1、Designation: D 6836 02 (Reapproved 2008)1Standard Test Methods forDetermination of the Soil Water Characteristic Curve forDesorption Using Hanging Column, Pressure Extractor,Chilled Mirror Hygrometer, or Centrifuge1This standard is issued under the fixed designation D 6836; the number immediately fo
2、llowing the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEMercury warning and o
3、ther minor changes were editorially added in November 2008.1. Scope1.1 These test methods cover the determination of soil watercharacteristic curves (SWCCs) for desorption (drying).SWCCs describe the relationship between suction and volu-metric water content, gravimetric water content, or degree ofw
4、ater saturation. SWCCs are also referred to as soil waterretention curves, soil water release curves, or capillary pressurecurves.1.2 This standard describes five methods (A-E) for deter-mining the soil water characteristic curve. Method A (hangingcolumn) is suitable for making determinations for su
5、ctions inthe range of 0 to 80 kPa. Method B (pressure chamber withvolumetric measurement) and Method C (pressure chamberwith gravimetric measurement) are suitable for suctions in therange of 0 to 1500 kPa. Method D (chilled mirror hygrometer)is suitable for making determinations for suctions in the
6、rangeof 500 kPa to 100 MPa. Method E (centrifuge method) issuitable for making determinations in the range 0 to 120 kPa.MethodAtypically is used for coarse soils with little fines thatdrain readily. Methods B and C typically are used for finer soilswhich retain water more tightly. Method D is used w
7、hensuctions near saturation are not required and commonly isemployed to define the dry end of the soil water characteristiccurve (that is, water contents corresponding to suctions 1000kPa). Method E is typically used for coarser soils where anappreciable amount of water can be extracted with suction
8、s upto 120 kPa. The methods may be combined to provide adetailed description of the soil water characteristic curve. Inthis application, Method A or E is used to define the soil watercharacteristic curve at lower suctions (0 to 80 kPa for A, 0 to120 kPa for E) near saturation and to accurately ident
9、ify the airentry suction, Method B or C is used to define the soil watercharacteristic curve for intermediate water contents and suc-tions (100 to 1000 kPa), and Method D is used to define the soilwater characteristic curves at low water contents and highersuctions ( 1000 kPa).1.3 All observed and c
10、alculated values shall conform to theguide for significant digits and rounding established in PracticeD 6026. The procedures in Practice D 6026 that are used tospecify how data are collected, recorded, and calculated areregarded as the industry standard. In addition, they are repre-sentative of the
11、significant digits that should generally beretained. The procedures do not consider material variation,purpose for obtaining the data, special purpose studies, or anyconsiderations for the objectives of the user. Increasing orreducing the significant digits of reported data to be commen-surate with
12、these considerations is common practice. Consid-eration of the significant digits to be used in analysis methodsfor engineering design is beyond the scope of this standard.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5
13、WarningMercury has been designated by EPA andmany state agencies as a hazardous material that can causecentral nervous system, kidney, and liver damage. Mercury, orits vapor, may be hazardous to health and corrosive tomaterials. Caution should be taken when handling mercury andmercury-containing pro
14、ducts. See the applicable product Ma-terial Safety Data Sheet (MSDS) for details and EPAs website(http:/www.epa.gov/mercury/faq.htm) for additional informa-tion. Users should be aware that selling mercury or mercury-containing products, or both, in your state may be prohibited bystate law.1These tes
15、t methods are under the jurisdiction ofASTM Committee D18 on Soiland Rock and are the direct responsibility of Subcommittee D18.04 on HydrologicProperties and Hydraulic Barriers.Current edition approved Sept. 1, 2008. Published November 2008. Originallyapproved in 2002. Last previous edition approve
16、d in 2002 as D 6836 02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1.6 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
17、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 421 Practice for Dry Preparation of Soil Samples forParticle-Size Analysis and Determination of Soil Con-stantsD 425 Test Method for
18、 Centrifuge Moisture Equivalent ofSoilsD 653 Terminology Relating to Soil, Rock, and ContainedFluidsD 698 Test Methods for Laboratory Compaction Character-istics of Soil Using Standard Effort (12 400 ft-lbf/ft3(600kN-m/m3)D 854 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD 221
