1

2 3

Tab

le o

f C

on

ten

tsINTRODUCTION ................................................................................... 3

EQUATION VARIABLES ........................................................................ 4

BENEFITS OF HELICAL PILES .............................................................. 7

HELICAL PILE SIZES ............................................................................ 8 HSS2.875”HelicalPile ..................................................................... 8HSS4.000(3.500SCH80) ...............................................................10STRUCTURAL HELICES....................................................................... 11

NEw CONSTRUCTION ........................................................................14

CalculationofHouseLoad................................................................14SOIL PROPERTIES TO CAPACITy CALCULATIONS ...............................17

CalculatedCapacityExamplesfromSoilData....................................19TORQUE TO CAPACITy ESTImATE .......................................................20

CapacityPredictionfromTorque(Kt).................................................20SandinCompression.......................................................................32TENSION ANCHORS ...........................................................................34

ShallowTensionAnchors..................................................................34 Sand...........................................................................................34SiltandClay................................................................................35DeepTensionAnchors......................................................................36 Sand...........................................................................................36Clay............................................................................................36Multi-HelixAnchors..........................................................................36 Sand...........................................................................................36SiltandClay................................................................................37FIELD DETERmINATION OF PILE CAPACITy ........................................38

BRACkETS ..........................................................................................39

NewConstructionBracket................................................................39UnderpinningBracket.......................................................................39UnderpinningBracketInstallation.................................................44CantsinkSlabBracket......................................................................44SlabBracketInstallation...............................................................46SolarFoundationPiles......................................................................46TiebackAnchor.................................................................................47OtherBrackets................................................................................48CORROSION .......................................................................................49

BucklingAffectedbyCorrosion.........................................................53CAPACITy SUmmARy .........................................................................54

GALLERy OF DIFFERENT APPLICATIONS ............................................54

REFERENCES ......................................................................................58

2 3

INTRODUCTIONFormorethan200years,helicalpileshavebeenimplementedforspecialcircumstanceswithinthefieldof construction.However, itwasn’tuntil recently that theyhavebecomecommonknowledgewithintheengineeringandconsumerworld.Theuseofhelicalpileshasincreasedrapidlywiththeintroductionofhightorquehydraulicdriveheadsthatfacilitatetheinstallationprocess.Theseendbearingpileswithaslendershaftandascrewshapedbearingplateareinstalledbytorquingthemintotheground,wheretheloadisthentransferredtothehelicalplate(s)nearthetip.Auniquebenefitoftheslendershaftisthattherecanbemorethanonebearingpointifmultiplehelicesareinstalled.Whileinitiallypileswereusedfortensionappli-cations,theyhavefoundwidespreadacceptanceascompressionpiles.ThiswasfurtheredwiththeadoptionofAC358bytheICC-ESinJuneof2007,thusestablishingauniversalacceptancestandardforallhelicalpilemanufacturers.Theuniversalstandardnowrecognizesthathelicalpilesarepartofanengineeredfoundation.Thisprocessinvolvespre-constructionsoilbearingcapacitytesting,gradebeamdesign,andqualitycontrol.

Thismanualwillalsogiveadetaileddescription related tohelicalpilesizeaswellas theirstructure, intentionallyallowing foruser familiarityof theproduct.More importantly itwillprovideanindepthproceduralapplicationforinstallationoftheproductsproducedbyCan-tsinkManufacturingfornewconstructionandvarioussoilproperties.Here,thereaderwillfindsectionsforcapacitycalculations,atorquetocapacityestimation,tensionanchors,fielddeter-minationofpilecapacity,bracketsandanothersectiontoaccountforcorrosionwithinhighlyaggressivesoils.FollowingisagalleryofscenarioswhereCantsinkTMhelicalpileshavebeenbeneficiallyutilized.Thiswillhelptheusertogainanunderstandingoftheproduct’sfunction-alityandtheproperwaystoapproachbasicdesignusingCantsinkhelicalpiles.

3

4 5

EQUATION VARIABLES

Wallslenderness

Columnslenderness

Maximumwallslendernessforcompactsection

Maximumwallslendernessfornon-compactsection

Resistancefactor

Bendingresistancefactor

Compressionresistancefactor

Overburdenpressure

V Poisson’sratio

A Area

Ag Grossareaofcross-section,in2

B Helixdiameter

C Cohesion

Cc Slendernessratio

Cm Reductionfactor

ds Shaftdiameter

Da Helixdiameter

Dh Helixdiameter

E Modulusofelasticity

Es Modulusofelasticityofsoil

Fa Allowablecompressionstress

Fb Allowableflexuralstress

Fcr Criticalstressforcolumnbuckling,ksi

Effectivepin-endlength

Fy Specifiedminimumyieldstrength

FS Factorofsafety

fu Steeltensilestrength

Fya Averageyieldstrengthofthesteel

Fyc Tensileyieldstrengthofcorners

φb

λc

φc

λp

λr

σ p'

φ

λ

Fe'

4 5

EQUATION VARIABLESFyv Tensileyieldstrengthofvirginmaterial

Fuv Ultimatetensilestrengthofvirginmaterial

H1 Depthtotophelix

Hn Depthtobottomhelix

I MomentofInertia

ID Interiordiameternominal,alsoequalto“d”

J Polarmomentofinertia

K Compressionmembereffectivelengthfactor

Ku Lateralstressvalue

L Length

L/D Distancebetweenhelices

l Length

M Moment

Mn Allowablemoment

Mp Plasticmomentofsection

Mu Requiredflexuralstrength

N Blowcounts

N60 Blowcountat60%energytransfer

Nc Bearingcapacityfactorforcohesion

OD Outsidediameternominal,alsoequalto“D”

P Load

Pcr Criticalload

Pn Nominalaxialstrength

Pu Requiredaxialstrength

Q Effectiveareafactor

Q Bearingcapacity

Qf Cylindricalcapacity

S Sectionmodulus

R Insidebendradius

6 7

R1 Forceattopofbracketshell

Rn Weldingcapacity

S Settlement

sc Settlementinsand

Su Undrainedshearstrength

Tu Ultimatetorsionalstress

T Torque

Vc Criticalshear

Y Centroidlocation

Z Plasticsectionmodulus

c Distancefromcentertooutsidefiber

f Areductionfactorforremolding

Nominalaxialcompressionstress

Nominalbendingstress

Compressivestrengthofconcrete

r Radiusofgyration

Torsionalstress

t Basemetalthicknessbeforebending

t Wallthickness

y Distancefromthebottomtothecentroid

EQUATION VARIABLES

fc'

fa

fb

τ

6 7

BENEFITS OF HELICAL PILES•Torquemonitoringallowspilecapacityestimation.

•Smallinstallationrigallowsaccesstodifficultsites.

•Nodepthlimit.

•Noneedtowaitonconcretedeliveryortheuseofgroutpumps,becausecasingisnotnecessary.

•Nospoiltoremove.

•Canbeinstalledinunstablesoilsandhighwatertableareas.Notsensitivetoclimaticconditions.

•Smallershaftwithlargebearingplatereducesdown-dragandweight.

•Canbeinstalledinlownoiseandrestrictedheadroomsites.

•Rapidinstallation.

•Canbeinstalledatanangle.

•Addedweightofpileisslight.

•Environmentallyfriendly–madefromrecycledsteel.

•Canbeeasilyremovedfromsoil.

•EstablishedcriteriabyIBC.

8 9

HELICAL PILE SIZESAlthoughtherearedifferentsizesofshaftswithinthisnichemarket,Cantsinkhasfoundtwosizesinparticularthataresuitabletofulfillthemostcommonapplications,thesebeingHSS2.875”(2.500SCH40)andHSS4.000”.However,uponrequestCantsinkhasthecapabilitytocustomizeordersbymanufacturingothersizesaccordingtocustomerneeds.

HSS 2.875” HELICAL PILETheslenderpipelikeshaftismadeofA500GradeBsteel,witha0.203”wallthathasaminimumyieldstrengthof50,000PSI.

Buckling FirmSoil,N>=5

OD=2.88”

ID=2.47”

r=0.952

K=0.8forfixed/pinned

L=fixedat5’belowgrade.

For

PSI

k l×=

×=

r0 80 60

0 95250 52

.

..

Ccyf

= = =755 755

50 000106 77

,. k l

C×

≤r c

Fk l

Ca yc

f r= −×( )×

⎡

⎣

⎢⎢⎢

⎤

⎦

⎥⎥⎥

= −×

12

50 000 150 42

2 1

2

2

2

,.

006 7744 4492.

,⎡

⎣⎢

⎤

⎦⎥ =

P = Fa × = × −( ) × =A 44 449 2 88 2 474

76 5752 2, . . ,π

8 9

Connection

Theconnectionbetweenahelicalpileleadandahelicalpileextensionisforgedfromtheendofthe2.875”shaft.Hereitisconnectedbythree0.75”bolts.

TorqueAcapacity/torquefactorof10inclayand14insandwasdeterminedbythirdpartytesting.Ourtestinginsiltyieldedacapacity/torqueof9.

ShaftWeatCantsinkwilluse65,000PSItensilex0.75for.J=2.89.Allowabletorqueis ,

wherecis½theODso =8167#’for2-1/2”SCH40pipe.

Ultimatecapacityinsiltis8167x9=74,000#.

ThirdpartytestingshowedtheCantsinkshafttobecapableofwithstanding6167lb-ftoftorque,beforeelongationofaboltholeexceeded¼”.TheyalsoshowedanaverageKtof12inallsoils(10.23inclayand13.86insand).Ultimatecapacityofthe2.875”pileisthen6167x12=74,000#.

TherangeofKtindifferentsoilscanvarythecapacitypredictedbytorque,solocalsoilcondi-tionsmustbeconsidered.Forexample,theclayinColoradoshoweda14%increaseinKtoverthesiltinGeorgia.

τ =×T cJ

Tc

=×

=×( ) ×τ J 0 75 65 000 2 89

1 437598 008

. , .

., #"

τ

10 11

HSS 4.000 (3.500 SCH 80)Thissizepileis4”ODx0.318”wallASTMA500.

Connection

Theconnectionbetweenahelicalpileleadandahelicalpileextensionisforgedfromtheendofthe4.000”shaft.Here,itisconnectedbythree0.875”bolts.

Torque

WeatCantsinkuseacapacity/torquefactorof8insilt,9inclayand10insand.

Shaft

Wewilluse65,000PSItensilex0.75for .

.Allowabletorquesare wherecis½theODso

=25,594#’for3-1/2”SCH80pipe.

UltimatecapacityoftheHSS4.000pileis25,594x8=204,750#.

Buckling

FirmSoil,N>=5

OD=4.00

ID=3.36

r=1.31

K=.8forfixed/pinned

L=fixedat5’belowgrade.

ultimate.P =Fa A× = ×−( )

=47 0694 00 3 36

4174 132

2 2

,. .

,π

J=π × −( )

=4 00 3 36

3212 6

2 2

. .. τ =

×T cJ

T=Jτ ×

=×( ) ×

=c

0 75 65 000 12 6

2 0307 125

. , .

., #"

k l×=

×=

r0 80 60

1 3136 64

.

..

Ccyf

= = =755 755

50 000107

,

F PSIa = −×

⎛⎝⎜

⎞⎠⎟

=50 000 136 64

2 10747 069

2

2,.

,

τ

10 11

STRUCTURAL HELICES

FIGURE1.PlanviewofCantsinkhelix. Ribbingdepictediswhatallowsthehelixto havemorestrength.

Helicesare0.375”thickA36steelinvariousdiametersforthe2.875”ODshaftand½”thickforthe4”ODshaft.

HelicescapacitiesaredependentuponsoilstiffnessasdescribedinSection3.0

WeatCantsinknoticedthereboundofthe14”x0.375”helixtobeabout¼”morethanthatfromtheelasticshorteningof theshaftwhenperforming load tests.Computermodeling thehelixdeterminedthedifferencebetweenrigidand.375”14”helicesona2.875”shaftin55blowsiltloadedto55,000#,wouldbe1.64”versus1.84”.

Thefactthattheflexibilityofahelixcouldlose11%ofcapacitywhenmeasuredagainstafixeddeflectionissomethingtobeconsidered.

Sinceaplatewithribscanbetailoredtothedesiredcapacity,itwasnecessarytodeterminethisload.Thefirst issueisoptimumequivalentplatethicknessfordifferentdiameters.Clearlythethinnertheplate,thebetteritcutsthesoilandinstallsinatruehelicalpath.Itwasnecessarytodeterminesoilmodulusconsistentwiththepileloadingforthosesoils,whichwouldsupporta14”helixto60,000pounds.UsingtheStandardBearingEquationFormulaforclay ,60,000=1.07(9)125N,N=50.Eforclayis600(N+5)KPa=33,000KPaandEforsandabovethewatertableis500(N+15)KPa=21,500KPa.

Secondarybenefitsofcoldformingribsareanincreaseinthetensileandyieldstrength.It isonlynecessarytoaddribstowithin2”oftheperimeterasthebendingstressesdecreasewithincreasingradius.Tensilestrengthcanbeeasilyconfirmedbyhardnesstesting,ashardnessisproportional tostrength.Hardness testingofapointon thehelixouterperiphery,oneat theinner leadingedgeandanotheratan interiorrib,yieldedRockwellBresultsof76,90and96respectively.Thisequatestotensilestrengthsof66,000PSI,87,000PSIand100,000PSIrespec-tively.Theinneredgeisstretched5%tomakea3”helixwithparallelleadingandtrailingedges.Elongationinexcessof0.2%isenoughtomovethesteelbeyondtheyieldpointintothestrain

Q =A N× ×c c

12 13

hardeningrange.Theyieldstrengthincreasesfasterthanthetensilestrength,whichnarrowsthemetal’sductilityrange.SinceweatCantsinkareusingtheminimumbendradiusbeforecrackingwewouldexpectthesetwonumberstobenearlyequal.WecandeterminetheincreaseinthesteelyieldstrengthwiththeformulafromAISI.Theaverageyieldstrengthacrosstheinnerhelixperipheryassuming

and

Fya=averageyieldstrength=CFyc+ (1 –C)Fyv=0.72(89,300)+ (1-0.72)47,500=77,600PSIwhereC=ratioofthetotalcornercross-sectionalareatothefullcross-sectionalarea=0.72sincealltheplateexcept1-1/4”neartheleadingandtrailingedgesisbent .

