problematic soils - a euphemism for problematic geo-engineers? · 1 2009-04-23 problematic soils -...

12009-04-23 Problematic soils - a euphemism ..

Geoteknikdagen 2009-06-12

Problematic soils -

a euphemism for problematic geo-engineers?

Jørgen S. Steeenfelt

COWI


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


Problematic soils?

• 3rd Int. Conf. Problematic Soils, Adelaide 2010

Paper aspects

• Identification of problem soils

• Test methods

• Engineering geological aspects

• Avoiding distress to infrastructure

• Case studies

• Peat and organic soils• Volcanic soils• Expansive soils• Collapsible soils• Carbonate rich soils• Lateritic soils• Tailings• Deep fills• Dispersive soils• Unsaturated soils


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


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


Postulate:problematic = failure to recognize or understand

• Local, comparable experience

• Importance of adequate and timelyground 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 propertheoretical framework

• Abuse of numerical tools(garbage in garbage out)


Euphemism?

• Problematic soils?

• Challenging soils

No!Yes!

Avnstrøm (DGF's 40th anniversary): Øresund soil conditions - straight forward; no work for geo-engineers!


Challenge is our middle name-not problematic


Case histories

Rødsand 2Offshore Wind Farm


Location of Rødsand 2 offshore wind farm


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


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


Foundation in Clay till/sand till business as usual?

• CPT tests very shallow

• Stop on Rf (<0.8 MPa)

Row 2

-12

-10

-8

-60 500 1000 1500

cu [kPa]

Level[m]

Foundationlevel

• Design Basis:cu = 200 (250) kPa below CPT/borehole data

• Need for confirmation

• Correlation of SPT - su

• Drained strength parameters from CU triax


Comparison of UU and CU

0

5

10

15

20

0 200 400 600 800 1000

Undrained shear strength (kPa)

Dep

th b

elow

sea

bed

(m)


Foundation in Clay till/sand till Triaxial CU-tests

• Individual tests vary

tr' = 24.4 to 39.5°c' = 23 to 116 kPa

• Plot minimum and maximum failure points

• Agree on design values

0

250

500

750

1000

0 500 1000 1500

MIT stress s (kPa)

t (kPa)

Maximum failureMinimum failureFi =33, c' =25


Foundation in Clay till/sand till business as usual?

• Steel, concrete, challenging soil= wind power in near future

• Foundations on chalk & Palaeogene deposits pending


Case histories

Ruwais Sulphur extensionPile load testing


Ruwais Sulphur Expansion - Abu Dhabi

Future structureExisting structure


DesignConcrete 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


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)


Quadrant beam and pivot foundation


c d

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


Pile installation and testing offshore

Ø762 mm

Wirth drilling rig

Loading platform


Unconfined compressive strength of bedrock

Soil parameters

-25

-20

-15

-10

-5

00 5 10 15 20 25

UCS (MPa)Le

vel (

m)


How do we trust the design assumptions?

Comparable experience

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

10.00

0 1 2 3 4 5 6 7 8 9 10

UCS [MPa]

Dep

th [m

]

0

2

4

6

8

10

12

14

16

0 2 4 6 8 10 12 14

Bearing Capacity [MN]

Dep

th b

elow

top

of ro

ck [m

]

Shaft adhesionFleming

Shaft adhesionTomlinson

Shaft adhesionAASHTO

Design profile

10 - 16.5 MN


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 cappingbeam

Design application


Available borehole information

N

N

New facility


Principle of load testing


Evaluation of load testing

ultmob

mob

ult

mob

34

-1

0

1

2

3

4

5

0 2 4 6 8 10 12 14Tension load on trial pile (MN)

Top

of ro

ck s

ocke

t (m

m)

Top rock socket Appendix A

Pile head - elastic Appendix

ult = 832 kPa

ult = 3.5 mm

(Design ult 615 kPa)


Evaluation of onshore load testing

0

200

400

600

800

1000

0 1 2 3 4 5 6

Depth below top of trial pile (m)

Mob

ilize

d sh

ear s

tres

s (k

Pa) 2L-14

2L-122L-81L-41L-2



0.0

0.1

0.2

0.3

0.4

0.5

0.6

1 10 100

Time (minutes)

Cre

ep d

ispl

acem

ent (

mm

)Extensometer 1

Pile head

0.33 mm/lct

0.07 mm/lct



0

2

4

6

8

600 700 800 900 1000

Ultimate shear stress ult (kPa)

Ulti

mat

e di

spla

cem

ent

ult (

mm

)

dult derivedAverage stress in L2-14

max. pile displ.Design UCS char.

UCS average

Conclusion

• Pile capacity >> design

• Pile system works

• Offshore tests confirm this

• Tension pull out not an issue

• Results forms back-bone data


Evaluation of 762 mm offshore pile capacity (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

Ø762 mm net capacity > 7.2 MN


Keep challenges at bay!

• Problems challenges engineering solutions

• Soil - structure - water - environment interaction

• Have fun with your projects

problematic soils - a euphemism for problematic geo-engineers? · 1 2009-04-23 problematic soils -...

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