Guide to Foundation_7

7/28/2019 Guide to Foundation_7

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Piling & Deep Foundations 2010

Geotechnicalnves ga on an

Design for Piling

Works

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Outline

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

-

Can you guys help us out as we have a problem with our foundations ...we have a eotechnical re ort .. 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

am a ng a conserva ve approac ....so can go c eap on my

geotechnical advice/investigation

I want to spend as little money as I can on the foundations as we never

....

go and get decent geotechnical advice/investigation later on

get one from Joe for half the price

We have to take the chea est rice I know we will a for it in the end

but that is the policy

With eotechnical advice/investi ation ou et what ou a for4


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Levels of Geotechnical Input

Ground investigation, analysis, design, construction services...

You et what ou a for...

Gold

Silver

Bronze

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You get what you pay for !

Bronze Silver Gold Platinum

boreholes > toe de th ofSilver+moreboreholes, Gold+comprehensive

GroundInvestigation

shallowboreholesnotestingand/orsampling

piles

SPTtestingIndextesting

someinsitutestingformodulus,laboratory

testingforpermeability,modulusandstrength

testingformodulus,

strengthandpermeability,staticpileloadtesting

GeotechnicalEngineer

LimitedexperienceNonexpert ExperiencedLimitedinexpertise ExperiencedExpert ExperiencedExpert

Desi nParameters

Guesse Gener c S tespec c En ance s tespec c

Analysis None EmpiricalSilver+simple

theoreticalorbasic Gold+advancednumericalmodelling

Design Rulesofthumb(overlyconservative)

Empirical,Loadbased,standardindustry ImprovedServiceabilitybased OptimisedServiceabiltybased

Usuallyover

designed Usuallyoverdesigned Partiallyoptimiseddesign Optimiseddesign

Maybeunsafe Safe Safe SafeRisk High Low VeryLow VeryLowCost $50k $80k $120k $250k

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Implications of Enhanced Geotechnical Input

How does enhanced eotechnical in ut hel ou? 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 parameters

.

serviceability)

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

v. Reduced duration for foundation works

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Improved Strength Reduction Factors

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Hypothetical Example 1

Simple Geology 30 m compressible soils over weathered rock, highgroun water ta e

50 No. 1.2 m diameter bored piles, no basement

Pile working load of 15 MN

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Improved Strength Reduction factors

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Improved Parameters, Analysis and Design

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Pile Construction Time

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Hypothetical Example 2

Complex Geology e.g. Two separate flows of basalt of variablet c ness, qua ty an extent separate y st so over s opngweathered 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

e wor ng oa s rom o

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Example 2 - Risks and Opportunities

Risks Opportunities

Excavation

Optimised retention Groun water/ ewaterng

Pile founding levels Optimised pile lengths

Socket lengths - dykes Differential settlement/tilt

. .

different levels inbasalt/bedrock

gn can oppor un es orreducing foundation costs, Longer piles

Construction difficulties

Alternative footing

systems

construction time and risk

Delays

Latent conditions

Shorter construction time

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Case Study 1 Royal Domain Towers, Melbourne

EW-MW siltstone from

0

GARSP - as

0

GARSP - as

sur ace - eepweathering

dykes 10 EW - MWSiltstone/Sandstone

cons ruc e

10 EW - MWSiltstone/Sandstone

cons ruc e

~ 85 piles0.75 m to 1.5 m dia

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Depth(m) Traditional

approach15

Depth(m) Traditional

approachGold level investigation provided significantserv cea y oa s

5 MN to 15 MN

design pile head

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Saving of 9.5 m

20

Saving of 9.5 m

Benefits - savings

950 m socket length

se emen : a2525

1.2 m dia. ile SL= 15.3 MN

m concre e

1400 m3 spoil

$$ + 42 days

Addi tional Cost for3030

Pressuremete testng, UCS

testing, analysis

on-site presence


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Case Study 2 Freshwater Place, Melbourne

30 m overburden over

1.2 m diameter pile, serviceability load = 27 MN

30

- s s one(variable)

