1、Designation: D 6527 00Standard Test Method forDetermining Unsaturated and Saturated HydraulicConductivity in Porous Media by Steady-StateCentrifugation1This standard is issued under the fixed designation D 6527; the number immediately following the designation indicates the year oforiginal adoption
2、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 the determination of the hy-draulic conductivity, or
3、 the permeability relative to water, ofany porous medium in the laboratory, in particular, the hydrau-lic conductivity for water in subsurface materials, for example,soil, sediment, rock, concrete, and ceramic, either natural orartificial, especially in relatively impermeable materials ormaterials u
4、nder highly unsaturated conditions. This testmethod covers determination of these properties using anyform of steady-state centrifugation (SSC) in which fluid can beapplied to a specimen with a constant flux or steady flowduring centrifugation of the specimen. This test method onlymeasures advective
5、 flow on core specimens in the laboratory.1.2 This standard may involve hazardous materials, opera-tions, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate
6、safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 420 Guide to Site Characterization for Engineering, De-sign, and Construction Purposes2D 653 Terminology Relating to Soil, Rock, and ContainedFluids2D 2216
7、Test Method for Laboratory Determination of Water(Moisture) Content of Soil and Rock2D 3740 Practice for Minimum Requirements for AgenciesEngaged in the Testing and/or Inspection of Soil and Rockas Used in Engineering Design and Construction2D 4753 Specification for Evaluating, Selecting, and Speci-
8、fying Balances and Scales for Use in Testing Soil, Rock,and Related Construction Materials2D 5084 Test Method for Measurement of Hydraulic Con-ductivity of Saturated Porous Materials Using a FlexibleWall Permeameter3D 5730 Guide for Site Characterization for EnvironmentalPurposes With Emphasis on So
9、il, Rock, the Vadose Zone,and Ground Water3D 6026 Practice for Using Significant Digits in Calculatingand Reporting Geotechnical Test Data33. Terminology3.1 DefinitionsFor common definitions of terms in thisguide, such as porosity, permeability, hydraulic conductivity,water content, and matric poten
10、tial (matric suction, watersuction, or water potential), refer to Terminology D 653.3.2 Definitions of Terms Specific to This Standard:3.2.1 hydraulic steady statethe condition in which thewater flux density remains constant along the conductingsystem. This is diagnosed as the point at which both th
11、e massand volumetric water contents of the material are no longerchanging.3.2.2 SSCM or SSC-UFAApparatus to achieve steady-state centrifugation. The SSCM (steady-state centrifugationmethod) uses a self-contained flow delivery-specimen system(1)4. The SSC-UFA (unsaturated flow apparatus) uses anexter
12、nal pump to deliver flow to the rotating specimen (2). Thistest method will describe the SSC-UFA application, but otherapplications are possible. Specific parts for the SSC-UFA aredescribed in Section 6 as an example of a SSC system.3.2.3 steady-state centrifugationcontrolled flow of wateror other f
13、luid through a specimen while it is rotating in acentrifuge, as distinct from water retention centrifugationmethods which measure drainage from a wet specimen bycentrifugation with no flow into the specimen.3.2.4 water flux densitythe flow rate of water through across-sectional area per unit time, f
14、or example, 5 cm3/cm2/s,written as 5 cm/s.3.3 Symbols:K = hydraulic conductivity, cm/sq = water flux density, cm3/cm2/s or cm/sr = distance from axis of rotation, cm1This test method is under the jurisdiction of ASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.
