deformation properties of highly plastic fissured ... · 2 dtu civil engineering, technical...

Deformation properties of highly plastic fissured Palaeogene clay– Lack of stress memory?

Anette KrogsbøllOle HededalNiels Foged

11. maj 2012NGM 2012 - Copenhagen2 DTU Civil Engineering, Technical University of Denmark

Outline• Introduction

• Oedometer test – Long term test of Lillebælt Clay

• Selected test results from Fehmarn Belt project– stress paths in K0-tests– Overconsolidation ratios

• Discussions

• Conclusions


Lillebælt Clay – oedometer test• Deformation properties – several load cycles

– Compression and swelling index, Cc, Cs

– Oedometer modulus, Eoed

– Secondary strain index, s

• very long time curves

Lillebælt Clay• Eocene clay• Depth 21 m below surface• Initial water content 40%• Initial porosity 50%• Clay content 80%• Plasticity Index 140%


Lillebælt Clay – oedometer testSwelling pressure250 kPa

900 kPa340 kPa

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]


Swelling pressure250 kPa

900 kPa340 kPa900 kPa170 kPa

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]

Lillebælt Clay – oedometer test



900 kPa340 kPa900 kPa170 kPa900 kPa85 kPa

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]




900 kPa340 kPa900 kPa170 kPa900 kPa85 kPa4800 kPa25 kPa

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]

1

2

3

4

Cc = 0.349




900 kPa340 kPa900 kPa170 kPa900 kPa85 kPa4800 kPa25 kPa4800 kPa170 kPa

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]

12345Cc = 0.349



Compression and Swelling index

Compression:Cc,max = 0.35

Swelling:Cs,max = 0.22

0,00

0,10

0,20

0,30

0,40

10 100 1000 10000

Cc, Cs

v [kPa]

1 - Cs 1 - Cc 2 - Cs 2 - Cc

3 - Cs 3 - Cc 4 - Cs 4 - Cc

5 - Cs 5 - Cc


Oedometer modulus

Low values of Eoed

Low values of pc

(Janbu)

0

10000

20000

30000

40000

50000

60000

70000

0 1000 2000 3000 4000 5000

Eoed[kPa]

v [kPa]

12345NC


Secondary Strain index

Determined from longtimecurves (T>2)

Very high valuesin swelling

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

0,0

0,2

0,4

0,6

10 100 1000 10000 s

[%/lo

gt]

v [kPa]

1 2 3 4 5


Seems to ”forget” stresses …

Secondary strain index is veryhigh in unloading

Probably due toDestructurization/Debonding

(Burland 1990)

0,8

0,9

1,0

1,1

1,2

1,310 100 1000 10000

e

v [kPa]

12345Cc = 0.349



Just after test


Drying out


Palaeogene clays below glacial deposits

Miocene

Oligocene

Eocene

Paleocene

Cretaceous

Pre-Cretaceous

Palaeogene

Little Belt

(Eocene)

Fehmern Belt

(Eocene & Paleocene)

Great Belt

(Paleocene)

Holmstrup

(Paleocene)


Simplified geological profile – Fehmarn Belt


Samples – and formations

• Lillebælt sample (test at DTU)– Lillebælt Clay (1)

• Fehmarn Belt samples (test results from GIR, 2011)– Røsnæs Clay (14)

• Intact formation• Folded formation

– Holmehus Clay (1)– Lillebælt Clay (2)– Ølst Clay (1)

Samples for tests and data provided by Fehmarn Belt


Fehmarn Belt - Test principles• Oedometer tests with K0 measurements

• Overconsolidation ratio OCRlab achieved by

– Unloading from estimated preconsolidation stress level– Unloading from high stress level (referred to as ”destructured”)– Unloading from low stress with swelling

Tests carried out by Deltares


K0-testRøsnæs Clay’a,max=1904 kPa

' '13

' '

