Advances in Design and Practice for Combined Pile-Raft ... · Soil Classification for Seismic...

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by

Prof. Deepankar Choudhury, PhD

Humboldt Fellow, JSPS Fellow, BOYSCAST Fellow, TWAS-VS Fellow

Professor, Dept. of Civil Engg., IIT Bombay, Mumbai, India.Also, Adjunct Professor, Academy of CSIR (AcSIR), New Delhi, India.

Advances in Design and Practice for Combined Pile-Raft Foundation (CPRF)

under Earthquake Conditions

Lecture at Conference of IAStructE, New Delhi on 7th December, 2016

Deepankar Choudhury, IIT Bombay, India

* PhD Scholars : Mr. Ashutosh Kumar, Dr. KaustavChatterjee, Dr. V. S. Phanikanth, Mr. Milind Patil, Ms. SujathaManoj.

* Collaborators : Prof. Rolf Katzenbach, TU Darmstadt,Germany; Prof. Harry Poulos, Australia.

* Funding Agencies: British Petroleum, UK; Alexander vonHumboldt Foundation, Germany; ThyssenKrupp Pvt. Ltd.,Germany, NPCIL, India, Chemie-Tech. Pvt. Ltd., India.

* Society/Code Committee: ISSMGE TC 212 - DeepFoundations , International Building Code (IBC-1803), USA

Acknowledgements

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Glory of Deep Foundations

7 December 2016

Burj Khalifa, Dubai

Poulos and Bunce (2008)

Introduction - Super Tall Towers

ongoing construction boom - supertall towers of 200 to 600 m

- 800 to 1000m tall vertical cities

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Future of Deep Foundations

7 December 2016

Proposed Kingdom Tower, 1001 m, Jeddah

Katzenbach, Choudhury and Chang (2013)

Foundation system of World’s Tallest (1001m) Building at Jeddah

Foundation raft (4.5 m thick)

Piles (45 m long)

Piles (65 m long)

Katzenbach, Choudhury and Chang (2013)

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Concept of Combined Pile-Raft Foundation (CPRF)

Skin friction Pile

Foundations

Raft foundation Deep (Pile) foundation Combined Pile-Raft Foundation (CPRF)

Base pressure

INTRODUCTION to CPRF

Piled raft foundation(also called composite foundation)solve:

1. Settlement – through interaction and load sharing.2. Differential settlement – raft provide stiffness

against load.3. Economical - reducing number of piles.

Poulos et al. (2001) has examined a number ofidealized soil profiles, and found that soil profilesconsisting of relatively stiff clays and relativelydense sands may be favourable for piled raftfoundation.

Construction: 1988 - 1990

Foundation: CPRF

Height: 256 m Messeturm tower, Germany

(Katzenbach et al. 2005)8

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• CPRF (Composite foundation ) – shallow(raft) + Deep(pile) foundation

• Cost optimized solution for the foundations of HIGH RISE BUILDINGS

• Reduces settlement(through soil- structure interaction)

• Reduces differential settlement (raft provide stiffness against load)

D. Choudhury, IIT Bombay, India

ISSMGE CPRF guideline by TC 212 – Deep Foundation, 2013

INTRODUCTION to CPRF

→ → Combined Pile-Raft Foundation (CPRF) Katzenbach et al. (2009)

Settlements calculated for a shallow foundation:s > 40 cmz = 0 - 20 m → 75 - 80 %

Messeturm · Frankfurt am Main, Germany

Settlements:


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Accomplished: CPRF of 64 piles (laverage = 30 m)

Costs of pile production: 64 piles of 30 m at 780 US$/m 1.5 Mio. US$

Pile foundation: 316 piles (l = 30 m)

Costs of pile production: 316 piles of 30 m at 780 US$/m 7.4 Mio. US$

Savings in costs of pile production 5.9 Mio. US$

Comparison of costs for the piles


Katzenbach and Choudhury (2011)

International Design Guideline for CPRF –by ISSMGE TC 212 – Deep Foundations (2013)

7 December 2016Eds. Katzenbach and Choudhury (2013)

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dydxy,x,s)s(R k,raft

m

1jk,raftj,k,pilek,tot sRsRsR

sRsRsR j,k,sj,k,bj,k,pile

Total resistance of the CPRF:

Pile resistance:

Raft resistance:

Bearing concept of a Combined Pile-Raft Foundation (CPRF)

Katzenbach and Choudhury (2013)

Analytical study:

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Katzenbach et al. (2011) suggested that designing Combined Pile-Raft Foundations (CPRF) requires the qualified understanding of soil-structure interaction.