,yieldstrengthofcorners, , andangle<1200=89,300 PSI

R=insidebendradius,1.5tminforA36and3tforA572=0.5625

t=basemetalthicknessbeforebending=0.375

Fyv=yieldstrengthofvirginsteel=47,500

Fuv=ultimatetensilestrengthofvirginsteel=79,000

FPSI 87

PSIya =×

=36 000

6647 500

,, F

PSI 60PSI

uv=

×=

87 000

6679 000

,,

2 875

2 8750 72

.

..

p-2.5

p=

FB F

Ryc =

⎛⎝⎜

⎞⎠⎟

c yvm

t

F

F

Ruv

yv

≥ ≤1 2 7. ,t

BF

F

F

Fcuv

yv

uv

yv

= ×⎛

⎝⎜⎞

⎠⎟−

⎛

⎝⎜⎞

⎠⎟− =3 69 0 819 1 79 2

2

. . . .0082

m =0.192F

Fuv

yv

×⎛

⎝⎜⎞

⎠⎟− =0 068 0 2513. .

12 13

FIGURE2:Testingwithstraingauges

Thereislowerstressnearthesplitduetonohoopstress.ThisiswhyweatCantsinkdonotfeeltheneedtoaddribsnearthecuttingedgeastheymightalsoaffectpenetration.Thecuttingedgewouldrequirealargerribtoachieveequalstrength,howevertheribsizeisalreadymaximized,soweallowthisportiontodeflectandexertalesserloadonthesubsoil.

Inordertodothis,itisnecessarytocalculatetheequivalentthicknessofaflatplate.Thisisdonebytakingtheribbedportionoftheinneredgewhichis0.72x2.875p,andcalculatingthesectionfortworectanglesthroughthecenterofgravityandtaking½asthetopandbottomalternate,

and for

S=0.473= d=0.56”.Thereforeaflatplatewillhavetobe0.56”thicktoequalthe

strengthofa0.375”thickplatewithribs.

FromthecomputerprograminDesignAnalysisofBeams,CircularPlatesandCylindricalTanksonElasticFoundationsbyEdmundS.MelerskiweatCantsinkranatestfora30Kworkingload(60Kultimate),withapileofa14”helixinstalledtoa2:1safetyfactorina50blow(32500KPa)siltperBroms’Eforclay=500(N+15)KPa,andanodalloadof30,000#abouta2.875”periphery(581.8kN/m).Fromthiswegetaverticaltranslationatthecenterof0.475”and0.43”attheedgeforahelixdeflectionofonly0.045”.Thebendingstressesarehighestclosetotheinnerperipheryandare25,500PSI.Knowingthis,withattentiontodesign,weatCantsinkareabletoachievehighercapacitywithlessdeflectionandlessmaterial.

Whereasmosthelicalmanufacturersuseaflat0.375”thickhelicalplateor½”forhigherloads,Cantsinkhaspatentedtheadditionofstampedribstotheir0.375”thickhelixtoincreasecapac-itywithoutincreasingmaterialthickness.Thecurrent0.625”highribsyieldtwicethestrengthofflatplate.Deflectionisalsoreduced.Theuseofribsinlieuofthickermaterialallowsthehelixtobettercutthesoilandtoinstallinatruehelicalpath.

S=p0 5 0 72 2 875 0 875 0 125

6 0 8750 414

2 2. . . . .

..

× × × −( )×

=0 28 2 875

60 0599

2. ..

× ×=

p 0.375

2 875

6

2.;

× ×π d

υ = 0 33.

14 15

New ConstructionCalculation of House Load

Todeterminepilespacing,itisnecessarytoestimatetheweightofahouse.Manyfactorsmustbetakenintoconsiderationinordertodoso.Withtheincreaseduseoftrussframing9’isabouthalfthetypicalroomsize.Weconsiderfloorsasdiaphragms.Ifawallparalleltothejoistswerejackedup,itwouldraisethefloortothemiddleoftheroom,sothatitisjustasmuchsupportingthefloorasthewallsaresupportingthejoistends.WeatCantsinktaketheslabas3”,aspres-suregroutingafterliftingrevealsthisistheaffectedarea.Wefiguretheroofandatticashalfthehousewidthassumingtrussesupto36’housewidth.Largerhouseswillhavestickroofframingsosameweight.Wemakedistinctionforgableendsasthoughtheywouldstillcarry7’ofroofaswellasthegablesidingorbrick.Footingsarefigured,astheydon’thavereinforcementasitisusuallyinthelowerthirdandthehighermomentisoverthepileswherethereisnosteel.

Weusethefollowingloadstofigurehouseweights. Floordeadload 5lb/ft2 First-floorliveload 40lb/ft2 Second-andthird-floorliveloads 30lb/ft2 Roofandceilingdeadload 16lb/ft2 Roofliveload 16lb/ft2 Atticliveload 20lb/ft2 maximum clear span Roofclearspan(unsupported) 40ft

NotethatnorthernclimateswillhaveadditionalfootingdepthandsnowloadifitexceedsliveloadsperIRC2006-R301.6.Beawarethatflatortileroofsandclearspanbasementswilladdtotheload.AlsohousedepthsgreaterthanL=40”willneedtobeassessed.

Floorloads

Roofloads

14 15

Herearesomeexamplesofloadsforagivenhouse.

20”turndownof16”atthebottomand32”atthetop(1:1oninside)for24”avg.

A 1-story siding on slab

20”x24”footing150PCF 5003½”slab(3’-1.33’)x12PSF/” 70Wall12PSFx9’ 110 680x1.2= 820#/LF Live 40PSFx(3-0.67) 93x1.6= 150#/LF

AtticandRoof Dead Attic5PSFx20’ 100Roof10PSFx22’ 220 320x1.2= 380 #/LF

Live Attic20PSFx20’ 400Roof16PSFx22’ 352 752x1.6= 1,200#/LF

A 3-story brick house

Additionalstory(ies)sidingaddDead Floor7PSFx(7’-0.67) 110Wall9’x12PSF 110 220x1.2= 260 #/LF

Live 30PSFx(7-0.67) 250x1.6=400 600 #/LF

Eachstorybrickaddadeadloadof35PSFx9’x0.5(windows,doors&vents) 160x1.2= 190

Whilethesenumberswillworkforcalculatingfootingspans,thepilingandattachedunderpin-ningbracketuseunfactoredloadsperACI318-0815.2.2.“Baseareaoffootingornumberofpilesshallbedeterminedfromunfactoredforcesandmomentstransmittedbyfootingtosoilorpilesandpermissiblesoilpressureorpermissiblepilecapacitydeterminedthroughprinciplesofsoilmechanics.”

16 17

ForlightframenewconstructionweatCantsinkwilladdamatoftwo#4rebarinboththeupperandlowerthirdsofthefooting.Wedesigntoensurethatshearislessthanhalfthecriticalshear,sostirrupsarenotrequiredperACI318-0811.4.6.1.

WeatCantsinktypicallyspecify34kipultimatecapacitypilesfora1-,2-or3-storylightframehousewithspacingsof8’,7’and6’respectively.Multiplyingthespacingsbylinearloadsof1845,2315and2785PLFwegetsafetyfactorsof2.3,2.1and2.0.

Forbrickwespecify34kippileswithspacingsof7’,6’and5’for1-,2-or3-storieswithlinearloadsof2005,2310and2815PLFforsafetyfactorsof2.3,2.2and2.1.

Youwillnotethesafetyfactorincreaseswithdecreasingloadassoftersoilshavelowermoduli.

Finalspacingwillultimatelybedeterminedbytheneedtosupportcornersandopeningsandinconsiderationoftypesofmaterialsandsizeoffoundation.

No. of stories above grade

weight, lb/lineal foot

Unfactored weight, lb/lineal foot

One-story 2550 1845

Two-story 3210 2315

Three-story 3870 2785

One-story 2740 2005

Two-story 3590 2635

Three-story 4440 3265

Conventionalwoodframeconstruction

(abovegrade)

4in.brickveneeroverwoodframe;

8in.hollowconcretemasonryunit(abovegrade)

16 17

Soil Properties to Capacity CalculationsMostsoilinformationisgivenintheformofStandardPenetrationTestblowcounts,orSPTN.Theseinvolvedroppinga140#hammer30”andcountingtheblowstodriveasplitspoonsam-pler.Smallerjobsmayusea15#hammerfalling20”todrivea1-1/2”conicalpoint1-3/4”.Fromthesenumbersitispossibletocalculateahelicalpilecapacity.

Insiltsandclayswetakethecohesionas125timestheblowcount,N.ThecapacityistheareaofthehelixtimesNctimesc.FromexperiencewetakeNcas14–1.7Ln(N)whichgivesanNcrangingfrom12insoftsoilto6inhardsoil.ThisagreeswithSelvadurai,BauerandNicholas’“Screwplatetestingofasoftclay”CanadianGeotechnicalJournal(Nov.1980).TheyquotedNcof11.35to5.69.Ifwesetthecylindricalshearbetweentwosamesizehelicesinclayequaltotheendbearingofeachhelix,weget equaltotheloadcarriedinendbearing,

where

fisareductionfactorforremolding

cisundrainedshearstrength

Dhishelixdiameter

ds=shaftdiameter

Lisdistancebetweenhelices

Ignoringdsasinsignificant,weget .

Alan Lutenegger “Cylindrical Shear or Plate Bearing?-Uplift Behavior of Mult-Helix ScrewAnchorsinClay”(2009)foundidealspacingsof3diametersinsoftclayand1.5diametersinhardclaywhichwouldsuggestanNcthatvariesfrom12to6isneeded.Selvadurai,BauerandNicholasin“ScrewPlateTestingofasoftClay”(1980)showtestingofundrainedshearstrengthfrom screw plate tests by Shield (1955), Eason and Shield (1960), Skempton (1951), Meyer-hoff(1951)SelvaduraiandSzymanski (1980)andSelvaduraiandSzymanski (1980)togivepult/cuof5.69,6.05,9.00,9.34,10.97,and11.35respectively.Selvaduraisetpult/cuas9.00-11.35bycomputationasthefirsttwowerebytestingofacircularpunchonahalfspace.BlowcountstypicallydoublebetweentestsfromN=50oninthePiedmontarea.Terzaghi,PeckandMesri’s“SoilMechanicsinEngineeringPractice”forpiersfoundedonastratumofstiffclaylocatedbe-neathsoftcompressibledeposits“ThevalueofNcisnotincreasedabovethevaluecorrespond-ing to thatofashallowfooting,because the lowstrengthandcompressiblecharacterof theoverlyingmaterialspreventthedevelopmentofthezonesofplasticequilibriumcharacteristicofahomogeneouscohesivematerial(Article34).”Ncforashallowcircularfootingis6.2su.Ncis(14-1.7Ln(N)).For14”helixpilesfoundedin50+blowmaterialthepreviousSPTsamplingislessthanhalfthatnumber.Thesameappliesto8”helixpilesin120+blowmaterial.

OurNcformula,Nc=(14-1.7Ln(N))rangesfrom6forN=100to11forN=5sowithhelicesspacedgreaterthanthisdividedbyfourendbearingwillgovern.Thesetensionanchorfailures

f c× × × ×π D Lh

f c× × × −( )N D dc h h

π4

2 2

L

D

N

h critical

c⎛⎝⎜

⎞⎠⎟

=4

18 19

fromRao(Figure2.4)atspacingsof1.5D,2.3Dand4.6Dshowthecylindricalshearbeginstobreakdownabout2.3Dforequalsizedhelices.

Forunequalsizehelices,capacitycanbecalculatedby

sothecriticallengthcanbeestimatedby .

Foran8”/12”combinationwemayconsiderthe12”tomostlyrestonsoilthatisundisturbedas

LcriticalforNof20= and cylindrical shear will govern. So the addi-

tionalhelixsizeisnotwellutilized.Thecylindricalshearforan8”/12”heliceswith3’spacingin

siltis whileendbearingforthe12”helixisNcxcohesionx(area

14”helix-area8”helix+area8”helix–areashaftxreductionforshearstrengthxmodulus

reductionforremolding)= andusinganNof35=4.5c.Itwouldappearmultiplehelicesofthesamesizewouldservebetter.Theruleof3Dspacingisbasedonacylindersoildisturbanceto0.75oforiginalstrengthduetoaboredshaftandnodisturbanceundertheunderreams.Thiscannotbedirectlyappliedtoaheli-calpile.Ifweexaminetestsofpileswithhelixspacingof3D,Liu,ZubeckandSchubertshowedtheloaddistributionbetweenthetwohelicesona10”/10”piletobe75%/25%.Themovementatthisload,20,000#wasnotnoted.Howeverthemovementat25,000#wasnotedat5.5”.This

f c× × × × × × × −( )π πD L =c N D davg c h h2 2

L

D

D Ln(N)

D Dh critical

h⎛⎝⎜

⎞⎠⎟

=× × −( )

× +( )2 142

1 2f

14 12 2

4 0 43 8 1275

2−( ) × ×× × +( ) =

Ln(N)

."

0 43 3 1 0 67

23 4

. ' ..

× × × × +( ) =c π

c

14 1 74

1 08 0 365−( ) × × ×

−( ) (.

. .Ln(35)

SF+ 0.365-0.045c

π )) × × ×( )0 43 0 43. . N+6

N+6

Fig2.4RaoCylindricalshear

18 19

wouldputthemovementat20,000#atabout40%ofthehelixdiameter.ThisagreeswellwiththeBassettwhoshows18%atx/D=10%.RoweandBookerget17%,andWitherspoon,20%.

Helixspacingofthreetimeshelixdiameterwillachievefullcapacityinendbearingofthehelicesinclayswithablowcountof18orhigher.Wetypicallydonotrecommendterminationinsoftersoilsduetocreep.

