measurement of soil suction - foundation · measurement of soil suction rifat bulut, ph.d....
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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
Prof. Dr. Robert L. LyttonProf. Dr. Robert L. LyttonProfessor of Civil Engineering
Texas A&M UniversityCollege Station, TX 77843-3135
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