Rtotal,k = ΣRpile,k, j + RRaft, k

Total resistance of the CPRF:

Pile resistance: sRsRsR jksjkbjkpile ,,,,,,

Raft resistance: dydxyxssR kraft ,,)(,

αCPRF is set between 0.45-0.55

s =

(Katzenbach and Choudhury, 2013).

, ,1

,

( )

( )

m

p i le k jj

C P R Fto t k

R s

R s

CPRF coefficient:

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Cost efficiency analysis of CPRF

Pile Foundation CPRF

Approximate weight of 50 storey building over 50m2 area= 25000kN

assume pile axial resistance= 2000kN

No.of piles in pile foundationTotal superstructure load=

axial resistance in single pile

No.of piles in CPRFTotal superstructure load=

axial resistance in single pileCPRF

25000Number of piles= =12.5 132000

0.5 25000Number of piles= =6.25 72000

no. of piles in CPRFCPRF efficiency= no. of piles in pile foundation alone

CPRF CPRF PFCost Cost

Suitable FOS may be adopted in finding the superstructure load and axial resistance of piles

Tall Tower ProjectPreliminary Site Investigation

(e.g. Desktop Study, Geological Model, Risk Assessment, etc.

Moderate Risk

Low Risk

High Risk

Ground Investigation

(disturbed sampling, coring)

General Testing(Sieve Analysis, AtterbergLimits, UCS, Point Loads)

Empirical Correlations

Dominate

Ground Investigation(as for Low Risk + the

followings)

In-situ Testing(e.g. PMT, Packer, FHT)

General Testing

(as for Low Risk)

Site Specific Correlations

Preliminary Ground

Investigation(as for Low Risk)

In-situ Testing

(identify critical zones)

Detailed Ground

InvestigationHigh Quality Undisturbed

Samples

Site Specific Correlations

High Quality Laboratory Testing

(Triaxial)

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Dynamic Design Parameters

Characteristic stiffness-strain behavior of soil with ranges for typical geotechnical structures and different test

• Stiffness parameter

• Damping Parameters

• Poisson's ratio of material

• Density of material

• Stiffness Parameters required at low shear strains

• The small-strain shear modulus (Gmaxor G0) is typically associated with strains on the order of 10-3%


Seismic Zonation Map of India as per IS 1893: Part I (2002)Zone DBEII 0.10gIII 0.16gIV 0.24gV 0.36g

• Only 3 types of soil!!!Soft soil, Medium

soil, Hard rock• Characterization of Soil Based on SPT ‘N’ Value, irrespective of soil type !!

• No DYNAMICS (for soil characterization) is involved!!!

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Soil Classification for Seismic Design in USA (NEHRP)

Choudhury (2010) in Structural Longivity, 3(2), 155-170.

Also getting included in International Building Code (IBC 1803 on Foundations), USA.

Dr. Deepankar Choudhury, IIT Bombay

Soil Classification as per Eurocode 8 (2004)

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21Deepankar Choudhury, IIT Bombay

• Base isolation technique adopted(Peak acceleration at 1st and 12thfloor – 0.527m/s2 and 0.619m/s2

respectively whereas PGA was 1.748m/s2

• Very little effect of earthquake of suchlarge magnitude felt on CPRFmagnitude which lead to very minordisturbance in the building

Yamashita et al. (2012) – Field data from Tohuku Earthquake• Reported the performance of CPRF of a twelve

storey building (38.7m high) of Tokyo, Japan foundedon silty sand in Mw=9, 2011 Tohoku earthquake

• Ground improvement technique(deep soil mixing)was adopted to improve the ground and baseisolation was done

Building photo and ground displacement, (Yamashita et al. 2012)

22Deepankar Choudhury, IIT Bombay

Three dimensional view of soil and CPRF model in PLAXIS3D

Response of CPRF under Pseudo-static load

Kumar, A., Choudhury, D. and Katzenbach,R. (2016). In International Jounral ofGeomechanics, ASCE, doi:10.1061/(ASCE)GM.1943-5622.0000637.

