Technical Pile Foundations Supplement 14Fjdfields.candela.io/media/pages/deep-foundation/...Pile...

(210–VI–NEH,August2007)

Pile FoundationsTechnical Supplement 14F

Part 654 National Engineering Handbook


(210–VI–NEH,August2007)

Advisory Note

Techniquesandapproachescontainedinthishandbookarenotall-inclusive,noruniversallyapplicable.Designingstreamrestorationsrequiresappropriatetrainingandexperience,especiallytoidentifyconditionswherevariousapproaches,tools,andtechniquesaremostapplicable,aswellastheirlimitationsfordesign.Notealsothatprod-uctnamesareincludedonlytoshowtypeandavailabilityanddonotconstituteendorsementfortheirspecificuse.

Cover photo:Pilefoundationsmaybeneededwherethebearingstrengthoftheearthmaterialsislow.

IssuedAugust2007

(210–VI–NEH,August2007) TS14F–i

Contents

TechnicalSupplement 14F

Pile Foundations

Purpose TS14F–1

Introduction TS14F–1

Bearing capacity TS14F–1

Lateral load capacity TS14F–4

Tables Table TS14F–1 Prescriptivevaluesforcohesionlesssoils TS14F–2

Table TS14F–2 Prescriptivevaluesforcohesivesoils TS14F–3

Figures Figure TS14F–1 Schematicshowingappliedlateralforceand TS14F–5 assumedsoilreactionsforsinglerigidpile

drivenintoacohesivesoil.Concentratedloadappliedattopofpile

Figure TS14F–2 Schematicshowingappliedlateralforceand TS14F–5 assumedsoilreactionsforasinglerigidpile drivenintoacohesivesoil.Uniformlydecreasing loadapplied

Figure TS14F–3 Schematicshowingappliedlateralforceand TS14F–6 assumedsoilreactionsforsinglerigidpile drivenintoacohesivesoil.Concentratedload appliedattopofpile

Figure TS14F–4 Schematicshowingappliedlateralforceand TS14F–6 assumedsoilreactionsforsinglerigidpile drivenintoacohesivesoil.Uniformlydecreasing loadappliedasshown

(210–VI–NEH,August2007) TS14F–1

TechnicalSupplement 14F

Pile Foundations

Purpose

Pilesareusedtotransferfoundationforcesthroughrelativelyweaksoiltostrongerstratatominimizesettlement.Themostlikelyapplicationsforpilefoun-dationsinstreamrestorationandstabilizationprojectsareassupportforbankstabilizationstructures(retain-ingwall)andanchorsforlargewoodymaterial(LWM).Pilesmaybeusedtosupportancillarystructuressuchasculverts,structuralchannels,bridges,andpump-ingstations.Thistechnicalsupplementaddressestheanalysesrequiredtodesignpilefoundations.

Introduction

Foundationstructuresmaybeclassifiedintotwocategories:shallowanddeep.Thereisnospecificrulethatdefineswhenaparticularstructureisconsideredtobeshallowordeep.Ingeneral,shallowstructuresareconstructedfairlyclosetogroundsurfaceandareusuallyconstructedupwardsfromthebottomsurfaceofanexcavation.

Traditionally,deepfoundationsrefertopilesthataredrivenintotheground.However,pilesaresometimessetintoholesthatarepreboredordrilledintotheground.Aholeboredintothegroundandfilledwithconcreteiscalledadrilledshaft.Usually,reinforcingsteelisplacedintothedrilledholejustpriortoplace-mentoftheconcrete.Othertermsfordrilledshaftsare:drilledpiers,drilledcaissons,cast-in-placepiles,cast-in-drilled-holepiles,andaugeredpiles.Anothertypeofdrilledshaftfoundationisanauger-castpile.

Pilesarenormallyusedtoprovidefoundationcapac-itytosupportastructurewhenthebearingcapacityofthesoilisinsufficienttodoso.Ifasoil’sbearingcapac-ityislessthanthatneededtosupportastructure,ashallowfoundationmaybecomeimpracticalorexpen-sive.Bydrivingpilesintotheground,thepilestructurecantakeadvantageofthesoil’sshearstrength,aswellasitscompressive(orbearing)strength.Pilesarealsousedtotransferfoundationforcesthroughrelativelyweaksoilstratatostrongerstratatominimizesettle-ment.

PilesmaybesteelH-sections;steelpipe;precast,prestressedconcrete;concrete-filledsteelshells;or

timber.Pileswithsolidcrosssections,orhollowpileswithclosedends,typicallydisplacethesoilastheyaredrivenandaretermeddisplacementpiles.Pileswithopencrosssections,suchasH-sections,orpipepileswithoutclosedends,typicallycutthroughthesoil,ratherthandisplacingitastheyaredriven,sotheyaretermednondisplacement piles.Whetherapilebehavesinadisplacingornondisplacingmannerdependsheavilyonthesoilproperties.Piledrivingmaycausecohesivesoilstoremoldandcausedensitychangesincohesionlesssoils.Thesechangesmayresultingroundsurfaceelevationchanges(heavingorsettling)inthegeneralareaofthedrivingoperation.Properpiledrivingequipmentselectionandoperationcangreatlyminimizethepossibleadverseeffectsofpileinstalla-tion.