70 x 1.2 m dia. Piles 35GARSP - as

constructed

pus o ers

serviceability loads17 MN to 30 MN

-

40HW - SW

Siltstone /

Gold level investigation provided significant

design top of socketsettlement : 1 % dia

900 m socket length 1000 m3 concrete

1500 m3 spoil

45

Depth(m

)

Sandstone

Traditional

approach Saving of up to 17 m

ana ys s $$ + 40 days

Addi tional Cost for

Pressuremeter testing, UCS

50

, ,

on-site presence55

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Case Study 3 SU Building, Melbourne

Multi storey building

Subsurface strati ra h weathered siltstone

Recommended Gold level geotechnical investigation. Client wanted

only to pay for silver (for about $20 k less) ver carre out, ootngs es gne accor ngy

Piling contractor engaged on lump sum price design and construct

Piling contractor requested additional geotech Gold

Footings redesigned significant savings to piling contractor (>>$20k)

Original client unhappy !!!!!

Th ilin ntr t r w th n fit f llevel investigation and reaped the benefits


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Case Study 4 - Eureka Tower, Melbourne

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Case Study 5 - Eureka Tower, Melbourne


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Inferred Stratigraphy Section AA

Upper basalt

Siltstone


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Inferred Stratigraphy Section BB

U erbasal

25m

35 m

Lower basalt

Siltstone


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Limits of basalt

Upper Basalt

ower asa


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CFA and Bored Pile solution

Gold level investigation provided significant

cost and time savin s to ro ect and mana edthe risks of complex ground conditions


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Case Study 6 Residential Building, Melbourne

40 level building, small site

Subsurface strati ra h weathered siltstone shallow footin s/raft

Recommended Gold level geotechnical investigation.

Silver (by others) carried out (for $30 k less), piled footingsrecommen e not practca or t s s te.

Original Gold investigation carried out to estimate deformationro erties

Raft footing proposed and built

Silver investigation provided impractical

solution. Gold rovided ractical footinsolution at reduced cost and construction time.


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Case Study 5 Esplanade, Darwin

Case Study

Darwin

Deeply weatheredphyllite

Bored piles

Difficult to sample

UCS not possibleThe original Silver level investigation did not

Is(50) < 0.05 MPa

Pressuremetertesting unsuccessful

.

identified the risks and resulted in significant

Slakes

PDA testing allowed

Analysis

Founded on shallowfootings


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Case Study 6 Oracle Towers, Gold Coast

Two x 40 level towers

Stratigraphy 25 m sand, 8 mclay, 4 m gravel, hard rock

socketed into rock. Piled raftconsidered but discounted.

e orgna ver eve nves ga on was nosufficient for alternative design options. Gold

No bored piling rigs available

Delay to project startlevel investigation allowed alternative footingo tions to be considered and resulted in

Piled raft using CFA piles

Reduction in piling costs and

significant foundation cost and construction

construction time

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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 groundwate

Soft calcareous rock to 200 m


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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 mept to mt settements

Settlement estimate of about 500 mm risk of tilt Subse uent Investi ation

Boreholes to 300 m, triple tube coring Extensive laboratory testing for strength, stiffness and constitutive

behavioue a num eve nves ga ongave everyone the confidence that

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

Extensive 3D finite element anal sis lus others

this could be done

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 s izes

. .

1.2m x 2.8 m

Raft thicknesses

2.5 m

4.0 m6.0 m to 8.0 m


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Case Study 7 Basement

2 level basement in alluvium onbeach

Tertiary clay at about 12 m depth

Potential buried channels ecant p es to exten mnmum

3 m into tertiary clay

Additional investi ation

The original Silver level investigation identified

recommended to confirm depthto tertiary clay not done

.

difficulties with increased cost and time followed.

during CFA piling

Not done - not all pilespenetrated 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 acce t lower cost investi ations

The market is competitive you are not being ripped off.

Dont take bids for geotechnical advice based on price look what theyo er. a prce s g er t ere are pro a y geotec nca rs s t eothers have not forseen or there is opportunity for significant savingson 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 for

You a for the round investi ation sooner or later

Thank you

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Guide to Foundation_7

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