1、Designation: D 5298 03Standard Test Method forMeasurement of Soil Potential (Suction) Using Filter Paper1This standard is issued under the fixed designation D 5298; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last r
2、evision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers laboratory filter papers aspassive sensors to evaluate the soil matric (matrix) and totalpotential
3、(suction), a measure of the free energy of thepore-water or tension stress exerted on the pore-water by thesoil matrix (1, 2)2. The term potential or suction is descriptiveof the energy status of soil water.1.2 This test method controls the variables for measurementof the water content of filter pap
4、er that is in direct contact withsoil or in equilibrium with the partial pressure of water vaporin the air of an airtight container enclosing a soil specimen. Thefilter paper is enclosed with a soil specimen in the airtightcontainer until moisture equilibrium is established; that is, thepartial pres
5、sure of water vapor in the air is in equilibrium withthe vapor pressure of pore-water in the soil specimen.1.3 This test method provides a procedure for calibratingdifferent types of filter paper for use in evaluating soil matricand total potential.1.4 The values stated in SI units are to be regarde
6、d as thestandard. The inch-pounds units given in parentheses areapproximate.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determi
7、ne the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:C 114 Test Methods for Chemical Analysis of HydraulicCement3D 653 Terminology Relating to Soil, Rock, and ContainedFluids4D 1125 Test Method for Electrical Conductivity and Resis-tivity of Water5D
8、2216 Test Method for Laboratory Determination of Water(Moisture) Content of Soil and Rock4D 2325 Test Method for Capillary-Moisture Relationshipsfor Coarse and Medium-Textured Soils by Porous-PlateApparatus4D 3152 Test Method for Capillary-Moisture Relationshipsfor Fine-Textured Soils by Pressure-Me
9、mbrane Apparatus4D 4542 Test Method for Pore-Water Extraction and Deter-mination of the Solute Salt Content of Soils by Refracto-meter4D 4753 Specification for Evaluating, Selecting, and Speci-fying Balances and Scales for Use in Testing Soil, Rockand Related Construction Materials3E 337 Test Method
10、 for Measuring Humidity With a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures6E 832 Specification for Laboratory Filter Papers73. Terminology3.1 Definitions:3.1.1 Refer to Terminology D 653 for standard definitions ofterms.3.2 Definitions of Terms Specific to This Standard:3.2.1 a
11、tmospherea unit of pressure equal to 76 cm Mer-cury or 101 kPa at 0C.3.2.2 matric (matrix) suction, hm (kPa)the negative pres-sure (expressed as a positive value), relative to ambientatmospheric pressure on the soil water, to which a solutionidentical in composition with the soil water must be subje
12、ctedin order to be in equilibrium through a porous permeable wallwith the soil water; pressure equivalent to that measured byTest Methods D 2325 and D 3152. Matric suction is a functionof the relative humidity due to the difference in air and waterpressure across the water surface; the relative humi
13、dity orwater vapor pressure decreases as the radius of curvature of the1This test method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.04 on HydrologicProperties.Current edition approved June 10, 2003. Published August 2003. Orig
14、inallyapprovd in 1992. Discontinued December 2002 and reinstated as D 5298 03.2The boldface numbers given in parentheses refer to a list of references at theend of the text.3Annual Book of ASTM Standards, Vol 04.01.4Annual Book of ASTM Standards, Vol 04.08.5Annual Book of ASTM Standards, Vol 11.01.6
15、Annual Book of ASTM Standards, Vol 11.03.7Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.water surface decreases. The term “matric” is grammaticallycorrect, while matrix is commonly used in t
16、he civil engineeringliterature.3.2.3 molality, moles/1000 gnumber of moles of soluteper 1000 g of solvent.3.2.4 molemolecular weight of a substance in grams.3.2.5 osmotic (solute) suction, hs (kPa)the negative pres-sure to which a pool of pure water must be subjected in orderto be in equilibrium thr
17、ough a semipermeable membrane witha pool containing a solution identical in composition with thesoil water; decrease in relative humidity due to the presence ofdissolved salts in pore-water.3.2.6 pFa unit of negative pressure expressed as thelogarithm to the base ten of the height in centimeters tha
18、t acolumn of water will rise by capillary action or negative gagepressure (Mg/m2) divided by the unit weight of water (Mg/m3)times 1000. pF 3 + logarithm to the base ten of the negativepressure in atmospheres. Refer to capillary head or capillaryrise in Terminology D 653.3.2.7 soil relative humidity
