectofpilewidthinthePHRImethod.
+
Pile width (cm)
Late
ral r
esis
tanc
e co
nsta
nt ks (
kN/m
3.5 )
12
10
8
6
4
2
00
10
20 30 40 50 60
×103
Legend
Pile headdisplacement p-y curve
Maximumbendingmoment
1st Series2nd Series3rd Series
Fig. 2.4.16 Relationship between ks and Pile Width
⑥ EffectofpileinclinationForbatterpiles,arelationshipshowninFig 2.4.17existsbetweentheinclinationangleofthepilesandtheratioofthelateralresistanceconstantofbatterpilestothatofverticalpiles80)Thistigureshowsthein-situtestsexampleswhichexamineddrivingofbatterpilesinhorizontalgroundandthelaboratorytestsexamplesobtainedbypreparingthegroundafterdrivingofthebatterpileandthensufficientlycompactingthegroundaroundthepile.Inthein-situtests,whenfillingwasperformedafterthebatterpilesweredriven,resultswereobtainedinwhichthecoefficientofthesubgradereactiondidnotincreaseevenwhentheangleofinclinationof thepile isminus. In thiscase,however, an increase in thecoefficientof the subgrade reactiondue tosubsequentcompactionofthesurroundinggroundcanbeexpected.81),82)
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
0-30 -20 -10 10 20 30
2.5
2.0
1.5
1.0
0.5
:Indoor tests:In-situ tests
k0:
x=k/k 0
(in) (out)
θ
Value of k, when θ = 0
-θ +θ
Fig. 2.4.17 Relationship between Pile Inclination Angle and Lateral Resistance Constants
(5)Chang’sMethod
① CalculationEquationUsingtheelasticitymodulusofthegroundEs =B kCH,theelasticityequationofpilesisexpressedasfollows;
Exposedsection
(2.4.40)Embeddedsection
BycalculatingthesegeneralsolutionswithB kCH asaconstantandinputtingtheboundaryconditions,thesolutionforpilesofsemi-infinitelengthcanbeobtained(seeTable 2.4.6).83) AccordingtoYokoyama,pilesoffinite lengthmaybeequivalent to thepilesof infinite lengthifβL ≥ π .Whenapileisshorterthanthis,apilemustbetreatedasafinitelengthpile.Diagramsareavailabletosimplifythisprocess.85)
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
–463–
Tabl
e 2.
4.6
Cal
cula
tions
for P
iles
of S
emi-I
nfini
te L
engt
h if
k ch
is C
onst
ant
Differentialequationsofdeflection
curveandexplanationofsy
mbols
Exposedsections:
[Sym
bols]
Embeddedsections:
Ht :Lateralforceonpilehead(kN
)M
t :Externalforcemom
entonpile
head
(kN
・m)
B :Pilediameter
(m)
EI :Flexuralrigidity
(kN
・m2 )
k CH
:Coefficientofhorizontalsubgradereaction(kN
/m3 )
h :Heightofpileheadaboveground
(m)
β :
(m–1
)
Situationofpile
Protrudingaboveground(h≠0)
Embeddedunderground
(h=0
)Deflectioncurvediagram
Flexuralmom
entdiagram
①Basicform
ation
②Ifpileheaddoesnotrotate
③Basicsy
stem
(butM
t=0)
④Ifpileheaddoesnotrotate
Deflectioncurvey
(IfM
t≠0,useequationsin①
putting
h0=M
t/Ht:thesameappliesb
elow
)Pileheaddisplacement
y t
Groundleveldisplacem
ent
y 0
Pileheadinclinationθ
t
Flexuralmom
entofpilemem
bersM
Shearstrengthofpilemem
bers
S
Pileheadflexuralm
oment
Maximum
flexuralmom
entof
embeddedpartsM
s,max
Depthatw
hich
Ms,m
axoccurs m
Depthof1ststeadypoint0
Depthofdeflectionanglezeropoint
L Pileheadrig
idityfactor
K 1,K
2,K3,K
4
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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN
② EstimationofkCH inChang’smethod
(a) Terzaghi’sproposal86)Terzaghiproposedthefollowingvaluesforthecoefficientoflateralsubgradereactionincohesiveorsandysoil:
1) Incaseofcohesivesoil
(2.4.41)where
kCH :coefficientoflateralsubgradereaction(kN/m3) B :pilewidth(m) :valueshowninTable 2.4.7
(2.4.42)
2) Incaseofsandysoil
(2.4.43)where
x :depth(m) B :pilewidth(m) nh :valuelistedinTable 2.4.8
(2.4.44)
Insandysoil,Es isafunctionofdepthandthuscannotbeapplieddirectlytoChang’smethod.Forsuchcases,ChangstatesthatEs canbetakenthevalueatthedepthofonethirdofy1whichisthedepthofthefirstzero-displacementpoint.However,y1itselfisafunctionofEs,thusrepeatedcalculationshavetobemadetoobtainthevalueofEs.Reference87)describesthemethodofcalculationwithouttherepetitioncalculation. Terzaghi assumes that the value of kCH is inversely proportional to the pilewidthB, as shown inequations(2.4.43)and(2.4.44).OtheropinionssuggestthatpilewidthisirrelevanttokCH(see(4)⑤).
