Piling & Deep Foundations 2010

Geotechnical I ti ti dInvestigation and Design for Piling WorksChris HaberfieldChris Haberfield

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Outline

Client Moments Client Moments You get what you pay for Benefits of Doing More Case Studies Closing Remarks

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Client Moments

Just do a basic investigation the piling contractors can take the risk

A primary risk to my project involves the in-ground constructionA primary risk to my project involves the in ground construction

Can you guys help us out as we have a problem with our foundations ... we have a geotechnical report .. but.....?we have a geotechnical report .. but.....?

The piling contractor cant install the piles to the design depth in the way I want them to install them

Geotechnical advice during construction is an expense I dont need the investigation, analysis and design have all been done I dont need construction advice

The piling contractor is claiming latent conditions can you help

I must have bored piles on this project, and you cant use bentonite or polymer to install them

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Client Moments

You pay for geotechnical advice/investigation one way or another

I t ki ti h I hI am taking a conservative approach....so I can go cheap on my geotechnical advice/investigation

It worked down the road so it will work hereIt worked down the road so it will work here

I want to spend as little money as I can on the foundations as we never see them what we cant see wont hurt us and if it does I can alwayssee them what we can t see won t hurt us .... and if it does I can always go and get decent geotechnical advice/investigation later on

Your proposal for the geotechnical investigation is too expensive I canYour proposal for the geotechnical investigation is too expensive I can get one from Joe for half the price

We have to take the cheapest price I know we will pay for it in the endWe have to take the cheapest price I know we will pay for it in the end but that is the policy

With geotechnical advice/investigation you get what you pay forg g y g y p y4

Levels of Geotechnical Input

Ground investigation, analysis, design, construction services...You get what you pay for...g y p y

PlatinumPlatinumGoldSilver

Bronze

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You get what you pay for !Bronze Silver Gold Platinum

boreholes > toe depth ofSilver+moreboreholes, Gold+comprehensive

insitu and laboratoryGroundInvestigation

shallowboreholesnotestingand/orsampling

boreholes toedepthofpiles

SPTtestingIndextesting

someinsitutestingformodulus,laboratory

testingforpermeability,modulusandstrength

insituandlaboratorytestingformodulus,

strengthandpermeability,staticpileloadtesting

GeotechnicalEngineer

LimitedexperienceNonexpert

ExperiencedLimitedinexpertise

ExperiencedExpert

ExperiencedExpert

DesignG d G i Si ifi E h d i ifi

gParameters

Guessed Generic Sitespecific Enhancedsitespecific

Analysis None EmpiricalSilver+simple

theoreticalorbasicnumerical modelling

Gold+advancednumericalmodelling

numericalmodelling

Design Rulesofthumb(overlyconservative)

Empirical,Loadbased,standardindustry

ImprovedServiceabilitybased

OptimisedServiceabiltybased

FoundationsUsuallyoverdesignedMay be impractical

UsuallyoverdesignedPartiallyoptimiseddesign

Practical to buildOptimiseddesignPractical to buildFoundations Maybeimpractical

MaybeunsafeSafe

PracticaltobuildSafe

PracticaltobuildSafe

Risk High Low VeryLow VeryLowCost $50k $80k $120k $250k

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Implications of Enhanced Geotechnical Input

How does enhanced geotechnical input help you? g p p y Relatively small increase in initial cost (as % of total foundation cost) Potential significant savings in overall foundation costs due to:

i. Improved strength reduction factors (AS2159 2009)ii. Improved design parametersiii Improved estimate of foundation performance (design foriii. Improved estimate of foundation performance (design for

serviceability)iv. Improved confidence (due to ii and iii and reduced risk) allowing

optimisationv. Reduced duration for foundation works

Reduction in risk due to improved knowledge Reduction in risk due to improved knowledge

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Improved Strength Reduction FactorsPiling Code AS2159 2009Piling Code AS2159 2009

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Hypothetical Example 1

Simple Geology 30 m compressible soils over weathered rock, high d t t blgroundwater table

50 No. 1.2 m diameter bored piles, no basement 40 m x 40 m in plan 40 m x 40 m in plan Pile working load of 15 MN

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Improved Strength Reduction factorsSame Design ParametersSame Design Parameters

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Improved Parameters, Analysis and Design

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Pile Construction TimeImproved Parameters, Analysis and DesignImproved Parameters, Analysis and Design

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Hypothetical Example 2

Complex Geology e.g. Two separate flows of basalt of variable thi k lit d t t t d b tiff il l ithickness, quality and extent separated by stiff soil over sloping weathered bedrock surface. Bedrock varies in weathering with depth and location and is intersected by dykes. High groundwater table.