Pilefoundationsareusedinstreamrestorationandstabilizationprojectsassupportforbankstabilization(retainingwall)structuresandanchorsforLWM.Pilesmaybeusedtosupportancillarystructuressuchasculverts,structuralchannels,bridges,andpumpingstations.

Pilesaretypicallyinstalledusingspecializedpiledriv-ingequipment.Themotiveforcethatdrivesthepileintothegroundisappliedbyapiledrivinghammer,whichisattachedtothetopofapile.Acraneisusedtosupportthepiledrivingequipmentandhandletheindividualpiles.

Bearing capacity

Theallowablebearingoraxialcapacityofadrivenpilemaybedeterminedfromthefollowingequation:

QQ

Allowabletotal=

factorofsafety (eq.TS14F–1)

Q Q Q Wttotal po friction pile= + −int (eq.TS14F–2)

where:Q

total =ultimatecapacityofpile

Qpoint =end-bearingcapacityofpileQ

friction =capacityduetofrictionalong

lengthofpileWt

pile =weightofpile

factorofsafety =3.0



TS14F–2 (210–VI–NEH,August2007)

Foracohesionlesssoil,thefollowingformulasmaybeusedtodeterminevalues(tableTS14F–1)forthecomponentsofthebearingcapacityequation:

Q DN Apo q point int= ′ ′γ (eq.TS14F–3)

where:γ′ = effectiveunitweightofsoilD = embeddeddepthofpileA

point = areaofpiletip

′ = +′′N eq

π φ φtan tan ( )2 452

(eq.TS14F–3a)

where:φ′ =tan-1(0.67tanφ)φ =angleofinternalfrictionofsoil

Q K Dfriction average o shape= ′ ∑τ (eq.TS14F–4)

where: ′ = ′ ′τ γ φaverage ozK tan (eq.TS14F–4a)

where:γ′ =effectiveunitweightofsoilz =depth(alongpile)atpointofanalysisΚ

=ratiooflateraltoverticalsoilstresson

pileΚ

o =0.7forpilesloadedincompression

Κo =0.5forpilesloadedintension

φ′ =tan-1(0.67tanφ)φ =soilangleofinternalfriction

Σο =perimeterofpileΚ

shape=pileshapefactor

Κshape

=1.000forroundperimeter =0.785forsquareperimeter

I-beampilesareconsideredtohaveasquareperimeterwithsidelengthsequivalenttotheirrespectivedepthandwidthdimensions.

= 0.95foroctagonperimeter = 0.84forhexagonperimeter = 0.60fortriangularperimeter

D = depthofpile

Table TS14F–1 Prescriptivevaluesforcohesionlesssoils

Soil typeAngle of internal friction (°)

Angle of friction between soil and pile (°)

Bearing capacity coefficient Nq

Maximum allowable capacity, Q

Friction(tons/ft2)

Bearing(tons/ft2)

Cleansand 35 30 11 1.00 100

Siltysand 30 25 7 0.85 50

Sandysilt 25 20 5 0.70 30

Silt 20 15 4 0.50 20

TS14F–3(210–VI–NEH,August2007)



Table TS14F–2 Prescriptivevaluesforcohesivesoils

Clay Shear strength

Normallyconsolidated c z Kz o

= ′ −( )0 5 1. γ

Underconsolidated c z Kz o

= ′ −( )0 125 1. γ

Overconsolidatedbyerosion

Overconsolidatedbydesiccation

c z Kz o

= + ′ −( )600 0 5 1lb/ft2 . γ

c z

c z

z

z

= =

= =

2 000 0 20

1 200 2

,

,

lb/ft for ftto ft

lb/ft for

2

2 00 60

3 000 60 160

ftto ft

lb/ft for ftto ft2c zz = =,

Forhighlyfissuredclays,usethefollowing:′ =c 0

′ =φ 5 10 to and′ = ′ ′τ γ φaverage o

z K tan

Notes:Forpilesloadedinaxialcompression,K

o=0.7

Forpilesloadedinaxialtension,Ko=0.5

Effectiveshearstrength,c´=0.67cZ=depthalongpilefromgroundsurface(ft)Z=0atgroundsurface

Foracohesivesoil,thefollowingformulasmaybeusedtodeterminevalues(tableTS14F–2)forthecom-ponentsofthebearingcapacityequationcitedabove.

Q A c Dpo point int .= + ′( )7 4 γ (eq.TS14F–5)where:A

point =areaofpiletip

c =shearstrengthofcohesivesoilatpiletip depth

γ′ =effectiveunitweightofsoilD =depthofpile

Q c K Dfriction average o shape= ′ ∑ (eq.TS14F–6)

where:′caverage =averageeffectiveshearstressofsoil,

alongwithagivenlength,orsegmentof thepileΣο =perimeterofpileΚ

shape =pileshapefactor

Κshape

=1.000forroundperimeter =0.785forsquareperimeter

I-beampilesareconsideredtohaveasquareperimeterwithsidelengthsequivalenttotheirrespectivedepthandwidthdimensions.

