ASTM D4221-18

Standard Test Method for Dispersive Characteristics of Clay Soil by Double Hydrometer

SIGNIFICANCE AND USE
5.1 Dispersive clays are those which normally deflocculate when exposed to water of low-salt concentration, the opposite of aggregated clays that would remain flocculated in the same soil-water system  (3, 4, 7). Generally, dispersive clays are highly erosive, possibly subject to high shrink-swell potential, may have lower shear strength, and have lower permeability rates than aggregated clays.  
5.2 When the percent dispersion equals 100, it indicates a completely dispersive clay-size fraction. When the percent dispersion equals 0, it indicates completely nondispersive clay-size fraction.  
5.3 Available data (1) indicates that the test method has about 85 % reliance in predicting dispersive performance (85 % of dispersive clays show more than 35 % dispersion).  
5.4 Since this test method may not identify all dispersive clays, design decisions based solely on this test method may not be conservative. It is often run in conjunction with the crumb test (D6572) (4, 7), the pinhole test (D4647/D4647M), or the analysis of the pore water extract (D4542) (4, 7), or combination thereof, to identify possible dispersive clay behavior.
Note 1: The quality of the result produced by this standard is dependent on the competence of the personal performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depends on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
1.1 This test method provides an indication of the natural dispersive characteristics of clay soils by comparing the amount of particles finer than 2-μm as determined by this method compared to the amount of particles finer than 2-μm as determined by Test Method D7928 (1).2 In order to do this comparison, two similar specimens must be obtained from the sample.  
1.2 This test method follows the procedure given in Test Method D7928 with the exception that the soil slurry is not mechanically dispersed and no dispersing agent is added.  
1.3 This test method is applicable only to soils where the position of the plasticity index versus liquid limit plots (Test Methods D4318) falls on or above the “A” line (Practice D2487) and more than 12 % of the soil fraction is finer than 2-μm as determined in accordance with Test Method D7928 (2).  
1.4 Since this test method may not identify all dispersive clay soils, other tests such as, pinhole dispersion (Test Methods D4647/D4647M), crumb (Test Methods D6572) (3-5) and the analysis of pore water extraction (Test Methods D4542) (4-7) may be performed individually or used together to help verify dispersion.  
1.5 Units—The values stated in SI units are to be regarded as the standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method.  
1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.  
1.6.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user's objectives; and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.  
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use...

General Information

• Status: Published
• Publication Date: 31-Dec-2017
• ICS: 91.100.15 - Mineral materials and products
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.06 - Physical-Chemical Interactions of Soil and Rock

Relations

• Replaces: ASTM D4221-17 - Standard Test Method for Dispersive Characteristics of Clay Soil by Double Hydrometer
• Effective Date: 01-Jan-2018
• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D2487-17e1 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2488-17 - Standard Practice for Description and Identification of Soils (Visual-Manual Procedures)
• Effective Date: 15-Jul-2017
• Refers: ASTM D4318-17e1 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D4318-17 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D7928-16 - Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
• Effective Date: 01-May-2016
• Refers: ASTM D7928-16e1 - Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
• Effective Date: 01-May-2016
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D6572-13 - Standard Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test
• Effective Date: 01-Nov-2013
• Refers: ASTM D6572-13e1 - Standard Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test
• Effective Date: 01-Nov-2013
• Refers: ASTM D6572-13e2 - Standard Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test
• Effective Date: 01-Nov-2013

Overview

ASTM D4221-18: Standard Test Method for Dispersive Characteristics of Clay Soil by Double Hydrometer provides a laboratory procedure for determining the natural dispersive characteristics of clay soils. This method focuses on quantifying the degree to which clay particles are prone to deflocculate, or separate, when exposed to water with low salt concentrations. Dispersive clays are known to be highly erosive, to have potential for shrink-swell behavior, to exhibit reduced shear strength, and to display lower permeability than their aggregated counterparts. Given these characteristics, identifying dispersive clays is crucial in geotechnical engineering to prevent slope failures, piping, and erosion, particularly in earth dam construction and road embankments.

Key Topics

• Dispersive Clays: Soils that readily separate in water with low salt content, increasing risks of erosion and piping.
• Double Hydrometer Test: Compares the percentage of fine particles (less than 2-μm) in two soil specimens - one treated (fully dispersed) and one untreated (natural dispersiveness).
• Percent Dispersion: Indicates dispersive behavior - with 100% showing complete dispersion and 0% showing no dispersion. Soils are classified as nondispersive, intermediate, or dispersive based on the result.
• Standardization: The method adheres to strict guidelines, uses SI units as standard, and references other procedures for consistent and reliable results.
• Testing Limitations: The test provides an indication of dispersion but may not identify all dispersive clays. For complete characterization, it is recommended to use this method in combination with other standard tests such as the crumb test (ASTM D6572), the pinhole test (ASTM D4647/D4647M), and pore water extraction analysis (ASTM D4542).

Applications

This standard is widely used in the geotechnical, civil, and environmental engineering fields for:

• Site Assessment: Assessing the suitability of soils for use in earth structures like dams, embankments, levees, and canals where clay dispersiveness could compromise structural integrity.
• Erosion Control: Identifying soils at risk of internal erosion or piping, allowing for proactive design adjustments or soil treatment.
• Soil Classification: Providing supporting data for soil classification systems, especially when Atterberg limits suggest problematic clays.
• Quality Assurance: Ensuring the use of stable, non-dispersive materials in major infrastructure projects, thereby helping to prevent costly failures.
• Design Optimization: Informing selection of soil stabilization techniques (e.g., addition of chemical amendments) where dispersive clays are present.