15、21 on Ground Water andVadose Zone Investigations.Current edition approved Feb. 10, 2000. Published June 2000.2Annual Book of ASTM Standards, Vol 04.08.3Annual Book of ASTM Standards, Vol 04.09.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright
16、ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.r = dry density, g/cm3v = rotation speed, radians/s4. Summary of Test Method4.1 Using a SSC-UFA is effective because it allows theoperator to control the independent variables in Darcys Law.Darcys Law states that the water
17、flux density equals thehydraulic conductivity times the fluid driving force (SeeSection 11). The driving force is fixed by imposing anacceleration on the specimen through an adjustable rotationspeed. The water flux density is fixed by setting the flow rateinto the specimen with an appropriate consta
18、nt-flow pump anddispersing the flow front evenly over the specimen. Thus, thespecimen reaches the steady-state hydraulic conductivitywhich is dictated by that combined water flux density anddriving force. The operator can impose whatever hydraulicconductivity is desired within the operational range
19、of rotationspeeds and flow rates, from 104cm/s (0.l darcy; 109cm2)to1011cm/s (108darcy; 1016cm2). Higher conductivities aremeasured using falling head or constant head methods (3).These methods are also convenient to saturate the specimen.Following saturation and constant or falling head measure-men
20、ts, the specimen is stepwise desaturated in the SSC-UFAby increasing the speed and decreasing the flow rate, allowingsteady state to be reached at each step. Because a relativelylarge driving force is used, the SSC-UFA can achieve hydraulicsteady state in a matter of hours for geologic materials, ev
21、en atvery low water contents. Sample size is up to about 5-cmdiameter and 6-cm length cores. This test method is distinctfrom water retention centrifugation methods which measuresimple drainage from a wet specimen by centrifugation with noflow into the specimen. Hydraulic steady state cannot beachie
22、ved without flow into the specimen.5. Significance and Use5.1 Recent results have demonstrated that direct measure-ments of unsaturated transport parameters, for example, hy-draulic conductivity, vapor diffusivity, retardation factors, ther-mal and electrical conductivities, and water potential, ons
23、ubsurface materials and engineered systems are essential fordefensible site characterization needs of performance assess-ment as well as restoration or disposal strategies. Predictivemodels require the transport properties of real systems that canbe difficult to obtain over reasonable time periods u
24、singtraditional methods. Using a SSC-UFA greatly decreases thetime required to obtain direct measurements of hydraulicconductivity on unsaturated systems and relatively imperme-able materials. Traditionally, long times are required to attainsteady-state conditions and distributions of water becausen
25、ormal gravity does not provide a large enough driving forcerelative to the low conductivities that characterize highlyunsaturated conditions or highly impermeable saturated sys-tems (Test Method D 5084). Pressure techniques sometimescan not be effective for measuring unsaturated transport prop-ertie
26、s because they do not provide a body force and cannot acton the entire specimen simultaneously unless the specimen issaturated or near-saturated. A body force is a force that acts onevery point within the system independently of other forces orproperties of the system. High pressures used on saturat
27、edsystems often induce fracturing or grain rearrangements andcause compaction as a result of high-point stresses that aregenerated within the specimen. A SSC-UFA does not producesuch high-point stresses.5.2 There are specific advantages to using centrifugal forceas a fluid driving force. It is a bod
28、y force similar to gravity and,therefore, acts simultaneously over the entire system andindependently of other driving forces, for example, gravity ormatric potential. Additionally, in a SSC-UFA the accelerationcan dominate any matric potential gradients as the Darcydriving force. The use of steady-
29、state centrifugation to measuresteady-state hydraulic conductivities has recently been demon-strated on various porous media (1,2).5.3 Several issues involving flow in an acceleration fieldhave been raised and addressed by previous and currentresearch (1,4). These studies have shown that compaction
30、fromacceleration is negligible for subsurface soils at or near theirfield densities. Bulk densities in these specimens have re-mained constant (60.1 g/cm3) because the specimens arealready compacted more than the acceleration can affect them.The notable exception is structured soils. Special arrange
31、mentsmust be made to preserve their densities, for example, the useof speeds not exceeding specific equivalent stresses. As anexample, for most SSC-UFA specimen geometries, the equiva-lent pressure in the specimen at a rotation speed of 2500 rpmis about 2 bar. If the specimen significantly compacts
32、under thispressure, a lower speed must be used. Usually, only very finesoils at dry bulk densities less than 1.2 g/cm3are a problem.Whole rock, grout, ceramics, or other solids are completelyunaffected by these accelerations. Precompaction runs up to thehighest speed for that run are performed in th
33、e SSC-UFA priorto the run to observe any compaction effects.5.4 Three-dimensional deviations of the driving force as afunction of position in the specimen are less than a factor oftwo. Theoretically, the situation under which unit gradientconditions are achieved in a SSC-UFA, in which the change int
34、he matric potential with radial distance equals zero (dc/dr =0), is best at higher water flux densities, higher speeds, orcoarser grain-size, or combination thereof. This is observed inpotential gradient measurements in the normal operationalrange where dc/dr = 0. The worst case occurs at the lowest
35、water flux densities in the finest-grained materials (1).5.5 There is no sidewall leakage problem in the SSC-UFAfor soils. The centrifugal force maintains a good seal betweenthe specimen and the wall. As the specimen desaturates, theincreasing matric potential (which still operates in all direc-tion
36、s although there is no potential gradient) keeps the waterwithin the specimen, and the acceleration (not being a pres-sure) does not force water into any larger pore spaces such asalong a wall. Therefore, capillary phenomena still hold in theSSC-UFA, a fact which is especially important for fracture
37、d orheterogeneous media (2). Cores of solid material such as rockor concrete, are cast in epoxy sleeves as their specimen holder,and this also prevents sidewall leakage.5.6 The SSC-UFA can be used in conjunction with othermethods that require precise fixing of the water content of aporous material.