=0.95foroctagonperimeter =0.84forhexagonperimeter =0.60fortriangularperimeterD =depthofpileorlengthofpilesegment




Lateral load capacity

Anapproximatelateralcapacityofashort,rigidpiledrivenintoacohesivesoilcanbedeterminedfromthefollowingequation(figs.TS14F–1andTS14F–2):

P

PAllowable

Ultimate=


where:P

Allowable =allowablelateralloadappliedto

exposedportionofpilefactorofsafety =3

P B

DH D

DHUltimate = +

+

− +

σ 42

22

2

2

(eq.TS14F–8)where:σ =allowablesoilstress,σ=9cB =widthordiameterofpileD =depthofpileembedmentH =heightofpile(aboveground)tocentroidofap-

pliedload

Ifadesignloadisknown,therequireddepthofem-bedmentmaybedeterminedfromthefollowingequa-tion:

DP

B

P

B

HP

BUltimate Ultimate Ultimate= +

+σ σ σ

24

2

(eq.TS14F–9)

Formoststreamrestorationandstabilizationappli-cations,adrivenpilemaybeconsideredtoberigidwhen:

H

B≤ 12 (eq.TS14F–10)

Anapproximateallowablelateralloadforashort,rigidpiledrivenintoacohesionlesssoilmaybedeter-minedusingthefollowingequation(figs.TS14F–3andTS14F–4.

PP

AllowableUltimate=


where:P

Allowable =allowablelateralloadappliedto

exposedportionofpilefactorofsafety =3

PBK D

H DUltimatep=

′+( )

γ 2

2 (eq.TS14F–12)

where:γ′ =effectiveunitweightofsoilB =widthordiameterofpileK

p=passivepressurecoefficient

Kp =

= +

Passivepressurecoefficient

tan2 452

φ (eq.TS14F–13)

φ =soilangleofinternalfrictionD =embeddeddepthofpile

Ifadesignloadisknown,therequireddepthofem-bedmentmaybedeterminedfromthefollowingequa-tion.

DP

BKH DUltimate

p

=′

+( )2γ (eq.TS14F–14)

ThisequationissolvediterativelyuntilbothvaluesforDareequivalent.

TS14F–5(210–VI–NEH,August2007)



H

P

D

B

= 9c

σ

σ

σ

Figure TS14F–2 Schematicshowingappliedlateralforceandassumedsoilreactionsforasinglerigidpiledrivenintoacohesivesoil.Uniformlydecreasingloadapplied

H

P

D

B

= 9c

σ

σ

σ

Figure TS14F–1 Schematicshowingappliedlateralforceandassumedsoilreactionsforsinglerigidpiledrivenintoacohesivesoil.Concentratedloadappliedattopofpile




Figure TS14F–4 Schematicshowingappliedlateralforceandassumedsoilreactionsforsinglerigidpiledrivenintoacohesivesoil.Uniformlydecreasingloadappliedasshown

= 3γ ′ZKp

= 3γ′DKp

D

B

z

D

z

Z

σ

σ

Dσ

σ

H

P

H

P

D

B

z

D

z

Z

σ

σ

D= 3γ′DKp

= 3γ ′ZKp

σ

σ

Figure TS14F–3 Schematicshowingappliedlateralforceandassumedsoilreactionsforsinglerigidpiledrivenintoacohesivesoil.Concentratedloadappliedattopofpile

NRCS Stream Restoration Design HandbookCONTENTSTECHNICAL SUPPLEMENTSTS 2 Use of Historic Information for DesignTS 3A Stream Corridor Inventory and Assessment TechniquesTS 3B Using Aerial Videography and GIS for Stream Channel Stabilization in the Deep Loess Region of Western IowaTS 3C Streambank Inventory and EvaluationTS 3D Overview of United States BatsTS 3E Rosgen Stream Classification Technique-Supplemental MaterialsTS 5 Developing Regional Relationships for Bankfull Discharge Using Bankfull IndicesTS 13A Guidelines for Sampling Bed MaterialTS 13B Sediment Budget ExampleTS14A Soil Properties and Special Geotechnical Problems Related to Stream Stabilization ProjectsTS 14B Scour CalculationsTS 14C Stone Sizing CriteriaTS 14D Geosynthetics in Stream RestorationTS 14E Use and Design of Soil AnchorsTS 14F Pile FoundationsTS 14G Grade Stabilization TechniquesTS 14H Flow Changing TechniquesTS 14I Streambank Soil BioengineeringTS 14J Use of Large Woody Material for Habitat and Bank ProtectionTS 14K Streambank Armor Protection with Stone StructuresTS 14L Use of Articulating Concrete Block Revetment Systems for Stream Restoration and Stabilization ProjectsTS 14M Vegetated Rock WallsTS 14N Fish Passage and Screening DesignTS 14O Stream Habitat Enhancement Using LUNKERSTS 14P Gullies and Their ControlTS 14Q Abutment Design for Small BridgesTS 14R Design and Use of Sheet Pile Walls in Stream Restoration and Stabilization ProjectsTS 14S Sizing Stream Setbacks to Help Maintain Stream Stability

REFERENCES

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