ASTM D7928-21
(Test Method)Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
SIGNIFICANCE AND USE
5.1 Particle-size distribution (gradation) is a descriptive term referring to the proportions by dry mass of a soil distributed over specified particle-size ranges. The gradation curve generated using this method yields the distribution of silt and clay size fractions present in the soil based on size definitions, not mineralogy or Atterberg limit classification.
5.2 Unless the sedimentation sample is representative of the entire sample, the sedimentation results must be combined with a sieve analysis to obtain the complete particle size distribution.
5.3 The clay size fraction is material finer than 2 µm. The clay size fraction is used in combination with the Plasticity Index (Test Methods D4318) to compute the activity, which provides an indication of the mineralogy of the clay fraction.
5.4 The gradation of the silt and clay size fractions is an important factor in determining the susceptibility of fine-grained soils to frost action.
5.5 The gradation of a soil is an indicator of engineering properties such as hydraulic conductivity, compressibility, and shear strength. However, soil behavior for engineering and other purposes is dependent upon many factors, such as effective stress, mineral type, structure, plasticity, and geological origin, and cannot be based solely upon gradation.
5.6 Some types of soil require special treatment in order to correctly determine the particle sizes. For example, chemical cementing agents can bond clay particles together and should be treated in an effort to remove the cementing agents when possible. Hydrogen peroxide and moderate heat can digest organics. Hydrochloric acid can remove carbonates by washing and Dithionite-Citrate-Bicarbonate extraction can be used to remove iron oxides. Leaching with test water can be used to reduce salt concentration. All of these treatments, however, add significant time and effort when performing the sedimentation test and are allowable but outside the scope of this test method. ...
SCOPE
1.1 This test method covers the quantitative determination of the distribution of particle sizes of the fine-grained portion of soils. The sedimentation by hydrometer method is used to determine the particle-size distribution (gradation) of the material that is finer than the No. 200 (75-µm) sieve and larger than about 0.2-µm. The test is performed on material passing the No. 10 (2.0-mm) or finer sieve and the results are presented as the mass percent finer of this fraction versus the log of the particle diameter.
1.2 This method can be used to evaluate the fine-grained fraction of a soil with a wide range of particle sizes by combining the sedimentation results with results from a sieve analysis using D6913 to obtain the complete gradation curve. The method can also be used when there are no coarse-grained particles or when the gradation of the coarse-grained material is not required or not needed.
Note 1: The significant digits recorded in this test method preclude obtaining the grain size distribution of materials that do not contain a significant amount of fines. For example, clean sands will not yield detectable amounts of silt and clay sized particles, and therefore should not be tested with this method. The minimum amount of fines in the sedimentation specimen is 15 g.
1.3 When combining the results of the sedimentation and sieve tests, the procedure for obtaining the material for the sedimentation analysis and calculations for combining the results will be provided by the more general test method, such as Test Methods D6913 (Note 2).
Note 2: Subcommittee D18.03 is currently developing a new test method “Test Method for Particle-Size Analysis of Soils Combining the Sieve and Sedimentation Techniques.”
1.4 The terms “soil” and “material” are used interchangeably throughout the standard.
1.5 The sedimentation analysis is based on the concept that larger particles will fall through a fluid faster than...
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Designation: D7928 − 21
Standard Test Method for
Particle-Size Distribution (Gradation) of Fine-Grained Soils
1
Using the Sedimentation (Hydrometer) Analysis
This standard is issued under the fixed designation D7928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope particles. Stokes’ Law gives a governing equation used to
determine the terminal velocity of a spherical particle falling
1.1 This test method covers the quantitative determination
through a stationary liquid. The terminal velocity is propor-
of the distribution of particle sizes of the fine-grained portion
tionaltothesquareoftheparticlediameter.Therefore,particles
of soils. The sedimentation by hydrometer method is used to
are sorted by size in both time and position when settling in a
determine the particle-size distribution (gradation) of the
container of liquid.
material that is finer than the No. 200 (75-µm) sieve and larger
1.5.1 Stokes’ Law has several assumptions which are: the
than about 0.2-µm. The test is performed on material passing
particles are spherical and smooth; there is no interference
theNo.10(2.0-mm)orfinersieveandtheresultsarepresented
between the particles; there is no difference between the
as the mass percent finer of this fraction versus the log of the
current in the middle of the container and the sides; flow is
particle diameter.
laminar; and the particles have the same density. These
1.2 This method can be used to evaluate the fine-grained
assumptions are applied to soil particles of various shapes and
fraction of a soil with a wide range of particle sizes by
sizes.
combining the sedimentation results with results from a sieve
1.6 A hydrometer is used to measure the fluid density and
analysis using D6913 to obtain the complete gradation curve.
determine the quantity of particles in suspension at a specific
The method can also be used when there are no coarse-grained
time and position. The density of the soil-water suspension
particles or when the gradation of the coarse-grained material
depends upon the concentration and specific gravity of the soil
is not required or not needed.
particlesandtheamountofdispersantadded.Eachhydrometer
NOTE 1—The significant digits recorded in this test method preclude
measurement at an elapsed time is used to calculate the
obtaining the grain size distribution of materials that do not contain a
percentageofparticlesfinerthanthediametergivenbyStokes’
significant amount of fines. For example, clean sands will not yield
Law.Theseriesofreadingsprovidethedistributionofmaterial
detectable amounts of silt and clay sized particles, and therefore should
not be tested with this method. The minimum amount of fines in the
mass as a function of particle size.
sedimentation specimen is 15 g.