Calculated Capacity Examples from Soil Data

SomeCantsinkManufacturingsoildataexamplesofcalculatedcapacityare:

ExampleNo.1

A14”x10’pilewasinstalledina21blowsiltto3000ft-lbsandtestedto25,000#with1.4”move-

ment. .PileultimatecapacityfromtheStandardBearingEquationFormulais

theAreaofa14”helixxNcxc+perimeterareaofshaftxlengthfromonehelixdiameterabovethehelixtothefirstcouplingxadhesionxremoldingreduction=1.08x(14-1.7Ln(120))x2625+0.75x(7’-1.17’))SFx788PSFx0.43=26,498#.Adhesionisnotcountedwithinadistanceequaltothehelixdiameterduetoshadowing,perZhang.Testedpilecapacitytopredictedultimatecapacitywas94%andpiledeflectionbycomputationwas1.4”.

ExampleNo.2

An8”/14”x41’pilewasinstalledina51blowsiltforthe14”helixand120blowsiltforthe8”

helixto6785ft-lbs.Itwastestedto70,000#witha1.1”ofmovement. . The

pileultimatecapacityis0.365x(14-1.7Ln(120))x15,000+(1.12-0.365)x(14-1.7Ln(51))x6375+0.365x(14-1.7Ln(51))x6375x0.43x(0.43x51+6)/(51+6)=70,889#.Thetestedpilecapacitytopredictedultimatecapacitywas99%.

ExampleNo.3

A14”/14”x34’pilewasinstalledina43blowsiltto6195ft-lbandtestedto70,000#witha1.4”movement.Thepileultimatecapacityis1.08x(14-1.7Ln(43))cx(1+0.43)+0.75x(10.5’-2(1.17’))x1075=69,718#.Thetestedpilecapacitytopredictedultimatecapacitywas100%anddeflectionbycomputationwas1.1”.

TheStandardBearingEquationFormulainsiltsandclayscanaccuratelypredictthepilecapacityifNcisvariedtodecreasewithincreasingblowcounts.Settlementwillusuallydictatepilecapac-ityinsand,aspunchingshearismuchhigher.Thus,settlementcalculationsareusedinsteadoftheGeneralBearingEquationFormulaforsiltsandclayswhichestimatespunchingshear.

Kt =25 000

30008 3

, #

#'.=

Kt =70 000

6 78510 3

, #

, #'.=

20 21

Torque to Capacity EstimateCapacity Prediction from Torque (kt)

Wecan justifyKtbycalculatingthe individualpilecomponentsandaddingsoil resistancetothemtogetatorque.Themaximumtorqueapilewith65,000PSItensilecanwithstandis

whereJ=2Iand .

Torquetocapacityisbasedmainlyuponthefrictionbetweenthehelixandthesoil,whichgivesanindicationoftheground’sstrengththatit ispenetrating.WhilethereisgeneralagreementthatKtdecreaseswith increasingshaftsize,helix thickness, tensionversuscompressionandincreaseswithnumberofhelices,previousstudieshaveoverestimatedthesefactors.Alsomosttestingwasdonefortensionanchors,whichignoressoilsthatareundisturbedbelowtheleadhelix.Anotherpointofcontentionisthattheallowablemovementsusedfortestingvariedcon-siderably.Onestudydiduseremoldedstrengthsfortheareabetweenhelicesandundisturbedstrengthabovethetophelixfortensionanchors,buttheheliceswouldhavetopassthroughthatareatoo.

AC358hassetallowablemovementat10%ofhelixdiametersothefollowingisbasedonthat.Withasafetyfactorof2thismakesmovementswithinanL/240rangeacceptablefornewcon-structionwithapilespacingoffivetoeightfeet.ThisisparticularlyusefulinthePiedmontpla-teauregionalsoils,assiltsdilateduringshear,sothereisnotadefinitivebreakingpointintheloadcurves.

OurtestinghasdeterminedtheKtfactor,whichistheratioofcapacity(measuredinpounds)totorque(measuredinfoot-pound),isinfluencedmorebythehelixsizeandcombinationsratherthantheshaftsize.Thisisbecausetheshafthasasmallradiusrelativetothehelicessoitcon-tributeslittleresistancetorotationincomparisontothehelices.

Atthesametorqueadoublehelixpileofthesamesizesinglehelixwouldhave25%morecapac-ity,not100%.ThisisduetothegaininKt.

Sincethetensionanchorhelixbearsonremoldedsoil, itscapacitywillbereducedbythera-tiooftheremoldedstrengthtotheinsitustrengthtimestheratiosofthemoduliofelasticity.Remoldingis0.43forsiltsfromcomparisonofuplifttocompressiontestsandE=300(N+6)

inkPa,sothetensionanchorhelixwillhave

ofthecompressionpilehelixfora21blowcountinsilt.Thisfallsoffto21%atN=50asstiffersoilswillexperienceslightlymorestrengthlossduetoremolding.Thesensitivity-1forstiffclayisroughlyequaltoitsadhesiononroughsurfaces,whichis0.33.So,remoldingforclayis0.33andE=600(N+5).Previousattemptstomodelupliftbehaviorinclaysassumedtherotaryac-tionduringinstallationoftheanchorsmaycausesubstantialremoldingofthesoilinthezonebetweenthetopandbottomhelix.Thisusesundisturbedstrengthabovethetophelix,butre-membertwohelices,notone,wentthroughthisarea.WeatCantsinkassumecompleteremold-ingforthepassageofevenonehelix.Ifthepassageofadrilledholeissufficienttouseremoldedstrengthattheperipheryoftheunderreamsseveralinchesaway,thenthepassageofahelical

T=J

c

τ ×=

×( ) ×=

65 000 0 75 2 89

1 437598 009

, . .

., #" I=

π × −( )=

2 875 2 497

641 445

4 4. .. .

0 43 30021 0 43 6

300 21 6.

.× ×

× +( )× +( )⎡⎣ ⎤⎦

0 434 509

8 10024.

,

,%× =or

20 21

plateeverythreeincheswoulddictatethesoilinwhichahelixpassedthroughwouldalsoberemolded.Themodulusofelasticityisappliedtotheremoldedstrength.Itmustbeconsidered,especiallyifamovementcriterionisspecified.However,mostreportsusedultimatecapacitysomodulusisnotconsidered.

Imagineahelixasaninclinedrampwrappedaroundanaxis,theforcerequiredtoadvanceanygivenpointonthehelixisdecreasedasthedistanceitmusttravelisincreased.Whenlookingatahelixofanysize,anypointonthathelixwilltravel2Лperrevolution.Theforceonthatpointwillbetheratioof12”toitsradiussincetorqueisinft-lbs.Sothehelixdiameterisimmaterialintheratiooftorquetobearingasthetwofactorscanceleachotherout.Therelationshipfora3”pitchanditsradiusis .

Thefewitemswhichbearvertically,thepointandthecoupling,accountforlessthan1%ofthetorque.Anincreaseofpitchfrom3”to6”fora14”helixwillchangetheaverageanglefrom110to200.Thusthecosinewilldecreasefrom0.98to0.94sothetorquewillincreaseby4%.

Example1

A14”helixin21blowsiltwithacof21X125=2625PSF

Useahexshapedhelixsotheleadingedgeis5.875”andtheareais1.08SF.

Weachievethefollowingpredictedtorquesbybreakingdownthecomponentsofthepile,whicharepushedandrotatedintothesoil.

Bearing

Theannularareaof3.5”couplingis

4lb-ft

Thepiletipis

41

4.5”boltsstickout1”andareassumedtowipea4.25”areaperrevolutionastheywillclearma-

terialbetweenbolts.Theareais .Theywillreactdirectlywithtorqueat

0.03SFx.75x(14-1.7Ln(21))xcx0.1875’x0.43= 42

Thehelixedge5.875”x.375”=0.0153SF

2

3

128

π πr

r× =

3 5 2 875

144 40 02

2 2. ..

−× =

πSF

A c s× × × ×⎛⎝⎜

⎞⎠⎟

N remolded factorremoldedE

EcS

/ 8π

2 875

12 40 045

2.

.⎛⎝⎜

⎞⎠⎟

× =π

SF

1 4 25

1440 03

" . ".

×= SF

r =1 75 0 5

120 1875

. " . ". '

+=

0 02 14 1 70 43 21 6

21 6. .

.SF Ln(21) c 0.43× −( ) × × × × +

+⎡⎣⎢

⎤⎦⎥⎥ =8π

0 045 14 1 78

1. . :SF Ln(21)c

× −( ) ×π

22 23

Themoment’sarmforthehelixedge=

AstripfoundationhasanNcabout0.75thanthatofacircularfoundationso,

0.0153x.75x(14-1.7Ln(21))xcx0.365’= 97

Ahelixresultantactsatanangletotheverticalof

Theverticalforceis

Themoment’sarm=

Helixtopfrictionof0.20isactingat

25,375#x0.2x0.45’= 2284

AdhesionFromTomlinson,M.J.,thecohesionvariesaccordingtothefollowinggraph:

Adhesionisnotcountedwithinadistanceequaltothehelixdiameterduetoshadowing,perZhang.

7’lead(0.75’x(7’-1.17’))SFx788PSFx0.12’x0.40= 220

Thehelixbottom 383

Total predicted torque 3071 ft-lbThe10’pilewasinstalledto3000ft-lbsor98%ofpredictedtorque.

1 12 0 045 14 1 711 1

25 37. . ..

,−( ) × −( ) × ( ) =SF Ln(21)c

cos 55 #

1 4375 7 045 1 43752

25 4 0 45. . . . " . '+ −( ) × = =

α = × × =0 3 16252

3325. PSF

2 875

120 75

.. '× =π

1 085 4

12.

.SF 788PSF× × =

Figure4.Adhesion

kN/m2 50 100 150 200 250 300

PSF 1044 2090 3135 4180 5225 6270

SPT N 8 16 24 32 40 48

1 4375 5 8752

120 365

. .. '

+⎛

⎝⎜⎜

⎞

⎠⎟⎟

=

tan tan− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

314 03

2 11. .π π ..1

α = × =0 3 2625 788. PSF

22 23

Example2

An8”helixin120blowsiltmaterial,withac1of120x125=15,000PSF

A14”helixin51blowsiltmaterialwithac2of51x125=6375PSF

Bearing

3.5”Coupling

8ft-lbs

Theareofthepiletipis

= 157

4.5”boltsstickout1”andareassumedtowipea4-1/4”areaperrevolutionastheywillclear

materialbetweenbolts.Theareais . They will react directly with torque at

0.03SFx¾x(14-1.7Ln(51))xc2x0.1875’x0.43= 85

14”helixedge5.875”x.375”=0.0153SF

0.0153x.75x(14-1.7Ln(51))xcx0.365’= 195

An8”helixedge2.75”x.375”=0.007SF

0.007SFx.75x(14-1.7Ln(120))xc1x0.365’x0.43= 72

14”helixresultantisactingatanangletotheverticalof

The14”verticalforceis

37,187#

Thehelixtopfrictionof0.20x2/3belowWTactingatmidpointofarea,5.37”

37,187#x0.133x0.45’= 2225

3 5 2 875

144 40 02

2 2. ..

−× =

πSF

2 875

12 40 045

2.

.⎛⎝⎜

⎞⎠⎟

× =π

SF

1 4 25

120 03

" . ".

×= SF

r =1 75 0 5

120 1875

. " . ". '

+=

1 43755 875 1 4375

24 57.

. .. "+

−=

1 4375 5 8752

120 365

. .. '

+⎛

⎝⎜⎜

⎞

⎠⎟⎟

=

1 08 0 365 14 1 7 0 365 0 042. . . . .−( ) × −( )⎡⎣ ⎤⎦ × + −SF Ln(51) c 55 14 1 7 0 430 43 51 6

51 62( ) × −( ) × × ×

× ++( ) ×

. ..

Ln(51) ccos 111 1. ( ) =

tan tan− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

314

2 11 1. .π π

0 02 14 1 7 0 430 43 51 6

51 62. . ..

SF Ln(51) c× −( ) × × × × ++

⎡⎣⎢

⎤⎦⎦⎥ =8 1π :

0 045 14 1 78

1. . :SF Ln(120)c

× −( ) ×π

24 25

The8”helixverticalforceis

28,874#x0.133x0.27’= 1037

Adhesion

belowtheWT

belowtheWT

Adhesionisnotcountedwithinadistanceequaltothehelixdiameterduetoshadowing,perZhang.

7’Lead 199

An8”helixbottom 298

14”helixbottom 212 4488lbs-ft

Thepilewas installed to6785 ft-lbsor151%of thepredicted torque. Itcanbenoted that thepredictiondifferedsignificantlyfromtherealinstallation’sfindings.

Example3

ADouble14”helixina43blowsiltmaterialwithacof43x125=5375PSF

Bearing

3.5”Coupling

7ft-lbs

Thepiletipis

73

4.5”boltsstickout1”andareassumedtowipea4.25”areaperrevolution,astheywillclear

materialbetweenbolts, Theywillreactdirectlywithtorqueat

0.03SFx.75x(14-1.7Ln(43))xcx0.1875’x0.43= 74

0 365 0 045 14 1 713

28 81. . . ,−( ) × −( ) × ( ) =SF Ln(120)c

cos 774 #

α1 0 36375

2956= × =. PSF

α2 0 315 000

22250= × =.

,PSF

2 875

120 75

.. '× =π

0 75 7 1 17 0 672250 956

2. ' ' ( . ' . ')× − +( )⎡⎣ ⎤⎦ ×

+×SF PSF 0.122' 0.20=×

0 3755 37

12.

.SF 1275PSF 1.43× × × =

1 12 0 3656 12

120 35 525 0 27 0 20. .

.. . .−( ) × × + × × ×SF 525PSF ==

3 5 2 875

144 40 02

2 2. ..

−× =

πSF

2 875

12 40 045

2.

.⎛⎝⎜

⎞⎠⎟

× =π

SF

1 0 5

1440 03

" . ".

