PILE FOUNDATIONS - Gnpgeo.com.my

PILED FOUNDATIONDESIGN & CONSTRUCTIONBy Ir. Dr. Gue See Sew &Ir. Chow Chee Menghttp://www.gnpgeo.com.my

Contents• Overview• Preliminary Study• Site Visit & SI Planning• Pile Design• Pile Installation Methods• Types of Piles

Contents (Cont’d)• Piling Supervision• Pile Damage• Piling Problems• Typical Design and Construction Issues• Myths in Piling• Case Histories• Conclusions

Overview

What is a Pile FoundationIt is a foundation system thattransfers loads to a deeperand competent soil layer.

When To Use Pile Foundations• Inadequate Bearing Capacity of ShallowFoundations• To Prevent Uplift Forces• To Reduce Excessive Settlement

PILE CLASSIFICATION• Friction Pile– Load Bearing Resistance derived mainlyfrom skin friction• End Bearing Pile– Load Bearing Resistance derived mainlyfrom base

Overburden Soil LayerFriction Pile

End Bearing PileOverburden SoilRock / Hard Layer

Preliminary Study

Preliminary Study• Type & Requirements of Superstructure• Proposed Platform Level (ie CUT or FILL)• Geology of Area• Previous Data or Case Histories• Subsurface Investigation Planning• Selection of Types & Size of Piles

Previous Data & CaseHistoriesExistingDevelopmentAProposedDevelopmentExistingDevelopmentBOnly Need MinimalNumber of BoreholesBedrockProfile

Challenge The Norm ThruInnovation To Excel

SELECTION OF PILESFactors Influencing Pile Selection– Types of Piles Available in Market (see Fig. 1)– Installation Method– Contractual Requirements– Ground Conditions (eg Limestone, etc)– Site Conditions & Constraints (eg Accessibility)– Type and Magnitude of Loading– Development Program & Cost– etc

TYPE OF PILESDISPLACEMENT PILESNON-DISPLACEMENT PILESTOTALLY PREFORMED PILES(A ready-made pile is driven or jackedinto the ground)DRIVEN CAST IN-PLACE PILES(a tube is driven into ground toform void)Bored pilesMicro pilesHollowSmall displacementSolidConcrete TubeSteel TubeSteel PipeConcrete Spun PilesClosed endedtube concretedwith tube left inpositionClosed ended tubeOpen ended tubeextracted whileconcreting (Franki)ConcreteSteel H-piles(small displacement)Bakau pilesTreated timber pileRestricted use due toenvironmentalconsiderationsPrecast R.C.pilesPrecast prestressedpilesFIG 1: CLASSIFICATION OF PILES

PREFORMED PILESLEGEND :GEOTECHNICALSCALE OF LOAD(STRUCTURAL)BEARING TYPETYPE OFBEARINGLAYERUNIT COSTTYPE OF INTERMEDIATE LAYERGROUNDWATERENVIRONMENTDESIGNCONSIDERATIONSBAKAU PILESTIMPER PILESRC PILESPSC PILESSPUN PILES10000 x x ? a a a a x a ? x 70%)x x ? ? ? a a ? a a ?DENSE / VERY DENSE SANDx ? a a a a a a a a aSOFT SPT < 4a a a a a a a a a ? aCOHESIVE SOILM. STIFF SPT = 4 - 15 a a a a a a a a a a aV. STIFF SPT = 15 - 32 ? a a a a a a a a a aHARD SPT > 32x ? a a a a a a a a aLOOSE SPT < 10COHESIVELESS SOILSOIL WITH SOME BOULDERS /COBBLES (S=SIZE)ABOVE PILE CAPBELOW PILE CAPTYPE OF PILEM. DENSE SPT = 10 - 30NOISE + VIBRATION; COUNTER MEASURESREQUIREDSTEEL H PILESa a a a a a a a a a a? a a a a a a a a a aDENSE SPT = 30 - 50 x ? a a a a a a a a aV. DENSE SPT > 50 x x a a a a a ? a a ?S < 100 mm x ? a a a a a a a a ?100-1000mm x x ? ? ? a a ? a a x1000-3000mm x x ? ? ? ? ? ? ? a x>3000mm x x ? ? ? ? ? ? ? a xa a a a a a a a a a ax a a a a a a a a a aa a ? ? ? ? ? a a a aPREVENTION OF EFFECTS ON ADJOINING? ? ? ? ? ? ? a ? a aSTRUCTURES(SUPPLY & INSTALL) RM/TON/M 0.5-2.5 0.3-2.01.0-3.5 1-2 0.5-2 1.5-3 1-2.5STEEL PIPE PILESJACKED PILESBORED PILESMICROPILESAUGERED PILES8x?INDICATES THAT THE PILE TYPE ISSUITABLEINDICATES THAT THE PILE TYPE ISNOT SUITABLEINDICATES THAT THE USE OF PILETYPE IS DOUBTFUL OR NOT COSTEFFECTIVE UNLESS ADDITIONALMEASURES TAKENFIG 2 : PILE SELECTION CHART

