Experus State-of-the-Art Report

Vapour Equilibrium and Osmotic Technique for Suction Control

J.A. BlatzUniversity of Manitoba, Dept. of Civil Engineering, Manitoba, Winnipeg, Canada

Y-J. CuiEcole Nationale des Ponts et Chaussées – CERMES, Paris, France

L.A. OldecopIDIA, Universidad Nacional de San Juan, Argentina

Reporters

• James Blatz– University of Manitoba, Winnipeg, MB, CANADA

• Yu-Jun Cui– Ecole Nationale des Ponts et Chaussées – CERMES,

Paris, France

• Luciano Oldecop– IDIA, Universidad Nacional de San Juan, Argentina

Introduction

• State-of-Art-Report Background• Introduction - Vapour Equilibrium Method• Use of VET in Traditional Laboratory Tests• Introduction - Osmotic Method• Use of OM in Traditional Laboratory Tests• Unique Application of the Methods• Limitations and Uncertainty• Conclusions / Discussion Period

State-of-Art-Report Background

• Contacted researchers from all corners of the world.– 28 research groups were solicited for input

• Conducted extensive literature review.– 53 references in the final manuscript for the report.

• Reviewed and edited by the reporters.– Aim was to provide a reasonably comprehensive

summary of past and recent work.

Reference Dates

>1959 1960-1969 1970-1979 1980-1989 1990-1999 2000-20050

5

10

15

20

25

N

umbe

r of C

itatio

ns

Time Period

53 Total Citations

Contributing Groups• Universitat Politècnica de Catalunya

Barcelona, Spain• Ecole Nationale des Ponts et Chaussées

CERMES, Paris, France• Imperial College

London, England• University of Saskatchewan (USG)

Saskatoon, Saskatchewan• Università degli Studi di Trento

Trento, Italy

Suction and Relative Humidity

π+−= )( wa uuS

)ln()/1(

RHM

TRSww

⋅⋅

=ρ

Importance of Suction Control

• Fundamental stress state variable for unsaturated materials (Fredlund and Morgenstern 1976)

• Application of stress paths consistent with our physical environment.

• Necessary for development of constitutive models that can predict the behaviour of unsaturated soils.

Vapour Equilibrium Method

After Tang and Cui (2005)

Vapour Equilibrium Method

VET in Traditional Laboratory Tests

After Bernier et al. (1997)

VET in Traditional Laboratory Tests

After Cuisinier and Masrouri (2004)

VET in Traditional Laboratory Tests

After Hoffman et al. (2005)

UPC Barcelona Oedometer

Combines VET and axis translation to optimize the capabilities of the apparatus over a large range of suction control.

VET in Traditional Laboratory Tests

After Cunningham et al. (2003)

VET in Traditional Laboratory Tests

After Blatz and Graham (2003)

VET in Traditional Laboratory Tests

After Lourenço et al. (2006)

Osmotic Method (OM)

History of the Osmotic Method (OM)

• MEDICINE : Dialysis membrane• BIOLOGY : Lagerwerff et al. (1961)• SOIL SCIENCE : Zur (1966)• GEOTECHNICAL Eng. : Kassiff & Ben

Shalom (1971)

MATERIALS for OM

• PEG : POLYETHYLENE GLYCOL (C2H4)n

– high molar mass : 1500 to 20 000– aqueous solution

• DYALISIS CELLULOTIC MEMBRANES– variable molecular weight cut-off

(MWCO), corresponding to PEG molar mass :

PEG 20 000 / MWCO 14 000 , PEG 6 000 / MWCO 4 000…

PEG CALIBRATION for OM

After Delage et al. (1998)

Imposing suction using OM

After Cui and Delage (1996)

OM in Laboratory Tests

After Kassiff & Ben Shalom (1971) and Delage et al. (1992)

OM in Laboratory Tests

After Cui & Delage (1996)

Unique applications• 5 papers presented in the current session

Type of application

TECHNIQUESAUTHORS

VET

VET/OM

VET/ATT

VET/ATT

VET/OM

uniqueTaïbi et al

uniqueVillar et al

uniqueHoffmann et al

traditionalAgus & Schanz

traditionalAbou-Bekr et al

Unique applications

After Oldecop and Alonso (2004)

Rockfill testing:- Sharp edges of rock particles- No continuity of the liquid phase.

Other methods for suction control are not applicable.

3 Load cellsHygrometer

Displacement transducer

Air pump

Salinesolution

Solution vessel(not to scale)

ROWE OEDOMETER (300 mm in diam.)

Advantages of VET

• High versatility (no interface elements needed). Easy to install in most test setup.

• No air pressure within the specimen.

• Very high (total) suction values can be attained with VET (as with no other method).

• Suitable for producing gradual and uniform changes in moisture across the specimen.

Limitations and drawbacks of VET• Long equilibration periods (can be reduced by

forcing air circulation)

• An environment with controlled temperature is required. Temperature gradients in the system should be strictly avoided.

• Inconsistency of measured/controlled suction variable with the rest of the methods.

• VET is ill-suited for the low suction range (less than 10 MPa).

Limitations of VET

After Oldecop and Alonso (2004)

+2%

RH-2%

RH

+1%RH

-1%RH

+0,5%RH

-0,5%RH

-100

-80

-60

-40

-20

0

20

40

60

80

100

0,1 1 10 100 1000Total suction [MPa]

Unc

erta

inty

in th

e de

rived

tota

l suc

tion

[%]

T = 22°C

ADVANTAGES of OM

• Liquid water transfer• No air pressure inside the sample, water

really under suction– closer to reality, specially near saturation

(cf. air occlusion)– safer (no air pressures containment)– higher suctions easily attained : 1.5 MPa – 10 MPa

possibly 12 MPa

• Easy, inexpensive determination of Water Retention Curves (WRC)

DRAWBACKS of OM

• Membrane fragility– bacteria attacks : several drops of Penicillin in solution : ⇒ 1 month resistance

– mechanical resistance to shear– Temperature affected (Taïbi et al , EXPERUS)

• High solution viscosity at higher suctions (> 5 MPa)

Final remarks

• VET and OM are well established methods for controlling suction. New application possibilities are still developing.

• Both methods provide higher suctions ranges than others available methods. Good complementation possibilities.

• A common attractive feature of both methods is that the air pressure within the specimen is the atmospheric.

• Comparative experimental results (as those presented by Abou-Bekr et al, Experus) would be helpful in developing more confident testing procedures

Instituto de Investigaciones Antisísmicas “Ing. Aldo Bruschi” Facultad de IngenieríaUniversidad Nacional de San Juan

Centre d'Enseignement et de Recherche enMécanique des Sols Ecole nationale des ponts et chaussées

Geotechnical GroupDepartment of Civil EngineeringUniversity of Manitoba, Winnipeg, MB

QUESTIONS?

Unique Applications of VET and OM

After Villar et al. (2005)

Sample Porous plate SteelSample Porous plate Steel

Unique Applications of VET and OM

After Taibi et al. (2005)

Comparison of VET and OM

After Abou-Bekr et al. (2005)

Advantages VET

• No air pressure inside the sample, water really under suction– Better representation of the physical

environment, specially near saturation (cf. air occlusion)– higher suctions easily attained :

approximately 4MPa to the theorecticallimit.

Drawbacks (VET)

• Long equilibration times– Unless an advective flow system is utilized.

• Very difficult to precicely control suctions in the lower range– Due to measurement error with mass of dissicant

especially for unsaturated solutions.

• Very sensitive to temperature changes– Important to have appropriate control of

temperature.

Limitations of VET

After Agus and Schanz (2005)