Table 2.4.7 Coefficient of Lateral Subgrade Reaction
Consistencyofcohesivesoil Hard Veryhard SolidUnconfinedcompressivestrengthqu (kN/m2) 100–200 200–400 400orgreaterRangeofkCH1(kN/m2) 16,000–32,000 32,000–64,000 64,000orgreaterProposedvalueofkCH1(kN/m3) 24,000 48,000 96,000
Table 2.4.8 Value of nh
Relativedensityofsand Loose Medium Densenh fordryorwetsand(kN/m3) 2,200 6,600 17,600nh forsubmergedsand(kN/m3) 1,300 4,400 10,800
(b)Yokoyama’sproposalYokoyamacollectedtheresultsoflateralloadingtestsonsteelpilesconductedinJapanandperformedreversecalculationsforkCH, andobtainedFig. 2.4.18 bycomparingtheresultsandthemeanN-valuesatdepthsdowntoβ-1fromthegroundlevel.88)Inthiscase,Es = kCHB isassumedtobevalidforbothsandysoilandcohesivesoil,andkCH itselfisassumednottobeaffectedbyB.AlthoughthevaluesofkCH obtainedbyreversecalculationfromthemeasuredvaluesdecreaseasloadingincreases,Fig. 2.4.18 ispreparedusingkCHwhenthegroundsurfacedisplacementis1cm.Fig. 2.4.18 maybeusedwhenmakingroughestimatesofthevalueofEs fromsoilconditionsalonewithoutconductingloadingtestsin-situ.
PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS
–465–
1. Yamaborigawa2. Tobata3. Tobata K-I4. Tobata L-II5. Tobata K-II6. Tobata K-III7. Tobata L-IV8. Tobata K-IV9. Shell Ogishima10. Ibaragigawa11. Takagawa12. Tokyo SupplyWarehouse13. Kasai Bridge14. Aoyama15. Den-en
4
1
2
3
5
6 7
8
9
10
11
12
13
14
15
1 10 50103
104
105
N-value
k CH
(kN
/m3 )
Fig. 2.4.18 Values of kCH obtained by Reverse Calculation from Horizontal Loading Tests on Piles
(c) Relationshipbetweenkc,ks,andkCH 89),90)
FromFig. 2.4.14,Fig. 2.4.15,andFig. 2.4.18,therelationshipsbetweentheSPT-N-valuesorN -valuesshownintherespectivefiguresandthecorrespondingcoefficientsofsubgradereactionareasshowninTable 2.4.9.Ascanbeunderstoodfromtheseresults,therearelargelydispersedrelationshipsbetweenkCHandtheN-value.TheseresultsareduetothefactthatthevalueofkCHcannotbedeterminedfromthesoilconditionsalone. Hence,therelationshipbetweenkcandkCHandthatbetweenks andkCHcanbeobtainedinsuchawaythatgroundsurfacedisplacementwasequalunderthesameloadingconditions.Then,substitutingtherelationalequationsofkc,ks,andtheN-valueorN -value,thefollowingequationscanbeobtained.
(freepilehead)
(fixedpilehead) (2.4.45)
(freepilehead)
(fixedpilehead)
Table 2.4.9 Relationships between SPT-N-value or N -value and Respective of Subgrade Reaction
Correlationequation Correlationcoefficient Coefficientofvariation
(kN/m2.5) 0.872 0.111
(kN/m3.5) 0.966 0.077
(kN/m3) 0.917 0.754