' ( 2 )a r

a r

pq

-500

0

500

1000

0 500 1000 1500

q [kPa]

p' [kPa]

RC Intact

= 19.6˚



' '13

' '

' ( 2 )a r

a r

pq

-500

0

500

1000

0 500 1000 1500

q [kPa]

p' [kPa]

RC Intact K0 = 0.566

c=0 kPa c=14 kPa

= 19.6˚



Lillebælt CLay’a,max=7-800 kPa

Holmehus’a,max=2000 kPa

Ølst’a,max=1400 kPa

' '13

' '

' ( 2 )a r

a r

pq

-500

0

500

1000

0 500 1000 1500

q [kPa]

p' [kPa]

Lillebælt RC IntactØlst HolmehusK0 = 0.566 c=0 kPac=14 kPa

= 19.6˚


K0-test

' '13

' '

' ( 2 )a r

a r

pq

-500

0

500

1000

0 500 1000 1500

q [kPa]

p' [kPa]

RC Folded LillebæltRC Intact ØlstHolmehus K0 = 0.566c=0 kPa c=14 kPa

= 19.6˚


K0-test

Intact Clay

0,1

1

10

1 10 100

K0

OCR

RC Intact


K0-test

Intact Clay

0,1

1

10

1 10 100

K0

OCR

RC Intact LillebæltØlst Holmehus


K0-test

Røsnæs Clay

0,1

1

10

1 10 100

K0

OCR

RC IntactRC FoldedTrend - RC Folded


K0-test

Røsnæs Clay

0,1

1

10

1 10 100

K0

OCR

RC IntactRC FoldedRC Folded Destr.RC SwellingTrend - RC Folded


K0-test

Røsnæs Clay

MC-criterion = 19.6˚c’=0 kPa

0,1

1

10

1 10 100

K0

OCR

RC IntactRC FoldedRC Folded Destr.RC SwellingShear failureTrend - RC Folded


Summary of K0 versus OCR

Formation K0,nc NRøsnæs Folded 0.57 0.58 10Røsnæs Folded, Destr. 0.56 0.41 2Røsnæs Folded, Swell. 0.96 0.59 1Røsnæs Intact 0.54 0.67 1Lillebælt 0.58 0.60 2Holmehus 0.51 0.77 1Ølst 0.53 0.58 1

0.580, 0, 0.57oc nc labK K OCR OCR


Lillebælt Clay – oedometer

From Lillebælt-FB (intact)

From Lillebælt-FB (intact), :

From Røsnæs-folded& desctructurized – new

0.600, 0.58oc labK OCR

0.410, 0.58oc labK OCR

0, 0.58ncK

-1000

0

1000

2000

3000

0 2000 4000

q [kPa]

p' [kPa]

LC#1 (0.41) LC#1 (0.60)Lillebælt-FB RC Folded desctrMC-criterion c=14 kPa

= 19.6˚


Feasible stress states

High OCRlab:

Lower stresses →Expansion

Limited by MC-criterionLimits also K0 →

Shear strains

-500

0

500

0 500 1000

q [kPa]

p' [kPa]

LC#1 (0.41) LC#1 (0.60)Lillebælt-FB RC Folded desctrMC-criterion c=14 kPa

= 19.6˚


Conclusions• Samples are destructurized by high loading and by swelling

– deformation parameters are significantly changed (Cc, s)

• Destructurization/debonding by swelling is explained by the limit of feasible stresses (MC-criterion)

• K0 – OCR relation depend on formation and lab-test procedure

• For Palaeogene clays of high plasticity OCR is not perfect as a stateparameter

• Due to destructurization/debonding the clay forgets preconsolidation stress when unloaded significantly

Acknowledgements: We thank Fehmarn Belt A/S for access to results and for the opportunity to

perform tests on samples from Fehmarn Belt A/S.

deformation properties of highly plastic fissured ... · 2 dtu civil engineering, technical...

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