1、Designation: D6836 02 (Reapproved 2008)2D6836 16Standard 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 D6836; the number immediat
2、ely following 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.1 NOTEMercury warnin
3、g and other minor changes were editorially added in November 2008.2 NOTE“1n” was editorially corrected to “ln” in Eq 12 in March 2009.1. Scope1.1 These test methods cover the determination of soil water characteristic curves (SWCCs) for desorption (drying). SWCCsdescribe the relationship between suc
4、tion and volumetric water content, gravimetric water content, or degree of water saturation.SWCCs are also referred to as soil water retention curves, soil water release curves, or capillary pressure curves.1.2 This standard describes five methods (A-E) for determining the soil water characteristic
5、curve. MethodA(hanging column)is suitable for making determinations for suctions in the range of 0 to 80 kPa. Method B (pressure chamber with volumetricmeasurement) and Method C (pressure chamber with gravimetric measurement) are suitable for suctions in the range of 0 to 1500kPa. Method D (chilled
6、mirror hygrometer) is suitable for making determinations for suctions in the range of 500 kPa to 100 MPa.Method E (centrifuge method) is suitable for making determinations in the range 0 to 120 kPa. Method A typically is used forcoarse soils with little fines that drain readily. Methods B and C typi
7、cally are used for finer soils, which retain water more tightly.Method D is used when suctions near saturation are not required and commonly is employed to define the dry end of the soil watercharacteristic curve (that is, water contents corresponding to suctions 1000 1000 kPa). Method E is typicall
8、y used for coarsersoils where an appreciable amount of water can be extracted with suctions up to 120 kPa.The methods may be combined to providea detailed description of the soil water characteristic curve. In this application, Method A or E is used to define the soil watercharacteristic curve at lo
9、wer suctions (0 to 80 kPa forA, 0 to 120 kPa for E) near saturation and to accurately identify the air entrysuction, Method B or C is used to define the soil water characteristic curve for intermediate water contents and suctions (100 to1000 kPa), and Method D is used to define the soil water charac
10、teristic curves at low water contents and higher suctions ( 1000(1000 kPa).1.3 All observed and calculated values shall conform to the guide for significant digits and rounding established in PracticeD6026. The procedures in Practice D6026 that are used to specify how data are collected, recorded, a
11、nd calculated are regardedas the industry standard. In addition, they are representative of the significant digits that should generally be retained. Theprocedures do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations forthe objectives of
12、the user. Increasing or reducing the significant digits of reported data to be commensurate with theseconsiderations is common practice. Consideration of the significant digits to be used in analysis methods for engineering designis beyond the scope of this standard.1.4 UnitsThe values stated in SI
13、units are to be regarded as standard. No other units of measurement are included in thisstandard.1.5 WarningMercury has been designated by EPA and many state agencies as a hazardous material that can cause centralnervous system, kidney, and liver damage. Mercury, or its vapor, may be hazardous to he
14、alth and corrosive to materials. Cautionshould be taken when handling mercury and mercury-containing products. See the applicable product Material Safety Data Sheet(MSDS) for details and EPAs website (http:/www.epa.gov/mercury/faq.htm ) for additional information. Users should be awarethat selling m
15、ercury or mercury-containing products, or both, in your state may be prohibited by state law.1 These test methods are under the jurisdiction of ASTM Committee D18 on Soil and Rock and are the direct responsibility of Subcommittee D18.04 on HydrologicProperties and Hydraulic Barriers.Current edition
16、approved Sept. 1, 2008Nov. 15, 2016. Published November 2008December 2016. Originally approved in 2002. Last previous edition approved in 20022008as D6836 02.D6836 02(2008)2. DOI: 10.1520/D6836-02R08E02.10.1520/D6836-16.This document is not an ASTM standard and is intended only to provide the user o
17、f an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as pu
18、blished by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibil
19、ityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D421 Practice for Dry Preparation of Soil Samples for Particle-Size Analysis and Determination of Soil
20、 Constants (Withdrawn2016)3D425 Test Method for Centrifuge Moisture Equivalent of SoilsD653 Terminology Relating to Soil, Rock, and Contained FluidsD698 Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft3 (600 kN-m/m3)D854 Test Methods for Specific
21、 Gravity of Soil Solids by Water PycnometerD2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by MassD3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used inEngineering Design and ConstructionD4753
22、 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and ConstructionMaterials TestingD5084 Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible WallPermeameterD6026 Practice for Using Significant Digits
23、 in Geotechnical Data2.2 API Standard:API RP 40 Recommended Practice for Core-Analysis Procedure43. Terminology3.1 For common definitions of other terms in this standard see Terminology D653.Definitions:3.1.1 For common definitions of technical terms in this standard, refer to Terminology D653.3.2 D
24、efinitions of Terms Specific to This Standard:3.2.1 air entry pressurethe air pressure required to introduce air into and through the pores of a saturated porous plate.3.2.2 air entry suction, athe suction required to introduce air into and through the pores of a saturated porous material.3.2.3 axis
25、 translationthe principle stating that a matric suction can be applied to a soil by controlling the pore gas pressure,ug, and the pore water pressure, uw, so that the difference between the pore gas pressure and pore water pressure equals the desiredmatric suction, that is, = ug uw.3.2.4 gravimetric
26、 water content, wthe ratio of the mass of water contained in the pore spaces of soil or rock to the mass ofsolid particles.3.2.5 matric suction, the negative gagegauge pressure, relative to an external gas pressure acting on the soil water, that mustbe applied to a solution identical in composition
27、to the soil water to maintain equilibrium through a porous membrane existingbetween the solution and the soil water. Matric suction is also referred to as matric potential, capillary suction, and capillarypotential. By definition, matric suction is the difference between the pore gas pressure, ug, a
28、nd the pore water pressure, uw, thatis, = ug uw. In most cases the pore gas is air.3.2.6 osmotic suction, othe negative gagegauge pressure derived from the measurement of the vapor pressure of water inequilibrium with a solution identical in composition with the soil water, relative to the vapor pre
29、ssure of water in equilibrium withfree pure water. Osmotic suction is also referred to as osmotic potential.3.2.7 porous membranea porous polymeric membrane that can transmit water and has a air entry pressure exceeding thehighest matric suction to be applied during a test.3.2.8 porous platea plate
30、made of metal, ceramic, or other porous material that can transmit water and has an air entry pressureexceeding the highest matric suction to be applied during a test.3.2.9 pressure chambera vessel used to apply a gas pressure on the specimen and the soil pores to induce a specified matricsuction.3.
