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Dubai Tower Piled Dubai Tower Piled Raft FoundationRaft FoundationCatherine Murrells Catherine Murrells –– Hyder ConsultingHyder ConsultingOlivier Gastebled Olivier Gastebled –– TNO DIANATNO DIANA

Advances in 3D Geotechnical Analysis, 14 February 2007, I.Struct.E., London

www.midas-diana.com2

• Dubai Tower Overview

• Why 3D Finite Element Analysis

• Geology and Selection of Parameters

• Midas GTS Model

• Comparison with Other Analyses

• Benefits of 3D Finite Element Analysis

• Conclusions

IntroductionIntroduction


Dubai TowerDubai Tower

•• Located in Doha, Qatar

• 80 Storey Tower

• Piled Raft Foundation

• Parties Involved• Client: Sama Dubai Developers

• Architect and Structural Engineer: Robert Matthew, Johnson-Marshall

• Structural and Geotechnical Engineers: Hyder Consulting

• 3D Geotechnical FE Modelers: TNO DIANA

• Peer Reviewer: Coffey Geotechnics


Why 3D FE AnalysisWhy 3D FE Analysis

•• Tall Heavily Loaded Structure

• Wind

• Seismic

• Large Pile Group

• Complex Geometry



•• Tall Heavily Loaded Structure

• Large Pile Group

• Complex Geometry

• Model Raft Contribution

• Model Superstructure Effect

• Non-Linear Analysis


GeologyGeologyFill and Marine

Deposits

Simsima Limestone

Midra Shale

Rus Chalk and Limestone

Um Err Radhuma Limestone


Selection of ParametersSelection of Parameters

••Installation of BoreholesInstallation of Boreholes

••Standard InStandard In--Situ and Situ and Laboratory TestingLaboratory Testing

••Pressuremeter TestingPressuremeter Testing

••GeophysicsGeophysics

••Specialist Laboratory Specialist Laboratory TestingTesting

••Preliminary Trial Pile Preliminary Trial Pile TestingTesting

0

1

2

3

4

5

6

7

8

9

10

0 0.1 0.2 0.3

Strain

Stre

ss (M

Pa)

Simsima Limestone

Midra Shale Upper Rus

Lower Rus


Single pile test: calibrationSingle pile test: calibration•• Calibration against Calibration against

single pile testsingle pile test•• Aim:Aim: calibrate the maximum friction force/length to be adopted for pile-ground interface.

• Experimental data: Experimental data: Load-settlement curve from single pile test

• Single pile model: Single pile model: same FE technique as in foundation model

•• Conclusion:Conclusion:• max. friction force = 1667 kN/m1667 kN/m• Good fit between model Good fit between model

and site dataand site data

AxialForce

RelativeDisp.


Dubai Tower FE ModelDubai Tower FE Model•• Model components:Model components:

•• 6 ground layers• Podium slab• Tower raft• Lift pit• 5 basement levels (slabs + walls)• 191 piles

•• Statistics:Statistics:• 53,510 nodes = 150,000 DOF53,510 nodes = 150,000 DOF• 2,761 beam elements• 2,422 interface elements• 191 spring elements• 9,533 plate elements• 89,122 solid elements


FE Model CharacteristicsFE Model Characteristics•• ElementsElements

• Ground: 3D linear pentahedron elements (wedges)3D linear pentahedron elements (wedges)• Rafts and superstructure slabs: linear triangular flat shellslinear triangular flat shells• Superstructure columns: 2 noded beam elements2 noded beam elements• Piles: embedded piles, embedded piles,

i.e. beam + linei.e. beam + line--toto--solid interface elements + tip plastic springsolid interface elements + tip plastic spring

•• Material modelsMaterial models• Structural elements: linear elasticitylinear elasticity• Ground: Tresca plasticityTresca plasticity• Pile-ground interface: nonnon--linear elasticity, max. friction force/mlinear elasticity, max. friction force/m

•• Statistics:Statistics:• 1 non-linear analysis in 10 load steps (per load combination)• PC specs: 3.6 GHz CPU, 8 GB RAM• run time = 5 hrun time = 5 h


Pile modelingPile modeling

Superstructures

Tower and podium rafts

191 piles connected to ground by interface elements

Node-to-node pile-raft connection

Side viewSide viewPiles and ground layers

Lift pit

3D view3D view


Load casesLoad cases•• Tower loads:Tower loads:

•• Dead loads• Live loads• Wind load•• Applied on GL slabApplied on GL slab

•• Hydrostatic pressureHydrostatic pressure• uplift under rafts

•• Podium loads:Podium loads:•• Dead loads• Live loads•• Applied at columnApplied at columnlocationslocations

Birdseye viewfrom above

Birdseye viewfrom beneath


Settlement resultsSettlement results

3D view 3D view –– quarter cutquarter cut Top viewTop view

Vertical sliceVertical slice

Max. settlementMax. settlement9 cm9 cm


Pile ForcesPile ForcesAxial ForcesAxial Forces Bending MomentsBending Moments

Lift pit Lift pit

Factors influencing distribution of pile forces:Factors influencing distribution of pile forces:• group effect, proximity of piles of different length• proximity of stiff lift pit structure• relative stiffness of ground layers


Ground stress increaseGround stress increase

Vertical stress change (kPa)Vertical stress change (kPa)

Main phenomena:Main phenomena:• Larger stress increase under deeper pile groups (+600 kPa)• Zero stress change at the centre of the pile scheme


Use of FE Results in DesignUse of FE Results in Design

•• Piles grouped according to loading and Piles grouped according to loading and design loads assigneddesign loads assigned

•• Appropriate factors of safety appliedAppropriate factors of safety applied

• Deflected shape used to calibrate structural model


Comparison of ResultsComparison of Results

•• Validation of settlements from:• Standard pile group analyses (REPUTE, PIGLET)

• Equivalent raft assessment (VDISP)

•• Validation of pile loads from:• Structural analysis

•Overall block failure was checked


Benefits of 3D FE AnalysisBenefits of 3D FE Analysis

•• Cost for Dubai Tower• 20% Raft Contribution

• 20% Reduction in Pile Length

• £400k Cost Saving for Dubai Tower

•• More realistic model of foundation

• Drawback – Extension of Programme


ConclusionsConclusions

•• Dubai Tower piled-raft foundation modeled in midas GTS with new 3D pile feature

• Contribution of the Raft and Structure included

• Results validated using other methods

• Depending on geology pile cost can be reduced

• Adequate information for geotechnical parameters has to be obtained

Further questions?

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