1.7 This test method does not cover procurement of the
1.3 When combining the results of the sedimentation and
sample or processing of the sample prior to obtaining the
sieve tests, the procedure for obtaining the material for the
reduced sample in any detail. It is assumed that the sample is
sedimentation analysis and calculations for combining the
obtained using appropriate methods and is representative of
results will be provided by the more general test method, such
site materials or conditions. It is also assumed that the sample
as Test Methods D6913 (Note 2).
has been processed such that the reduced sample accurately
NOTE 2—Subcommittee D18.03 is currently developing a new test reflects the particle-size distribution (gradation) of this finer
method “Test Method for Particle-Size Analysis of Soils Combining the
fraction of the material.
Sieve and Sedimentation Techniques.”
1.8 Material Processing—Material is tested in the moist or
1.4 The terms “soil” and “material” are used interchange-
as-received state unless the material is received in an air-dried
ably throughout the standard.
state. The moist preparation method shall be used to obtain a
1.5 The sedimentation analysis is based on the concept that
sedimentation test specimen from the reduced sample. Air-
larger particles will fall through a fluid faster than smaller
driedpreparationisonlyallowedwhenthematerialisreceived
in the air-dried state. The method to be used may be specified
by the requesting authority; however, the moist preparation
1
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
method shall be used for referee testing.
Rock andisthedirectresponsibilityofSubcommitteeD18.03onTexture, Plasticity
and Density Characteristics of Soils.
1.9 This test method is not applicable for the following
Current edition approved May 1, 2021. Publi
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it 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 version
of the standard as published by ASTM is to be considered the official document.
Designation: D7928 − 17 D7928 − 21
Standard Test Method for
Particle-Size Distribution (Gradation) of Fine-Grained Soils
1
Using the Sedimentation (Hydrometer) Analysis
This standard is issued under the fixed designation D7928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method covers the quantitative determination of the distribution of particle sizes of the fine-grained portion of soils.
The sedimentation orby hydrometer method is used to determine the particle-size distribution (gradation) of the material that is
finer than the No. 200 (75-μm) sieve and larger than about 0.2-μm. The test is performed on material passing the No. 10 (2.0-mm)
or finer sieve and the results are presented as the mass percent finer of this fraction versus the log of the particle diameter.
1.2 This method can be used to evaluate the fine-grained fraction of a soil with a wide range of particle sizes by combining the
sedimentation results with results from a sieve analysis resulting in using D6913 to obtain the complete gradation curve. The
method can also be used when there are no coarse-grained particles or when the gradation of the coarse-grained material is not
required or not needed.
NOTE 1—The significant digits recorded in this test method preclude obtaining the grain size distribution of materials that do not contain a significant
amount of fines. For example, clean sands will not yield detectable amounts of silt and clay sized particles, and therefore should not be tested with this
method. The minimum amount of fines in the sedimentation specimen is 15 g.
1.3 When combining the results of the sedimentation and sieve tests, the procedure for obtaining the material for the sedimentation
analysis and calculations for combining the results will be provided by the more general test method, such as Test Methods D6913
(Note 2).
NOTE 2—Subcommittee D18.03 is currently developing a new test method “Test Method for Particle-Size Analysis of Soils Combining the Sieve and
Sedimentation Techniques.”
1.4 The terms “soil” and “material” are used interchangeably throughout the standard.
1.5 The sedimentation analysis is based on the concept that larger particles will fall through a fluid faster than smaller particles.
Stokes’ Law gives a governing equation used to determine the terminal velocity of a spherical particle falling through a stationary
liquid. The terminal velocity is proportional to the square of the particle diameter. Therefore, particles are sorted by size in both
time and position when settling in a container of liquid.
1.5.1 Stokes’ Law has several assumptions which are: the particles are spherical and smooth; there is no interference between the
particles; there is no difference between the current in the middle of the container and the sides; flow is laminar; and the particles
have the same density. These assumptions are applied to soil particles of various shapes and sizes.
1
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.03 on Texture, Plasticity
and Density Characteristics of Soils.
Current edition approved May 1, 2017May 1, 2021. Published May 2017May 2021. Originally approved in 2016. Last previous edition approved in 20162017 as
ε1
D7928 – 16D7928 – 17. . DOI: 10.1520/D7928-1710.1520/D7928-21
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D7928 − 21
1.6 A hydrometer is used to measure the fluid density and determine the quantity of particles in suspension at a specific time and
position. The density of the soil-water suspension depends upon the concentration and specific gravity of the soil particles and the
amount of dispersant added. Each hydrometer measurement at an elapsed time is used to calculate the percentage of particles finer
than the diameter given by Stokes’ Law. The series of readings provide the distribution of material mass as a function of particle
size.
1.7 This test method does not cover procurement of the sample or processing of the sample prior to obtaining the reduced sample
in any detail. It is assumed that the sample is obtained using appropriate methods and is representative of si
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