Dubai Tower Piled Raft Foundation

Transcription

1 Advances in 3D Geotechnical Analysis, 14 February 2007, I.Struct.E., London Dubai Tower Piled Raft Foundation Catherine Murrells Hyder Consulting Olivier Gastebled TNO DIANA

2 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 Introduction 2

3 Dubai Tower 3 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

4 Why 3D FE Analysis Tall Heavily Loaded Structure Wind Seismic Large Pile Group Complex Geometry 4

5 Why 3D FE Analysis 5

6 Why 3D FE Analysis Tall Heavily Loaded Structure Large Pile Group Complex Geometry Model Raft Contribution Model Superstructure Effect Non-Linear Analysis 6

7 Fill and Marine Deposits Simsima Limestone Midra Shale Geology Rus Chalk and Limestone Um Err Radhuma Limestone 7

8 Selection of Parameters 10 Installation of Boreholes 9 Simsima Limestone Standard In-Situ and Laboratory Testing Pressuremeter Testing Geophysics Stress (MPa) Midra Shale Upper Rus Specialist Laboratory Testing 2 1 Lower Rus Preliminary Trial Pile Testing Strain 8

9 Single pile test: calibration Calibration against single pile test 9 Aim: calibrate the maximum friction force/length to be adopted for pile-ground interface. Experimental data: Load-settlement curve from single pile test Single pile model: same FE technique as in foundation model Conclusion: max. friction force = 1667 kn/m Good fit between model and site data Axial Force Relative Disp.

10 Dubai Tower FE Model Model components: 6 ground layers Podium slab Tower raft Lift pit 5 basement levels (slabs + walls) 191 piles 10 Statistics: 53,510 nodes = 150,000 DOF 2,761 beam elements 2,422 interface elements 191 spring elements 9,533 plate elements 89,122 solid elements

11 FE Model Characteristics 11 Elements Ground: 3D linear pentahedron elements (wedges) Rafts and superstructure slabs: linear triangular flat shells Superstructure columns: 2 noded beam elements Piles: embedded piles, i.e. beam + line-to to-solid interface elements + tip plastic spring Material models Structural elements: linear elasticity Ground: Tresca plasticity Pile-ground interface: non-linear elasticity, max. friction force/m Statistics: 1 non-linear analysis in 10 load steps (per load combination) PC specs: 3.6 GHz CPU, 8 GB RAM run time = 5 h

12 Pile modeling 3D view Superstructures Tower and podium rafts Node-to-node pile-raft connection Lift pit 191 piles connected to ground by interface elements Side view Piles and ground layers 12

13 Birdseye view from above 13 Load cases Birdseye view from beneath Tower loads: Dead loads Live loads Wind load Applied on GL slab Hydrostatic pressure uplift under rafts Podium loads: Dead loads Live loads Applied at column locations

14 Settlement results 3D view quarter cut Top view Max. settlement 9 cm 14 Vertical slice

15 Pile Forces Axial Forces Lift pit Bending Moments Lift pit 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 15

16 Ground stress increase Vertical stress change (kpa) 16 Main phenomena: Larger stress increase under deeper pile groups (+600 kpa) Zero stress change at the centre of the pile scheme

17 Use of FE Results in Design Piles grouped according to loading and design loads assigned Appropriate factors of safety applied 17 Deflected shape used to calibrate structural model

18 Comparison 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 18

19 Benefits 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 19

20 Conclusions 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? 20