×= SF

r =1 75 0 5

120 1875

. " . ". '

+=

1 43755 875 1 4375

24 57.

. .. "+

−=

0 02 14 1 70 43 43 6

43 6. .

.SF Ln(43) c 0.43× −( ) × × × × +

+⎡⎣⎢

⎤⎦⎥⎥

8 1π :

0 045 14 1 78

1. . :SF Ln(43)c

× −( ) ×π

24 25

The1sthelixedgeis5.875”x.375”=0.0153SF

0.0153x.75x(14-1.7Ln(43))xcx0.365’= 171

The2ndhelixedgeis5.875”x.375”=

0.0153SFx.75x(14-1.7Ln(43))xcx0.365’x0.43= 74

Thehelixresultantisactingatanangletotheverticalof

Theverticalforceis acting at the midpoint of anarea,5.37”.

The1stand2ndhelixtopfrictionof0.20 3861

Adhesion

Adhesion=0.25x5375=1344PSFaboveWTand896below

10.5’lead(.75’x(10.5’-2x1.17’))SFx896PSFx0.12’= 339

The1sthelixbottom 442

The2ndhelixbottom 190

5231lbs-ftThe34’pilewasinstalledto6195ft-lbsor118%ofthepredictedtorque

Example4

An8”helixin120blowsiltmaterialwithacof120x125=15,000PSF

Weuseahexshapedhelixsothebearingedgeislongerat2.75”andtheareais0.365SF.

Bearing

3.5”Coupling 14 ft-lbs

Thepiletipis 157

4.5”boltsstickout1”andareassumedtowipea4.25”areaperrevolutionastheywillclear

materialbetweenbolts, .Theywillreactdirectlywithtorqueat

1 43755 875

212 0 365

..

. '+⎛

⎝⎜⎞⎠⎟ =

1 08 14 1 711 1

64 342. ..

, #SF Ln(43)c

cos× −( ) × ( ) =

64 342 0 202

30 45, # . . '× × × =

2 875

120 75

.. '× =π

1 084 57

12.

.SF 1075PSF× × =

1 084 57

120 43.

..SF 1075SF× × × =

1 4 25

1440 03

" . ".

×= SF

r =1 75 0 5

120 1875

. " . ". '

+=

0.02SF Ln(120) c 0.43× −( ) × × × × ++

⎡⎣

14 1 70 43 120 6

120 6.

.⎢⎢

⎤⎦⎥

8 1π :

0 04514 1 7

81.

.:SF

Ln(120) c×

−( ) ×π

tan− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

314

2 11 1.tan

.π π

26 27

(.75Ncsinceitisstripbearing)0.03SFx.75x(14-1.7Ln(120))xcx0.1875’x0.43= 159Thehelixedgeis2.75”x.375”=0.0072SF

0.0072SFx¾x(14-1.7Ln(120))xcx0.23’= 109

Thehelixresultantisactingatanangletotheverticalof

Theverticalforceis

Thehelixtopfrictionof0.20(NAVFACDM-7.2-63)x2/3belowthewatertableis=0.133actingat

midpointofthearea,

(Sandswillhaveafrictionof0.30andnoreductionbelowthewatertable.)

28,816#x0.133x0.274’= 1050

Adhesion

=0.2xc=3000aboveWTand4500x2/3=2000belowWT

A7’Lead(.75x(7-0.67))SFx2000PSFx0.12’x0.43= 653

Thehelixbottom(0.365-0.045)SFx2000PSFx0.274’= 175

2317ft-lbsThe44’pilewasinstalledto4000ft-lbsor173%ofthepredictedtorque.

Example5

A14”helixina51blowsiltmaterialwithacof51X125=6375PSF

Bearing

3.5”Coupling

8 ft-lbs

Thepiletipis

84

1 43752 75

212 0 23

..

. '+⎛

⎝⎜⎞⎠⎟ =

0 365 0 045 14 1 712 5

28. . ..

,−( ) × −( ) × ( ) =SF Ln(120)c

cos 8816 #

1 4375 4 0625 1 43752

23 29 0 274. . . . " . '+ −( ) × = =

3 5 2 875

144 40 02

2 2. ..

−× =

πSF

0 02 14 1 70 43 51 6

51 6. .

.SF Ln(51) c 0.43× −( ) × × ×

× +( )+

⎡⎣⎢

⎤⎤⎦⎥ =8π2 875

12 40 045

2.

.⎛⎝⎜

⎞⎠⎟

× =π

SF

0 045 14 1 7

8

. .SF Ln(51) c× −( ) ×=

π

α

tan.

tan.

− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

38 125

2 12π π ..5

26 27

4.5” bolts stick out 1” and are assumed to wipe a 4.25” area per revolution, as they

willclearmaterialbetweenbolts, . They will react directly with torque at

0.03SFx¾x(14-1.7Ln(51))xcx0.1875’x0.43= 85

Thehelixedgeis5.875”x.375”=0.0153SF

0.0153x¾x(14-1.7Ln(51))xcx0.365’= 195Thehelixresultantisactingatanangletotheverticalof

Theverticalforceis

Thehelixtopfrictionof0.20x2/3isbelowWTactingatmidpointofthearea,

49,192#x0.133x0.45’= 2944

Adhesion

=0.3x6375=1913PSFaboveWTand1275below

Adhesionisnotcountedwithinadistanceequaltothehelixdiameterduetoshadowing,perZhang.

A7’lead(0.75’x(7’-1.17’))SFx394PSFx0.12’x0.22= 147

Ahelixbottomis 616 4079ft-lbsThe38’pilewasinstalledto4000ft-lbsor98%ofthepredictedtorque.

Example6

Adouble14”helixina21blowsiltmaterialwithacof21x125=2625PSF.

Bearing

3.5”coupling

4ft-lbs

1 4375 7 045 1 43752

25 4 0 45. . . . " . '+ −( ) × = =

1 0 5

120 03

" . ".

×= SF

r =1 75 0 5

120 1875

. " . ". '

+=

1 43755 875

212 0 365

..

. '+⎛

⎝⎜⎞⎠⎟ =

1 08 0 045 14 1 711 1

49 19. . ..

,−( ) × −( ) × ( ) =SF Ln(51)c

cos 22 #

α

2 875

120 75

.. '× =π

1 085 4

12.

.SF 394 PSF× × =

3 5 2 875

144 4

2 2. .−× =

πSF

0 02 14 1 70 43 21 6

21. .

.SF Ln(21) c 0.43× −( ) × × ×

× +( )⎡⎣⎢

⎤⎦⎥⎥ =8π

tan.

tan.

− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

314 09

2 11π π ..1

28 29

Thepiletipis

41

4.5”boltsstickout1”andareassumedtowipea4.25”areaperrevolutionastheywillclear

materialbetweenbolts, .Theywillreactdirectlywithtorqueat

0.03SFx.75x(14-1.7Ln(21))xcx0.1875’x0.43= 42

The1sthelixedgeis5.875”x.375”=0.0153SF

0.0153x.75x(14-1.7Ln(21))xcx0.365’= 97

The2ndhelixedgeis5.875”x.375”=

0.0153SFx.75x(14-1.7Ln(21))xcx0.365’x0.43= 42

Ahelixresultantisactingatanangletotheverticalof

Theverticalforceis actingatmidpointofarea,5.37”

The1stand2ndhelixtopfrictionof0.20

36,455#x0.20x0.45’= 3281

Adhesion

Adhesion=0.3x2625=788PSF

A7’lead(0.75’x(7’-2x1.17’))SFx788PSFx0.12’x0.40= 132

The1sthelixbottomis 381

The2ndhelixbottomis 153

4173ft-lbsThe10’pilewasinstalledto4000ft-lbsor96%ofthepredictedtorque.

2 875

12 40 045

2.

.⎛⎝⎜

⎞⎠⎟

× =π

SF

0 045 14 1 7

8

. .SF Ln(21) c× −( ) ×=

π

1 4 25

1440 03

" . ".

+= SF

r =1 75 0 5

120 1875

. " . ". '

+=

1 43755 875

212 0 365

..

. '+⎛

⎝⎜⎞⎠⎟ =

1 08 14 1 711 1

1 43 36 455. ..

. , #SF Ln(21)c

cos× −( ) × ( ) × =

2 875

120 75

.. '× =π

1 085 37

12.

.SF 788PSF× × =

1 085 37

120 40.

..SF 788PSF× × × =

tan.

tan.

− −⎛⎝⎜

⎞⎠⎟ + ⎛

⎝⎜⎞⎠⎟

⎡⎣⎢

⎤⎦⎥ =

1 132 875

314

2 11 1π π

28 29

Conclusions:• Theshaftsizeof3.5”orless,onlyaccountsfor2%ofthetorque.

• Similarsizetensionanchorsinthesamematerialhave20-25%capacityreductionof

compressionanchors.Capacitywillvarybasedonsoilquality.

• DoublehelixpileswillhaveaKt25%higherthanasinglehelixpile.

• Doubling the helix thickness increases torque by 5%. In a side-by-side test at our

facility,weatCantsinkrecordeda5%increaseintorqueforadouble14”helixovera

single 14” until the second helix penetrated the water table, after which the torque

differencesweretoosmalltomeasure.

• Doublingthehelixpitchwillincreasethetorqueby4%.

• Helixfriction,adhesionandleadingedgebearingaccountsfor52%ofthetorquefor

the8”helixpiles tested,87%for thesingle14”,88%for the8”/14”and94%for the

double14”.Thusthelargerthehelixarea,thebetterthepredictionasotherlossesbe

comeproportionatelyless.

• WeatCantsinkfoundanaverageKtof6.5for8”,8.5.

• SettlementinclaycanbecalculatedusingaformulafromDas,where

.WeatCantsinkcutthechartoffat15%ofhelixdiameteras

shearwilloccurinthisrangeofmovement.

s=q D

Es

×× −( ) ×1 0 852υ .

30 31

Predicted Settlement in Cohesive Soils (inches)

Forpilesunderbuildingsweusethefollowingchart,whichsetscapacityatasettlementof10%ofthehelixdiameter.

Fora14”helixina35blowsiltmaterialtheultimateloadisfoundwhen

SPT 10 15 20 25 30 35 40 45 50Helix Q(lbs) 8” 10000 1.11 0.90 0.75 0.65 0.57 0.51 0.46 0.42 20000 1.30 1.14 1.01 0.91 0.83 30000 1.37 1.25 40000 SPT 10 15 20 25 30 35 40 45 5014” 10000 0.83 0.63 0.51 0.43 0.37 0.32 0.29 0.26 0.24 20000 1.67 1.27 1.02 0.86 0.74 0.65 0.58 0.52 0.48 30000 1.90 1.54 1.29 1.11 0.97 0.87 0.78 0.71 40000 2.05 1.72 1.48 1.30 1.16 1.05 0.95 50000 2.15 1.85 1.62 1.45 1.31 1.19 60000 2.22 1.95 1.74 1.57 1.43 70000 2.03 1.83 1.67 55 60 65 70 75 80 85 90 958” 10000 0.38 0.35 0.33 0.31 0.29 0.27 0.26 0.24 0.23 20000 0.76 0.71 0.66 0.61 0.58 0.54 0.51 0.49 0.46 30000 1.15 1.06 0.99 0.92 0.86 0.81 0.77 0.73 0.69 40000 1.23 1.15 1.08 1.02 0.97 0.92 50000 1.28 1.21 1.15 55 60 65 70 75 80 85 90 9514” 10000 0.22 0.20 0.19 0.18 0.16 0.15 20000 0.44 0.40 0.38 0.35 0.33 0.31 30000 0.66 0.61 0.56 0.53 0.49 0.46 40000 0.87 0.81 0.75 0.70 0.66 0.62 50000 1.09 1.01 0.94 0.88 0.82 0.77 60000 1.31 1.21 1.13 1.05 0.99 0.93 70000 1.53 1.41 1.31 1.23 1.15 1.08

Q =A N Ln(35)c× × = × −( ) × × =c 1 12 14 1 7 35 125 38 984. . , #

30 31

Capacity in Silt

A8”=0.365SF A14”=1.08SF A19”=2.0SF Nc=14-1.7Ln(N) c=125N

kt8”=7 kt14”=9 kt8”/14”=11 kt14”/14”=11 kt19”=8 2nd helix @25% SPT 10 15 20 25 30 35 40 45 50 558” ULT LD 4602 6431 8128 9727 11248 12705 14105 15457 16766 180368” wk LD 2301 3215 4064 4864 5624 6352 7053 7729 8383 9018TQ @ ULT 657 919 1161 1390 1607 1815 2015 2208 2395 2577PSI 54 Head 398 557 704 842 974 1100 1221 1338 1452 1562 14” ULT LD 14120 19732 24940 29848 34515 38984 43282 47431 51447 5534414” wk LD 7060 9866 12470 14924 17258 19492 21641 23715 25723 27672TQ @ ULT 1569 2192 2771 3316 3835 4332 4809 5270 5716 6149PSI 54 Head 951 1329 1679 2010 2324 2625 2915 3194 PSI 55 Head 550 769 972 1164 1346 1520 1687 1849 2006 2158SPT 10 15 20 25 30 35 40 45 50 558”/14” ULT LD 15270 21340 26972 32279 37328 42160 46808 51295 55638 598538”/14” wk LD 7635 10670 13486 16140 18664 21080 23404 25647 27819 29927TQ @ ULT 1647 2302 2910 3482 4027 4548 5050 5534 6002 6457PSI 54 Head 998 1395 1763 2110 2440 2756 3060 3354 3638 3913PSI 55 Head 578 808 1021 1222 1413 1596 1772 1942 2106 2266 14”/14” ULT LD 17650 24665 31175 37310 43144 48730 54102 59288 64309 6918014”/14” wk LD 8825 12333 15588 18655 21572 24365 27051 29644 32154 34590TQ @ ULT 1647 2302 2910 3482 4027 4548 5050 5534 6002 6457PSI 54 Head 998 1395 1763 2110 2440 2756 3060 3354 PSI 55 Head 578 808 1021 1222 1413 1596 1772 1942 2106 2266 19” ULT LD 25214 35236 44536 53299 61635 69614 77289 84698 91870 9882919” wk LD 12607 17618 22268 26650 30817 34807 38645 42349 45935 49414TQ @ ULT 3152 4405 5567 6662 7704 8702 9661 10587 11484 12354PSI HI SPD 841 1175 1485 1778 2056 2322 2578 2825 3064 3296SPT 60 65 70 75 80 85 90 95 100 1058” ULT LD 19271 20473 21646 22791 23910 25004 26076 27126 28156 291678” wk LD 9635 10237 10823 11395 11955 12502 13038 13563 14078 14583TQ @ ULT 2753 2925 3092 3256 3416 3572 3725 3875 4022 4167PSI 54 Head 1668 1773 1874 1973 2070 2165 2258 2349 2438 2525PSI 55 Head 966 1026 1085 1142 1198 1253 1307 1360 1411 1462 14” ULT LD 59133 62822 66420 69933 73366 14” wk LD 29566 31411 33210 34966 36683

32 33

Sand in Compression

PeterT.Brown’s“ScrewPlateInsertioninSand”,saysthathelicescannotscrewintomediumordensesandattherateoftheirpitch.Insertionofthescrewplatecausesshearingofthesandandatendencytodilateasitmovesabovethecriticalstateofdensity.Therefore,thesandbelowthescrewplateseesincreasedpressure.Thispointisobviousinthefollowinggraph,whichshowspenetrationperrevolution.ItisimportanttomonitorthepenetrationrateinsandifKtistobeaccurate.