Site Visit and SI Planning

Site VisitThings To Look For …• Accessibility & Constraints of Site• Adjacent Structures/Slopes, Rivers,Boulders, etc• Adjacent Activities (eg excavation)• Confirm Topography & Site Conditions• Any Other Observations that may affectDesign and Construction of Foundation

Subsurface Investigation (SI)Planning• Provide Sufficient Boreholes to get Subsoil Profile• Collect Rock Samples for Strength Tests (eg UCT)• In-Situ Tests to get consistency of ground (eg SPT)• Classification Tests to Determine Soil TypeProfile• Soil Strength Tests (eg CIU)• Chemical Tests (eg Chlorine, Sulphate, etc)

Typical Cross-Section at Hill SiteHard Material LevelGround LevelVery Hard Material LevelBedrock LevelGroundwater Level

CROSS SECTIONBHEXISTINGGROUNDLEVELBHC’ 1, ø’ 1BHPerched WTClayey LayerC’ 2, ø’ 2SeepageC’ 3, ø’ 3Water Table

Placing Boreholes in LimestoneAreas• Stage 1 : Preliminary S.I.- Carry out geophysical survey (for large areas)• Stage 2: Detailed S.I.- Boreholes at Critical Areas Interpreted fromStage 1• Stage 3: During Construction- Rock Probing at Selected Columns tosupplement Stage 2

Pile Design

PILE DESIGNAllowable Pile Capacity is the minimum of :1) Allowable Structural Capacity2) Allowable Geotechnical Capacitya. Negative Skin Frictionb. Settlement Control

PILE DESIGNStructural consideration• Not overstressed during handling, installation & inservice for pile body, pile head, joint & shoe.• Dimension & alignment tolerances (commondefects?)• Compute the allowable load in soft soil (

Pile Capacity DesignStructural Capacity• Concrete PileQ all = 0.25 x f cu x A c• Steel PileQ all = 0.3 x f y x A sQ all= Allowable pilecapacityf cu= characteristic strengthof concretef s= yield strength of steelA c= cross sectional area ofconcreteA s= cross sectional area ofsteel• Prestressed Concrete PileQ all = 0.25 (f(cu – Prestress after loss) x A c

Pile Capacity DesignGeotechnical CapacityCollection of SI DataDepth (m)024681012141618Depth Vs SPT-N Blow Count0 50 100 150 200 250 300 350 400Upper Bound02468202224LowerBoundDesign Line(ModeratelyConservative)10260 50 100 150 200 250 300 350SPT Blow Count per 300mm Penetration40012

Pile Capacity DesignGeotechnical CapacityCollection of SI DataDepth Vs SPT-N Blow CountDepth Vs SPT-N Blow Count0 50 100 150 200 250 300 350 4000 50 100 150 200 250 300 350 400000022424266Depth (m)8101214Upper Bound46Depth (m)810121446161618202224LowerBoundDesign Line81018202224LowerBoundDesign LineUpper Bound810261226120 50 100 150 200 250 300 350 400SPT Blow Count per 300mm Penetration0 50 100 150 200 250 300 350 400SPT Blow Count per 300mm Penetration

Moderately ConservativeDesign Parameters• Eurocode 7 definition:– Characteristic value of a geotechnicalparameter shall be selected as a cautiousestimate of the value affecting the occurrenceof the limit state– In other words, moderately conservative

Moderately ConservativeDesign Parameters• If at least 10 test results are available:– A value of 0.5D below the mean of the testresults provides a useful indication of thecharacteristic value1. Contribution to Discussion Session 2.3, XIV ICSMFE, Hamburg, Balkema, Schneider H R (1997) – Definition anddetermination of characteristic soil properties. Discussion to ISSMFE Conference, Hamburg.2. Extracted from Prof. Brian Simpson’s Course Note (2-day Course on Eurocode 7 Geotechnical Design to EC7, 13-14November 2007, PJ, Malaysia).

Extracted from Prof. Brian Simpson’s Course Note (2-day Course on Eurocode 7 Geotechnical Design to EC7, 13-14November 2007, PJ, Malaysia).

