1、Designation: D 6836 02Standard Test Methods forDetermination of the Soil Water Chararcteristic Curve forDesorption Using a Hanging Column, Pressure Extractor,Chilled Mirror Hygrometer, and/or Centrifuge1This standard is issued under the fixed designation D 6836; the number immediately following the
2、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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers t
3、he 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 ofwater saturation. SWCCs are also referred to as soil waterretention curves, soil water release cur
4、ves, 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 suctions inthe range of 0 to 80 kPa. Method B (pressure chamber withvolumetric measurement) and Met
5、hod 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 rangeof 500 kPa to 100 MPa. Method E (centrifuge method) issuitable for making determinations in
6、the range 0 to 120 kPa.Method A typically 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 whensuctions near saturation are not required and commonly isemployed to define the dry end of t
7、he 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 suctions upto 120 kPa. The methods may be combined to provide adetailed description of the soil water
8、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 identify the airentry suction, Method B or C is used to define the soil watercharacteristic curve fo
9、r 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) and1.3 All observed and calculated values shall conform to theguide for significant digits and rounding established i
10、n 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 significant digits that should generally beretained. The procedures do not consider material
11、 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 these considerations is common practice. Consid-eration of the significant digits to be used
12、 in analysis methodsfor engineering design is beyond the scope of this standard.1.4 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 det
13、ermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 421 Practice for Dry Preparation of Soil Samples forParticle-Size Analysis and Determination of Soil Contents2D 425 Test Method for Centrifuge Moisture Equivalent ofSoils2D 653 Terminology Re
14、lating to Soil, Rock, and ContainedFluids2D 698 Test Method for Laboratory Compaction Character-istics of Soil Using Standard Effort 600 kN-mJ/m32D 854 Test Method for Specific Gravity of Soils2D 2216 Method for Laboratory Determination of Water(Moisture) Content of Soil, Rock, and Soil-AggregateMix
15、tures2D 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and Construction2D 4753 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Desi
16、gn and Construction21This test method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.04 on HydrologicProperties of Soil and Rocks.Current edition approved Nov. 11, 2002. Published February 2003.2Annual Book of ASTM Standards, Vol
17、04.08.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.D 5084 Test Methods for Measurement of Hydraulic Con-ductivity of Porous Materials Using a Flexible WallPermeameter3D 6026 Practice for Using Significant Digits in Geotechni-cal D
18、ata32.2 API Standard:API RP 40 Recommended Practice for Core-Analysis Pro-cedure43. 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 a
19、nd through the pores of a 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,
20、 ug, and the pore water pressure, 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 part
21、icles.3.2.5 matric suction, 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. Matr
22、ic suctionis also referred 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
23、 gage pressure de-rived from 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 memb
24、ranea porous polymeric membranethat 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 mat
25、ric suction to be appliedduring 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 characteristi
26、c curvea graph of suction(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 gag
27、e pressure derivedfrom the 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 p
28、otential.3.2.13 volumetric 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. Wa
29、ter activity is also referred 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
30、apply thesuction. In Method A, 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 porewater pressure is maintained at atmospheric pressure, and thepore gas pressure is raised to apply the sucti
31、on 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 matric suctioncauses water to flow from the spe
32、cimen 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 soil water character-istic curve.4.1.2 The wate
33、r 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 specimen and the volume of waterexpelled. For Meth
34、od 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 Methods A-C, thewater content of the soil is controlled in Method D, and thecorresponding
35、 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 will be used to define the soilwater characteri
36、stic curve. In the other approach, a singlespecimen is used. The specimen is tested, dried to a lower3Annual Book of ASTM Standards, Vol 04.09.4American Petroleum Institute, 2nd Edition, 1998.D6836022water content, and then tested again. This process is repeateduntil suctions have been measured at a
37、ll of the desired watercontents.4.2.1 In Method D, the 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 por
38、tion of the soil watercharacteristic curve corresponding 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 ca
39、n be combined to form asingle soil water characteristic 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 ch
40、amber that is subjected toa centrifugal force in a centrifuge. 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
41、water characteristic curve is measured bysubjecting the 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 t
42、o hydrological characterization of unsaturated soils andis 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 usingpro
43、perties of the SWCC and the saturated hydraulic conduc-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 exces
44、siveshrinkage or swelling of the soil matrix.5.3 A full 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 appl
45、ied to field situations with caution and byqualified personnel.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 genera
46、lly 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 thes
47、e factors.6. Apparatus6.1 Hanging Column Apparatus (Method A)A hangingcolumn apparatus consists of three parts: a specimen chamber,an outflow measurement tube, and a suction supply (Fig. 1).The specimen chamber consists of a glass or rigid plasticfunnel containing a porous plate that is large enough
48、 to containthe specimen being tested. Such funnels are commonly referredto as “Buchner” funnels. A photograph of a funnel used for ahanging column apparatus is shown in Fig. 2. Water expelledfrom the specimen during the test is measuring using acapillary tube connected to the outflow end of the funn
49、el. Theother end of this capillary tube is connected to suction supplyconsisting of two reservoirs. The relative elevation of the tworeservoirs is adjusted to develop a vacuum, which is transmit-ted to the capillary tube. The magnitude of the applied suctionis measured with a manometer.6.2 Pressure Chamber (Methods B and C)Pressure cham-bers are used for the pressure extraction method to apply a gaspressure (typically air pressure) to the specimen and the gas inthe pores. Typically the pressure chamber is a metallic vessel.The pressure chamber shall be pressure-rat
