Geoteknikdagen 2009-06-12
Problematic soils a euphemism for
problematic geo-engineers?
Jørgen S. Steeenfelt
COWI
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2009-04-23
Problematic soils - a euphemism ..
Outline - introduction
• Problematic soils?
- does the term make sense?
- what are the clues?
- global/local validity
• Is it a euphemism?
- soul searching question for all
• Case histories
- Rødsand 2 Offshore Wind Farm
- Ruwais Sulphur Extension
• Closing remarks
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2009-04-23
Problematic soils - a euphemism ..
Problematic soils?
• 3rd Int. Conf. Problematic Soils, Adelaide 2010
•
•
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•
•
•
•
•
•
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Peat and organic soils
Volcanic soils
Expansive soils
Collapsible soils
Carbonate rich soils
Lateritic soils
Tailings
Deep fills
Dispersive soils
Unsaturated soils
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2009-04-23
Problematic soils - a euphemism ..
Paper aspects
• Identification of
problem soils
• Test methods
• Engineering geological
aspects
• Avoiding distress to
infrastructure
• Case studies
How about closer to home?
• Danish Code of Practice
- only indirect reference (GC 3)
•
•
•
•
Tertiary clays
Palaeogene clays
Chalk with cavities
Soils with incr. k
with depth below GWT
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2009-04-23
Problematic soils - a euphemism ..
How about closer to home?
DS 415 (Geotechnical Category 3)
• Multi-storey basements
• Structures with large differential water pressures
• Temporary or permanent GW-lowering involving
serious risk of damage to structures or soil strata
• Fills and pavements subjected to significant
dynamic loading
• Machine foundations subject to significant
dynamic exitation
• Structures with extreme cyclic loading
• Larger bridges and tunnels
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2009-04-23
Problematic soils - a euphemism ..
Postulate:
problematic = failure to recognize or understand
• Local, comparable experience
• Importance of adequate and timely
ground investigations
• Difficulties in
specifying, testing and interpreting
lab. and field tests
• Confusion of measured, derived,
characteristic & design values
• Geological set-up and stratification
• Application of proper
theoretical framework
• Abuse of numerical tools
(garbage in  garbage out)
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2009-04-23
Problematic soils - a euphemism ..
Euphemism?
• Problematic
soils?
• Challenging
soils
No!
Yes!
Avnstrøm (DGF's 40th anniversary):
Øresund soil conditions - straight forward;
no work for geo-engineers!
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2009-04-23
Problematic soils - a euphemism ..
Challenge is our middle namenot problematic
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Problematic soils - a euphemism ..
Case histories
Rødsand 2
Offshore Wind Farm
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Problematic soils - a euphemism ..
Location of Rødsand 2 offshore wind farm
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Problematic soils - a euphemism ..
Project with 90 wind turbines (2.3 MW)
• Client:
E.ON with Grontmij Carl Bro as consultant
• Contractor:
Aarsleff-Bilfinger Berger JV with
COWI as designer
• Certifying body: DNV
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2009-04-23
Problematic soils - a euphemism ..
Ground conditions:
predominantly glacial deposits, clay till/sand till
Extent of site assessment data
• 183 CPTs tests
- depth 2.9 ± 2.4 m; 86 outside footprint
• 37 vibrocores
• 80 geotechnical boreholes
- majority to 7 m depth
• 200 UU tests - in lieu of field vane testing
• 19 triaxial CU tests
• supplementary soil investigations by ABJV
- geotechnical boreholes with SPT
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Problematic soils - a euphemism ..
Foundation in Clay till/sand till
business as usual?
cu [kPa]
• CPT tests very shallow
0
500
1000
1500
-6
• Stop on Rf (<0.8 MPa)
• Design Basis:
cu = 200 (250) kPa below
CPT/borehole data
• Need for confirmation
• Correlation of SPT - su
• Drained strength
parameters from CU triax
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Problematic soils - a euphemism ..
-8
Level
[m]
-10
Foundation
level
Row 2
-12
Comparison of UU and CU
Undrained shear strength (kPa)
0
200
Depth below seabed (m)
0
5
10
15
20
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Problematic soils - a euphemism ..
400
600
800
1000
Foundation in Clay till/sand till
Triaxial CU-tests
1000
750
t (kPa) 500
• Individual tests vary
tr' = 24.4 to 39.5°
c'
Maximum failure
Minimum failure
Fi =33, c' =25
= 23 to 116 kPa
• Plot minimum and
maximum failure points
• Agree on design values
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2009-04-23
250
Problematic soils - a euphemism ..
0
0
500
1000
MIT stress s (kPa)
1500
Foundation in Clay till/sand till
business as usual?
• Steel, concrete, challenging soil
= wind power in near future
• Foundations on chalk &
Palaeogene deposits pending
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Problematic soils - a euphemism ..
Case histories
Ruwais Sulphur extension
Pile load testing
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Problematic soils - a euphemism ..
Ruwais Sulphur Expansion - Abu Dhabi
Future structure
Existing structure
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Problematic soils - a euphemism ..
Design
Concrete Design
Mooring Dolphins