Pile Capacity DesignGeotechnical Capacity• Piles installed in a group may fail:• Individually• As a block

Pile Capacity DesignGeotechnical Capacity• Piles fail individually• When installed at large spacing

Pile Capacity DesignGeotechnical Capacity• Piles fail as a block• When installed at close spacing

Pile Capacity DesignSingle Pile Capacity

Pile Capacity DesignFactor of Safety (FOS)Factor of Safety (FOS) is requiredfor•Natural variations in soil strength &compressibility

Pile Capacity DesignFactor of Safety (FOS)Factor of Safety is(FOS) required for• Different degree ofmobilisation for shaft& for tipLoadq smobq bmob≈ 5mmSettlement

Pile Capacity DesignFactor of Safety (FOS)Partial factors of safety for shaft & basecapacities respectively• For shaft, use 1.5 (typical)• For base, use 3.0 (typical)• QΣQ su + Q buall =1.5 3.0

Pile Capacity DesignFactor of Safety (FOS)Global factor of safety for total ultimatecapacity• Use 2.0 (typical)• Q all =ΣQ su + Q bu2.0

Pile Capacity DesignFactor of Safety (FOS)• Calculate using BOTH approaches(Partial & Global)• Choose the lower of the Q all values

Pile Capacity DesignSingle Pile CapacityQ u = Q s + Q bQ u= ultimate bearing capacityQ s= skin frictionQ b= end bearingOverburden Soil Layer

Pile Capacity DesignSingle Pile Capacity : In Cohesive SoilQ suQ buQ u = α.s us .A s + s ub .N c .A bQ u = Ultimate bearing capacity of the pilea = adhesion factor (see next slide)s us = average undrained shear strength for shaftA s = surface area of shafts ub = undrained shear strength at pile baseN c = bearing capacity factor (taken as 9.0)A b = cross sectional area of pile base

Pile Capacity DesignSingle Pile Capacity: In Cohesive SoilAdhesion factor (α)(– Shear strength (S u )(McClelland, 1974)1.00.8PreferredDesign Line0.6C α/S u0.4AdhesionFactor0.2025 50 75 100 125 150 175Su (kN/m 2 )

MeyerhofFukuokaSPT Nf su =2.5N(kPa)s u =(0.1+0.15N)*50(kPa)αf su =α.s u(kPa)0 0 5 1 51 2.5 12.5 1 12.55 12.5 42.5 0.7 29.7510 25 80 0.52 41.615 37.5 117.5 0.4 4720 50 155 0.33 51.1530 75 230 0.3 6940 100 305 0.3 91.5

Pile Capacity DesignSingle Pile Capacity: In Cohesive SoilCorrelation Between SPT N and f suf su vs SPT N110100908070fsu(kPa)60504030201000 5 10 15 20 25 30 35 40 45SPT NMeyerhofFukuoka

Pile Capacity DesignSingle Pile Capacity: In Cohesive Soil• Values of undrained shear strength, s u can beobtained from the following: Unconfined compressive test Field vane shear test Deduce based on Fukuoka’s Plot (minimum s u )Deduce from SPT-N values based on MeyerhofNOTE: Use only direct field data for shaft friction predictioninstead of Meyerhof

Pile Capacity DesignSingle Pile Capacity: In Cohesive SoilModified Meyerhof (1976):Ult. Shaft friction = Q su ≅ 2.5N (kPa)Ult. Toe capacity = Q bu ≅ 250N (kPa)or 9 s u (kPa)(Beware of base cleaning for bored piles –ignore base capacity if doubtful)

Pile Capacity DesignSingle Pile Capacity: In Cohesionless SoilModified Meyerhof (1976):• Ult. . Shaft Friction = Q su ≅ 2.0N (kPa(kPa)• Ult. . Toe Capacity= Q bu ≅ 250N – 400N(kPa)

Pile Capacity DesignLoad (kN)0 100 200 300 400 5000044ΣQ suDepth (m)812ΣQ su + Q bu1.5 3.016Q buΣQ su + Q buΣQ su + Q bu2.081216200 200 400 60020

Pile Capacity DesignSingle Pile Capacity: For Bored PilesSemi-empirical empirical Method (SPT-N)Shaft : f su = K su × SPT-NTip : f bu = K bu × SPT-NFrom Malaysian experience:K suK busu = 2.0bu = 7.0 to 60 (depending on workmanship)

Pile Capacity DesignSingle Pile Capacity: For Bored Piles• Base cleaning of bored piles– Difficult and no practical means of verificationduring construction avaliable• Base resistance require large movement tomobilise• Base contribution in bored pile designignored unless proper base cleaning can beassured and verified (or base grouting, etc.)