TQ @ ULT 6570 6980 7380 7770 8152 PSI 5016-54 PSI 5016-55 2305 2449 2589 2726 2860 19” ULT LD 105594 112183 118607 124880 131011 137009 142882 148637 154280 15981719” wk LD 52797 56091 59304 62440 65506 68505 71441 74319 77140 79909TQ @ ULT 13199 14023 14826 15610 16376 17126 17860 18580 19285 19977PSI HI SPD 3522 3741 3956 4165 4369 4569 4765 4957 5145PSI LO SPD 2147 2261 2372 2480 2587 2691 2793 2893 SPT 110 115 120 125 130 135 140 145 150 1558” ULT LD 30159 31133 32090 33032 33958 34868 35765 36648 37517 383738” wk LD 15079 15566 16045 16516 16979 17434 17882 18324 18758 19187TQ @ ULT 4308 4448 4584 4719 4851 4981 5109 5235 5360 5482PSI 5016-55 1512 1561 1609 1656 1702 1748 1793 1837 1881 1923SPT 110 115 19” ULT LD 165253 170591 19” wk LD 82626 85296 TQ @ ULT 20657 21324 PSI HI SPD PSI LO SPD 2992 3088

32 33

While theStandardBearingEquation formula isoftenutilized,whichusesNqand Лh, itoverestimatesthecapacityatlargedepths.Thesettlementofthebaseofapieronsandatadepthoffourormoretimesitswidthishalfthesettlementofanequallyloadedfootingofthesamesizeinsimilarsandnearthegroundsurface.Sobearingcanbetwicethatforafootingandthensettlementwillbelessthanoneinch.Sincebasefailureisunlikely,capacitycalculationsshouldbebasedonsettlement.Fora14”helixina14blowsandmaterialwithapressureof

40,500#/1.08SF=1796kPaandadepthof12.5’in100PCFsand(60kPa)

34mm=1.36inwhereScis

thesettlementinmm,Bishelixdiameterinm,andqistheunitloadinkPa.TestingCantsink

Manufacturinghelicalpiles,byathirdpartylab,returnedresultsof40,500#,35,900#,and40,600#

for14”helixpilesina14blowsand.Rearrangingthisequationforloadbasedonsettlementand

discountingthepartasitisverysmallweget .We at Cantsink cut the

chartoffat15%ofhelixdiametersinceshearwilloccurinthe10-20%ofhelixdiameterrangeof

settlement.Someexamplesarepresentedinthetablebelow:

Predicted Settlement in Sand, in Inches

Helix size Load SPT 10 15 20 25 30 8” 10K 0.60 0.40 0.29 0.23 8” 20K 1.20 0.80 0.59 0.45 8” 30K 1.20 0.88 0.68 8” 40K 1.17 0.91 8” 50K 1.14 8” 60K 8” 70K 14” 10K 0.53 0.30 0.20 0.15 0.11 14” 20K 1.05 0.60 0.40 0.29 0.23 14” 30K 1.58 0.89 0.60 0.44 0.34 14” 40K 2.10 1.19 0.80 0.58 0.45 14” 50K 1.49 1.00 0.73 0.56 14” 60K 1.79 1.19 0.87 0.68 14” 70K 1.39 1.02 0.79

S

BN

qc

0 75

601 4

1 7..

.× ⎛⎝⎜

⎞⎠⎟

=

SB

Nq-c

p=×

××⎛

⎝⎜⎞

⎠⎟= ⎛

⎝⎜⎞⎠⎟

0 75

601 4

1 7 2

3

14

39 37

.

.

'.

.

σ 00 75

1 4

1 7

141796

2 60

3

.

.

.× ⎛

⎝⎜⎞⎠⎟

× −×⎛

⎝⎜⎞⎠⎟

=

2

3σ p

'

34 35

Tension AnchorsShallow Tension Anchors

SandMeyerhoff andAdams (1968) for shallow anchors in sand states the angle of the cone side

dependsondensityandangleoffrictioninthesoilandvariesfrom to w i t h

anaverageof.Theirformulaincorporatesthesideresistanceasanequivalentweight

ofsoil.where

Fora5’helicalpilewitha14”helixona10blowcountmaterial,,H=depth=5’,h=helix

diameter=1.17’,Ku=0.95.ThecriticalembedmentratiorunsfromH/h=2.5attoH/h=11

at.mrunsfrom0.05forto0.6forat.mcanberepresentedbytheequa-

tion .Peck’srelationshipbetweenSPTandis-0.0013N2+0.35N+26.779.Fora10

blow,andanangleφ of,thecriticalembedmentdepthis2.6h.

Thecapacityfor14”helixpile5’deepin

sandis:

903

−φ

902

3 −

φ

902

−φ

F mH

h

H

hK tanc u= + + ×⎛

⎝⎜⎞⎠⎟

⎛⎝⎜

⎞⎠⎟

×1 2 1 φ

0 0139 0 074. .e φ

F tan30c = + + ×⎛⎝⎜

⎞⎠⎟

⎛⎝⎜

⎞⎠⎟

× ×1 2 1 0 135

1 17

5

1 170 95.

. .. == 5 6.

Qu = × × × × =5 6 1004

1 17 5 3 0132. . , #π

φ = 20

φ = 48

φ = 20φ = 48

30

φ = 48φ = 20

φ

34 35

SiltandClay

Dasproposedthefollowingformulaforthecriticalembedmentratio(D/B)cr-s=(0.107cu+2.5)<7.Fora10blowcountinclaycu=60,(D/B)cr-s=(0.107x60+2.5)<7=7,wherecuiscohesioninkPa.

ForshallowanchorsinclayorsiltMooney(1985)states: .

Usingthesame14”(0.356m)anchorona10blowmaterialclay,whereFcisthebreakoutfactor,

itiscalculatedasfollows:

and((H1/D1)cr=0.107cu+2.5<7wherecuis

inkN/m2.So1250PSF=60kN/m2and

Fc=-8.5714(0.6)2+17.657x0.6–0.0857=7.4

Fora5’imbedmentthecapacityis

Thiswouldbereducedto20%duetothedisturbancefromthehelixinstallationto4200#.MitschandClemencein“TheUpliftCapacityofHelixAnchorsinSand”showedKtof20.7,20.7,24.6,21.7,23.7and22.5(thesixhighestKt)forinstallationtorquesof1500,1500,1750,17501900and2000ft-lbs(thesixlowesttorques)respectivelyandKt14.9,17.3,12.2,16.8,16and18(thesixlowestKt)forinstallationtorquesof3500,3000,2700,2500,2000and2000(thesixhighestinstallation torques). Here,asimilardegradationofKtwith increasingblowcountexists forsandasitdidforcohesivesoils.

F

HD

H D

HD

c

cr

= −×( )

⎡

⎣

⎢⎢⎢⎢

⎤

⎦

⎥⎥⎥⎥

+ ×8 5714 17 657

1

1

1 1

1

1. .HH D

cr1 1

0 0857×( ) = .

Q KN =21,000#p = × × × + ×( ) =π4

0 0356 60 7 4 100 5 942. .

Q A c F Hp u c= +( )γ 1

H

D

H

D

HD

HD

cr

cr

1

1

1

1

1

1

1

1

5

1 174 27 7= =

⎛⎝⎜

⎞⎠⎟

=⎛⎝⎜

⎞⎠⎟

.. , ; == 0 6.

36 37

Deep Tension Anchors

SandForsand,insteadofusingthecompressioncapacityformulawereducethecapacityby40%

timesthereductioninmodulusof or forsaturatedsand.

Clay

ForclayusetheCapacityinSilttable(pages31-32)andmultiplyby20-25%fortension.Capacitywillvarybasedonsoilquality.

multi-Helix Anchors

Sand

Cylindrical shear isnota factor in sand.This isbecausewhenmodeling the topof thehelixcapacity,aswellasthecylindricalsheartothebottomhelixcapacity,itwillbemuchlessthanjustmodelingthebottomhelixcapacity.Ifitisacylindricalfailure,thenthecapacitycanbees-timatedasfollows: whereDa=theaveragehelixdiameter,Ku=0.95,Hn=heighttobottomofthehelixandH1=heighttotopofthehelix.

Foradouble14”helicalpilewithhelices3.5’apartandthetophelix5’deep,thecylindricalshearcontributes:

Thetophelixcontributes .

Ifwecheckthebearingofthebottomhelixfor

for,itwouldbe:

500 0 6

500

× ( )× ( )

. N+15

N+15

250 0 6

250

× ( )× ( )

. N+15

N+15

Q D H H K tanf a u= × × × −( ) ×π γ φ4 1

222

Q tan30f = × × × −( ) × =π4

1 17 100 8 5 5 4 7632 2. . , #

Qu = × × × × =5 6 1004

1 17 5 3 0132. . , #π

Q F D Hu c= × × × × = × × × × =π γ π4 4

24 5 100 1 17 8 5 22 38912

22. . . , #

φ = 30

Fq = − + − =0 0693 6 1457 182 17 180 5 24 53 2. . . . .φ φ φ

φ = 30

36 37

Fqcanbedeterminebythefollowingtable:

Clearlyitwouldbebettertojusttakethebearingofthesecondhelixat22,389#ratherthanthetopofthehelixbearingpluscylindricalshearat7,776#,assuggestedbyTappenden,SegoandRobertsonin“LoadTransferBehaviorofFull-ScaleInstrumentedScrewAnchors”.

Thedisturbanceisnotshownhereasjustcomparingcylindricalsheartotheendbearing,butasthoughitwouldreducethepreviouslycalculatedcapacitiesby75%.

SiltandClay

Forthesewesetspacingbetweenhelicesatthreediameters.Thiswillensurethattheendbear-ingoftheindividualheliceswillgovern,ratherthanthecylindricalshearofthesoilbetweenthehelices.Forclay,cylindricalshearis

Ifwecheckthebearingofthesecondhelix,itwouldbe:

Thus,individualhelixbearinggoverns.Disturbanceduetothehelixpassagehasnotbeenshownhere,butitiscoveredintheSoilPropertiestoCapacityCalculationssection.

Q D D H H cu=f n n= × +( ) −( ) × × +( ) −( ) ×π π2 4

1 17 1 17 8 5 5 11 1 . . . 00 125 16 000× = , #

Q Ln(10)p = × −( ) × × =1 12 14 1 7 10 125 14 100. . , #

H1/D1 φ = 25 φ = 30 φ = 35 φ = 40 φ = 45

0.5 5.27 5.54 5.87 6.23 6.611.0 6.74 7.38 8.25 9.18 10.171.5 8.41 9.54 11.16 12.91 14.772.0 10.27 12.01 14.64 17.49 20.532.5 12.33 14.82 18.72 22.99 27.543.0 14.60 17.97 23.44 29.46 25.913.5 21.48 28.84 36.99 45.744.0 25.35 34.95 45.64 57.134.5 41.81 55.44 70.185.0 49.46 66.56 85.005.5 78.97 101.686.0 92.76 120.346.5 108.01 141.067.0 124.78 163.987.5 189.148.0 216.698.5 246.739.0 279.34

38 39

Field Determination of Pile CapacityWe at Cantsink determine the capacity of the pile in the field by monitoring the hydraulicpressureandmultiplyingitbyafactortodeterminethetorqueinfoot-pounds.Weapplyaratioofninetimesthetorquetodeterminetheultimatecapacity.Thecurrentdrillheadsincludemotormodelnumbers54and55and78-48.

The 54 has a 10.3 CID (cubic inch displacement) hydraulic motor and the 55 has a 17.1 CIDhydraulicmotorwith thesame16:1 ratiogearboxso that ithas66%more torque.PSIhasadirectrelationshiptotorque.WeatCantsinkuseT=1.65xPSIforthe54headandT=2.85xPSIforthe55head.Forexample,apressurereadingof2000PSIwitha54headwillhaveatorquethatwouldbe3300ft-lbs.ThismultipliedbyaKtfactorof9willhaveanultimatecapacitythatwouldbe29,700pounds.However,thisiswiththepressuredroppingacrossthemotoronly.Anybackpressuremustbesubtractedfromtheworkingreading.Forthe78-48head,thetorquewillbe6.905xPSIinlowspeedand3.748xPSIinhighspeed.

Pressuregaugesonthehydrauliclinesareusedtoestimatetorqueandpilecapacities.Loadtestingisnotrequired.

Installerismonitoringthepressuregauge.

38 39

BracketsNew Construction Bracket

Anewconstructionbracketisaplateusedtotransmittheloadfromtheshaftofthepiletothefootingsofthestructure.Italsopreventspunchingontheconcrete.