Precast shell with cast-in steel girders

Shell positioned on top of the piles

Filled with in-situ concrete -> Reduces the weight
during construction
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Problematic soils - a euphemism ..
Pile Design
 Tubular steel piles
- Ø1067 mm, 22 mm (Dolphins)
- Ø 914 mm, 19 mm (Trestle & Pivot)
 Raking 1:4
 Vertical capacity: Fleming et al.
s = 0.41 sqrt(UCS/1 MPa)
 Horizontal capacity: p-y curves
- sand acc. to API for superficial deposits
- weak rock acc. to Reese (1977)
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Problematic soils - a euphemism ..
Quadrant beam and pivot foundation
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Problematic soils - a euphemism ..
Pile installation procedure
 Temporary casing driven
to bedrock
 Coring rock socket
 Flush & clean
 Tremie concrete socket
 Place pile with spacers
 Fill annulus with sand
 Retract temp. casing
 Pour mass concrete
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Problematic soils - a euphemism ..
c
d
Pile installation and testing offshore
Loading
platform
Wirth
drilling
rig
Ø762
mm
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Problematic soils - a euphemism ..
Unconfined compressive strength of bedrock
 Soil parameters
0
5
0
Level (m)
-5
-10
-15
-20
-25
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Problematic soils - a euphemism ..
UCS (MPa)
10
15
20
25
How do we trust the design assumptions?
Bearing Capacity [MN]
Comparable experience
0
1
2
3
4
5
4
6
8
10
12
14
0
UCS [MPa]
0
2
6
7
8
9
10
0.00
2
1.00
2.00
3.00
Design
profile
4.00
5.00
6.00
Depth [m]
7.00
Depth below top of rock [m]
4
6
8
10
12
8.00
14
9.00
Shaft adhesion
Fleming
Shaft adhesion
Tomlinson
Shaft adhesion
AASHTO
16
10.00
25
2009-04-23
10 - 16.5 MN
Problematic soils - a euphemism ..
Design application
Dolphins
Non-linear springs
FEM analysis
Breasting Dolphins and
Mooring Dolphins:
–
FEM program Robot
–
Three- dimensional
space frame / plate
model
–
Governing forces in
piles and capping
beam
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Problematic soils - a euphemism ..
Available borehole information
N
New
facility
N
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Principle of load testing
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Problematic soils - a euphemism ..
Evaluation of load testing
 mob
4 mob

 ult
3 mob   ult
5
Top rock socket Appendix A
Pile head - elastic Appendix
ult = 832 kPa
ult =
3.5 mm
(Design ult 615 kPa)
Top of rock socket (mm)
4
3
2
1
0
-1
0
2
4
6
8
10
Tension load on trial pile (MN)
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Problematic soils - a euphemism ..
12
14
Evaluation of onshore load testing
Mobilized shear stress (kPa)
1000
2L-14
2L-12
2L-8
1L-4
1L-2
800
600
400
200
0
0
1
2
3
4
Depth below top of trial pile (m)
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Problematic soils - a euphemism ..
5
6
Evaluation of onshore load testing
0.6
Creep displacement (mm)
Extensometer 1
0.5
Pile head
0.4
0.33 mm/lct
0.3
0.2
0.07 mm/lct
0.1
0.0
1
10
Time (minutes)
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Problematic soils - a euphemism ..
100
Evaluation of onshore load testing
Conclusion
Ultimate displacement  ult (mm)
8
dult derived
• Pile capacity >>
design
Average stress in L2-14
max. pile displ.
6
Design UCS char.
• Pile system works
UCS average
4
• Offshore tests
confirm this
2
• Tension pull out
not an issue
0
600
• Results forms
back-bone data
700
800
900
Ultimate shear stress ult (kPa)
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2009-04-23
Problematic soils - a euphemism ..
1000
Evaluation of 762 mm offshore pile
capacity (MN)
Ø762 mm net capacity > 7.2 MN
Char. shear stress
Design Onshore test
615 kPa
832 kPa
Cone
Pile diameter
3.3
5.9
uplift
Socket diam.
4.2
7.7
no
Pile diameter
4.3
8.0
uplift
Socket diam.
5.5
10.5
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2009-04-23
Problematic soils - a euphemism ..
Keep challenges at bay!
• Problems  challenges  engineering solutions
• Soil - structure - water - environment interaction
• Have fun with your projects
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2009-04-23
Problematic soils - a euphemism ..