38、The SSC-UFA is used to achieve the steady-state water content in the specimen and other test methods areD 65272applied to investigate particular problems as a function ofwater content. This has been successful in determining diffu-sion coefficients, vapor diffusivity, electrical conductivity,monitor
39、ing the breakthrough of chemical species (retardationfactor), pore water extraction, solids characterization, and otherphysical or chemical properties as functions of the watercontent (2,5).5.7 Hydraulic conductivity can be very sensitive to thesolution chemistry, especially when specimens contain e
40、xpand-able, or swelling, clay minerals. Water should be used that isappropriate to the situation, for example, ground water fromthe site from which the specimen was obtained, or rainwater ifan experiment is being performed to investigate infiltration ofprecipitation into a disposal site. Appropriate
41、 antimicrobialagents should be used to prevent microbial effects within thespecimen, for example, clogging, but should be chosen withconsideration of any important chemical issues in the system.A standard synthetic pore water solution, similar to the solutionexpected in the field, is useful when it
42、is difficult to obtain fieldwater. Distilled or deionized water is generally not usefulunless the results are to be compared to other tests using similarwater or is specified in pertinent test plans, ASTM testmethods, or EPA procedures. Distilled water can dramaticallyaffect the conductivity of soil
43、 and rock specimens that containclay minerals, and can induce dissolution/precipitation withinthe specimen.5.8 This test method establishes a dynamic system, and, assuch, the steady-state water content is usually higher than thatwhich is attained during a pressure plate or other equilibriummethod th
44、at does not have flow into the specimen duringoperation. This is critical when using either type of data formodeling purposes. This test method does not measure watervapor transport or molecular diffusion of water, both of whichbecome very significant at low conductivities, and may actu-ally dominat
45、e when hydraulic conductivities drop much below1010cm/s.5.9 The quality of the result produced by this test methoddepends upon the competence of the personnel performing it,and the suitability of the equipment and facilities used.Agencies that meet the criteria of Practice D 3740 are generallyconsid
46、ered capable of competent and objective testing andsampling. Users of this test method are cautioned that compli-ance with Practice D 3740 does not in itself ensure reliableresults. Reliable results depend on many factors; PracticeD 3740 provides a means of evaluating some of those factors.6. Appara
47、tus6.1 A SSC-UFA instrument consists of an ultracentrifugewith a constant, ultralow flow pump that provides water to thespecimen surface through a rotating seal assembly and micro-dispersal system. An example of a rotor and seal assembly isshown in Fig. 1. Fig. 2 shows an actual SSC-UFA apparatus.Th
48、is commercially available SSC-UFA can reach accelerationsof up to 20 000 g (soils are generally run only up to 1 000 g),temperatures can be adjusted from 20 to 150C. Infusion andsyringe pumps can provide constant flow rates as low as 0.001FIG. 1 SSC-UFA Rotor with Seal AssemblyD 65273mL/h. Effluent
49、from the specimen is collected in a transparent,volumetrically calibrated chamber at the bottom of the speci-men assembly. Using a strobe light, an observer can check thechamber while the specimen is being centrifuged. Two speci-mens are run at the same time in a SSC-UFA with waterflowing into each by means of two feedlines, the central feed orinlet path, and the annular feed. Specific parts are defined asfollows (see Fig. 1):6.1.1 Specimen HolderThe metal, polysulfone, fiberglass,or epoxy shell that contains the soil, rock, cement, or aggregatespecimen to be tested.6.1.2 S