50 No. 1.2 m diameter bored piles, 3 level basement, diaphragm wall 40 m x 40 m in plan

Pil ki l d f 10 MN t 50 MN Pile working loads from 10 MN to 50 MN

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Example 2 - Risks and Opportunities

Risks Opportunities

ExcavationG d /d i

Optimised retention system Groundwater/dewatering

Pile founding levels

system Optimised pile lengths

e g piles founding atSi ifi t t iti f Socket lengths - dykes Differential settlement/tilt

e.g. piles founding at different levels in basalt/bedrock

Significant opportunities for reducing foundation costs,

Longer piles Construction difficulties

Alternative footing systems

construction time and risk

Delays Latent conditions

Shorter construction time

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Case StudiesCase Studies

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Case Study 1 Royal Domain Towers, Melbourne

EW-MW siltstone from f d

0

5GARSP - as

t t d

0

5GARSP - as

t t dsurface - deep weathering

dykes

5

10EW - MW Siltstone/Sandstone

constructed5

10EW - MW Siltstone/Sandstone

constructed

~ 85 piles0.75 m to 1.5 m dia

i bilit l d

15

D

e

p

t

h

(

m

) Traditional approach15

D

e

p

t

h

(

m

) Traditional approachGold level investigation provided significant

cost and time savings to projectserviceability loads5 MN to 15 MN

design pile head ttl t 1 % di

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Saving of 9.5 m

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Saving of 9.5 m

Benefits - savings 950 m socket length

950 3 t

cost and time savings to project

settlement : 1 % dia2525

1.2 m dia. pile, SL= 15.3 MN

950 m3 concrete 1400 m3 spoil $$ + 42 days Additional Cost for

P t t ti UCS30301.2 m dia. pile, SL 15.3 MN Pressuremeter testing, UCS

testing, analysis on-site presence

Case Study 2 Freshwater Place, Melbourne

30 m overburden over HW MW ilt t

1.2 m diameter pile, serviceability load = 27 MN30

HW-MW siltstone (variable)

70 x 1.2 m dia. Piles ( l th )

35 GARSP - as constructed

(plus others)

serviceability loads17 MN to 30 MN

Benefits - savings

40HW - SW Siltstone /

Gold level investigation provided significant cost and time savings to project

design top of socket settlement : 1 % dia

FE l i

Benefits savings 900 m socket length 1000 m3 concrete 1500 m3 spoil

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D

e

p

t

h

(

m

)

Sandstone

Traditional approach Saving of up to 17 m

cost and time savings to project

FE analysis $$ + 40 days Additional Cost for Pressuremeter testing, UCS

testing analysis +$20k

50

testing, analysis, +$20k on-site presence55

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Case Study 3 SU Building, Melbourne

Multi storey building Subsurface stratigraphy weathered siltstoneg p y Recommended Gold level geotechnical investigation. Client wanted

only to pay for silver (for about $20 k less)Sil i d t f ti d i d di l Silver carried out, footings designed accordingly

Piling contractor engaged on lump sum price design and construct Golder novated to piling contractor Golder novated to piling contractor Piling contractor requested additional geotech Gold Footings redesigned significant savings to piling contractor (>>$20k) Original client unhappy !!!!!

