1、Designation: D7928 16Standard Test Method forParticle-Size Distribution (Gradation) of Fine-Grained SoilsUsing the Sedimentation (Hydrometer) Analysis1This standard is issued under the fixed designation D7928; the number immediately following the designation indicates the year oforiginal adoption or
2、, 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. Scope1.1 This test method covers the quantitative determinationof the distribution of pa
3、rticle sizes of the fine-grained portionof soils. The sedimentation or hydrometer method is used todetermine the particle-size distribution (gradation) of thematerial that is finer than the No. 200 (75-m) sieve and largerthan about 0.2-m. The test is performed on material passingthe No. 10 (2.0-mm)
4、or finer sieve and the results are presentedas the mass percent finer versus the log of the particle diameter.1.2 This method can be used to evaluate the fine-grainedfraction of a soil with a wide range of particle sizes bycombining the sedimentation results with a sieve analysisresulting in the com
5、plete gradation curve. The method can alsobe used when there are no coarse-grained particles or when thegradation of the coarse-grained material is not required or notneeded.NOTE 1The significant digits recorded in this test method precludeobtaining the grain size distribution of materials that do n
6、ot contain asignificant amount of fines. For example, clean sands will not yielddetectable amounts of silt and clay sized particles, and therefore shouldnot be tested with this method. The minimum amount of fines in thesedimentation specimen is 15 g.1.3 When combining the results of the sedimentatio
7、n andsieve tests, the procedure for obtaining the material for thesedimentation analysis and calculations for combining theresults will be provided by the more general test method, suchas Test Methods D6913 (Note 2).NOTE 2Subcommittee D18.03 is currently developing a new testmethod “Test Method for
8、Particle-Size Analysis of Soils Combining theSieve and Sedimentation Techniques.”1.4 The terms “soil” and “material” are used interchange-ably throughout the standard.1.5 The sedimentation analysis is based on the concept thatlarger particles will fall through a fluid faster than smallerparticles. S
9、tokes Law gives a governing equation used todetermine the terminal velocity of a spherical particle fallingthrough a stationary liquid. The terminal velocity is propor-tional to the square of the particle diameter.Therefore, particlesare sorted by size in both time and position when settling in acon
10、tainer of liquid.1.5.1 Stokes Law has several assumptions which are: theparticles are spherical and smooth; there is no interferencebetween the particles; there is no difference between thecurrent in the middle of the container and the sides; flow islaminar; and the particles have the same density.
11、Theseassumptions are applied to soil particles of various shapes andsizes.1.6 A hydrometer is used to measure the fluid density anddetermine the quantity of particles in suspension at a specifictime and position. The density of the soil-water suspensiondepends upon the concentration and specific gra
12、vity of the soilparticles and the amount of dispersant added. Each hydrometermeasurement at an elapsed time is used to calculate thepercentage of particles finer than the diameter given by StokesLaw. The series of readings provide the distribution of materialmass as a function of particle size.1.7 T
13、his test method does not cover procurement of thesample or processing of the sample prior to obtaining thereduced sample in any detail. It is assumed that the sample isobtained using appropriate methods and is representative ofsite materials or conditions. It is also assumed that the samplehas been
14、processed such that the reduced sample accuratelyreflects the particle-size distribution (gradation) of this finerfraction of the material.1.8 Material ProcessingMaterial is tested in the moist oras-received state unless the material is received in an air-driedstate. The moist preparation method sha
15、ll be used to obtain asedimentation test specimen from the reduced sample. Air-dried preparation is only allowed when the material is receivedin the air-dried state. The method to be used may be specifiedby the requesting authority; however, the moist preparationmethod shall be used for referee test
16、ing.1.9 This test method is not applicable for the followingsoils:1.9.1 Soils containing fibrous peat.1.9.2 Soils containing less than approximately 5 % of fine-grained material (Note 1).1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility
17、 of Subcommittee D18.03 on Texture, Plasticityand Density Characteristics of Soils.Current edition approved May 1, 2016. Published May 2016. DOI: 10.1520/D7928-16Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States11.9.3 Soils containing e