31、2.10 saturated water contentvolumetric or gravimetric water content when the specimen is saturated.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Docu
32、ment Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.4 Available from American Petroleum Institute (API), 1220 L. St., NW, Washington, DC 20005-4070, http:/www.api.org.D6836 1623.2.11 soil water characteristic curvea graph of suc
33、tion (matric or total) versus water content (gravimetric or volumetric) orsaturation. The soil water characteristic curve is also referred to as the soil water retention curve, the soil water release curve, andthe capillary pressure curve.3.2.12 total suction, tthe negative gagegauge pressure derive
34、d from the measurement of the vapor pressure of water inequilibrium with water in the soil pores, relative to the vapor pressure of water in equilibrium with free pure water. Total suctionis the sum of matric and osmotic suction, t = + o. Total suction is also referred to as total potential.3.2.13 v
35、olumetric water content, the ratio of the volume of 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 of water in the soil gas to the saturated vapor pressure at the existing soiltemperature. Water activity is
36、also referred to as the relative humidity.4. Summary of Methods4.1 Methods A-CMethods A-C yield soil water characteristic curves in terms of matric suction. Various suctions are appliedto the soil and the corresponding water contents are measured. Two different procedures are used to apply the sucti
37、on. In MethodA, the matric suction is applied by reducing the pore water pressure while maintaining the pore gas pressure at the atmosphericcondition. In Methods B and C, the pore water pressure is maintained at atmospheric pressure, and the pore gas pressure is raisedto apply the suction via the ax
38、is translation principle.4.1.1 For all three methods, saturated soil specimens are placed in contact with a water saturated porous plate or membrane.The matric suction is applied by one of the two aforementioned procedures.Application of the matric suction causes water to flowfrom the specimen until
39、 the equilibrium water content corresponding to the applied suction is reached. Equilibrium is establishedby monitoring when water ceases to flow from the specimen. Several equilibria are established at successive matric suctions toconstruct a soil water characteristic curve.4.1.2 The water content
40、corresponding to the applied suction is determined in one of two ways. For Methods A and B, thevolume of water expelled is measured using a capillary tube.The water content is then determined based on the known initial watercontent of the specimen and the volume of water expelled. For Method C, the
41、water content is measured gravimetrically byweighing the specimen after removal from the apparatus.4.2 Method DMethod D yields a soil water characteristic curve in terms of total suction. In contrast to MethodsA-C, the watercontent of the soil is controlled in Method D, and the corresponding suction
42、s are measured. Two different approaches arecommonly used. In one approach, a set of specimens are prepared that are essentially identical, but have different water contents.Water contents are selected that span the range of water contents that will be used to define the soil water characteristic cu
43、rve. Inthe other approach, a single specimen is used. The specimen is tested, dried to a lower water content, and then tested again. Thisprocess is repeated until suctions have been measured at all of the desired water contents.4.2.1 In Method D, the water activity of the pore water is measured usin
44、g a chilled mirror hygrometer (also known as a chilledmirror psychrometer) and then the total suction is computed using the Kelvin equation. In many cases, Method D is used todetermine only that portion of the soil water characteristic curve corresponding to higher suctions (typically 1000 1000 kPa)
45、and lower water contents. Under these conditions, the osmotic component of total suction is generally small, and the matric andtotal suctions are comparable. Thus, the data from Methods A-C and Method D can be combined to form a single soil watercharacteristic curve. An example of this type of soil
46、water characteristic curve is provided in Section 11.4.3 Method EMethod E yields a soil water characteristic curve in terms of matric suction (or capillary pressure).The specimenis contained in a support chamber that is subjected to a centrifugal force in a centrifuge. Different matric suctions are
47、applied byvarying the angular velocity of the centrifuge. Water displaced from the soil at a given angular velocity is collected and measuredin a calibrated cylinder at the base of the support chamber.Asoil water characteristic curve is measured by subjecting the specimento a series of angular veloc
48、ities (each corresponding to a matric suction) and measuring the volume of water displaced from thesoil at each velocity.5. Significance and Use5.1 The soil water characteristic curve (SWCC) is fundamental to hydrological characterization of unsaturated soils and isrequired for most analyses of wate
49、r movement in unsaturated soils. The SWCC is also used in characterizing the shear strengthand compressibility of unsaturated soils. The unsaturated hydraulic conductivity of soil is often estimated using properties of theSWCC and the saturated hydraulic conductivity.5.2 This method applies only to soils containing two pore fluids: a gas and a liquid. The liquid is usually water and the gas isusually air. Other liquids may also be used, but caution must be exercised if the liquid being used causes excessive shrinkage orswelling of
