MEASUREMENT OF SOIL SUCTION

Rifat Bulut, Ph.D.Rifat Bulut, Ph.D.Postdoctoral Research AssociateTexas Transportation Institute

Texas A&M UniversityCollege Station, TX 77843-3135

r-bulut@tamu.edu

Prof. Dr. Robert L. LyttonProf. Dr. Robert L. LyttonProfessor of Civil Engineering

Texas A&M UniversityCollege Station, TX 77843-3135

r-lytton@tamu.edu

TOTAL AND MATRICSUCTION MEASUREMENTSWITH THE FILTER PAPER

METHOD

Rifat Bulut, Ph.D.Rifat Bulut, Ph.D.

FUGRO SOUTH, INC.

2880 Virgo Lane

Dallas, Texas 75229

Phone : 972-484-8301

Fax : 972-620-7328

• A General View of LabMaterial Needed for the Filter

Paper Method

� Filter Papers

� Sensitive Balance

� Constant Temperature Container

� Oven

�Moisture Tins

� Glass Jars

� Tweezers

� Gloves

� PVC-Rings

� Electrical Tape

� Aluminum Block

=

ot P

PVRT

h ln

φνπ RTmh −=

THEORY OF CALIBRATION BASED ONWATER VAPOR MEASUREMENTS

• If initially dry filter papers are used for soil suction measurementsthen one of the wetting filter paper calibration curves given in thenext two slides can be adopted.

• A more detailed information about the calibration curves and soilsuction measurements can be found in the publications:

� Bulut, R., Lytton, R. L., and Wray, W. K. (2001).“Suction Measurements by Filter Paper,” Expansive ClaySoils and Vegetative Influence on Shallow Foundations,ASCE Geotechnical Special Publication No. 115 (eds. C.Vipulanandan, M. B. Addison, and M. Hasen), ASCE,Reston, Virginia, pp. 243-261.

� Bulut, R., Hineidi, S. M., and Bailey, B. (2002). “SuctionMeasurements – Filter Paper and Chilled MirrorPsychrometer,” The Proceedings, Texas Section ASCE, FallMeeting, Waco, Texas.

Schleicher & SchuellNo. 589-WH Filter Paper

|h| = -8.247w + 5.4246

R2 = 0.9969(1.5 < |h| < 4.15)

|h| = -6.6595w + 5.2262

R2 = 0.9905(1.82 < |h| < 3.66)

|h| = 1.1451w-0.6526

R2 = 0.9821(0.95 < |h| < 1.82)

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Filter paper water content, w

Su

ctio

n, i

n lo

g k

Pa

From initially dryfilter papers(Wetting Curve)

From initially wet filter papers(Drying Curve)

CALIBRATION CURVE [Bulut, R., Lytton, R. L., and Wray, W. K. (2001)]

Schleicher & Schuell No. 589-WH Filter Papers,NaCl Salt Solutions,Equilibrium Period: 21 Days,

Equilibrium Temperature: 25oC

h = -8.2414w + 6.3662

R2 = 0.9899(h > 2.5 pF)

Sensitivity Starts Below 2.5 pF

0

1

2

3

4

5

6

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55

Filter Paper Water Content, w

Tot

al S

uctio

n, h

, pF

CALIBRATION CURVE [Bulut, R., Hineidi, S. M., and Bailey, B. (2002)]

BEFORE COMMENCING THE TESTING,MAKE SURE THAT ALL ITEMS

RELATED TO FILTER PAPER METHODARE CLEAN, MOISTURE, OIL, AND

DUST FREE!

NOTE:

• Make sure that tweezers are used to handle filter papers

• Make sure that moisture tins, O-rings are handled with gloves

• Use a container that aShelby-tube soil sample canbe fit into easily without thedisturbance of the soil sample.

• Cut the soil sample into twohalves for matric suctionmeasurements.

• Make sure that the surfacesof the soil samples are smoothand flat for establishing anintimate contact between thesoil sample and the filter paperfor matric suctionmeasurements.

NOTE: When preparing the soilsamples make sure that sampledisturbance is minimal.

• Remove a Schleicher &Schleicher &

Schuell No. 589-WHSchuell No. 589-WH filter paperfrom the box using tweezers(5.5 cm in diameter)

Almost any brand of high permeability andlarger diameter filter paper can be used asprotective filter papers for matric suctionmeasurements (as shown in the lower left boxand in the picture, about 70 mm in diameter)

• For matric suctionmeasurements, insert asingle Schleicher & SchuellNo. 589-WH filter paper inbetween two larger indiameter protective filterpapers as shown on the right

• Using tweezers put thesandwiched filter papers ontop of the soil sample asshown on the left

• Put the other half ofthe soil sample on top,keeping thesandwiched filterpapers in betweenand in intimatecontact with the soilsamples

• Tape the two piecesof the soil sampletogether

NOTE: Electricaltape works nicely forthis purpose

• Insert a clean PVC O-ring,with the sharp edge facing up,on top of the soil sample fortotal suction measurements

• Place two Schleicher & Schuell No.Schleicher & Schuell No.

589-WH589-WH filter papers on top of thering as shown on the left

NOTE: Bend the edge of the topfilter paper up a little so that itwill be easy to remove them later!

