ASTM_D_7928_-_21e1.pdf

Designation:D7928211Standard 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,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.1NOTESummary of Changes section was editorially added in June 2021.1.Scope*1.1 This test method covers the quantitative determinationof the distribution of particle sizes of the fine-grained portionof soils.The sedimentation by 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)or finer sieve and the results are presentedas the mass percent finer of this fraction versus the log of theparticle 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 results from a sieveanalysis using D6913 to obtain the complete gradation curve.The method can also be used when there are no coarse-grainedparticles or when the gradation of the coarse-grained materialis not required or not needed.NOTE1The significant digits recorded in this test method precludeobtaining the grain size distribution of materials that do not 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 sedimentation 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).NOTE2Subcommittee D18.03 is currently developing a new testmethod“Test Method for 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.Stokes 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 acontainer 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.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 gravity 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 This 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 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 shall 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 testing.1This test method is under the jurisdiction ofASTM Committee D18 on Soil andRock and is the direct responsibility of Subcommittee D18.03 on Texture,Plasticityand Density Characteristics of Soils.Current edition approved May 1,2021.Published May 2021.Originallyapproved in 2016.Last previous edition approved in 2017 as D7928 17.DOI:10.1520/D7928-21E01*A Summary of Changes section appears at the end of this standardCopyright ASTM International,100