Seismically induced load isreplaced with equivalent statichorizontal load, equal to seismiccoefficient times the vertical load.

Seismically induced loads areapplied at the level of raft and isnamed as pseudo-statichorizontal load in the presentstudy.

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23D. Choudhury, IIT Bombay, India

Numerical Modelling of Messetrum Tower foundation • Height of Tower- 256.5m (63000m2 office area)• Foundation type- CPRF, Raft: 6m thick raft at center and 3m at edges• Pile: 64 nos. (1.3m dia. bored piles) Calculation shows that CPRF saves

approximately 5.9 Million USD.

View of Messetrum Tower and arrangement of piles (Kumar et al. 2016)

• Located in easternpart of Frankfurtam Main on toover consolidatedclay with presenceof aquifer at depthof 5m.

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Static test results – Validation with Field Measured Data


• Maximum setllementobserved is 16.95cmin CPRF ofMesseturm Tower inFE calculation butmaximum settlementmeasured on17.12.1998 was14.4cm.

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Recent Major Projectson

Design of CPRF1. Oil Tank Foundations in Iraq – for BP, UK.

2. Heavy material Storage Unit Foundation in

Vietnam – for ThyssenKrupp, Germany.

3. NB Foundation in India – for NPCIL, India.


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Project completedon

“Seismic Design of Foundation System for

Oil Tanks at SKA terminal, Iraq”

Owner: British Petroleum, UK.Involved Geotechnical Agencies & Experts:

Fugro (Dubai); Arup (UK); Mott MacDonald (UK),

Chemie Tech. (India), IIT Bombay (India).Prof. Deepankar Choudhury, IIT Bombay, India

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27Prof. Deepankar Choudhury, IIT Bombay, India

• The site is located approximately 40 km south of Basrah in the Free Trade

zone at KAFZA in Iraq (Latitude 47.9294οN and Longitude 30.0342οE)

• It is Iraq’s third largest port in scale of size and for goods shipped to the

port of Basrah

Seismic Design of CPRF and DSSI analysis

Kumar, A. and Choudhury, D.(2016). in Proc. of the ICE – Geo.Eng.169,(2), 129–138.


Typical Soil property of the site (Ref: Fugro, Dubai)• Fine to medium silica sand as fill material at

top• Below it, very soft to soft clay underlain by

stiff clay encountered• Dense sand extends to greater depth at bottom

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Description Load Unit

Total Empty Weight 1400 kN

Operating Weight 51000 kN

Hydrotest Weight 62000 kN

Shear Wind 160 kN

Moment Wind 1200 kN.m

'(( tan ) ) ( ) -u i i i Di s c D q p p pQ c K P A cN P N A A L Vertical compression and lateral loading tests are carried out on test pile of

diameter 800 mm and length 26 m Characteristic strength of concrete is 35 N/mm2

Safe vertical capacity is 2052kN The group interaction factor is chosen as 0.65 on the basis of soil

homogeneity, slenderness ratio and pile spacing as per Randolph andWorth (1979)

Loading details and static design of pile


Seismic Hazard Distribution Map of Iraq (Ref: ARUP)

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D. Choudhury, IIT Bombay, India31

Field Pile load test (Ref: Chemie Tech.)

Pile load test result Lateral load test result

• Vertical compression and lateral loadings test are carried out ontest pile of diameter 800 mm and length 26 m

• Characteristics strength of concrete is 35 N/mm2

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Design Model Layout

View of different layers of soil model and pile arrangement

(89 nos. 800mm dia pile group)D. Choudhury, IIT Bombay, India

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Input acceleration time history used in FLAC3D based on the PSHA report and RSP Match computer programme

Input acceleration time history• The Uniform Hazard Response Spectra (UHRS) is selected from the provided

Probabilistic Seismic Hazard Analysis (PSHA)

• Synthetic earthquake time-history for MCE is generated using RSP Match software

• Target response spectra at the bedrock level and Seed accelerogram are then used to

develop input motion using RSP Match that

is further used as an input in FLAC3D

UHRS for SKA site developed by Mott Macdonald

Dynamic analysis of foundation system


Modulus reduction curve chosen for different layers of soil

Numerical Fits chosen for soil model as input in FLAC3D to input Hysteresis damping

