Piling & Deep Foundations 2010
Geotechnical
I
Investigation
ti ti and
d
Design for Piling
Works
Chris Haberfield
1
Outline

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2
Client Moments
You get what you pay for
Benefits of Doing More
Case Studies
Closing Remarks
Client Moments
“Just do a basic investigation – the piling contractors can take the risk”
“A
A primary risk to my project involves the in-ground
in ground construction
construction”
“Can you guys help us out as we have a problem with our foundations ...
we have a geotechnical report .. but.....?”
but.....?
“The piling contractor can’t install the piles to the design depth in the way
I want them to install them”
“Geotechnical advice during construction is an expense I don’t need –
the investigation, analysis and design have all been done – I don’t need
construction advice”
“The piling contractor is claiming latent conditions – can you help”
“I must have bored piles on this project, and you can’t use bentonite or
polymer to install them”
3
Client Moments
“You pay for geotechnical advice/investigation one way or another”
“I am taking
t ki a conservative
ti approach....so
h
I can go cheap
h
on my
geotechnical advice/investigation”
“It
It worked down the road so it will work here”
here
“I want to spend as little money as I can on the foundations as we never
see them – what we can
can’tt see won’t
won t hurt us .... and if it does I can always
go and get decent geotechnical advice/investigation later on”
“Your
Your proposal for the geotechnical investigation is too expensive – I can
get one from Joe for half the price”
“We
We have to take the cheapest price – I know we will pay for it in the end
but that is the policy”
“With g
geotechnical advice/investigation
g
–y
you get
g what yyou p
pay
y for”
4
Levels of Geotechnical Input
Ground investigation, analysis, design, construction services...
“You g
get what yyou p
pay
y for”...
Platinum
Gold
Silver
Bronze
5
You get what you pay for !
Bronze
Ground Investigation
Geotechnical Engineer
Design g
Parameters
Silver
boreholes > toe depth of boreholes
toe depth of
piles
shallow boreholes
SPT testing
no testing and/or sampling
Index testing
Gold
Silver + more boreholes, Design Foundations
Risk
Cost
Gold + comprehensive insitu and laboratory
insitu and laboratory some insitu testing for testing for modulus, modulus, laboratory strength and permeability, testing for permeability, static pile load testing
modulus and strength
Limited experience
Non expert
Experienced
Limited in expertise
Experienced
Expert
Experienced
Expert
G
Guessed
d
G
Generic
i
Si
Site specific
ifi
E h
Enhanced site specific
d i
ifi
Silver + simple Analysis
Platinum
None
Empirical
Rules of thumb (overly conservative)
Usually over designed
May be impractical
May be impractical
May be unsafe
High
Empirical, Load based, standard industry
Low
theoretical or basic numerical modelling
numerical modelling
Improved
Serviceability based
Partially optimised design
Practical to build
Practical to build
Safe
Very Low
$50k
$80k
$120k
Usually over designed
Safe
6
Gold + advanced numerical modelling
Optimised
Serviceabilty based
Optimised design
Practical to build
Practical to build
Safe
Very Low
$250k
Implications of Enhanced Geotechnical Input
How does enhanced g
geotechnical input
p help
p you?
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 parameters
iii
iii.
Improved estimate of foundation performance (design for
serviceability)
iv.
Improved confidence (due to ii and iii and reduced risk) allowing
optimisation
v.
Reduced duration for foundation works
 Reduction in risk due to improved knowledge
7
Improved Strength Reduction Factors
Piling Code AS2159 2009
8
Hypothetical Example 1

Simple Geology – 30 m compressible soils over weathered rock, high
groundwater
d t table
t bl
 50 No. 1.2 m diameter bored piles, no basement
 40 m x 40 m in plan
 Pile working load of 15 MN
9
Improved Strength Reduction factors
Same Design Parameters
10
Improved Parameters, Analysis and Design
11
Pile Construction Time
Improved Parameters, Analysis and Design
12
Hypothetical Example 2

Complex Geology – e.g. Two separate flows of basalt of variable
thi k
thickness,
quality
lit and
d extent
t t separated
t d by
b stiff
tiff soilil over sloping
l i
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
 Pile
Pil working
ki lloads
d ffrom 10 MN tto 50 MN
13
Example 2 - Risks and Opportunities
Opportunities
Risks
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
 Optimised retention
Excavation
system
G
Groundwater/dewatering
d
/d
i
 Optimised pile lengths –
Pile founding levels
e g piles founding at
e.g.
Socket lengths
Si ifi- dykest opportunities
Significant
tdifferent
iti levels
for
f in
Differential
settlement/tilt
reducing
foundation
costs,
basalt/bedrock
Longer piles
 Alternative
construction time
and riskfooting
Construction difficulties
systems
Delays
 Shorter construction time
Latent conditions
14
Case Studies
15
Case Study 1 – Royal Domain Towers, Melbourne
0
EW-MW siltstone from
surface
f
- deep
d
weathering
dykes
~ 85 piles
0.75 m to 1.5 m dia
GARSP - as
constructed
t t d
5
10
EW - MW
Siltstone/Sandstone
Depth (m)
Gold level investigation provided significant
serviceability
i
bilit lloads
d cost and time savings to project
5 MN to 15 MN
15
Traditional
approach
20
design pile head
settlement
ttl
t : 1 % dia
di
Saving of 9.5 m
25
1.2 m dia. pile, SL=
SL 15.3 MN
30
Benefits - savings