19、, Rhthe ratio of the vaporpressure of pore water in the soil to the vapor pressure of freepure water. Relative humidity in the soil is defined as relativehumidity measured by Test Method E 337.3.2.8 total potential (kPa)the sum of gravitational, pres-sure, osmotic and external gas potentials. Potent
20、ial may beidentified with suction when gravitational and external gaspotentials are neglected.3.2.9 total soil suction, h (kPa)the negative pressure,relative to the external gas pressure on the soil water, to whicha pool of pure water must be subjected to be in equilibriumwith the soil water through
21、 a semipermeable membrane that ispermeable to water molecules only. Total soil suction (ex-pressed as a positive value) is the sum of osmotic (solute) andmatric (matrix) suctions.3.2.10 vapor pressure of free pure water (kPa)the satura-tion vapor pressure of free pure water at a given dry-bulbtemper
22、ature.3.2.11 vapor pressure of pore water in soil (kPa)thepartial pressure of water vapor that is in equilibrium withpore-water in soil at a given dry-bulb temperature.4. Summary of Test Method4.1 Filter papers are placed in an airtight container with aspecimen for seven days to allow sufficient tim
23、e for the vaporpressure of pore-water in the specimen, vapor pressure of porewater in the filter paper, and partial vapor pressure of water inthe air inside the container to reach equilibrium. The mass ofthe filter papers is subsequently determined and the suction ofthe specimen is determined from a
24、 calibration relationship ofthe filter paper water content with suction applicable to the typeof filter paper and the test procedure of this test method.5. Significance and Use5.1 Soil suction is a measure of the free energy of thepore-water in a soil. Soil suction in practical terms is a measureof
25、the affinity of soil to retain water and can provide informa-tion on soil parameters that are influenced by the soil water; forexample, volume change, deformation, and strength character-istics of the soil.5.2 Soil suction is related with soil water content throughwater retention characteristic curv
26、es (see Test Method D 2325).Soil water content may be found from Test Method D 2216.5.3 Measurements of soil suction may be used with othersoil and environmental parameters to evaluate hydrologicprocesses (1)8and to evaluate the potential for heave orshrinkage, shear strength, modulus, in situ stres
27、s and hydraulicconductivity of unsaturated soils.5.4 The filter paper method of evaluating suction is simpleand economical with a range from 10 to 100 000 kPa (0.1 to1000 bars).6. Apparatus6.1 Filter PaperThe paper used must be ash-free quanti-tative Type II filter paper, see Specification E 832; fo
28、r example,Whatman No. 42, Fisherbrand 9-790A,9Schleicher andSchuell No. 589 White Ribbon.9A suitable diameter is 5.5 cm(2.2 in.).NOTE 1Filter papers may be treated by dipping each paper in a 2 %concentration of formaldehyde prior to use to prevent organism growth onor biological decomposition of the
29、 filter paper. Biological decompositionmay be significant when filter papers are subject to a moist, warmenvironment for more than 14 days. Appropriate precautions should betaken when preparing formaldehyde solutions and treating filter paper.6.2 Specimen Container120 to 240 mL (4 to 8 oz)capacity m
30、etal or glass (rust free) container and lid (forexample, coated with zinc chromate to retard rusting) tocontain the specimen and filter papers. The inside of thesecontainers may also be coated with wax to retard rusting.6.3 Filter Paper ContainerThis container holds filterpaper following the equilib
31、ration of suction and removal fromthe specimen container.6.3.1 Metal Container AlternateTwo nominal 70 mL (2oz) capacity metal moisture containers (aluminum or stainless)with lids to dry the filter paper. The containers should benumbered by imprinting with a metal stamp. The containersshould not be
32、written on with any type of marker or labelled inany manner. Throw-away vinyl surgical non-powdered orsimilar gloves should be used anytime the small containersdesignated for filter paper measurements are handled to preventbody oils from influencing any mass measurements made priorto handling.6.3.2
33、Plastic Bag AlternatePlastic bag large enough toaccommodate the filter paper disks (approximately 50 mm indimension) capable of an airtight seal.6.4 Insulated ChestA box of approximately 0.03 m3(1 ft3)capacity insulated with foamed polystyrene or other materialcapable of maintaining temperature with
34、in 6 1C whenexternal temperatures vary 6 3C.6.5 BalanceA balance or scale having a minimum capac-ity of 20 g and meeting the requirements of 4.2.1.1 ofSpecification C 114 for a balance of 0.0001 g readability. Inaddition, balances for performance of Test Method D 2216,meeting requirements of Specifi
