(210–VI–NEH, August 2007) Pile Foundations Technical Supplement 14F
(210–VI–NEH,August2007)
Pile FoundationsTechnical Supplement 14F
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
(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:
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
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
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)
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
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
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
TS14F–4 (210–VI–NEH,August2007)
Lateral load capacity
Anapproximatelateralcapacityofashort,rigidpiledrivenintoacohesivesoilcanbedeterminedfromthefollowingequation(figs.TS14F–1andTS14F–2):
P
PAllowable
Ultimate=
factorofsafety (eq.TS14F–7)
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=
factorofsafety (eq.TS14F–11)
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)
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
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
Part 654 National Engineering Handbook
Pile FoundationsTechnical Supplement 14F
TS14F–6 (210–VI–NEH,August2007)
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