18、xtraneous matter, such as organicsolvents, oil, asphalt, wood fragments, or similar items (Note3).NOTE 3If extraneous matter, such as wood, can be easily removed byhand, it is permissible to do so. However, there may be cases where theextraneous matter is being evaluated as part of the material and
19、it shouldnot be removed from the material.1.9.4 Materials that contain cementitious components, suchas cement, fly ash, lime, or other stabilization admixtures.1.10 This test method may not produce consistent testresults within and between laboratories for the following soils.To test these soils, th
20、is test method must be adapted and theseadaptations documented.1.10.1 Soils that flocculate during sedimentation. Such ma-terials may need to be treated to reduce salinity or alter the pHof the suspension.1.10.2 Friable soils in which processing changes the grada-tion of the soil. Typical examples o
21、f these soils are someresidual soils, most weathered shales, and some weakly ce-mented soils.1.10.3 Soils that will not readily disperse, such as glauco-nitic clays or some dried plastic clays.1.11 Samples that are not soils, but are made up of particlesmay be tested using this method. The applicabl
22、e sections aboveshould be used in applying this standard.1.12 UnitsThe values stated in SI units are to be regardedas standard. Except the sieve designations, they are identifiedusing the “alternative” system in accordance with Practice E11,such as 3-in. and No. 200, instead of the “standard” of 75-
23、mmand 75-m, respectively. Reporting of test results in units otherthan SI shall not be regarded as non-conformance with this testmethod. The use of balances or scales recording pounds ofmass (lbm) shall not be regarded as nonconformance with thisstandard.1.13 All observed and calculated values shall
24、 conform to theguidelines for significant digits and rounding established inPractice D6026, unless superseded by this test method.1.13.1 The procedures used to specify how data arecollected/recorded and calculated in the standard are regardedas the industry standard. In addition, they are representa
25、tive ofthe significant digits that generally should be retained. Theprocedures used do not consider material variation, purpose forobtaining the data, special purpose studies, or any consider-ations for the users objectives; and it is common practice toincrease or reduce significant digits of report
26、ed data to becommensurate with these considerations. It is beyond the scopeof these test methods to consider significant digits used inanalysis methods for engineering data.1.14 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil
27、ity of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C702 Practice for Reducing Samples ofAggregate to TestingSizeD653 Terminology Relating to Soil, Ro
28、ck, and ContainedFluidsD854 Test Methods for Specific Gravity of Soil Solids byWater PycnometerD1140 Test Methods for Determining the Amount of Mate-rial Finer than 75-m (No. 200) Sieve in Soils by WashingD2216 Test Methods for Laboratory Determination of Water(Moisture) Content of Soil and Rock by
29、MassD2487 Practice for Classification of Soils for EngineeringPurposes (Unified Soil Classification System)D2488 Practice for Description and Identification of Soils(Visual-Manual Procedure)D3740 Practice for Minimum Requirements for AgenciesEngaged in Testing and/or Inspection of Soil and Rock asUs
30、ed in Engineering Design and ConstructionD4220/D4220M Practices for Preserving and TransportingSoil SamplesD4318 Test Methods for Liquid Limit, Plastic Limit, andPlasticity Index of SoilsD4753 Guide for Evaluating, Selecting, and Specifying Bal-ances and Standard Masses for Use in Soil, Rock, andCon
31、struction Materials TestingD6026 Practice for Using Significant Digits in GeotechnicalDataD6913 Test Methods for Particle-Size Distribution (Grada-tion) of Soils Using Sieve AnalysisE11 Specification for Woven Wire Test Sieve Cloth and TestSievesE100 Specification for ASTM HydrometersE126 Test Metho
32、d for Inspection, Calibration, and Verifica-tion of ASTM Hydrometers3. Terminology3.1 Definitions:3.1.1 For definitions of common technical terms used in thisstandard, refer to Terminology D653.3.2 Definitions of Terms Specific to This Standard:3.2.1 reduced sample, nthe minus38-in. (9.5-mm) sieveor
33、 finer material that has been separated from the sample andthen worked to reduce the mass while still having sufficientquantity to meet the minimum mass requirements of Table 1.3.2.2 sample, nmaterial collected without limitation onthe total mass or size range of particles meeting the minimummass re
34、quirements provided in Table 1.3.2.3 sedimentation sample, nthe minus No. 10 (2.0-mm)or finer material that is separated from the reduced sampleusing the separation sieve from which the sedimentationspecimen and water content are obtained.2For referenced ASTM standards, visit the ASTM website, www.a