The piling contractor saw the benefits of a GoldThe piling contractor saw the benefits of a Gold level investigation and reaped the benefits

Case Study 4 - Eureka Tower, Melbourne

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Case Study 5 - Eureka Tower, Melbourne

Inferred Stratigraphy Section AA

Upper basalt

Lower basaltLower basalt

Siltstone

Inferred Stratigraphy Section BB

Upper basaltUpper basalt

25m

35 m

Lower basalt

Siltstone

Limits of basalt

Upper Basalt

L B ltLower Basalt

CFA and Bored Pile solution

Gold level investigation provided significant cost and time savings to project and managed g p j g

the risks of complex ground conditions

Case Study 6 Residential Building, Melbourne

40 level building, small site Subsurface stratigraphy weathered siltstone shallow footings/raftg p y g Recommended Gold level geotechnical investigation. Silver (by others) carried out (for $30 k less), piled footings

d d t ti l f thi itrecommended not practical for this site. Original Gold investigation carried out to estimate deformation

propertiesp p Raft footing proposed and built

Silver investigation provided impractical solution. Gold provided practical footing p p g

solution at reduced cost and construction time.

Case Study 5 Esplanade, Darwin

Case StudyDarwin

Deeply weathered phyllite

Bored piles

Difficult to sample

UCS not possibleThe original Silver level investigation did not

identify the risks Gold level investigationIs(50) < 0.05 MPaPressuremetertesting unsuccessful

identify the risks. Gold level investigation identified the risks and resulted in significant

foundation cost and construction time savingsSlakesPDA testing allowed modulus estimate

foundation cost and construction time savings

modulus estimate

Analysis

Founded on shallow f ifootings

Case Study 6 Oracle Towers, Gold Coast

Two x 40 level towers Stratigraphy 25 m sand, 8 m

clay, 4 m gravel, hard rock Original design bored pilesTh i i l Sil l l i ti ti t Original design bored piles socketed into rock. Piled raft

considered but discounted.

The original Silver level investigation was not sufficient for alternative design options. Gold

No bored piling rigs available Delay to project start Further borehole test clay

level investigation allowed alternative footing options to be considered and resulted in Further borehole test clay

Piled raft using CFA piles Reduction in piling costs and

options to be considered and resulted in significant foundation cost and construction

time savingsconstruction time time savings

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Case Study 6 Nakheel Tower, Dubai

> 1km high tower Mass > 2,000,000 tonnes, , 90 m diameter 20 m deep basement, 120 m diameter High saline groundwater Soft calcareous rock to 200 m

Worlds Tallest Towers

Platinum Level Investigation

Initial investigation Boreholes to 60 m, one borehole to 120 m, lower standard of drilling, laboratory testing only (disturbed samples) Preliminary recommendations piles possibly in excess of 120 m

d th (t li it ttl t )depth (to limit settlements) Settlement estimate of about 500 mm risk of tilt

Subsequent InvestigationTh Pl ti l l i ti tiq g Boreholes to 300 m, triple tube coring Extensive laboratory testing for strength, stiffness and constitutive

behaviour

The Platinum level investigation gave everyone the confidence that

Extensive insitu testing including pressuremeter, crosshole seismic, full scale pile load tests and construction trials

Extensive 3D finite element analysis plus others

this could be done y p

Settlement estimate of about 80 mm Basement retention no anchors

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Footing Layout

Barrette toe levels

-55 m DMD

-60 m DMD

-79 m DMD

Barrette sizes

1 5 m x 2 8 m 1.5 m x 2.8 m

1.2m x 2.8 m

Raft thicknesses

2.5 m

4.0 m

6.0 m to 8.0 m

Case Study 7 Basement

2 level basement in alluvium on beach

Tertiary clay at about 12 m depth Potential buried channels

S t il t t d i i Secant piles to extend minimum 3 m into tertiary clay

Additional investigation The original Silver level investigation identified risks but insufficient for design Constructiongrecommended to confirm depth to tertiary clay not done

Penetration to be confirmed

risks but insufficient for design. Construction difficulties with increased cost and time followed. Penetration to be confirmed

during CFA piling Not done - not all piles

penetrated to tertiary clay Construction issues

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Concluding Comments

Numerous examples of the value of better geotechnical investigations But ... Our clients continue to accept lower cost investigationsp g The market is competitive you are not being ripped off. Dont take bids for geotechnical advice based on price look what they

ff If i i hi h th b bl t h i l i k thoffer. If a price is higher there are probably geotechnical risks the others have not forseen or there is opportunity for significant savings on foundations.

Be open minded - foundation solution, pile type or installation technique. Some piling methods can be impractical for some ground conditions.

You get what you pay forYou pay for the ground investigation sooner or laterp y g g

Thank you33