Rock Socket DesignRock Socket Design Factors :• Socket Roughness (Shearing Dilation)• Intact Rock UCS, q uc• Confining Stiffness (Rock mass fractures& Pile Diameter)• Socket Geometry RatioSocket Resistance, f s = α × β × q uc

α - Factor (after Tomlinson, 1995)

β - Factor (after Tomlinson, 1995)

Point Load Test(UCS of Intact Rock)

Load Transfer Profile of Rock Socket(after Pells & Tuner, 1979)

Summary of Rock Socket Friction DesignValues (updated from Tan & Chow, 2003)Rock Formation Working Rock Socket Friction* SourceLimestone 300kPa for RQD < 30%400kPa for RQD = 30 %500kPa for RQD =40 %600kPa for RQD =55 %700kPa for RQD =70 %800kPa for RQD > 85%The above design values are subject to 0.05xminimum of {q uc, f cu} whichever is smaller.AuthorsSandstone 0.10×q ucThorne (1977)Shale 0.05×q ucThorne (1977)Granite 1000 – 1500kPa for q uc> 30N/mm 2 Tan & Chow (2003)Where:RQD = Rock Quality Designationquc = Unconfined Compressive Strength of rockfcu = Concrete grade

End Bearing Design in RockOnly designed when• Dry Hole• Base Cleaning & Inspection are possible

Pile Capacity DesignBlock Capacity

Pile Capacity DesignBlock Capacity:In Cohesive SoilQ u = 2D(B+L) s + 1.3(s b .N c .B.L)WhereQ u = ultimate bearing capacity of pile groupD = depth of pile below pile cap levelB = width of pile groupL = length of pile groups = average cohesion of clay around groups b = cohesion of clay beneath groupN c = bearing capacity factor = 9.0(Refer to Text by Tomlinson, 1995)

Pile Capacity DesignBlock Capacity: In Cohesionless SoilNo risk of group failureif FOS of individual pile isadequate

Pile Capacity DesignBlock Capacity: On RockNo risk of block failureif the piles are properlyseated in the rockformation

Pile Capacity DesignNegative Skin Friction (NSF)

Pile Capacity DesignNegative Skin Friction• Compressible soil layer consolidateswith time due to:‣ Surcharge of fill‣ Lowering of groundwater table

Pile Capacity DesignNegative Skin FrictionOGLFillH fρ s01 2 3 MonthClay

Pile Capacity DesignNegative Skin FrictionPile to length (floating pile)‣ Pile settles with consolidating soil NO NSF

Pile Capacity DesignNegative Skin FrictionPile to set at hard stratum (end-bearing pile)‣ Consolidation causes downdrag forces onpiles as soil settles more than the pile

Design Considerations• Skin FrictionLoadOriginal Ground LevelSoil Settlement > Pile SettlementPositive SkinNegativeFrictionSkinFriction

Negative Skin FrictionLoadOriginal Ground LevelSoil Settlement > Pile SettlementNegative SkinFrictionEnd-BearingCrushing of Pile!!!

Negative Skin FrictionLoadLoadLoadOriginal Ground LevelSoil Settlement > Pile SettlementFriction Pile –Excessive Settlement

Negative Skin FrictionPile Settlement >Soil SettlementLoadLoadSoil Settlement > Pile SettlementNegativeLoadSkinFriction Pile –Positive SkinFrictionFrictionEnd-BearingPile –ExcessiveSettlementCrushing ofPile!!!

Pile Capacity DesignNegative Skin FrictionWARNING:‣ No free fill by the contractor to avoidNSF

Effect of NSF …Reduction of Pile Carrying Capacity

Effect of NSF …

NSF Preventive Measures• Avoid Filling• Carry Out Surcharging• Sleeve the Pile Shaft• Slip Coating• Reserve Structural Capacity for NSF• Allow for Larger Settlements

Pile Capacity DesignNegative Skin FrictionQ all = (Q su /1.5 + Q bu /3.0)Q all = (Q su /1.5 + Q bu /3.0) - Q negOGLSandFLOGLClayQ suClayQ negSandSandQ suQ baQ ba

0Pile Capacity DesignNegative Skin FrictionIncreased Pile Axial LoadCheck: maximum axial load < structural pileSPT-N (Blows/300mm)Settlement (mm)0 10 20 30 40 50capacity70 60 50 40 30 20 10 0Axial Compression Force (kN)100 0 -100 -200 -300-400-500-600 -700 -800 -900-1000510Depth (m, bgl)152025303540BoreholeBH-1BH-2Settlement Curves &Axial Compression Force14 May 9815 May 9818 May 9821 May 9804 Jun 9809 Jun 9819 Jun 9802 Jul 9813 Jul 98Datum = 36.300mMaximumaxial load

Pile Capacity DesignFactor of Safety (FOS)Without Negative Skin Friction:Allowable working loadQ ultFOSWith Negative Skin Friction:Allowable working loadQ ultFOS(Q neg + etc)

Pile Capacity DesignStatic Pile Load Test (Piles with NSF)• Specified Working Load (SWL) = Specified foundationload at pile head• Design Verification Load (DVL) = SWL + 2 Q neg• Proof Load: will not normally exceedDVL + SWL

Pile Settlement Design

Pile Settlement DesignIn Cohesive SoilDesign for total settlement &differential settlement for designtoleranceIn certain cases, total settlement not anissueDifferential settlement can causedamage to structures

