Large diameter dolphin piles

169 Pages·2016·15.16 MB·English

by  J. Winkel

Large diameter dolphin piles
The effect of the inner soil on their local
buckling resistance
J. Winkel

Large diameter dolphin piles
The effect of the inner soil on their local
buckling resistance
by
J. Winkel
toobtainthedegreeofMasterofScienceinCivilEngineering
attheDelftUniversityofTechnology,
tobedefendedpubliclyonMonday,31October2016at3:30p.m.
Faculty: CivilEngineeringandGeosciences
Department: StructuralEngineering
Programme: HydraulicStructures
Thesiscommittee: Prof.dr.ir.S.N.Jonkman, TUDelft,HydraulicEngineering
Ir.D.J.Peters, RoyalHaskoningDHV;
TUDelft,HydraulicEngineering
Dr.ir.S.H.J.vanEs, TUDelft,StructuralEngineering
Ing.H.J.Everts, TUDelft,GeoscienceandEngineering
Projectduration: 11January2016–31October2016
Anelectronicversionofthisthesisisavailableathttp://repository.tudelft.nl/.

Abstract
Eventhoughformosthydraulicandgeotechnicalstructuresclearguidelinesareavailable,thoseforflexible
dolphinsarestillmissing.Consequently,whetheradesignissafeisusuallysubjectofdebate.
Economicaldolphinpilesarelargediametertubularpiles,susceptibletolocalbuckling.Afterinstallationthe
embeddedpartofthesepilesremainspredominantlyfilledwithsoil. Theaimofthisresearchistoprovide
understandingoftheeffectsconcerninglocalbucklingandtherewithtocontributetothediscussionwhether
adolphindesignissafe.
Themainresearchquestionis:
Doesthesoilindolphinpilescontributetothelocalbucklingresistanceandcanthisbeusedinthedesignof
thesepiles?
Gresnigt[1]prescribesastrainbasedmethodtocheckapileonlocalbuckling. Thismethodisincorporated
inEN1993-4-3[2]. Theresistanceagainstlocalbucklingdependsontheslendernessratio D (cid:177)tε2. Also,
e
ovalisationinfluencestheresistance.Thepresenceofasoilplugreducestheovalisation,enhancingthelocal
bucklingresistance.
Ananalyticalmethodisproposedinwhichbeamtheoryisusedtodeterminethedolphinpiledeformation
andloadsonthepile. Literatureprovidesequationstocalculatetheovalisationthatcanbeappliedinthree
distinctparts:abovethebedlevel,betweenthebedlevelandpluglevelandbelowthepluglevel.Theprovided
equationshowever,showinconsistenciesatthetransitions. Itisproposedtoapplybeamtheoryonthepile
wall,modelledasalinearbeamwithspringsprovidingresistanceagainstovalisation.Abovethepluglevel,the
resistanceisprovidedbytheringbehaviouroftheshell. Belowthepluglevel,thestiffnessisincreasedwith
thestiffnessofthesoilplug. Themodelovercomestheinconsistenciesinovalisation. Themethodassumes
thestiffnessofthepluginthepilecanbeapproximated.However,itisconcludedthatthesuggestedstiffness
inCUR211E[3]isnotabletodeterminetheplugstiffnessforsemi-filledpiles.
Keyparametersthataffectthelocalbucklingresistanceareidentified.Thesearetheplugpacking,pluglevel,
slenderness ratio and the soil packing. The influence of these key parameters are studied with the finite
elementprogramAbaqus.
The parametric study proves that the soil in dolphin piles contributes to the local buckling resistance. A
denserpackingoftheplugimprovesthecapacitiesofthebendingmomentandlateralload. Mostofall,the
dolphincandissipatemoreenergy.Thepluglevelinfluencesthelevelatwhichlocalbucklingisobserved,as
wellaswhetheraninwardoroutwardbuckleoccur. Thecontributionoftheinnersoilonthelocalbuckling
resistance can be compensated by designing a more slender dolphin pile. A more slender cross-section
reducesthecapacitiesofthepile. Thepackingoftheoutersoilalsoinfluencesthebucklinglevelandshape.
Furthermore, a looser soil packing improves the energy capacity of the dolphin pile. To obtain a dolphin
pilethatoptimisestheimprovementsonthelocalbucklingresistancebytheinnerandsurroundingsoil,an
installationmethodisusedthatdoesnotcompactthesoilandplugpackingandafterinstallation,theplug
packingiscompacted.
WiththeAbaqusanalysesthestiffnessofthesoilplugisstudied. Itrevealsthattheplugisstifferatdeeper
levels.Forapilewithadiametercomparableto914mm,whenthepredictedovalisationforthatpilewithout
asoilplugislessthan8mm,aplugstiffnessof30,000 kN(cid:177)m2 canbeassumedintheproposedanalytical
method,regardlessoftheplugpacking.Thestiffnessisindependentoftheslendernessratio.
ThePortofRotterdamfacilitatedafullscalefieldtestwitheightpiles. TheAbaqusmodelshowsreasonable
comparisonwiththefieldtest.Theobservedlocalbucklingbehaviourpilesthatwerenotmodelledcanwell
beexplainedwiththeresultsoftheparametricstudy.
iii

