c4_Long-term behaviour of soils stabilized with lime cement_Nancy University.pdf

8/14/2019 c4_Long-term behaviour of soils stabilized with lime cement_Nancy University.pdf

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Short and long term performance of lime

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an cement sta i ise soi s

Olivier CUISINIER, Associate ProfessorLaboratoire Environnement, Gomcanique & Ouvrages

Soil mechanics group

Ecole Nationale Suprieure de GologieNancy Universit

France


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Layout

Stabilisation basic principles

Short term performance Presence of potential deleterious compounds

Long term performance

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e n on o ura y Impact of water circulation

Influence of successive wetting and drying

Conclusions Perspectives


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Mixing soil and few % of binder (lime

/cement) to: Permit the construction of the structure: Reduce water content, plasticity

Im rove workabilit

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Ease the building of backfill, compacted layer,etc.

Improve design characteristics:

Increase shear strength properties Lower compressibility

Lower swelling and shrinkage


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Lime stabilisation : how does it work?

Physico-chemical processes

Immediate effects of lime addition :

Hydration of quicklime CaO + H2O Ca(OH)2 + 12 kJ.mol-1

decrease of water content

2+


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pH of saturated solution of portlandite = 12.4Cation exchange, modification of clay particles

electrical charges aggregation of clay particles

Results in short term: improvement of workability anddecrease of swelling/shrinkage potential


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Time-dependant effects of lime addition:


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Increase of silicon and aluminium solubility in high-pH environment


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Time-dependant effects of lime addition:

pH release of [Si] and [Al] Si + Al + Ca + OH CAH + CSH + CASH

Cementitious compounds


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Binder stabilization

Fundamental processes: hydraulic setting

reactions Clinker reacts with water to form cementitious

compounds (CSH CASH, etc.)


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Soil stabilisation in the field

Earthworks:


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Soil stabilisation in the field

Deep mixing: a ground improvement method


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Layout




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Short term performance: influence of

potential deleterious compounds

Presence of some chemicals may alter thesetting reactions: Sulphur formation of ettringite that lead to

excessive swelling Nitrates lower UCS, delay ?

Deleterious compounds

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Chlorides accelerate hydration but lead to theformation of Friedels salt and decrease

Other minerals (micas) prevent settingreactions, swelling

Key issues: Concentration thresholds Experimental procedures to determine how to use

soils containing deleterious compounds


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ber2010 Compaction Curing at constant

water contentTesting

8

10

8

10

Influence of gypsum on performance at

constant water content


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Soils with a high content in sulphate can be successfully stabilizedwith cement but

0 50 100 150 2000

2

4

6

UCS(MPa)

Curing period (days)

Rc Limon + 14 % sulfate 20C


Rc Limon 40CRc Limon 20C

0 50 100 150 2000

2

4

6

UCS(MPa)

Curing period (days)



Rc Limon 40CRc Limon 20C


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after compactionTesting

Impact of immersion


6

7

8

Rc Limon + sulfate

Rc Limon25

30

Gv Limon + sulfate

T = 20C

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Immersion leads to exessive swelling and loss of performance

0 10 200

1

2

3

4

5

UCS(MPa)

Days after immersion

0

5

10

15

20

Swelling(%)

Gv Limon


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Role of delayed immersion


Compaction

Immersion after 1, 7 or 28days at constant water

contentTesting

6

7

8

LVE + Gypsum+ CaO + CEM II

LVE + CaO + CEM II

1 day of immersion

28 days of immersion


1 day of immersion


25

30

LVE + Gypsum + CaO + CEM II

1 days of immersion



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0 10 20 300

1

2

3

4

5

UCS(MPa)

Curing time before immersion (days)


0 10 20 300

5

10

15

Swelling(%)

Curing time before immersion (days))

Delayed immersion permitted to: lower swelling increase UCS up to satisfactory value

Sulphate can be managed for design concern by preventing wettingin the short term (first month)


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Conclusion about deleterious compounds

Several compounds can alter the efficiency ofcement/lime stabilisation (fertilizers, chloride,sulphate, sulphide)

The impact of a compound is a function of: Concentration (threshold between 0,01% up to 1% for S)


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ur ng con t ons Cement type Etc

Issues:

How to predict in the lab the impact of stabilisation inthe field (design step)? What about long term behaviour (leaching with high-

sulphate water, low pH water, freeze/thaw, etc.) ?