Pile Settlement DesignIn Cohesive SoilPile Group Settlement in Clay=Immediate /Elastic Settlement+ConsolidationSettlement

IMMEDIATE SETTLEMENTWhereμ 1μ0qp =iEp i = average immediate settlementq n= pressure at base of equivalent raftB = width of the equivalent raftE u = deformation modulusPile Settlement DesignIn Cohesive SoilunBμ 1, μ 0 = influence factors for pile group width, B at depth Dbelow ground surfaceby Janbu, Bjerrum andKjaernsli (1956)

IMMEDIATE SETTLEMENTPile Settlement DesignIn Cohesive Soilμ 1μ 0Influence factors (afterJanbu, Bjerrum andKjaernsli, 1956)

Pile Settlement DesignIn Cohesive SoilCONSOLIDATION SETTLEMENTAs per footing (references given later)

Pile Settlement DesignOn RockNo risk of excessivesettlement

Pile Installation Methods

PILE INSTALLATIONMETHODS•Diesel / Hydraulic / Drop HammerDriving•Jacked-In•Prebore Then Drive•Prebore Then Jacked In•Cast-In-Situ Pile

Diesel Drop HammerDrivingHydraulic HammerDriving

Jacked-InPiling

Jacked-In Piling (Cont’d)

Cast-In-Situ In-SituPiles(Micropiles)

Types of Piles

TYPES OF PILES•Treated TimberPiles•Bakau Piles•R.C. Square Piles•Pre-StressedConcrete SpunPiles•Steel Piles•Boredpiles•Micropiles•Caisson Piles

R.C. Square Piles•Size : 150mm to 400mm•Lengths : 3m, 6m, 9m and 12m•Structural Capacity : 25Ton to 185Ton•Material : Grade 40MPa Concrete•Joints: Welded•Installation Method :–Drop Hammer–Jack-In

RCSquarePiles

Pile Marking

Pile Lifting

Pile Fitting to Piling Machine

PilePositioning

Pile Joining

Considerations in Using RCSquare Piles …•Pile Quality•Pile Handling Stresses•Driving Stresses•Tensile Stresses•Lateral Loads•Jointing

Pre-stressed Concrete SpunPiles•Size : 250mm to 1000mm•Lengths : 6m, 9m and 12m (Typical)•Structural Capacity : 45Ton to 520Ton•Material : Grade 60MPa & 80MPa Concrete•Joints: Welded•Installation Method :–Drop Hammer–Jack-In

Spun Piles

Spun Piles vs RC Square PilesSpun Piles have …•Better Bending Resistance•Higher Axial Capacity•Better Manufacturing Quality•Able to Sustain Higher Driving Stresses•Higher Tensile Capacity•Easier to Check Integrity of Pile•Similar cost as RC Square Piles

Steel H Piles•Size : 200mm to 400m•Lengths : 6m and 12m•Structural Capacity : 40Ton to 1,000Ton•Material : 250N/mm 2 to 410N/mm 2 Steel•Joints: Welded•Installation Method :–Hydraulic Hammer–Jack-In

Steel HPiles

Steel H Piles (Cont’d)

Steel H Piles Notes…•Corrosion Rate•Fatigue•OverDriving

OverDrivingof Steel Piles

Large Diameter Cast-InIn-SituPiles (Bored Piles)• Size : 450mm to 2m(Up to 3.0m for special case)• Lengths : Varies• Structural Capacity : 80Ton to 2,300Tons• Concrete Grade : 20MPa to 35MPa (Tremie)• Joints : None• Installation Method : Drill then Cast-In-Situ

DrillingBorepile ConstructionOverburden Soil LayerBedrock

Advance DrillingBorepile ConstructionOverburden Soil LayerBedrock

Drilling & AdvanceCasingBorepile ConstructionOverburden Soil LayerBedrock

Drill to BedrockBorepile ConstructionOverburden Soil LayerBedrock

LowerReinforcementCageBorepile ConstructionOverburden Soil LayerBedrock

Lower TremieChuteBorepile ConstructionOverburden Soil LayerBedrock

Pour TremieConcreteBorepile ConstructionOverburden Soil LayerBedrock

CompletedBorepileBorepile ConstructionOverburden Soil LayerBedrock

Bored Pile ConstructionBORED PILING MACHINEBG22

Cleaning BucketRock ReamerRock Auger

Rock ChiselHarden Steel

Bored Pile ConstructionDRILLING EQUIPMENTCleaningbucketCoringbucketSoil auger

Bored Pile ConstructionBENTONITE PLANTDesandingMachineWaterTankMixerSlurryTank

Drilling

LowerReinforcement

PlaceTremieConcrete

Completed Boredpile

Borepile Cosiderations…•Borepile Base Difficult to Clean•Bulging / Necking•Collapse of Sidewall•Dispute on Level of Weathered Rock

Micropiles•Size : 100mm to 350mm Diameter•Lengths : Varies•Structural Capacity : 20Ton to 250Ton•Material : Grade 25MPa to 35MPa Grout•Joints: None•Installation Method :N80 API Pipe as Reinforcement–Drill then Cast-In-Situ–Percussion Then Cast-In-Situ

Cast-InIn-SituPiles(Micropiles)

TYPES OF PILE SHOES•Flat Ended Shoe•Oslo Point•Cast-Iron Pointed Tip•Cross Fin Shoe•H-Section

Cross Fin ShoeDo more harm ininclined rock surface!

