Pile design

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qz curve

Lecture #5Pile design


Bearing capacity of a single pile> load settlement curveREALF [kN]IDEALIZEDF [kN]~0.02DTotalTotals[cm]Shaft resistanceTip resistance~0.1Ds [cm]Shaft resistanceTip resistance


Pile design > Settlement of pile groups> Settlement of a single pile~0.02D~0.1Ds [cm]F [kN]TotalTip resistanceShaft resistanceq-z curve:describes the relationship ofbase resistance & displacementconsequentlyo the mobilized base resistance is afunction of settlemento the ultimate bas resistance develops ata certain settlementt-z curve:describes the relationship ofshaft resistance & displacementconsequentlyo the mobilized shaft resistance is afunction of settlemento the ultimate shaft resistance develops ata certain settlement


Pile design > Settlement of pile groups> q-z & t-z curves for simplified designSHAFT RESISTANCEt-z curveUnit shaft resistanceBASE RESISTANCEq-z curveUnit base resistanceq smaxq bmaxD*Displacement between pileshaft and the surrounding soilD**Displacement between pileshaft and the surrounding soilBored & CFA pilesSoil displ. pilesD* 0.015÷0.03 · D 0.01÷0.015 · DBored & CFA pilesSoil displ. pilesD** ~0.1 · D ~0.05 · D


Pile design> Settlement of pile groups


Pile design> Settlement of pile groupsRS total =S single + S groupHS single : using t-z andq-z curvespB2Dm 0S group = pm 0 /2E sE S


Pile design > steps of design Caculation of design load acting on pilecap; Choosing the type, number anddisitribution of piles; Calculation of design load of a single pile; Calculation of pile length; Estimation of pile group settlement; Modifying pile distribution or number ifneccesary.


Pile design > Design conceptsEND BEARING PILESFRICTION PILESat least 2/3 of totalcapacity is provided bybase resistance;Spacing• displacement piles: t ≥ 3D• replacement piles:t ≥ 2.5D• recommended maximumdistance: 5DF group = n F pileThe bearing capacity ofunderlying weakerlayers must be checked.at least 2/3 of totalcapacity is provided byshaft resistance;Spacing• t ≥ 3D• recommended maximumdistance: 5DF group < n F pileShall not be used insoft claysShall not be used incase of large areabuildings


Pile design > Piled raft


Pile design> Piled raft


Pile design > Piled raftGeneral idea:The large surface of the slabprovides the required bearingcapacityBUTMobilizing this resistance requires(unacceptably) large deformation(settlements)SOPiles are used as settlementreducers (they take only a certainpart of the load)Guidelines for design:If the distrance between the pilesis larger than ~5 times thediameter of the piles (t>5D), thegroup effect will becomeneglectible.The larger the pile distance (=theless the pile number), the largerthe required slab thickness andthe larger settlements.OPTIMAZITAION IS NEEDED


Pile design > Piled raft


Pile design > Laterally loaded piles


Pile design > Laterally loaded pilesFree headFixed headShort pile(L/R < 2) E IR k h0.25Long pile(L/R > 4)


Pile design >Laterally loaded piles> Short pilesCohesive soils:Cohesionless soils:


Pile design >Laterally loaded piles> Long pilesCohesive soils:Cohesionless soils:


Laterally loaded piles > Ultimate horizontal resistance> Cohesionless soils & short pile (Broms, 1964)


Laterally loaded piles > Ultimate horizontal resistance> Cohesionless soils & long pile (Broms, 1964)


Laterally loaded piles > Ultimate horizontal resistance> Cohesive soils & short pile (Broms, 1964)


Laterally loaded piles > Ultimate horizontal resistance> Cohesive soils & long pile (Broms, 1964)


Laterally loaded piles > p-y curve


Laterally loaded piles > p-y curveNonlinear behaviourLinear behaviourSubgrade reactionk h = p/yRepresentative values of k h (after Analysis and design odshallow and deep foundation, 2006. Reese et al.)Soil type k h [MN/m 3 ]Clay (c u =50-100 kPa) ~135Clay (c u =200-300 kPa) ~270Clay (c u =300-400 kPa) ~540Loose sand (submerged) ~5.4Medium sand (subm.) ~16.3Dense sand (subm.) ~34Loose sand (above GWL) ~6.8Medium sand (above GWL) ~24.4Dense sand (above GWL) ~61


Laterally loaded piles > p-y curveThe subgrade reaction depends on depth:kxkhxLnwherek xk hxLn0.is the subgrade reaction at depth „x”is the subgrade reaction at the pile tipis the depth below ground surfaceis the pile lengthis a coefficient equal to or larger thanGenerally n=1 is used, but previousexperiences have shown:for sands n>1for clays n2) n=0


Pile design > Footing beamsSuperstructureFootingbeamPile foundations


Pile cap construction > soil excavation


Pile cap construction > forming bottomlevel


Pile cap construction > formwork


Pile cap construction > reinforcement


Pile cap construction > completed pile cap


Mid-term questions1. Types of precast piles, installation techniques.2. Types and installation techniques of screw piles.3. Types of soil replacement piles, excavation techniques, support of the drill hole.4. Piling technique of CFA piles.5. Micro piles.6. Jet-grouting.7. Vibro replacement technique.8. Construction sequences of diaphragm (slurry) walls.9. Advantages and limitations of diaphragm walls.10. Caisson foundation.11. Well foundation.12. Components of pile capacity, pile types based on load transfer.13. Pile load test types, determination (prediction) of pile capacity based on theresults.14. Estimation of pile capacity based on laboratory test results.15. Estimation of pile capacity based on in-situ test results.16. Steps of pile design17. Settlement of single piles and pile groups.18. Laterally loaded piles, design based on p-y curves.

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