Computermodelingofthe8”x8”x.375”A36plateonthe2.875”ODtubewhencastin2500PSI

concreteshowedtheradialbendingstresstobe32,600PSIataloadof74,000pounds.Theshear

stressis ,whichistheallowableshearstrengthofsteel.

Underpinning Bracket

An underpinning bracket is an assembly of components used together to repair existingstructures.Thesecomponentsareattachedtotheshaftofthepilethatwilltransmittheloadtothesoil.At thesametimethebracket is installedunderneath the footingsof thestructure tosupportthesectionthatneedstoberepaired.

TheCantsinkunderpinningbracketutilizesarectangularcrossarmto increaseitsstrength. Italsohasa60”longTpipetoreinforcethepileandtoshortenitsbucklinglength.Thebracket,anA500HSS10”x10”x.375”isdesignedtoallowverticalpileinstallationsothatthehouseisraisedalongthepileaxis,notforcingittobendthepiletoconform.CantsinkusesanASTMA500HSS3x2x.25tubecrossarmwitha0.875”boltspacingof7.25”withnuts1-5/16”acrosstheflatsandwashers1/8”thicksothatthesupportwillbeextended0.125”beyondthenutflat.

Foraloadof25,000#perbolt,theloadedareawouldneedtobe0.5squareinchessothatthedistancebetweentheboltpullis6.45”.Thecrossbarissupportedattwopointsthatare2.875”apartsothedistancebetweentheforceandsupportis1.77”.

74 000

2 875 0 37521 848

,

. .,

× ×=

πPSI=0.6Fy

DetailedviewofaCantsinknewconstructionbracket

40 41

Yc = −× × + ×

× × − × × −5

2 5 0 375 9 25 0 375

2 5 10 2 9 25 5 0 37

2 2. . .

. . 551 39( ) = .

I=2 0 375 5 9 25 0 375

37 22 5 3 61 17 46

2 22× × + ×

− −( ) =. . .

. . .

S=I

Yc

=−

=17 46

5 1 394 84

.

..

f fb b= ∴ ×M

SM =S

M=P(1.77)S=1.42fb=46,000(.6)=27,600

Sxfb=MsoP=22,000#andthetotalloadis44,000#.

Thetwo0.875”grade2threadedrodswillsupport0.419x55,000=23,000#eachor46,000#total.

Calculatingthecapacityofthe5x10Ushapedsupportleg,wefindthat:

A=5(10)-9.25(5-0.375)=7.22

4.84x46,000x0.6=M=P(3)

P=44,500#.

Assumingthatthebracketcontactsthefootingoveritsentirewidth,whichis12”,wefindthatthecentroidoftheloadislocatedat:

19,500=0.35x2500x12xX,X=1.86”.So,thecentroidisat0.93”.

40 41

Sincethebracketcarriesamomentandanaxialload,itis necessarytocheckthebehaviorofthecolumninorderto find themaximum load that this columncanwithstand undersimultaneousbendingandcompressionstresses.

37,000(5+0.5)+37,000(0.93)-37,000(0.45friction)(11”)-39R=0;R=2,182#.

Thepileispinnedatthetopwhereitconnectstothefootingofthestructure,andisfixedatfivefeetbelowgrade.So,thereactionatthetopcanbecalculatedasfollows:

Therefore,themomentactingwouldbeThedesignstrengthforflexuralbucklingofcompressionmembersis.

Pn=FcrAg

Fcrshallbedeterminedasfollows:

a. For

b. ForWhere

CantsinkUnderpinningBracketFreeBodyDiagram.

RP b

a+21

2

3

2

32

2 182 20

2 5939 2 59 334=

××

( ) =×

×× + ×( ) =

ll

,#

M R a =334 39=13,010#-inu = × ×1

λc Q ≤ 1 5.

F Q FcrQ c= ( )0 658

2

. λyλc Q > 1 5.

F Fcrc

=⎛⎝⎜

⎞⎠⎟

0 8772

.

λ y

0.45 x 37,000

37,000

37,000

R

11”3”

10”

3’

5.5”

0.93

A

BRACKET FBD

∑ =MA 0

∑ =MA 0

φc = 0 90.

42 43

Qshallbedeterminedasfollows:

a. For ;Q=1

b. For ;with

Since ;Q=1;then

Inordertodeterminethecombinedstressesitwillbenecessarytofindtheallowableflexuralstrength()asfollows:

When

For

ForSince ;then:

D

t= =

2 875

0 17616 1875

.

..

λπc =

××

× =0 804 60

0 947

50 000

29 000 0000 67

.

.

,

, ,.

λr

E

F= =

×=

0 114 0 114 29 000 000

50 00066 12

. . , ,

,.

y

λ λ≤ r

Fcr = × ( ) =50 000 0 658 41 3600 672

, . ,.

P F An cr= × = × =g 41 360 1 70 70 310, . ,

φPn = × =0 90 70 310 63 280. , , #

λπc

KL

r

F

E= × y

λ λ≤ r

λ λ> r λ < ×0 448.E

Fy

Q=F D

t

0 0379 2

3

.

y × ( ) +

φMn

Mn = × −⎛⎝⎜

⎞⎠⎟

=50 0002 875

6

2 469

672 606

3 3

,. .

,

λ λ≤ p

M M F Zn p= = ×y

λ λ λp r< ≤

ME

Dt F

F Sn y= ( ) ×+

⎡

⎣

⎢⎢

⎤

⎦

⎥⎥

0 02071

.

y

λ λr

E

F< ≤

0 448.

y

λ λ≤ p

42 43

Theinteractionofflexureandaxialforceshallbelimitedbythefollowingequations: a. For

b. For

Giventhat ;thencase“a”applies

Whenundertheinfluenceofbendingandcompression,thesteelcolumn(helicalpile)willbeabletostandanultimateloadof37.0kipsbaseduponthepreviouscalculations. Thebracketwastestedbyathirdpartylaboratorytodetermineitsultimatestrength,theirfindingscameto36,720#,whichrepresents99%ofthecalculatedcapacity.

InstallationofaCantsinkunderpinningbracketduetoconcretepierfailure

φMn = × =0 90 72 606 63 950. , ,

P

Pu

nφ≥ 0 2.

P

P

M

M

M

Mu

n

ux

nx

uy

nyφ φ φ+ +

⎛

⎝⎜⎞

⎠⎟≤

8

91

P

Pu

nφ< 0 2.

P

P

M

M

M

Mu

n

ux

nx

uy

ny2φ φ φ+ +

⎛

⎝⎜⎞

⎠⎟

P

Pu

nφ= =

37 000

63 2800 584

,

,.

37 000

63 280

8

9

13 010

63 9590 584 0 181 0

,

,

,

,. .+ ⎛

⎝⎜⎞⎠⎟

= + = ..766 1<

44 45

Underpinning Bracket Installation

Theprojectmanagershallexaminethefootingthicknessanddeterminepilespacingbasedonlayout,houseloadsandallowablefootingspans.Hewillcallforautilitylayoutandshallmarkthelocationoftheproposedunderpinningpiles.Ateachlocation,anexcavationapproximately3’ x 3’ and 1.5’ below the footing shall be made.The excavation shall extend 16” under thefooting.Thefootingshallbetrimmedwithachippingguntothefaceofthewallandanyearthclingingtotheundersideshallberemoved.Apileshallbeinstalledverticallytothetorquespecified on the work order completed by the project manager. If there is a coupling within3.5’ofthebottomofthefooting,thepileshallbewithdrawnandsectionlengthsexchangedtoensurethecouplingdoesnotinterferewiththeteepipe.Thebracketshallbeslidoverthepilefacingout,andthenrotatedunderthefooting.Thebracketshallberaisedandthepilecutoffwithaportablebandsaw.Thecutoffheightshallstartatthreeinchesbelowtheheightoftheverticalshelfandbeincreasedupwardsbytheanticipatedraisingheightofthestructure.Ateepipeshallbeinsertedinthepileandthebracketraisedandthetwohangingboltsinstalledfromtheteepipetothebracket.Couplingnutsshallbeaddedtotheexposedendsofthehangingbolts,ensuringatleast0.875”ofengagement.Thejackingbracketshallbeinstalledatthetopwithabottlejackusedtoraisethestructure.Theprocedureistostartjackingupthepilewiththemostsettlement,andthenasitreachestheelevationofthenextpile,thepairshallbejackeduptogetheruntiltheyreachtheelevationofthenextpile,etc.Jackingshallbemonitoredforsignsofdistressandmaybediscontinuedbeforecompletelevelingisachieved.Whenjackingiscompleted,tightenthenutsatoptheunderpinningbracketandremovethejackingbracketandjackandbackfillandcompacttheexcavation.

Cantsink Slab Bracket

Slabbracketsaresimilartounderpinningbrackets.Theseareusedprimarilyforrepairofinteriorspaces.

Slabbracketsweredesignedtoallowhydraulicassist,whichgreatlyincreasestheliftingcapac-ity.WeatCantsinkareabletousethesamehydraulicjackingbracketsusedonourunderpinningbrackets.Thisplacesthesupportboltsclosetothehole’sedge,andcombinedwitha6”channel,limitstheliftingcapacitytothepunchingshearofthefloor.TheCantsinksystemusesa6x13channelina10”holewithliftingpoints6”apart.Thelimitingfactorispunchingshearofan18”longchannelwhichwillextend5”outfromtheholeoneachside.FromACIR11.11.1.2fora3.5”thickslabwecalculatethattheshearperimeterwheretheslabwillbreakis:2(2(5.75”+1.875”)+9.5)=49.5”.Multiplyingthatbythedepthandshearstrengthoftheslabweget:V=perimeterxthicknessxV

c

WhereVcistheshearstrengthoftheconcreteandVistheallowableloadona3.5”thickconcrete

slab.

V=49.5 3.5 2× × × =3 000 19 000, , #

± 2

44 45

46 47

Slab Bracket Installation

A10”holeiscoredintheconcreteslabforabracketinstallation.Afterwards,dirt isremovedone foot deep underneath the slab, with 6” excavated around the hole outward.The pile isinstalledandcutoffafootbelowtheslab.Thechannelisslidintopositionundertheslabandapileextensionisthenfittedintothepileandmarked1”belowtheslabandremoved,cutandreinstalled.Thetwoliftingboltsareattachedtothechannelandfittedwiththejackingbracketatthetop.Liftingiscompletedandthenutsaretightenedtothetop.Theholeisthenpatched.

DetailedviewofaCantsinkslabbracket.

Solar Foundation Piles

AfoundationforaPVgroundmountsolararraymustaccommodateforbearing,upliftandover-turningmoments.

Helical piles will allow ground mounted solar panels to be installed quickly at the sameelevation,withouttheneedforgradingormovingofheavyconcreteballasts.

A2.875”shafthelicalpileiscapableofsupportingagroundbasedsolararray.Capacitiesforcompressionandtensioncanbedeterminedbasedonthesoilcharacteristicsofanygivensiteandthenbyapplyingtheprevioussectionscalculationsforsuchcharacteristics, for instance,upliftcapacitiesinsandsorclays.

Cantsinkhasdesignedandfabricatedtopplatestomatchtheattachmentsofrackingsystemswithourpiles,whichallowsforsmalladjustmentsinlocation.

46 47

APVgroundmountsolararray,supportedbyCantsinkpiles.

Tieback Anchor

Cantsink also uses helical piles for tension applications to support retaining walls, shotcretewalls,soldiertimberwalls,buoyantfootings,boardwalkbracingsamongmanyothers.Theseanchorsmustbepost-tensionedforacceptableperformance.

Here’saretainingwallwithtiebackhelicalpilesatLakeTugalo.

Thefinishedproduct.

48 49

Thisisatypicaldetailofaretainingwallwithatieback.

OTHER BRACkETS

Cantsinkalsomanufacturestimberwalkwaybrackets,lightdutyporchbrackets,solarbracketsandotherterminationsasrequestedbyclients.

Cantsinktypicaltimberbracket

48 49

CORROSION

Forpilesinhighlyaggressivesoilssuchaslandfills,minewaste,marineapplications,oratmo-sphericexposure,galvanizingisrecommended.Forallothercasestheshaftistorquelimitedsothisamountofcorrosiondoesnotaffectthestrengthat50years.

FHWA-SA-96-072, Corrosion/Degradation of Soil Reinforcements for Mechanically StabilizedEarthWallsandReinforcedSoilSlopes,whichisforsolidsectionsindisturbedsoils,statesTd=Tn–TswhereTnisnominalthicknessinmmandTsissacrificialthickness(t=50yrs).

Td<basesteelthickness

Zinc-coatedsteel:

Baresteel,

Forbaresteelandpowder-coatedsteel,Tnshallbethebase-steelthickness.Forzinc-coatedsteel,Tnmaybethesumofthebase-steelthicknessandzinccoatingthickness,providedtheminimumzinccoatingthicknessis86µm(0.0034in).ASTMA123specificationsare3oz./SFor0.005”.AISCgivesthethicknessof2.5”schedule40pipeas0.203”.Thethicknessat50yearsforgalvanizedpipeisthenreducedfrom0.208”to0.195”.Forbaresteel,thewallreducesfrom0.203”to0.167”.

Atubewillhavestagnantairinit,onlysecuringfreshairwhentherearefluctuationsinthewa-tertable.Caltrans(CaliforniaDepartmentofTransportation)uses0.025mmperyearinthesoilembeddedzoneandstates“ThecorrosionlossshouldbedoubledforsteelH-pilingsincetherearetwosurfacesoneithersideofthewebflangesthatareexposedtothecorrosivesoiland/orwater.Forpipepiles,shell,andcasings,thecorrosionallowanceisonlyneededfortheexteriorsurfacesofthepile.Theinteriorsurfaceofthepile(soilplugside)willnotbeexposedtosuf-ficientoxygentosupportsignificantcorrosion.”