Oslo Point Shoe

Cast Iron Tip ShoeDo more harm ininclined rock surface!

H-Section ShoeDo more harm ininclined rock surface!

Piling Supervision

Uniform Building ByLaw (UBBL)1984

PILING SUPERVISION•Ensure That Piles Are Stacked Properly•Ensure that Piles are Vertical During Driving•Keep Proper Piling Records•Ensure Correct Pile Types and Sizes are Used•Ensure that Pile Joints are Properly Welded withNO GAPS•Ensure Use of Correct Hammer Weights and DropHeights

PILING SUPERVISION(Cont’d)•Ensure that Proper Types of Pile Shoes are Used.•Check Pile Quality•Ensure that the Piles are Driven to the RequiredLengths•Monitor Pile Driving

FAILURE OF PILINGSUPERVISIONFailing to Provide Proper SupervisionWILL Result inHigher Instances of Pile Damage& Wastage

Pile Damage

Driven concrete piles are vulnerableto damages by overdriving.

Damage to Timber Pile

Damage To RC Pile Toe

Damage toRC PileHead

Damage toRC Piles

Damage to RC Piles – cont’d

Damage to Steel Piles

Damaged Steel Pipe Piles

Piling Problems

Piling Problems – Soft Ground

Piling Problems – Soft GroundGround heave due topressure relief at base &surcharge nearexcavationPile tilts & moves/walks

Piling Problems – Soft Ground

Piling in Kuala Lumpur LimestoneImportant Points to Note:• Highly Irregular Bedrock Profile• Presence of Cavities & Solution Channels• Very Soft Soil Immediately Above LimestoneBedrockResults in …• High Rates of Pile Damage• High Bending Stresses

Piling Problems in Typical LimestoneBedrock

Piling Problems – UndetectedProblems

Piling Problems – Coastal Alluvium

Piling Problems – Defective PilesSeriously damagedpile due to severedriving stress in softground (tension)Defect due to poorworkmanship of pilecasting

Piling Problems – Defective PilesDefective pile shoeProblems ofdefective pile head& overdriving!

Piling Problems – Defective PilesNonchamferedcornersCracks&fractured

Piling Problems – Defective PilesPile head defect due tohard driving or and poorworkmanship

Piling Problem - MicropilesSinkholes caused byinstallation methoddewatering?

Piling in Fill GroundImportant Points to Note:•High Consolidation Settlements If Original Ground isSoft•Uneven Settlement Due to Uneven Fill Thickness•Collapse Settlement of Fill Layer If Not CompactedProperlyResults in …•Negative Skin Friction (NSF) & Crushing of Pile Dueto High Compressive Stresses•Uneven Settlements

Typical Design andConstruction Issues #1Issue #1Pile Toe Slippage Due to Steep Incline BedrockSolution #1Use Oslo Point Shoe To Minimize Pile Damage

Pile Breakage on InclinedRock SurfaceNo Proper PileShoe

PileJointExtension Pile

First ContactB/W Toe andInclined Rock

Pile Joint BreaksPile Body BendsToe “Kicked Off”on Driving

Pile Breakage on InclinedRock SurfaceContinue“Sliding” ofToe

Use Oslo Point Shoe to MinimizeDamage

Design and ConstructionIssues #2Issue #2Presence of CavitySolution #2Detect Cavities through Cavity Probing thenperform Compaction Grouting

Presence of CavityPile Sitting onLimestonewith Cavity

Application ofBuilding Load

Application ofBuilding LoadRoof of Cavitystarts to Crack …

Building CollapsePile Plunges !Collapse ofCavity Roof

Design and ConstructionIssues #3Issue #3Differential SettlementSolution #3Carry out analyses to check the settlementcompatibility if different piling system is adopted

Differential Settlement of FoundationLinkSAFETYHouseofConstructionOriginal BuildingNot CompromisedSoftLayerOriginal Houseon PilesPiling in ProgressNo SettlementPilestransferLoad toHardLayerNopileCracks!!Renovation:ConstructExtensionsSettlementHard LayerSPT>50