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Layout




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Definition of durability

After construction: external stressescould alter design performance during the

service life Example : River levee in soil stabilized with

lime/cement

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WaterRiver levee in soilstabilized withlime/cement

Key characteristics thatmust be maintained:

1- permeability

2- shear strengthKey features:

1- lixiviation2- decrease of pH

Durability = Is the required performance preserved over the service life ?


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Layout




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e n on o ura y Influence of successive wetting and drying

Impact of water circulation



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Case 1: Effects of wet/dry cycles on a lime-

stabilised clayey soils

A34 clay (wL = 98,1 %, Ip = 61 %)

Short term effect of lime treatment

12

14

12

14

Without quicklime

3 % quicklime, 28 days of curing

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100 1000 10000

-4

-2

0

2

4

68

Swelling%

Time (min)100 1000 10000

-4

-2

0

2

4

68

Swelling(%)

Time (min)

Effect of successive wet/dry periods ?


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How to simulate wet/dry cycles in the

laboratory ?

1 : Oven full saturation

Disappearance of lime-stabilisation benefits after 2/3cycles (Khattab et al. 2007;Guney et. al 2007)

2 Unsaturated soil mechanictechnique

Perfect control of watercontent conditions

Amplitude of the wet/dry

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emar s :

Not representative ofactual wet/dry cycles dueto seasons alternation

Extreme cycles (kinetic,gradient)

cyc es morerepresentative of actualwet/dry cycles due toseasons

Unsaturated soil mechanic techniques Osmotic technique (suctions comprised between 0 and 8.5 MPa)

Salt solutions (above suction of 8.5 MPa)

Unsaturated soil mechanic techniques Osmotic technique (suctions comprised between 0 and 8.5 MPa)

Salt solutions (above suction of 8.5 MPa)


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Basic principle of the osmotic method

Osmotic principle

BA

waterC0h

BAFin l

Cf

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M M

Osmotic oedometer

Soil sample

Vertical stressv

Semi-permeable membrane

Contrle des changes deau

Pompe

PEG 6000 solution


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Influence of successive wet/dry cycles

Samples prepared in the laboratory :

10

)

w 50 %

Unstabilized10

15

)

3 % CaO, 1 month at 40C

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0 2000 4000 6000 8000 10000-5

0

5

Swellin

g(

Suction (kPa)

w 25 %w 30 %

0 2000 4000 6000 8000 10-5

0

5

Swellin

g(

Suction kPa

w 30 %

w 25 %

w 35 %

Short term efficiency of lime-stabilisation

regarding swelling and shrinkage


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Influence of successive wet/dry cycles Samples taken in the field (7 years after construction) :

2

4

6

8

10

(%)

Cycles between 0 and 1 MPa

w 43 %w 50 % 2

4

68

10

(%)

w 43 %

Cycles between 0 and 8.5 MPa

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0 200 400 600 800 1000 1200

-10

-8

-6

-4

-2

0

Swelling

Suction (kPa)

Swell/shrink potential null

0 2000 4000 6000 800

-10

-8

-6

-4

-2

Swelling

Suction (kPa)

w 30

w 43 %

Swell/shrink potential 8 %

The efficiency of lime stabilization has to be regardeds a function of the range of variation of the water content


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Effects of wet/dry cycles on a lime-stabilised clayeysoils

Conclusions Unsaturated soil mechanics techniques are able to

reproduce field conditions

The use of osmotic method demonstrated theability of stabilized soil to resist to wet/dry cycles

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on durability

Issues to assess durability of a lime-stabilisedstructure Prevision of the service life ? Wet/dry cycles amplitude ?

Impact of the initial conditions ?


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Layout




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e n on o ura y


Impact of water circulation



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Lime-stabilised silt under long term leaching

Determine the impact of water circulation on theshear strength of lime-stabilized soil

River levee Earth dam

Distilled water circulation e uilibrated with atmos here 80 kPa

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Flexible wall permeameter

Latex membrane

Porous stone

Soil sample

Frame

Confinin

g

pressure

Hydraulic head = 8 mi = 80

Cell confinment = 120 kPaCirculation duration = 320 days


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Characteristics of the tested soil

Selected soil : Jossigny silt

Geotechnical propertiesLiquid limit, wL (%) 37,0

Plastic limit, wP (%) 18,7

Index of plasticity , IP 18,3

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Preparation of the samples 0, 1 or 3% of quicklime