Preface
ThisreportismyMaster’sthesis,thefinalproducttoobtainthedegreeofMasterofScienceinCivilEngineering
attheDelftUniversityofTechnology.Anendhascometoananimated,enjoyabletimethatwaseducational
andinspiring.Sincesixyears,IaminDelftactivetowidelydevelopmyself.Lookingfornewknowledge,skills
andexperiences.
I am inspired by Maslow’s hierarchy of needs, that I encountered during the minor project management
within the BSc degree program. In order to be happy, one requires the basic needs. It is my purpose to
providepeoplesafety.Hence,IchoosetostudyHydraulicStructures.
DuringmyinternshipattheMaritimedepartmentofRoyalHaskoningDHV,Iwasfacedwiththedesignof
dolphinpiles. Itisnotalifesavingstructure,yettheoptimisationbetweenstrengthandflexibilityfascinates
me. DirkJanPetersofferedmethischallengingmasterthesisproject,thatrequiresknowledgeinstructural
engineeringaswellassoilmechanics.
In the course of this project, I learned a lot about soil structure interaction, thanks to Bert Everts. I am
alsogratefultoSjorsvanEs,forclarifyingthedifferencesbetweentheory,codesandpractice. BasJonkman
showedmehowaresearchprojectissetupandkeptmefocusedtowardstheend,whichIappreciate.Moreover,
throughoutthisprojectIexperiencedthatitcanbemoreefficienttomakeassumptionsandthentofindout
how to deal with the consequences, rather than first studying all the possible effects of an assumption. I
considertheseasvaluablelessons.
ThankstoRoyalHaskoningDHVforprovidingmethefacilitiesIneededtobeabletodothisresearch. Iam
thankfultothecolleaguesthatwerewillingtoanswerquestionsandthinkalong. SpecialthankstoDirkJan
Peters,forintroducingmetothisengineeringworld,withallitsuncertainties.Yet,youshowedmeinperson
thatwithawideknowledgetherealwaysisawaytocopewiththem.
JortWinkel
Delft,October2016
v