Eliminate Differential SettlementConstructExtension withSuitable PilesPiling in ProgressSoftLayerAll Load transferred to HardLayer – No Cracks!Hard LayerSPT>50

Problem of Short PilesCracks!!Piling in ProgressConstructExtensionswith ShortPilesSoftLayerSoft!Loadtransferred toSoft Layer,Extensionstill SettlesLoad from Original Housetransferred to Hard LayerHard LayerSPT>50

Cracks at Extension

Typical Design andConstruction Issues #4Issue #4Costly conventional piling design – piled to set todeep layer in soft groundSolution #4-Strip footings / Raft-Floating Piles

“Conventional” Foundation forLow Rise Buildings

Foundation forLow Rise Buildings (Soil Settlement)

Settling Platform Detached from BuildingSettlementExposed Pile

Conceptual Design ofFOUNDATION SYSTEM1. Low Rise Buildings :-(Double-Storey Houses)= Strip Footings or Raft orCombination.2. Medium Rise Buildings :-= Floating Piles System.

Low Rise Buildings onPiled Raft/StripsFill25-30mSoft ClayStrip / RaftSystemStiffStratumHard Layer

ComparisonBuilding on PilesBuilding on Piled StripsFill25-30mSoft ClayStripSystemStiffStratumHard Layer

Comparison (after settlement)Building on PilesBuilding on Piled StripsFill25-30mSoft ClayStripSystemStiffStratumHard Layer

Advantages ofFloating Piles System1. Cost Effective.2. No Downdrag problems on thePiles.3. Insignificant DifferentialSettlement between Buildings andPlatform.

Bandar Botanic

Bandar Botanic at Night

Soft Ground Engineering

Issue #5Typical Design andConstruction Issues #5Load test results far below predicted pile capacitySolution #5-Modifications to test set-up-Change of pile installation method-Adequate soil plug to prevent toe softening

Testing Set-up Using ReactionPiles

Testing Set-up• Long reaction piles at close spacingused• Case histories:– Load tests using reaction piles giveERRATIC results– Reference: Weele (1993)

Ref: A.F.van Weele,1993Testedusinganchorpiles≈ 1100kN≈ 2100kNTestedusingkentledgeApprox. 2timessmallerusingreactionpiles!

ReactionpilesZone ofinteractionwith testpileTestpile

Testing Set-up• Latest version of ASTM D1143• Published April 2007

Testing Set-up• ASTM D1143– Clear distance of at least 5 timesthe maximum diameter– Caution on factors influencingresults:•“Possible interaction ……….fromanchor piles……..”

Drilling to the Casing Tipto Form “Bored Pile”

Drilling to Form “Bored Pile”• Disturbance to soil at tip andsurrounding the pile• Potential hydraulic/basal heavefailure resulting in lower soil strength• Effect more severe for longer pile

Construction of “Bored Pile”1. Install Permanent SteelCasing to Pile Toe2. Removal of Soil within SteelCasing to Toe of Casing3. Installation ofReinforcement andConcreting

Drilling to Form “Bored Pile”• Pile behaviour COMPLICATED!– Influenced by steel casing which behavelike DRIVEN PILE– Influenced by soil removal which behavelike BORED PILE

SANDUPHEAVALAFTER 3HRS

Zone of Weakened Soil due toInstallation of Steel Casing usingVibro-hammerFurther Soil Disturbance –Magnitude of Disturbance?????PressurefromDrillingFluidPressure fromSoil + Water>Pressure fromDrilling FluidPressure fromSoil + Water

• Probable causes of erratic andunpredictable pile capacities:– Testing set-up using reaction piles– Drilling to the casing tip to form “bored pile”

Original Load Test– 1 st Load Test – Failed at 90% of WL• After 32 days– 2 nd Load Test – Failed at 110% of WL• After 94 days

• Recommendations:– Open-ended spun pile or steel pipe pile withadequate soil plug– Use of impact hammer instead of vibrohammer– Trial piles for correlation between static loadtest and high strain dynamic load test

Result forEmptyCasingResult forConcretedPileSettlement at 1WL = 12.5mmPile performssatisfactorilywithinacceptablesettlementlimits!!!

Load Test Results at P52W– Result for Empty Casing•1xWL: pile settlement= 20mm(residual settlement= 1mm)•1.9xWL: pile settlement= 50mm(residual settlement= 3mm)– Result for Cast Pile•1xWL: pile settlement= 12.5mm(residual settlement= 1mm)•2xWL: pile settlement= 33.4mm(residual settlement= 7mm)The Pile isStiffer afterConcreting !!Larger ResidualSettlement due toDisturbance fromRCD work !!

Load Test Results at P52W– Research by Ng et al., 2001:•Elastic compression of large diameter boredpiles:–½ PL/AE - Piles founded in soil–¾ PL/AE - Piles founded in rocks

Piles founded inSOIL: ½ PL/AEPiles founded inROCK: 3/4 PL/AEResult forConcreted PileSettlementis inaccordancetoprediction!!