From“CorrosionofSteelPipePiles”byJoukoTornqvist,“Thecorrosionwithinapipepilecanbeestimatedtheoreticallybycalculatingtheextentofsteeldegradationduetooxygencorrosionalone.Thecalculationisbasedontheassumptionthatthewaterenteringthepiledoesnotcon-tainenoughwater-dissolvedsubstancestoallowchemicalorhydrogencorrosiontotakeplace.Thisrequiresthatnosignificantamountsoforganicsubstanceorsulfurcompoundsgetinsidethepipepilesincetheycansustainmicrobiologicalcorrosionthereinforalongtime.Suchcir-cumstancesarenotconsideredpossiblewithnormalsoilconditions.

Thecorrosionwithinthepipeislimitedbytheamountofavailableoxygen.Ifweassumethatalltheoxygenoftheairinsidethepipepilegoestooxidizingiron,oneofthefollowingreactionsoccurs:

2Fe+1.5O2 Fe2O3or2Fe+1.5O2+H2O2FeO(OH)

Acubicmeterofairinthepilecontains21%oxygenbyvolumewithamolarvolumeof22.4to24.0liters/mole.Thus,theoxygeninacubicmeterofaircanbecalculatedasfollows:

ofoxygen.

T t m ins = × = ( )25 318 0 0130 65. .μ

T t m ins = × = ( )40 915 0 0360 80. .μ

0 211000

22 432 280.

.× × =

to24.0to 300g

50 51

2

1 5.74 5

32280

.× ( )to 300

Accordingtothereactionequations,onemoleofoxygen(O2,32g/mol)reactswith moles

ofsteel(74.5g).Then,theoxygeninonecubicmeterofairturns = 670 to

700gofironintorust.Letusfurtherassumethatoxygenisdepletedonlyattheanodebelowtheconstantwaterlevel,andpartlyabovewaterlevelasthecapillarityoftheprogressingrustraiseswater–theelectrolyte–fromthesurfaceontothewallofthepipepile.Thezonewherethereactionsoccurcanbeestimatedtobe100to200mmhigh.Theupperendofthepileisassumedtobetwometersabovetheexternalwaterlevel,whichiswhytheheightoftheinternalair-filledpilesectionisassumedtobe7metersincalculations.Corrosionisassumedtobeuniformandcorrosionheight80mm.Asthesizeofthepipepileincreases,corrosiondepthalsoincreases.This isduethefact that theratioof the internalvolumeofapipetothecorrodingsurface islargerwithlargepipesthansmallones.Waterlevelinsidefollowsfluctuationsinexternalwaterfairlyclosely.Whenthewaterlevelinsidethepilesinks,newairrichinoxygenenters.Whenthewaterlevelrises,newwatercontainingdissolvedoxygenenters.Watercontains,onaver-age,6mgofoxygenperliter.“Fresh”aeratedwatermaycontain10mg/literand“old”water,forinstance,deepwithinsoillayers,mayhave3-5mg/liter.Theoxygencontentofwatercanbeusedtocalculatetheamountofsteelthatoxygendissolvedinwatercancorrodepervolumetricunitofwater.Theoxygendissolvedinonecubicmeterofwaterreactswith23.3gofsteelwhentheassumedoxygen-contentofwateris10mg/liter.Thus,itcanbeconcludedthattheimpactofoxygendissolvedinwaterispracticallyinsignificantcomparedtotheimpactoftheoxygeninairasconcernstheinternalcorrosionofapipepile”.

“Letusfurtherassumethatallcorrosiontakesplacenearthewaterlevelandthatreactionsareperfectandoccurimmediatelyasnewoxygen–air–entersthepile.Asthewaterlevelfluctu-ates,thereactionareaswithinthepipepilechange.”(Figure12)

“Then,theamountofcorrodingmetalisindependentofthesizeofthefluctuationinthewaterlevel:witha0.5meterfluctuationinexternalwaterlevel,thecorrosionisdistributedoverabout0.5 meters while a two meter fluctuation causes corrosion over two meters. Since new aircannotflowintothepilewithoutachangeinwaterlevel,thefluctuationcycleiscontrolledbythewater tightnessof the lowerendof thepileand thesplicesbelowwater level.Thus, thefluctuationcanbeassumedtobeslowandconformtothetrend-likefluctuationoftheexternalwaterlevel.Ifweassumewater-levelfluctuationtobesinusoidaloverthecalendaryear,wecancalculatetheamountofcorrosion.”

50 51

Table 7

Dxt[mm]Corrosiondepth[mm]

76.1x6.30.15

88.9x6.30.18

ThismethodwasadoptedbytheFinnishGuidelinesforFoundationConstructionconformstothemethodofENV1993-5:1997Eurocode3:DesignofSteelStructures.

52 53

Thisgraphdepictsthetheoreticalcalculationsforthefluctuationsoffreshairandwaterlevelswithinapipepile.Intheexamplecasetherangeofwaterlevel

fluctuationis2mandusedpiletype(Dxt=139.7mmx10mm).

Thicknesslossfromcorrosion[mm]ofpilesandsheetpilinginsoils,aboveandbelowthewatertable,arerepresentedinthetablebelow.

Required service life 5 years 25 years 50 years 75 years 100 years

Undisturbednaturalsoil 0.00 0.30 0.60 0.90 1.20Non-compacted, 0.18 0.70 1.20 1.70 2.20non-aggressivefill

Corrosion rates are slower in compacted fills than in non-compacted fills. In the case ofcompactedfillstheabovevaluesaretobedividedbytwo.HooleandKinnestatethattheamountofcorrosiononsteelpipepilesinthegroundisnegligible.

TheNationalBureauofStandards(1962)studied7-to40-year-oldsheetpilesandbearingpilesinundisturbednaturalsoilswithapHfrom2.3to8.6andresistivityfrom300to50,200ohm-cm.MelvinRomanoffoftheNationalBureauofStandardsinCorrosionofSteelPilingsinSoilsfurtherstates“Thedataindicatesthatundisturbedsoilsaresodeficientinoxygenatlevelsafewfeetbelowthegroundlineorbelowthewatertablezone,thatsteelpilingsarenotappre-ciablyaffectedbycorrosion, regardlessof thesoil typesor thesoilproperties. Propertiesofsoilssuchastype,drainage,resistivity,pHorchemicalcompositionareofnopracticalvalueindeterminingthecorrosivenessofsoilstowardsteelpilingsdrivenunderground.HenceitcanbeconcludedthatNationalBureauofStandardsdatapreviouslypublishedonspecimensexposed

3 2.5

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0

-2.5

2.5

1.5

0.5

2

1

0 10 20 30 40 50 60

AIR

AN

D W

ATE

R E

NTE

RIN

G P

ILE

WEE

KLY

WA

TER LEV

EL OU

TSIDE P

ILE [m]

New watervolume/week,dm3

New airvolume/week,dm3

Water levelin relation toav. externalwater level

0

CORROSION

52 53

indisturbedsoilsdonotapplytosteelpilingswhicharedriveninundisturbedsoils.”

The“GuidelinesforFoundationConstruction”suggestthattheexternalsurfaceofsteelpilescanbeexpectedtocorrode,onaverage,1.2mmperhundredyearsinsoilsundernormalconditions.Internalpilecorrosioncanbeignoredif1.2mmisusedasthedimensioningcorrosionundernormalconditions.AsthisislessthanthecorrosionpredictedbyAC358,wewilluseAC358forexternalcorrosion.

Buckling Affected by Corrosion

Thedifferentcasesaresummedupwithcalculationspertheexampleforbaresteelat50years.Bucklingisgreatlyaffectedbysoilconditionsandisnotadefinitenumber,butdoesgiveanin-dicationofpilecapacity.Bjerrum(1957)proposedbucklingwillonlyoccurif

whereIpisthemomentofinertiaofthepile,khd=75lb/in2shearstrengthforasoftclay,Episthemodulusofelasticityofthepileand=52,000PSI.Fora2.875”ODpile

so that it will not buckle. Also, for the 4” OD pile sothatitwillnotbuckle.AnHP while an HP

14x73=0.570.Poulosstates“bucklingisonlylikelyif This only occurs for shapes

suchas roundandsquaresteel-barsand tram-railssuchasareused inunderpinningopera-

tions.”Foranysizesolidsquarebar andforanysizesolidroundbar

.Thus,thepossibilityofbucklingofahollowtubularpileisnogreaterthan

thatofanHpileatsimilarstresses.Itisonlyaconcernforsolidshapes.

I

Amax

k dE

p

h p

22

4

≤ σ

1 45

1 590 574

52 000

4 75 30 100 302

2

6

.

..

,.= >

× × ×=

I

Ap

2 2

5 94

3 440 502 0 30= = >

.

.. . 8 36

40 3

10 60 3592 2× = = =

I

Ay-y .

..

I

Ap

2 0 30< . .

D

D

4

212 1

12 0 0833= = .

π

π π

R

R

4

24 1

40 0796= = .

σ

Buckling of Piles FHWASA-096-720.072”ext.and0.004”int.at50yrs

OD ID Cap., Lbs. OD ID Cap., Lbs.

Baresteelat0yrs 2.88 2.47 76,575# 4.00 3.36 174,133#

Baresteelat50yrs 2.808 2.478 60,639# 3.928 3.368 150,798#

Galvsteelat0yrs 2.88 2.47 76,575# 4.00 3.36 174,133#

Galvsteelat50yrs 2.864 2.47 73,240# 3.984 3.36 169,245#

54 55

Capacity Summary

Ultimate Capacity Compression Tension

2.875”ODshafttorque 74,000# 74,000#

4”ODshafttorque 204,750# 204,750#

UnderpinningBracket 36,720# N/A

NewConstruction 74,000# Bracketfor2.875”pile

ThistableshowsCantsink’smostcommonlyusedproductsandtheirrespectiveultimatecapacities.

Tensionpileswillachievealowercapacitythancompressionpiles,duetosoildisturbance.

CantsinkpierswithcustombracketsforcommercialfootingsareshownhereattheCivilRightsMuseuminSavannah,Georgia.

HereareCantsinkcustombracketsforcommercialcolumnloads.

GALLERy

54 55

Here,tiebacksforasheetpilewallareinstalledfortheCityofAtlanta’sDepartment

ofWatershedManagement.

AtWalmart,tiebacksareusedforamodularblockwall.

CantsinkManufacturingproductsareabletobeinstalledatdifficultaccesssites,suchwasthecasehereataDozierCommunitieslot.

Pilescanbeinstalled,rebarplaced,andfoundationconcretepouredallinthesamedayusingourproducts.

CantsinkpilesinstalledforaboardwalkinColumbiaCounty,Augusta,Georgia

56 57

56 57

58 59

References:American Concrete Institute, 318-08 11.4.6.1; 15.2.2

American Iron and Steel Institute

Bassett, R.H. (1977) “Underreamed Ground Anchors” Specialty Session No. 4 9th International Conference on Soil Mechanics and Foundation Engineering, Tokyo.

Blodgett, Omer W., (2002) “Design of Welded Structures” The James F. Lincoln Arc Welding Foundation

Bowles. J.E. (1996) “Foundation Analysis and Design” Fifth Edition McGraw-Hill

Brown, Peter T. “Screw Plate Insertion in Sand” Geotechnical Testing Journal GTJODJ, Vol.18, No. 2, June 1995, pp.259-270

Chance Helical Screw Foundation Design Manual for New Construction Chance Div.of Hubbell Power Systems, Inc. Centralia, MO.

Clemence, S.P., editor (1985) “Uplift Behavior of Anchor Foundations in Soil” ASCE Convention, Denver

Das, Braja M., “Principles of Foundation Engineering” Brooks/Cole

Das, Braja M., (1990) “Earth anchors” Elsevier Science Publishing Company, Inc.

Eason and Shield, (1960). Screw plate test.

Hool, I.A. and Kinne, W.S, (1943) “Foundations, Abutments and Footings” 2d. Ed. McGraw-Hill Book Co., Inc. p204

Hoyt, R.M and Clemence, S.P. (1989). “Uplift Capacity of Helical Anchors in soil.” Proceedings of the 12th International Conference on Soil Mechanics and Foundation Engineering, Rio de Janeiro, Brazil.

International Residential Code (2006) –R301.6.

Liu, H., Zubeck, H.K. and Schubert, D.H. (2005). “Finite Element Analysis of Helical Piers in Frozen Ground” Journal of Cold Regions Engineering, ASCE

Lutenegger, Alan J., (2009). “Cylindrical Shear or Plate Bearing? Uplift Behavior of Multi Helix Screw Anchors in Clay.”

Lutenegger, A.J., Smith, B.L. and Kabir, M.G. (1988). “Use of In Situ Tests to Predict Uplift Performance of Multihelix Anchors” Special Topics in Foundations, ASCE

Melerski, Edmund S. (April 12,2006). “Design Analysis of Beams, Circular Plates and Cylindrical tanks on Elastic Foundations”. Taylor and Francis

Meyeroff, GG and Adams, JI (1968). “Ultimate Uplift Capacity of Foundations”. Canadian Geotechnical Journal Vol V, No. 4, pp225-244.

58 59

Meyeroff, (1951). Screw plate test. Geotechnique, V2, p301

Mitsch, A.M. and Clemence, S.P. “The Uplift Capacity of Helix Anchors in Sand” (1985) Uplift Behavior of Anchor Foundations in Soil, ASCE

Mooney, J.S., Adamczak, S., Jr. and Clemence, S.P. (1985) “Uplift Capacity of Helix Anchors in Clay and Silt” Uplift Behavior of Anchor Foundations in Soil, ASCE, pp48-72

National Bureau of Standards (1962)

Poulos, H.G. (1990). “Pile Foundation Analysis and Design” Robert E. Krieger Publishing Company

Rao, N., Prasad, Y.V.S.N. and Shelty, M.D. (1991) “The Behavior of Model Screw Piles in Cohesive Soils”, Soils and Foundations, 31(2) pp35-50

Romanoff, Melvin. The National Bureau of Standards in Corrosion of Steel Pilings in Soils

Rowe, R.K. and Booker, J.R. (1979). “The Elastic Response of Multiple Underream Anchors” International Journal of Numerical Analysis Methods, Geomechanique 4

Selvadurai, Bauer and Nicholas. (Nov. 1980). “Screw Plate Testing of a Soft Clay.” Canadian Geotechnical Journal

Selvadurai, A.P.S. and Szymanski, M.B. (1980). The Bearing Capacity of Rigid circular Anchor Plates Embedded in an Ideal Cohesive Soil (unpublished)

Shield, R.T. (1955). “On the flow of metals under conditions of axial symmetry” Proceedings of the Royal Society of London, Series A, 233 pp267-287

Skempton,A.W. (1951). “Bearing Capcity of Clays” Proceedings of the Building Research Congress, 1, pp180-189

Tappenden, Sego and Robertson in “Load Transfer Behavior of Full-Scale Instrumented Screw Anchors” Proceedings of selected papers of the 2009 International Foundation Congress and Equipment Expo.