Nomenclature
Abbreviations
CPT Conepenetrationtest
FEM Finiteelementmethod
IFR Incrementalfillingratio
LA Linearelasticshellanalysis
LBA Linearelasticbifurcation(eigenvalue)analysis
MNA Materiallynonlinearanalysis
OCR Overconsolidationratio
PLR Pluglengthratio
SLS Serviceabilitylimitstate
TEU TwentyFootEquivalentUnit
ULS Ultimatelimitstate
Symbols
Romanuppercaseletters
D Externaldiameter:D +t [m]
e m
D Diameterofthemid-lineofthepilewall [m]
m
D DiameterofthemodelledoutersoilinAbaqus [m]
soil
E Young’smodulusofelasticity [kPa]
E Young’smodulusofelasticityofthesoil [kPa]
g
E Young’smodulusofelasticityofthesoilplug [kPa]
plug
E Young’smodulusparameterofPlaxis [kPa]
ref
E Young’smodulusofelasticityofsteel [kPa]
s
E Berthingenergy [kNm]
v
EI Bendingstiffnessinbeamtheory [kNm2]
EI Bendingstiffnessofthepile [kNm2]
p
EI Bendingstiffnessofthepilewallperunitlength [kNm]
w
F Activeearthforce [kN]
a
F Passiveearthforce [kN]
p
F Ultimatelateralresistance [kN]
pt
F Lateralloadexertedbythevessel [kN]
v
G Shearmodulusofelasticity [kPa]
I Secondmomentofinertiaofthepile [m4]
p
I Secondmomentofinertiaofthepilewallperunitlength [m3]
w
K Lateralstresscoefficient [-]
K Neutralearthpressurecoefficient [-]
0
KNC Neutralearthpressurecoefficientfornonconsolidatedsoils [-]
0
KOC Neutralearthpressurecoefficientforoverconsolidatedsoils [-]
0
K Activeearthpressurecoefficient [-]
a
K Passiveearthpressurecoefficient [-]
p
L Lengthoftheunembedded(free)partofthepile [m]
f
L Lengthoftheembeddedpartofthepilewithoutplug [m]
np
L Pluglength [m]
p
L Lengthoftheembeddedpartofthepile [m]
s
M Bendingmoment [kNm]
M Plasticmomentcapacity [kNm]
p
vii
viii Nomenclature
M Yieldmomentcapacity [kNm]
y
Q Ultimateinnershaftfriction [kNm−1]
f,i
Q Supportreactionintheformofindirectlytransmittedearthpressure [kNm−1]
i
Q Ultimateplugendbearing [kNm−1]
p
(cid:177)
R Radiusoftheofthemid-lineofthepilewall: D 2 [m]
m m
R localradiusofcurvatureofanovalisedcrosssection [m]
o
U Initialdimpleparameter [-]
0
U Displacementinx-directioninAbaqus [mm]
1
U Displacementiny-directioninAbaqus [mm]
2
U Displacementinz-directioninAbaqus [mm]
3
U Out-of-roundness [-]
r
V Shearforce [kN]
Romanlowercaseletters
a Ovalisationparameter [m]
a Ovalisationparameterduetobending [m]
c
a Ovalisationparameterofanemptypile [m]
empty
a Ovalisationparameterduetoindirectearthpressure [m]
q
a Ovalisationparameterofasand-filledcrosssection [m]
sand-filled
(cid:48)
c Cohesion [kPa]
d Internaldiameter:D −t [m]
m
f Bucklingcapacity [MPa]
b
f Criticalstress [MPa]
cr
f Referencestrength(235MPa) [MPa]
ref
f Reroundingfactor [-]
rr
f Yieldstrength [MPa]
y
k Springstiffness [kPa]
kθ Circumferentialbucklinginteractionparameter [-]
kτ Shearbucklinginteractionparameter [-]
k Bucklinginteractionparameter [-]
i
k Stiffnessofthesoil [kPa]
g
k Stiffnessofthesoilappliedonasegmentofthepile [kPa]
g,applied
k Stiffnessofthesoilatthebottomofasegmentofthepile [kPa]
g,b
k Stiffnessofthesoilatthetopofasegmentofthepile [kPa]
g,t
k Stiffnessofthesandplug [kNm−2]
plug
k Stiffnessoftheberthingsystem [kNm−1]
sys
k Meridionalbucklinginteractionparameter [-]
x
k Deflectioncoefficientdependentontheloadingpatternoftheindirectsoilload [-]
yi
k Stiffnessofthepilewall [kNm−2]
wall
l Gaugelength [m]
g
m Stressdependencypower [-]
p Effectivepressure:p +p [kPa]
i e
p Externalpressureonthepile(positivewhenactinginward) [kPa]
e
p Internalpressureinthepile(positiveoutward) [kPa]
i
p Theoreticalvalueoftheimplosionpressure [kNm−1]
cr
q Distributedload [kNm−1]
q Distributedloadduetobending [kNm−1]
c
q Backpressurefromtheplug [kPa]
p
r Internaldiameter:Rm−t/2 [m]
r Elasticcriticalbucklingresistanceratio [-]
Rcr
r Plasticreferenceresistanceratio [-]
Rpl
t Pilewallthickness [m]
y Horizontaldisplacement [m]
y Horizontaldisplacementofthepileaxis [m]
p
y Horizontaldisplacementofthedolphinatthefenderheight [m]
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