Optimum water content

Dynamic compaction

Unit weight of solids, S (Mg.m-3

) 2,69Fines contents, < 2 m (%) 29,4

50 mm

Position of

blows

ompac on moH = 100 mm

= 50 mm

Dynamiccompaction


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Short term behaviour : impact of lime

addition

Shear strength after 90 days of curing at constant w

CU + u triaxial tests

300

400

300

400t(kPa

300

400

No treatment

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0 100 200 300 400 500 600 700 800

0

100

200

0 100 200 300 400 500 600 700 800

0

100

200

s' (kPa)0 100 200 300 400 500 600 700 800

0

100

200 1 % of quicklime3 % of quicklime

Shear strength enveloppe constant from 1 to 3 % of quicklime


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Impact of water circulation after 150 days

of water circulation

Results with 1 % of quicklime

400

400t(kPa

No treatment

400

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0 100 200 300 400 500 600 700 8000

100

200

0 100 200 300 400 500 600 700 8000

100

200

s' (kPa)

90 days of curingAfter 150 days of flow

0 100 200 300 400 500 600 700 8000

100

200

Total loss of the improvement brought by lime


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400t(kPa

Impact of water circulation after 150 days

of water circulation

Results with 3 % of quicklime

400

No treatment

400

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0 100 200 300 400 500 600 700 8000

100

200

s' (kPa)0 100 200 300 400 500 600 700 800

0

100

20090 days of curing220 days of flow

0 100 200 300 400 500 600 700 8000

100

200

Stability of the mechanical behaviour


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Distribution of the calcium in the samplesCarbonates Free lime Ca in water

Leached calcium Cementitious compounds

1,00

1,20

1,40

1 % quicklime

2,00

2,50

3,00

3 % quicklime

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0,00

0,20

0,40

0,60

0,80

T =0 T =25 T =25+150 T =25+200 T =25+320

%

Ca

Curing period Leaching

0,00

0,50

1,00

1,50

T =0 T =25 T =25+150 T =25+200 T =25+320

%

Ca

Curing period Leaching

Key factor = amount of Ca and pH to maintain stability,The higher the CaO content, the longer the durability


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Conclusion

Shear strength increase brought by limeaddition is reversible Amount of binder should not only be adapted to

the short term performance but also toenvironmental stresses

Key parameters :

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moun o me a e eac e ca c um Flow of water Competition between dissolution / precipitation

processess

Further studies Impact of flow rate Microstructural alteration during flow

Nature of the circulating fluid (pH, species insolution)


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General conclusions and perspectives

Durability is to be defined regarding certain

environmental conditions (water contentvariation, water flux) The fundamental mechanisms of degradation

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cannot be understood without the analysisof microstructure and physico-chemicalprocesses

Need : predictive models to assess long termbehaviour and degradation


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Publications Cuisinier, O., Le Borgne, T., Deneele, D. & Masrouri, F. 2010.

Quantification of the detrimental effects of some chemicalcompounds on soil stabilization. Engineering Geology (accepted).

Deneele, D., Cuisinier, O., Hallaire, V. & Masrouri, F. 2010.

Microstructural evolution and physico-chemical behavior ofcompacted clayey soil submitted to an alkaline plume. Journal ofRock Mechanics and Geotechnical Engineering, 2 , 169-177.

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, ., , , . .

behaviour of compacted clayey soils submitted to an alkaline plume.Engineering Geology, 108, 177-188.

Le Runigo, B., Cuisinier, O., Cui, Y.-J., Deneele, D. & Ferber, V. 2009.Impact of the initial state on fabric and permeability of a limetreated silt under long term leaching. Canadian Geotechnical Journal,

46, 1243-1257.

Cuisinier, O., Masrouri, F., Pelletier, M., Villiras, F. & Mosser-Ruck,R. 2008. Microstructure of a compacted soil submitted to an alkalineplume. Applied Clay Science, vol. 40, n1-4, 159-170.


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National project on soil stabilization

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TerDOUESTTerDOUESTTerDOUESTTerDOUESTTerDOUESTTerDOUESTTerDOUESTTerDOUEST

http://www.cnrs-imn.fr/TerDOUEST/


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Thank you for your attention

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Documents

c4_Long-term behaviour of soils stabilized with lime cement_Nancy University.pdf