19、6 Test Methods for Laboratory Determination of Wa-ter (Moisture) Content of Soil and Rock by MassD 3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUsed in Engineering Design and ConstructionD 4753 Guide for Evaluating, Selecting, and Specify
20、ingBalances and Standard Masses for Use in Soil, Rock, andConstruction Materials TestingD 5084 Test Methods for Measurement of Hydraulic Con-ductivity of Saturated Porous Materials Using a FlexibleWall PermeameterD 6026 Practice for Using Significant Digits in Geotechni-cal Data2.2 API Standard:API
21、RP 40 Recommended Practice for Core-Analysis Pro-cedure33. Terminology3.1 For common definitions of other terms in this standardsee Terminology D 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 air entry pressurethe air pressure required to intro-duce air into and through the pores of a
22、 saturated porous plate.3.2.2 air entry suction, cathe suction required to intro-duce air into and through the pores of a saturated porousmaterial.3.2.3 axis translationthe principle stating that a matricsuction c can be applied to a soil by controlling the pore gaspressure, ug, and the pore water p
23、ressure, uw, so that thedifference between the pore gas pressure and pore waterpressure equals the desired matric suction, that is, c = ug uw.3.2.4 gravimetric water content, wthe ratio of the mass ofwater contained in the pore spaces of soil or rock to the massof solid particles.3.2.5 matric suctio
24、n, cthe negative gage pressure, rela-tive to an external gas pressure acting on the soil water, thatmust be applied to a solution identical in composition to thesoil water to maintain equilibrium through a porous membraneexisting between the solution and the soil water. Matric suctionis also referre
25、d to as matric potential, capillary suction, andcapillary potential. By definition, matric suction is the differ-ence between the pore gas pressure, ug, and the pore waterpressure, uw, that is, c = ug uw. In most cases the pore gas isair.3.2.6 osmotic suction, cothe negative gage pressure de-rived f
26、rom the measurement of the vapor pressure of water inequilibrium with a solution identical in composition with thesoil water, relative to the vapor pressure of water in equilibriumwith free pure water. Osmotic suction is also referred to asosmotic potential.3.2.7 porous membranea porous polymeric me
27、mbranethat can transmit water and has a air entry pressure exceedingthe highest matric suction to be applied during a test.3.2.8 porous platea plate made of metal, ceramic, or otherporous material that can transmit water and has an air entrypressure exceeding the highest matric suction to be applied
28、during a test.3.2.9 pressure chambera vessel used to apply a gaspressure on the specimen and the soil pores to induce aspecified matric suction.3.2.10 saturated water contentvolumetric or gravimetricwater content when the specimen is saturated.3.2.11 soil water characteristic curvea graph of suction
29、(matric or total) versus water content (gravimetric or volumet-ric) or saturation. The soil water characteristic curve is alsoreferred to as the soil water retention curve, the soil waterrelease curve, and the capillary pressure curve.3.2.12 total suction, ctthe negative gage pressure derivedfrom th
30、e measurement of the vapor pressure of water inequilibrium with water in the soil pores, relative to the vaporpressure of water in equilibrium with free pure water. Totalsuction is the sum of matric and osmotic suction, ct= c + co.Total suction is also referred to as total potential.3.2.13 volumetri
31、c water content, uthe ratio of the volumeof water contained in the pore spaces of soil or rock to the totalvolume of soil and rock.3.2.14 water activity, awthe ratio of vapor pressure ofwater in the soil gas to the saturated vapor pressure at theexisting soil temperature. Water activity is also refe
32、rred to asthe relative humidity.4. Summary of Methods4.1 Methods A-CMethods A-C yield soil water character-istic curves in terms of matric suction. Various suctions areapplied to the soil and the corresponding water contents aremeasured. Two different procedures are used to apply thesuction. In Meth
33、odA, the matric suction is applied by reducingthe pore water pressure while maintaining the pore gas pressureat the atmospheric condition. In Methods B and C, the pore2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual
34、Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Petroleum Institute (API), 1220 L. St., NW, Wash-ington, DC 20005-4070, http:/www.api.org.D 6836 02 (2008)12water pressure is maintained at atmospheric pressure, and the