35、cation D 4753.8The boldface numbers in parentheses refer to the list of references at the end ofthis standard.9Available from Thomas Scientific Supply, P.O. Box 99, Swedesboro, NJ 08085.D52980326.6 Drying OvenThermostatically-controlled, preferablyof the forced-draft type, and capable of maintaining
36、 a uniformtemperature of 110 6 5C throughout the drying chamber andmeeting requirements of Test Method D 2216.6.7 Metal BlockA metal block 500 g mass with a flatsurface to hasten cooling of the metal containers with filterpaper.6.8 ThermometerAn instrument to determine the tem-perature of the tested
37、 soil to an accuracy of 6 1C.6.9 Miscellaneous EquipmentTweezers, trimming knife,flexible plastic electrical tape, O-rings, screen wire, brass discs,etc. Tweezers should be at least 110 mm (4.5 in.) in length.6.10 DesiccatorA desiccator jar of suitable size contain-ing silica gel or anhydrous calciu
38、m sulfate.NOTE 2Anhydrous calcium sulfate is sold under the trade nameDrierite.NOTE 3It is preferable to use a desiccant that changes color toindicate when it needs reconstitution.7. Calibration7.1 Obtain a calibration curve applicable to a specific filterpaper by following the procedure in Section
39、8, except forreplacing the soil specimen with salt solutions such as reagentgrade potassium chloride or sodium chloride of known mola-lity in distilled water.7.1.1 Suspend the filter paper above at least 50 cc of a saltsolution in the specimen container, see 6.2, by placing it on animprovised platfo
40、rm made of inert material such as plastictubing or stainless steel screen.7.1.2 Calculate the suction of the filter paper from therelative humidity of the air above the solution by:h 5RTv ln Rh(1)where:h = suction, kPa,R = ideal gas constant, 8.31432 Joules/moleK,T = absolute temperature, degrees ke
41、lvin (K),v = volume of 1000 moles of liquid water, 0.018 m3, andRh= relative humidity, fraction.7.1.3 Standard critical tables may be used to evaluate therelative humidity of water in equilibrium with the salt solutionas illustrated in Table 1. Refer to Test Method E 337 for furtherinformation on re
42、lative humidity.7.2 Typical calibration curves for filter papers (for example,Whatman No. 42,9Schleicher and Schuell No. 589),9see Fig.1, consists of two parts. The upper segment represents moistureretained as films adsorbed to particle surfaces, while the lowersegment represents moisture retained b
43、y capillary or surfacetension forces between particles. The filter paper water contentbreak point is wf= 45.3 percent for Whatman No. 42 (3, 4)9and wf= 54 % for Schleicher and Schuell No. 589 (2, 4).97.3 The calibration curves in Fig. 1 are applicable to totalsuction3. Variability in results is less
44、 than 2 % of the suctionabove 100 kPa. Soil disturbance has minimal influence onsuction above 20 kPa. At moisture contents with suctions lessthan 20 kPa, sample disturbance increases variability of mea-surement (2, 4). The right vertical axis of Fig. 1 provides thesuction in units pF and atmospheres
45、 pressure; for example, h= 2 log atmospheres is a suction of 100 atmospheres, while pF= 5 or 100 000 cm water.NOTE 4Filter paper may be calibrated by using the pressure mem-brane, see Test Method D 3152 for the range 100 to 1500 kPa (1 to 15atm), and the ceramic plate, see Test Method D 2325 for the
46、 range 10 to100 kPa (0.1 to 1 atm).8. Procedure8.1 Filter Paper PreparationDry filter papers selected fortesting at least 16 h or overnight in the drying oven. Place filterpapers in a desiccant jar over desiccant after drying for storageuntil use.8.2 Measurement of SuctionTotal suction will be mea-s
47、ured if filter papers are not in contact with the soil specimen;moisture transfer will be limited to vapor transfer through theair inside the specimen container. Matric suction will bemeasured if the filter paper is in physical contact with the soil.Physical contact between the soil and filter paper
48、 allows fluidtransfer including transfer of salts that may be dissolved in thepore water.NOTE 5When the soil is not sufficiently moist, adequate physicalcontact between the filter paper and soil may not always be possible. Thiscan cause an inaccurate measure of matric suction. Matric suction may bei
49、nferred by subtracting the osmotic suction from the total suction. Theosmotic suction may be determined by measuring the electrical conduc-tivity (see Test Method D 1125) of pore-water extracted from the soilusing a pore fluid squeezer (5) or using Test Method D 4542; a calibrationcurve (6) may be used to relate the electrical conductivity to the osmoticsuction.8.3 Filter Paper PlacementPlace an intact soil specimenor fragments of a soil sample, 200 to 400 g mass, in theTABLE 1 Salt Solution Concentrations for Evaluating SoilSuctionkPa log kPa pF