950 m socket length

950 m3 concrete
t

1400 m3 spoil

$$ + 42 days
Additional Cost for

P
Pressuremeter
t testing,
t ti
UCS
testing, analysis

on-site presence
Case Study 2 – Freshwater Place, Melbourne
1.2 m diameter pile, serviceability load = 27 MN
30 m overburden over
HW MW siltstone
HW-MW
ilt t
(variable)
30
GARSP - as
constructed
35
70 x 1.2 m dia. Piles
( l others)
(plus
th )
Gold level investigation provided significant
Benefits - savings
cost
and
time
savings
to
project
900 m socket length
design top of socket
serviceability loads
17 MN to 30 MN
Depth (m)
settlement : 1 % dia
40
HW - SW
Siltstone /
Sandstone

45
FE analysis
l i
50
55
60
Traditional
approach
1000 m3 concrete

1500 m3 spoil

$$ + 40 days
Additional Cost for

Pressuremeter testing, UCS
testing analysis,
testing,
analysis +$20k

on-site presence

Saving of up to 17 m
Case Study 3 – SU Building, Melbourne
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Multi storey building
Subsurface stratigraphy
g p y – weathered siltstone
Recommended “Gold” level geotechnical investigation. Client wanted
only to pay for silver (for about $20 k less)
Sil
Silver
carried
i d out,
t ffootings
ti
d
designed
i
d accordingly
di l
Piling contractor engaged on lump sum price – design and construct
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 Gold
level investigation and reaped the benefits
Case Study 4 - Eureka Tower, Melbourne
19
Case Study 5 - Eureka Tower, Melbourne
Inferred Stratigraphy Section AA
Upper basalt
Lower basalt
Siltstone
Inferred Stratigraphy Section BB
Upper basalt
25m
Lower basalt
35 m
Siltstone
Limits of basalt
Upper Basalt
L
Lower
B
Basalt
lt
CFA and Bored Pile solution
Gold level investigation provided significant
g to p
project
j
and managed
g
cost and time savings
the risks of complex ground conditions
Case Study 6 – Residential Building, Melbourne
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40 level building, small site
Subsurface stratigraphy
g p y – weathered siltstone – shallow footings/raft
g
Recommended “Gold” level geotechnical investigation.
Silver (by others) carried out (for $30 k less), piled footings
recommended
d d – nott practical
ti l ffor this
thi site.
it
Original Gold investigation carried out to estimate deformation
p p
properties
Raft footing proposed and built
Silver investigation provided impractical
provided p
practical footing
g
solution. Gold p
solution at reduced cost and construction time.
Case Study 5 – Esplanade, Darwin
Case Study
Darwin
Deeply weathered
phyllite
Bored piles
The original Silver level investigation did not
UCS not possible
identify the risks.
risks Gold level investigation
Is < 0.05 MPa
Pressuremeter
identified the risks and resulted in significant
testing unsuccessful
foundation cost and construction time savings
Slakes
Difficult to sample
(50)
PDA testing allowed
modulus estimate
Analysis
Founded on shallow
f i
footings
Case Study 6 – Oracle Towers, Gold Coast
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

Two x 40 level towers
Stratigraphy – 25 m sand, 8 m
clay, 4 m gravel, hard rock
Original design – bored piles
socketed into rock. Piled raft
considered but discounted.
No bored piling rigs available
Delay to project start
Further borehole – test clay
Piled raft using CFA piles
Reduction in piling costs and
construction time
The original
Th
i i l Sil
Silver llevell iinvestigation
ti ti was nott
sufficient for alternative design options. Gold

level
investigation
allowed
alternative
footing

options to be considered and resulted in

 significant foundation cost and construction

time savings
27
Case Study 6 – Nakheel Tower, Dubai
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
> 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
World’s 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
depth
(to lilimit
it settlements)
ttl
t )
 Settlement estimate of about 500 mm – risk of tilt
 Subsequent
q
Investigation
g
 Boreholes to 300 m, triple tube coring
 Extensive laboratory testing for strength, stiffness and constitutive
behaviour
 Extensive insitu testing including pressuremeter, crosshole seismic,
full scale pile load tests and construction trials
 Extensive 3D finite element analysis
y
p
plus others
 Settlement estimate of about 80 mm
 Basement retention – no anchors
The Pl
Th
Platinum
ti
llevell iinvestigation
ti ti
gave everyone the confidence that
this could be done
30
Footing Layout
Barrette toe levels
• -55 m DMD
• -60 m DMD
• -79 m DMD
Barrette sizes
• 1.5
15mx2
2.8
8m
• 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
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2 level basement in alluvium on
beach
Tertiary clay at about 12 m depth
Potential buried channels
S
Secant
t piles
il tto extend
t d minimum
i i
3 m into tertiary clay
Additional investigation
g
recommended to confirm depth
to tertiary clay – not done
Penetration to be confirmed
during CFA piling
Not done - not all piles
penetrated to tertiary clay
Construction issues
The original Silver level investigation identified
 risks but insufficient for design
design. Construction
difficulties with increased cost and time followed.

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32
Concluding Comments

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
Numerous examples of the value of better geotechnical investigations
But ... Our clients continue to accept
p lower cost investigations
g
The market is competitive – you are not being ripped off.
Don’t take bids for geotechnical advice based on price – look what they
offer.
ff
If a price
i iis hi
higher
h – there
th
are probably
b bl geotechnical
t h i l risks
i k th
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 for”
“You p
pay
y for the ground
g
investigation
g
sooner or later”
Thank you
33