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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
11. maj 2012NGM 2012 - Copenhagen3 DTU Civil Engineering, Technical University of Denmark
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%
11. maj 2012NGM 2012 - Copenhagen4 DTU Civil Engineering, Technical University of Denmark
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]
11. maj 2012NGM 2012 - Copenhagen5 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen6 DTU Civil Engineering, Technical University of Denmark
Swelling pressure250 kPa
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]
Lillebælt Clay – oedometer test
11. maj 2012NGM 2012 - Copenhagen7 DTU Civil Engineering, Technical University of Denmark
Swelling pressure250 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
Lillebælt Clay – oedometer test
11. maj 2012NGM 2012 - Copenhagen8 DTU Civil Engineering, Technical University of Denmark
Swelling pressure250 kPa
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
Lillebælt Clay – oedometer test
11. maj 2012NGM 2012 - Copenhagen9 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen10 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen11 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen12 DTU Civil Engineering, Technical University of Denmark
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
Lillebælt Clay – oedometer test
11. maj 2012NGM 2012 - Copenhagen13 DTU Civil Engineering, Technical University of Denmark
Just after test
11. maj 2012NGM 2012 - Copenhagen14 DTU Civil Engineering, Technical University of Denmark
Drying out
11. maj 2012NGM 2012 - Copenhagen15 DTU Civil Engineering, Technical University of Denmark
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)
11. maj 2012NGM 2012 - Copenhagen16 DTU Civil Engineering, Technical University of Denmark
Simplified geological profile – Fehmarn Belt
11. maj 2012NGM 2012 - Copenhagen17 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen18 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen19 DTU Civil Engineering, Technical University of Denmark
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˚
11. maj 2012NGM 2012 - Copenhagen20 DTU Civil Engineering, Technical University of Denmark
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 K0 = 0.566
c=0 kPa c=14 kPa
= 19.6˚
11. maj 2012NGM 2012 - Copenhagen21 DTU Civil Engineering, Technical University of Denmark
K0-testRøsnæs Clay’a,max=1904 kPa
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˚
11. maj 2012NGM 2012 - Copenhagen22 DTU Civil Engineering, Technical University of Denmark
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˚
11. maj 2012NGM 2012 - Copenhagen23 DTU Civil Engineering, Technical University of Denmark
K0-test
Intact Clay
0,1
1
10
1 10 100
K0
OCR
RC Intact
11. maj 2012NGM 2012 - Copenhagen24 DTU Civil Engineering, Technical University of Denmark
K0-test
Intact Clay
0,1
1
10
1 10 100
K0
OCR
RC Intact LillebæltØlst Holmehus
11. maj 2012NGM 2012 - Copenhagen25 DTU Civil Engineering, Technical University of Denmark
K0-test
Røsnæs Clay
0,1
1
10
1 10 100
K0
OCR
RC IntactRC FoldedTrend - RC Folded
11. maj 2012NGM 2012 - Copenhagen26 DTU Civil Engineering, Technical University of Denmark
K0-test
Røsnæs Clay
0,1
1
10
1 10 100
K0
OCR
RC IntactRC FoldedRC Folded Destr.RC SwellingTrend - RC Folded
11. maj 2012NGM 2012 - Copenhagen27 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen28 DTU Civil Engineering, Technical University of Denmark
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
11. maj 2012NGM 2012 - Copenhagen29 DTU Civil Engineering, Technical University of Denmark
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˚
11. maj 2012NGM 2012 - Copenhagen30 DTU Civil Engineering, Technical University of Denmark
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˚
11. maj 2012NGM 2012 - Copenhagen31 DTU Civil Engineering, Technical University of Denmark
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.
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