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Numerical Modelling of soil-pile-raft• Lateral dimension of soil model kept

as four times raft radius to avoidboundary effect

• Grid size near foundationfootprint=0.5m

• Pile as Structural element and raft asshell element

• 89 piles of 800mm diameter and 26mlength and raft thickness- 1.5m ofdiameter 24.1m


Layer No. Depth (m) Soil typeSoil density

(kg/m3)

Cohesion

(kPa)

Friction

angle

φ (deg)

Modulus of

elasticity (E, kPa)

Poisson’s

ratio

(µ)

1 0 - 2Dense

Sand1800 0 30 50000 0.30

2 2 - 20 Soft Clay 1700 10 0 10000 0.49

3 20-24 Stiff Clay 1700 250 0 70000 0.35

4 24-60

Very

Dense

sand

1900 0 35 60000 0.30

Input Soil and pile parameters in FLAC3D chosen fromexperimental results

MaterialGrade of

concrete

Young’s

Modulus (kPa),

(= 5000(fck)1/2)

(as per IS:456)

Poisson’s ratio

(µ)

Diameter

(m)

Length/thickness

(m)

Pile 35 29500000 0.15 0.8 26

Raft 35 29500000 0.15 24.1 1.5

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Maximum settlement= 23.3mm, Rotation= 5.81x 10-4, Permissible limit= 1/300 for liquid

storage tank

Vertical settlement contour

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Axial load contour in pile group in static case

Max. axial force=

697kN

Min. axial force=

478kN

Axial load varying from maximum to minimum magnitude from periphery towards center due to soil-pile-raft interaction


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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.0001 0.001 0.01 0.1 1

G/G

max

Cyclic Strain (%)

FLAC3D Input (Depth-(0-2m))

Seed and Idriss, (1970) (Depth-(0-2m))


Sun et al. (1988) (PI=20-40%) (Depth-(2-24m))


EPRI, (1993) (Depth-(24-60m))

Dynamic soil properties

2 (3 2 ), 0 S 1sM S S

2

2 1

S= L LL L

• Hysteresis damping is taken for soil model that incorporates strain dependentdamping ratio, shear modulus and plasticity based numerical fits.

• To avoid numerical distortion of propagating wave in the dynamic analysisspatial element size must be smaller than approximately one tenth to oneeighth of wave length associated with the highest frequency component ofInput wave

10

L

cf

L


Construction in progress

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Completed stage


Summary of CPRF Design Recommendations:Summary of CPRF Design Recommendations:

• The evaluation of displacements and stress resultants are highly importantfactors which govern the response of foundation components

• The factor of safety, defined as ratio of ultimate bearing capacity of CPRF to verticalload together with lateral load should be more than 1.5 (Yamashita et al. 2011)

• The factor of safety, expressed as ratio of ultimate bearing capacity of piles tomaximum axial load obtained in load sharing should be more than 1.5 (Yamashita etal. 2011)

• The connection rigidity between raft and piles should be chosen based onallowable rotation in raft. The permissible angular rotation under static load is1/1000 to 1/500 (AIJ, 2001)

• Soil-raft interaction dominates the design at initial stage of loading but at laterstage pile-soil interaction plays an important role. This peculiar behaviour ofCPRF can be utilized in the actual design depending on the tolerable lateraldisplacement.

• For seismic design of CPRF, the condition of resonance must be checked for thesoil media and the foundation itself

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•• Piles have to be set directly under the load of the superstructure. The center of the pile group should be under the center of the loads.

• Few long piles are better than many short piles.

• The length of the piles has to be adapted to the loads. At the edge and the corners of the raft shorter piles and in the inner part of the raft longer piles are recommended.

• Optimum of the CPRF-coefficient: αCPRF = 0.5 … 0.7

Recommendations for the design of CPRF

, ,1

,

( )

( )

m

pile k jj

CPRFtot k

R s

R s

CPRF coefficient:

Dr. Deepankar Choudhury, IIT Bombay, India

For More Details,

(1) Book

(2) Online NPTEL Video Course:

“Soil Dynamics” and“Geotechnical EarthquakeEngineering” – free in YouTube

http://www.nptel.iitm.ac.in/courses/105101134/

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Contact Email: [email protected]

[email protected]

Homepage: http://www.civil.iitb.ac.in/~dc/ 45

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