Terzahi, Peck and Mesri. “Soil Mechanics in Engineering Practice for Piers”

Tomlinson, M.J. “Pile Design and Construction Practice” (2004) Spon Press

Witherspoon, T. (2006) “Load Capacity Testing of Residential Underpinning in Expansive Clay Soil” PhD thesis University of Texas at Arlington

Zhang, J.Y. (1999) “Predicting capacity of Helical Screw Piles in Alberta Soils” MSc thesis University of Alberta.

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CONTRACTOR: Cantsink of Atlanta, LLC Lilburn, Ga.

ENGINEER: ECS Southeast, LLC Acworth, Ga

SITuATION:The listed property, owned by American Golf Corpora-tion, experienced settlement of their community pool, which measured roughly 84’ x 42’ and included an 8’ deep end. Additionally, the concrete pool deck and kiddie pool had settled. A large crack in the main pool was present measuring 1” in width, which basically separated the pool in half. Soil testing was recommended and performed by ESC Southeast, LLC. A total of five (5) soil test borings and three (3) test pits were performed in and around the pool area using an ATV-mounted drill rig. Representative soil samples were obtained by means of the split-barrel sampling procedure using an automatic drive hammer, in accordance with ASTM Specification D-1586. Undocu-mented fill with traces of organics were found at depths ranging from 12’ to 27’.

SCOpE Of WORk:The engineering firm offered two alternatives to the owner, both of which included complete demolition and replacement of the main and kiddie pools due to the severity of movement. The first alternative involved removal and replacement of the fill with proper com-paction. However, a number of factors made this option both impractical and costly, including disposal of the unsuitable soils, the depth of excavation, the temporary dewatering required, and the duration of the work.

The second alternative involved the use of helical piles to support the new pool, including interior grade beams for the pool shell. Cantsink helical piles were installed as a deep foundation support system for both the main pool and kiddie pool structures. Piles were placed on 7’ to 8’ centers for the perimeter walls and interior grade beams extending side to side. Buried debris to depths up to 10’ were discovered, resulting in the need for an 8” diameter helix instead of the standard 14” diameter. Pile depths ranged from 15.5’ to 28’, with the majority of the piles between 17.5’ and 22’. A 5,500 ft.-lb hydraulic drive head mounted on a Bobcat S250 skid steer loader was used to install the 109 piles used in the job.

SOIl CONdITIONS:The soil consisted of very loose to medium-dense san-dy silt, silty sand, sand with a high content of clay and sandy clay. Rock fragments, roots and other undocu-mented material were present to depths of 2’ to 9’ below grade. “N” values varied pending on boring location.

pIlING SySTEm:2.5” schedule 40 pipe (3” nominal) to include 7’ lead sections with a single flight 8” diameter helix. 5’, 7’ and 10.5’ extensions were used as required to meet load requirements. Pipe caps for each pile consisted of an 8” x 8” x 0.375” plate sleeved into the top of the pile and through-bolted for uplift restraint. Working loads per pile were 25 Kips.

CANTSINk mANUFACTURING

CASE STUDy 1 pROJECT: Brookstone Country Club

60 61

RESulTS:One hundred and nine piles were installed over a two-day period, which resulted in no delays in the construction of the pool. Due to the nature of the project, weather con-ditions came into play, as any rainfall resulted in water collection within the work site. The pile depths matched what was anticipated based on the soil borings report. The use of Cantsink helical piles, with their patented plate ribbing, allowed the piles to penetrate through the backfill debris for transfer of the pool loads onto proper bearing strata for a permanent foundation support.

62 63

CONTRACTOR: Cantsink of Atlanta, LLC Lilburn, Ga. ENGINEER:Don Moore, LLC. JOB CONdITION: Don Moore P.E. of Don Moore, LLC contacted Cantsink Project Manager Rick Pashman about a residence in Carrollton that was experiencing significant settlement within the entire residential home. The setting was a large residence in Sunset Country Club. Rick Pashman visited the site along with Bobby McMillan of R & R Enterprises and the engineer Don Moore. A visual in-spection depicted several areas of diagonal cracking in the brick and mortar over windows and door openings. The original building plans were reviewed and the area of failure was determined. Upon reviewing the borings which extended to sixty feet and read blow counts ranging from two to six blow, it was determined that approximately seventy five percent of the perimeter footings would need to be underpinned as well as all of the load bearing walls in the basement. SCOpE Of WORk:Cantsink was instructed by the engineer Don Moore to install eighteen underpinning piles around the perimeter of the residence extending from the front right corner down the right side and partial rear. Hand excavations were performed at each pile location to a depth of approximately four feet. The existing footing was poured almost three feet deep and was angled or beveled towards the house. This footing configuration required Cantsink to saw cut a portion of the footing and use a chipping gun to square the face of the foot-ing to receive the bracket. The piles were installed to an average depth of 55’0”. In addition to the exterior underpinning, Cantsink needed to underpin all of the load

bearing walls in the basement. This process required saw or strip cutting of the areas adjacent to the walls and installing a total of forty-nine interior underpinning brackets. The inside installation was accomplished by using the smaller MT55 Bobcat. The air quality was a primary concern so Cantsink used an industrial fan and conduit to pull the Bobcat exhaust out of the basement so the work environment would be safe for the work-ers and the homeowners. The interior pile depths were similar to the perimeter piles and ranged from forty five to fifty five feet. After completion of the installation the excavated holes were backfilled and R & R Enterprises performed the repour of the saw cut areas. The hom-eowner was relieved that now they were assured that the foundation credibility was restored.

SOIl CONdITIONS:Silty sand and sand with a high content of clay contain-ing a moderate to high amount of topsoil and organics was determined to be the soil conditions at the site.

pIlING SySTEm:2.875’ OD (2.5 SSC 40)” to include seven and ten and a half foot lead sections with a single flight fourteen inch diameter helix. Ten and a half, seven and five foot extensions were used during the installation to meet load requirements. Cantsink manufactured brackets were used to secure the footings.

dESIGN lOAd:Working load per pile- 30 kips.

CANTSINk mANUFACTURING

CASE STUDy 2 pROJECT: Copolini Residence 103 Sunset Court Carrollton, Georgia

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CONTRACTOR: Cantsink of Atlanta, LLC, Lilburn, Georgia

ENGINEER:Rhett Palmer, Palmer Construction Consultants

JOB CONdITION:Mr. Shaw, former owner of Shaw Carpets, contacted Jackie Cope of Cope Builders to perform an expansion of his current residence. The addition included a one story room at the rear of the residence and a new pool house adjacent to the pool. Footings were excavated and the footing contractor was not comfortable with the condition of the soil. Rhett Palmer was called to probe the footings. He determined that the soil was too soft to pour on grade and recommended a foundation support system consisting of helical piers. The footing contractor, Lyman King contacted Cantsink to visit the site, review the plans and help determine the neces-sary pile count. After consulting with the engineer, Can-tsink marked the footings for each structure for helical pier installation. A utility locate was necessary due to the proximity of the pile locations and the existing resi-dence. It was decided that the piles would be installed. SCOpE Of WORk:Rhett Palmer, of Palmer CCI, informed Cantsink that ten helicals were to be installed in the footings of each structure spaced approximately eight feet apart. Rhett asked for a minimum of 18 kips of working load per pile. Due to the limited access options to the site an MT 55 Bobcat with a 5500 ft lb head was used to install the piles. The piles depths ranged from 17’-26’. The installation was performed in about five hours and completed the same day. Light rain fell for the first two hours of the installation which highlighted the advan-tage of using helicals in these conditions. The builder

was very pleased primarily because the quick installa-tion allowed acceleration in his schedule. Rhett Palmer inspected the rebar configuration and passed the in-spection so the builder could proceed with pouring the footings.

SOIl CONdITIONS:Gray, wet alluvial soils were found at the site.

pIlING SySTEm:2.5” sch 40 A500 grade B pipe ( 3” nominal ) to include seven foot lead sections with a single flight fourteen inch diameter helix. Seven foot leads and five and sev-en foot extensions were used during the installation to meet load requirements. The top plate was a 0.375” x 8” x 8” A-36 steel cap sleeved into the top of the pile.

dESIGN lOAdS:Working load per pile-18 kips.

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CASE STUDy 3 pROJECT: Shaw Residence, Cope Builders 3930 E. Brookhaven drive Atlanta, Georgia

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CONTRACTOR: Cantsink of Atlanta, LLC, Lilburn, Ga.

ENGINEER:The Foundation Firm

SITuATION:The Devereaux Commons homeowners association was experiencing slope failure of an embankment at one of the detention ponds within the community. In-spection revealed soft soils on the slope, suggesting improper compaction of the site. At the base of the 10’ slope was a weir and drain structure designed to handle the detention pond. Continued subsidence of the embankment would have a dramatic impact on the structure and road at the top of the slope.

SCOpE Of WORk:A retaining wall system was recommended to stabilize the slope, preventing the threat of future damage and wasted expenses. An 8’ poured-in-place wall was de-signed to stabilize a 50’ section of the slope. Excavation to the designed wall footing elevation, approximately 2’ below the drain structure, took place with the spoils being stockpiled at the top of the slope. This allowed cleanup of the pond basin, which had been left unat-tended since construction in 2000.

A soil compaction test was performed using both a helical probe and Dynamic Cone Penetrometer (DCP), which confirmed insufficient soil bearing pressure to support a wall footing. Cantsink helical piles were in-stalled for the cantilevered wall design to include two rows of piles spaced 6’ on center and staggered. Pile depth ranged from 17.5’ to 24.5’ with one pile extend-ing to a depth of 28’. A 5,500 ft-lb hydraulic drive head mounted to a Bobcat S250 skid steer loader was used to install the piles. A 15’ boom on the end of the loader allowed installation from the top side of the slope.

SOIl CONdITIONS:The soil consisted of sandy silt with a high content of organic debris. “N” value to 5’ depth - 3

pIlING SySTEm:2.5” schedule 40 pipe (3” nominal) to include 7’ lead sections with a single flight 14” diameter helix. 7’ and 10.5’ extensions were used as required to meet load re-quirements. Pile caps were used for each pile where an 8” x 8” x 3/16” plate sleeved into the top of the pile.

dESIGN lOAdS:Working load per pile: 16 Kips.

RESULTS:Sixteen piles were installed within four hours, which resulted in no delays in the construction of footing. Since the project was located at a detention pond, weather conditions came into play. There was a high concentration of sub-surface drainage in the area, requiring time management in completing the footing. The use of Cantsink helical piles eliminated glitches in both design and construction, allowing for a permanent wall structure.

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CASE STUDy 4 pROJECT: devereaux Commons HOA Atlanta, Georgia

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CONTRACTOR: Skanska Building USA, Atlanta, GA

ENGINEER:Sedki & Russ Eng.United Consulting SITuATION:The listed General Contractor was hired for renovations to an existing seven-story building, including an eleva-tor addition. A geo-technical evaluation confirmed that there were unsuitable soils for the construction of an elevator shaft on a typical shallow foundation. Soil bor-ings concluded 12’ to 14’ of loose to firm fill. Helical piles were recommended as the lowest risk option for support of the elevator addition. The design called for fourteen (14) helical piles with an allowable compres-sion capacity of 40 Kips per pile and an allowable up-lift capacity of up to 10 Kips per pile. The geo-technical testing firm estimated pile depths ranging from 16’ to 18’ below existing grade, which is where partially weath-ered rock was identified.

SCOpE Of WORk:At the direction of the structural engineer, a test pile was first installed and load tested for confirmation as to the suitability of the selected foundation support sys-tem. Four (4) reactionary helical piles were installed around the test pile to depths of 14’ each. The test pile was installed to a depth of 16’. A 12,500 ft.-lb hydraulic drive head mounted on a Bobcat S250 skid steer loader was used to install the helical piles for this job. The lim-ited access to the site location restricted the use of any larger equipment for installation.

The load testing was overseen by the engineering firm in accordance with standard loading procedure of ASTM-D 1143-81. Deflections were measured using a single dial gauge accurate to 0.001 inch. The results of

the load test indicated a total deflection of 0.42 inches and a net deflection of 0.29 inches at the design work-ing load of 40 Kips. The testing engineering firm con-cluded that the Cantsink helical piles would be able to support the allowable working loads of 40 Kips per pile.

Following the excavation phase of the project, pile loca-tions were marked and installed using the same equip-ment as the test pile. The base of the elevator pit was 5’ below grade, which reduced the pile depths based on soil borings at grade level. All piles were installed to depths of 10.5’. The final pressure reading of torque for the piles ranged from 2,600 to 2,750 psi for the 12,500 ft.-lb drive head. Pile installation was completed within a four-hour period.

pIlING SySTEm:The piling system selected was a 3.5” OD schedule 40 steel shaft with an 8” diameter lead helix and a second 14” diameter helix located approximately 42” above the lead helix. The piles were manufactured by Cantsink Manufacturing and installed by Cantsink of Atlanta, LLC. The pipe caps for each pile included a 10” x 10” x 1” plate sleeved into the top of the pile and through-bolted for uplift restraint. Working loads of 40 Kips per pile were achieved.

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CASE STUDy 5 pROJECT: Wesley Woods Budd TerraceElevator Addition, Atlanta, GA