35、pore gas pressure is raised to apply the suction via the axistranslation principle.4.1.1 For all three methods, saturated soil specimens areplaced in contact with a water saturated porous plate ormembrane. The matric suction is applied by one of the twoaforementioned procedures. Application of the m
36、atric suctioncauses water to flow from the specimen until the equilibriumwater content corresponding to the applied suction is reached.Equilibrium is established by monitoring when water ceases toflow from the specimen. Several equilibria are established atsuccessive matric suctions to construct a s
37、oil water character-istic curve.4.1.2 The water content corresponding to the applied suc-tion is determined in one of two ways. For Methods A and B,the volume of water expelled is measured using a capillarytube. The water content is then determined based on the knowninitial water content of the spec
38、imen and the volume of waterexpelled. For Method C, the water content is measuredgravimetrically by weighing the specimen after removal fromthe apparatus.4.2 Method DMethod D yields a soil water characteristiccurve in terms of total suction. In contrast to MethodsA-C, thewater content of the soil is
39、 controlled in Method D, and thecorresponding suctions are measured. Two different ap-proaches are commonly used. In one approach, a set ofspecimens are prepared that are essentially identical, but havedifferent water contents. Water contents are selected that spanthe range of water contents that wi
40、ll be used to define the soilwater characteristic curve. In the other approach, a singlespecimen is used. The specimen is tested, dried to a lowerwater content, and then tested again. This process is repeateduntil suctions have been measured at all of the desired watercontents.4.2.1 In Method D, the
41、 water activity of the pore water ismeasured using a chilled mirror hygrometer (also known as achilled mirror psychrometer) and then the total suction iscomputed using the Kelvin equation. In many cases, Method Dis used to determine only that portion of the soil watercharacteristic curve correspondi
42、ng to higher suctions (typically 1000 kPa) and lower water contents. Under these conditions,the osmotic component of total suction is generally small, andthe matric and total suctions are comparable. Thus, the datafrom Methods A-C and Method D can be combined to form asingle soil water characteristi
43、c curve. An example of this typeof soil water characteristic curve is provided in Section 11.4.3 Method EMethod E yields a soil water characteristiccurve in terms of matric suction (or capillary pressure). Thespecimen is contained in a support chamber that is subjected toa centrifugal force in a cen
44、trifuge. Different matric suctions areapplied by varying the angular velocity of the centrifuge.Waterdisplaced from the soil at a given angular velocity is collectedand measured in a calibrated cylinder at the base of the supportchamber. A soil water characteristic curve is measured bysubjecting the
45、 specimen to a series of angular velocities (eachcorresponding to a matric suction) and measuring the volumeof water displaced from the soil at each velocity.5. Significance and Use5.1 The soil water characteristic curve (SWCC) is funda-mental to hydrological characterization of unsaturated soils an
46、dis required for most analyses of water movement in unsaturatedsoils. The SWCC is also used in characterizing the shearstrength and compressibility of unsaturated soils. The unsatur-ated hydraulic conductivity of soil is often estimated usingproperties of the SWCC and the saturated hydraulic conduc-
47、tivity.5.2 This method applies only to soils containing two porefluids: a gas and a liquid. The liquid is usually water and thegas is usually air. Other liquids may also be used, but cautionmust be exercised if the liquid being used causes excessiveshrinkage or swelling of the soil matrix.5.3 A full
48、 investigation has not been conducted regardingthe correlation between soil water characteristic curves ob-tained using this method and soil water characteristics curvesof in-place materials. Thus, results obtained from this methodshould be applied to field situations with caution and byqualified pe
49、rsonnel.NOTE 1The quality of the result produced by this standard depends onthe competence of the personnel performing the test and the suitability ofthe equipment and facilities used. Agencies that meet the criteria ofPractice D 3740 are generally considered capable of competent andobjective testing, sampling, inspection, etc. Users of this standard arecautioned that compliance with Practice D 3740 does not in itself ensurereliable results. Reliable results depend on many factors. Practice D 3740provides a means of evaluating some of these factors.6. Ap