ELASTIC COMPRESSION OF PILE• Depends on:– E – Elastic Modulus of Pile Material– A – Cross-sectional Area of Pile– L – Pile LengthElastic Compression = f (PL / AE)Therefore, after concreting of pile:- A increased significantly (composite E due tosteel and concrete reduced slightly)- Elastic compression will reduce

Pile Settlement Criteria• Pile settlement criteria depends on– Pile Size– Pile Material (e.g. steel, concrete, etc.)– Pile Length• Unrealistic to adopt same settlementcriteria (e.g. 12mm) for all piles (regardlessof length, size, etc.)

Myths in Piling

MYTHS IN PILING #1Myth:Dynamic Formulae such as Hiley’s FormulaTells us the Capacity of the PileTruth:Pile Capacity can only be verified by using:(i) Maintained (Static) Load Tests(ii)Pile Dynamic Analyser (PDA) Tests

MYTHS IN PILING #2Myth:Pile Achieves Capacity When It is Set.Truth:Pile May Only “Set” on Intermediate HardLayer BUT May Still Not Achieve RequiredCapacity within Allowable Settlement.

MYTHS IN PILING #3Myth:Pile settlement at 2 times working load mustbe less than certain magnitude (e.g. 38mm)Truth:Pile designed to Factor of Safety of 2.0.Therefore, at 2 times working load:Pile expected to fail unless capacity underpredictedsignificantly

Pile Capacity DesignFactor of Safety (FOS)Global factor of safety for total ultimatecapacity• Use 2.0 (typical)• Q all =ΣQ su + Q bu2.0

CASE HISTORIES• Case 1: Structural distortion & distresses• Case 2: Distresses at houses

CASE HISTORY 1Distortion & Distresses on 40Single/ 70 Double Storey Houses• Max. 20m Bouldery Fill onUndulating Terrain• Platform Settlement• Short Piling Problems• Downdrag on Piles

Distresses on Structures

Void

Reduced Level (m )706050403020Offset 36.2mOffset 13.1mN=30N=5N=25 ?N=29 ? ??Profile with SPT 'N'>50? ???Piling Contractor AOffset 13.1mN=40Profile with SPT 'N'≅30???Offset 13.1m?N=34OriginalGround ProfileFilled groundOriginal GroundHard StratumBoreholePile ToePile Toe of AdditionalPilesBuildingPlatform0 40000 80000 120000 160000 200000Coordinate-X (mm)

80PilingContractor APiling Contractor BR e d uced Level (m )7060504030N=30N=5N=29?Offset 9.1mProfile with SPT 'N'≅30? ???N=34N=28N=41Profile with SPT 'N'>50Offset 9.1mOriginal Ground ProfileBuilding PlatformFilled groundOriginal GroundHard StratumBoreholePile ToePile Toe of AdditionalPiles0 40000 80000 120000 160000 200000Coordinate-X (mm)

Prevention Measures• Design:– Consider downdrag in foundation design– Alternative strip system• Construction:– Proper QA/QC– Supervision

CASE HISTORY 2Distresses on 12 Double StoreyHouses & 42 Townhouses• Filled ground: platform settlement• Design problem: non-suspended floorwith semi-suspended detailing• Bad earthwork & layout design• Short piling problem

Diagonal cracks dueto differentialsettlement betweencolumnsLarger columnsettlement

SaggingGroundFloor Slab

SAGGING PROFILE OF NON-SUSPENDED GROUND FLOOR SLABNON-SUSPENDED GROUND FLOORSLAB BEFORE SETTLEMENTV e > V cρ sV cV c < V ePILEPILECAPBUILDING PLATFORM PROFILE AFTERSETTLEMENTρ sACTUAL FILLED PLATFORM SETTLEMENT

Distorted Car Porch Roof

Poor Earthwork LayoutSilt trapBLOCK 2BLOCK 1Temporaryearth drain

Prevention Measures• Planning:– Proper building layout planning to suit terrain(eg. uniform fill thickness)– Sufficient SI• Design:– Consider filled platform settlement– Earthwork layout• Construction:– Supervision on earthwork & piling

SUMMARY• Importance of Preliminary Study• Understanding the Site Geology• Carry out Proper Subsurface Investigationthat Suits the Terrain & Subsoil• Selection of Suitable Pile• Pile Design Concepts

SUMMARY• Importance of Piling Supervision• Typical Piling Problems Encountered• Present Some Case Histories

FERRARI ‘S PITSTOP WAS COMPLETED BY15 MECHANICS (FUEL AND TYRES) IN 6.0SECONDS FLAT.54 PEOPLE TOOK PART IN THISCONCERTED ACROBATIC JUMP.