• Put the lid on and tape ittight to prevent any moistureexchange between the airinside and the air outside ofthe jar

• Label the jar as necessary

• Insert the glass jar into awell-insulated containerfor suction equilibrium

NOTE: Temperaturecontrol is criticallyimportant

� Soil suction measurement set up, as described in theprevious slides, will be kept in a temperature-controlledenvironment for at least one week

� Temperature fluctuations should be kept as low aspossible, preferably below ± 1oC

� Refer to the publications that were cited before fordetailed information about the equilibration periods andtemperature control

• Before opening the lid ofthe temperature-controlledcontainer, take the dry, coldweight of the moisture tins

• Record all the weightswith their corresponding tinnumbers

NOTE: Use a balance atleast to the nearest 0.0001 g.accuracy

AT THE END OF AT LEASTONE WEEK OF

EQUILIBRIUM PERIOD:

• Remove a glass jarfrom the temperature-controlled container

• Time is critical at thisstage and thus it issuggested that twopeople share the work

• The time that the filterpapers are exposed to thelab environment shouldbe minimal, preferablyless than a few seconds

Note that while one person isopening the glass jar the otherperson is ready to pick up thefilter papers

• Open the glass jar andquickly carry the filterpaper to the moisture tinusing tweezers, in lessthan a few seconds

• Immediately close thelid of the moisture tinwith the wet filter paperinside

• After closing the lid ofthe moisture tin,immediately weigh thetin with the wet filterpaper inside

• Record the weight ascold tare plus wet filterpaper mass

Note that this is a totalsuction measurement

• Continue with the matric suctionmeasurement by removing the tapethat was holding the soil samplestogether

• Remove the filter paper thatwas sandwiched between thetwo protective filter papers

• Immediately carry the filterpaper to the moisture tin

• Record the weight as coldtare plus wet filter papermass

Note that this is a matricsuction measurement

• Immediately close thelid of the moisture tinand weigh the tin withthe wet filter paperinside

• After opening all the glass jars andrecording the weight of the moisturetins with the wet filter papers inside,carry them to a hot oven with thelids half open

• Leave them in the oven for at least10 hours

• Before taking them out fromthe oven, close their lids forequilibrium and leave them inthe oven for about 5 minutes

• Remove a hot tinfrom the oven and puton a large aluminumblock

NOTE: The aluminumblock will expedite theprocess of the cooling

• Leave the tin on the block for about 20seconds

• Weigh the hot tin with the dry filterpaper inside

• Record the weight as hot tare plus dryfilter paper mass

• Finally, take the dryfilter paper out of thetin

• Weigh the empty hottin

• Record the weight as hottare mass

• Repeat the above processfor other tins in the oven

• Calculate the moisture content of eachfilter paper for both total and matricsuction measurements. A calculationwork sheet as given in the next slide canbe used

• Obtain the suction value from anappropriate calibration curve that wasprovided above

MEASUREMENT OF SOIL SUCTION USING FILTER PAPER

BORING NO.:_________________ DATE TESTED:__________

DATE SAMPLED:______________ TESTED BY:____________

SAMPLE NO.:_________________

Depth

Moisture Tin No.

Top Filter Paper/Bottom Filter Paper (circle)

Top/Bot. Top/Bot. Top/Bot. Top/Bot. Top/Bot. Top/Bot.

Cold Tare Mass, g Tc

Mass of Wet Filter Paper + Cold Tare Mass, g

M1

Mass of Dry Filter Paper + Hot Tare Mass, g

M2

Hot Tare Mass, g Th

Mass of Dry Filter Paper, g (M2-Th)

Mf

Mass of Water in Filter Paper, g (M1-M2-Tc+Th)

Mw

Water Content of Filter Paper, g (Mw / Mf)

Wf

Suction, cm of water h

Suction, pF or log kPa h

A GOOD LABORATORY PROTOCOL ISA GOOD LABORATORY PROTOCOL ISESSENTIAL IN THE FILTER PAPERESSENTIAL IN THE FILTER PAPER

SOIL SUCTION MEASUREMENTSSOIL SUCTION MEASUREMENTS

-- Rifat Bulut, Ph.D.-- Rifat Bulut, Ph.D.

TRANSISTOR PSYCHROMETERTRANSISTOR PSYCHROMETER

(Total Suction Measurement)(Total Suction Measurement)

TWELVE-PROBE TRANSISTOR PSYCHROMETER

DATA LOGGER

THE PROBE TIP OF THE PSYCHROMETER

CALIBRATION CURVE

SALT SOLUTION CAPS AND TRAY

APPLYING WATER DROP

SEAL THE PROBE

SOIL SUCTION MEASUREMENTS

DISC OF SOIL SAMPLE

PLACE PLUG IN BOTTOM AND STOPPER IN TOP

SEAL THE PROBE

EIGHT PROBE MODEL INCLUDING DATA LOGGER

Transistor Psychrometeravailable at

http://www.smi-unsat.com

THERMOCOUPLE PSYCHROMETERTHERMOCOUPLE PSYCHROMETER

(Total Suction Measurement)(Total Suction Measurement)

HR 33T DEW POINT MICROVOLTMETER

THERMOCOUPLE PSYCHROMETERS

Thermocouple Psychrometeravailable at

http://www.wescor.com