35、stm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.D7928 1623.2.4 sedimentation specimen, nthe material obtainedfrom the sedimentation sample having a maximum particle-size
36、no greater than the No. 10 (2.0-mm) sieve to be used in thesedimentation test and in sufficient quantity to satisfy theminimum mass requirements of Table 1.3.2.5 separation sieve, nthe No. 10 (2.0-mm) sieve orfiner (Note 4) used to separate the reduced sample to obtain thematerial for the sedimentat
37、ion sample.NOTE 4The methodology for using a sieve finer than the No. 10 (2.0mm) is not defined in this standard. The methodology used to obtain arepresentative sample using a sieve finer than the No. 10 (2.0 mm) is notthe same as obtaining the representative sample using the No. 10 (2.0 mm)sieve as
38、 presented in this standard.Additional effort or steps are necessaryto make sure the material passing the finer sieve adequately represents thesample. Such additional effort or steps should be documented if using asieve finer than the No. 10 (2.0 mm) sieve to obtain the sedimentationspecimen.4. Summ
39、ary of Test Method4.1 This test method is used to determine the particle-sizedistribution (gradation) of material finer than the No. 200(75-m) sieve as a percentage of the mass used in thesedimentation test.4.2 When the source material contains particles larger thanthe38-in. (9.5-mm) sieve, a reduce
40、d sample passing the38-in.(9.5-mm) sieve shall be obtained using techniques presented inTest Methods D6913 or another standard. This reduced sampleshall meet the minimum mass requirements in Table 1 for the38-in. (9.5-mm) sieve. The material is processed using themoist (referee) preparation method u
41、nless the material isreceived in the air-dried state.4.3 The entire reduced sample is separated using the sepa-ration sieve. The sedimentation sample is then split to obtainthe appropriate mass for the sedimentation test specimen and awater content test specimen.4.4 The sedimentation test specimen i
42、s mixed with a dis-persing agent and test water. The slurry is allowed to conditionand is then thoroughly mixed and placed in a cylinder withadditional test water. Readings are taken with a hydrometer andthermometer over specific time intervals.4.5 The mass of particles passing specified particle di
43、am-eters are calculated and recorded. The results produce atabulation of particle size versus percent passing that can begraphically presented as a gradation curve. The plot is typicallyexpressed as percent passing/finer than the separation sievesize versus the log of the particle size in millimetre
44、s.5. Significance and Use5.1 Particle-size distribution (gradation) is a descriptiveterm referring to the proportions by dry mass of a soildistributed over specified particle-size ranges. The gradationcurve generated using this method yields the amount of silt andclay size fractions present in the s
45、oil based on size definitions,not mineralogy or Atterberg limit data.5.2 Determination of the clay size fraction, which is mate-rial finer than 2 m, is used in combination with the PlasticityIndex (Test Methods D4318) to compute the activity, whichprovides an indication of the mineralogy of the clay
46、 fraction.5.3 The gradation of the silt and clay size fractions is animportant factor in determining the susceptibility of fine-grained soils to frost action.5.4 The gradation of a soil is an indicator of engineeringproperties. Hydraulic conductivity, compressibility, and shearstrength are related t
47、o the gradation of the soil. However,engineering behavior is dependent upon many factors, such aseffective stress, mineral type, structure, plasticity, and geologi-cal origin, and cannot be based solely upon gradation.5.5 Some types of soil require special treatment in order tocorrectly determine th
48、e particle sizes. For example, chemicalcementing agents can bond clay particles together and shouldbe treated in an effort to remove the cementing agents whenpossible. Hydrogen peroxide and moderate heat can digestorganics. Hydrochloric acid can remove carbonates by washingand Dithionite-Citrate-Bic
49、arbonate extraction can be used toremove iron oxides. Leaching with test water can be used toreduce salt concentration.All of these treatments, however, addsignificant time and effort when performing the sedimentationtest and are allowable but outside the scope of this test method.5.6 The size limits of the sedimentation test are from about100 m to about 1 m. The length of time required to obtain astable initial reading on the hydrometer controls the upperrange of results, and the test duration controls the lower range.5.7 The shape and density of the grains
