COFFEY GEOTECHNICS

Challenging Design: Foundations for Tall BuildingsHelen Chow & Frances Badelow

COFFEY GEOTECHNICS

Introduction

• SuperTalls – 300m+• Challenging Task - Use

innovative design approaches• Innovative and Cost effective

foundation – Piled Raft83502411

680

550

236

13370

281611110

100

200

300

400

500

600

700

800

900

1940 1950 1960 1970 1980 1990 2000 2010 2012

Year

No. o

f Bui

ldin

gs

200m+

300m+

Data from Council on Tall Buildings and Urban Habitat

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Design ProcessPhase 1 – Subsurface Exploration

• Desktop study

• Site specific geotechnical investigation

•In-situ and laboratory testing

Phase 2 – Foundation Design

• Develop geotechnical models and parameters

• Preliminary foundation design

• Refine design

• Detailed design• Foundation Performance• Retention System• Seismic Assessment• Impacts on adjacent properties

Phase 3 – Foundation Testing and Monitoring

• Pile Load Test

• Performance Monitoring

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Foundation PerformanceOverall Stability • Ultimate load combinations

applied• Ultimate pile capacities

reduced by • Condition satisfied if

foundation system does not collapse

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Foundation PerformanceFoundation Settlement• Working load applied• Foundation resistance and stiffness unfactored• Condition satisfied if settlement and angular rotation within

allowable limits

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Incheon 151 Tower, Korea• Located in Songdo, South

Korea• 151 Storeys High (Height =

601m)• 8.5m Deep Basements• Geotechnical designer –

Coffey & Jin-Young ENC• Structural designer –

Thornton Tomasetti• Architect – John Portman

& Associates

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~ 30m

~ 20m

Incheon 151 TowerGround Conditions

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Incheon 151 Tower

• Ground Conditions– Divided into 8 Zones

Ground Conditions

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Foundation Layout: Raft thickness: 5.5m thick embedded into UMD• 172 piles @ 2.5m diameter• Lengths: 36m to 66m (2 x pile diameters socket length)

Challenges:• Variation in Ground Conditions• Interaction of Pile Group• Lateral Stability

Incheon 151 Tower

88m

77.5m

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PLAXIS 3D - Vertical Loading

200m

200m

100m

Incheon 151 Tower

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Incheon 151 Tower

PLAXIS 3DGARP – Overall Settlement = 0.067m

Differential Settlement = 1/2600

Angular Distortion = 0.07°

Settlement of Foundation

600m

Foundation

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Incheon TowerHorizontal Loading • Critical Issue due to high wind load

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Nakheel Tall Tower, Dubai

Nakheel IncheonBurj Dubai

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Nakheel Tall Tower• More than 200 Storeys High (Height > 1000m)• Centre piece of Nakheel Harbour• Ground Conditions

Sand20m

<2.5m Gypsum

>75mCemented Carbonate Siltstone

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Nakheel Tall Tower• Ground Conditions

– Compressibility controlled by Bond Yield Strength– Imposed Stress < Bond Yield Strength

• Very Stiff Material

Strain, e

Stre

ss, s

Bond yield strength

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Nakheel Tall Tower

Foundation Layout:

• Raft thickness: varies up to 8m• 392 Barrettes –2.8m x 1.2m

2.8m x 1.5m • Lengths: 37m , 42m & 72m

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Nakheel Tall Tower• Geotechnical Peer Review

– Review Geotechnical Designers’ Report and Design Method

– Independent Foundation Analyses • Overall Stability • Settlement < 0.1m

1000m

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Conclusion• Good Understanding of Ground Conditions• Critical Issue – Horizontal Loads• Good Communication between Structural and

Geotechnical Engineers

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Thank You