Related Standards

ASTM D4221-18 is often used in conjunction with several other ASTM soil standard methods to achieve comprehensive soil behavior characterization:

• ASTM D7928: Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis.
• ASTM D4318: Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.
• ASTM D2487: Practice for Classification of Soils for Engineering Purposes.
• ASTM D6572: Determining Dispersive Characteristics of Clayey Soils by the Crumb Test.
• ASTM D4647/D4647M: Identification and Classification of Dispersive Clay Soils by the Pinhole Test.
• ASTM D4542: Pore Water Extraction and Soluble Salt Content of Soils.
• ASTM D6026: Practice for Using Significant Digits in Geotechnical Data.

Conclusion

Understanding the dispersive characteristics of clay soils using ASTM D4221-18 is vital for engineering projects where soil stability is a concern. The double hydrometer method allows for a standardized, repeatable assessment of dispersion potential, thereby providing a key input for risk assessment and safe, cost-effective design. For optimal reliability, the test should be part of an integrated laboratory investigation employing multiple ASTM soil testing standards.

Keywords: dispersive clays, soil dispersion, double hydrometer, sedimentation analysis, ASTM D4221, geotechnical soil testing, erosion prevention, piping, soil classification, hydrometer analysis.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D4221 − 18
Standard Test Method for
Dispersive Characteristics of Clay Soil by Double
Hydrometer
This standard is issued under the fixed designation D4221; 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* obtaining the data, special purpose studies, or any consider-
ations for the user’s objectives; and it is common practice to
1.1 This test method provides an indication of the natural
increase or reduce significant digits of reported data to be
dispersive characteristics of clay soils by comparing the
commensuratewiththeseconsiderations.Itisbeyondthescope
amount of particles finer than 2-µm as determined by this
of this standard to consider significant digits used in analysis
method compared to the amount of particles finer than 2-µm as
2 methods for engineering design.
determined by Test Method D7928(1). In order to do this
1.7 This standard does not purport to address all of the
comparison, two similar specimens must be obtained from the
safety concerns, if any, associated with its use. It is the
sample.
responsibility of the user of this standard to establish appro-
1.2 This test method follows the procedure given in Test
priate safety, health, and environmental practices and deter-
Method D7928 with the exception that the soil slurry is not
mine the applicability of regulatory limitations prior to use.
mechanically dispersed and no dispersing agent is added.
1.8 This international standard was developed in accor-
1.3 This test method is applicable only to soils where the
dance with internationally recognized principles on standard-
position of the plasticity index versus liquid limit plots (Test
ization established in the Decision on Principles for the
Methods D4318) falls on or above the “A” line (Practice
Development of International Standards, Guides and Recom-
D2487) and more than 12 % of the soil fraction is finer than
mendations issued by the World Trade Organization Technical
2-µmasdeterminedinaccordancewithTestMethodD7928(2).
Barriers to Trade (TBT) Committee.
1.4 Since this test method may not identify all dispersive
2. Referenced Documents
claysoils,othertestssuchas,pinholedispersion(TestMethods
2.1 ASTM Standards:
D4647/D4647M), crumb (Test Methods D6572)(3-5) and the
D653 Terminology Relating to Soil, Rock, and Contained
analysis of pore water extraction (Test Methods D4542)(4-7)
Fluids
may be performed individually or used together to help verify
D2216 Test Methods for Laboratory Determination of Water
dispersion.
(Moisture) Content of Soil and Rock by Mass
1.5 Units—The values stated in SI units are to be regarded
D2487 Practice for Classification of Soils for Engineering
as the standard. Reporting of test results in units other than SI
Purposes (Unified Soil Classification System)
shall not be regarded as nonconformance with this test method.
D2488 Practice for Description and Identification of Soils
1.6 All observed and calculated values shall conform to the
(Visual-Manual Procedures)
guidelines for significant digits and rounding established in
D3740 Practice for Minimum Requirements for Agencies
Practice D6026.
Engaged in Testing and/or Inspection of Soil and Rock as
1.6.1 Theproceduresusedtospecifyhowdataarecollected/
Used in Engineering Design and Construction
recorded or calculated, in this standard are regarded as the
D4220/D4220M Practices for Preserving and Transporting
industry standard. In addition, they are representative of the
Soil Samples
significant digits that generally should be retained. The proce-
D4318 Test Methods for Liquid Limit, Plastic Limit, and
dures used do not consider material variation, purpose for
Plasticity Index of Soils
D4542 Test Methods for Pore Water Extraction and Deter-
1 mination of the Soluble Salt Content of Soils by Refrac-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
RockandisthedirectresponsibilityofSubcommitteeD18.06onPhysical-Chemical
tometer
Interactions of Soil and Rock.
Current edition approved Jan. 1, 2018. Published February 2018. Originally
approved in 1983. Last previous edition approved in 2017 as D4221–17. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D4221-18. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references appended to Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4221 − 18
D4647/D4647M Test Methods for Identification and Classi- 5.4 Since this test method may not identify all dispersive
fication of Dispersive Clay Soils by the Pinhole Test clays, design decisions based solely on this test method may
D6026 Practice for Using Significant Digits in Geotechnical not be conservative. It is often run in conjunction with the
Data crumb test (D6572) (4, 7), the pinhole test (D4647/D4647M),
D6572 Test Methods for Determining Dispersive Character- or the analysis of the pore water extract (D4542) (4, 7),or
istics of Clayey Soils by the Crumb Test combination thereof, to identify possible dispersive clay be-
D6913 Test Methods for Particle-Size Distribution (Grada- havior.
tion) of Soils Using Sieve Analysis
NOTE 1—The quality of the result produced by this standard is
D7928 Test Method for Particle-Size Distribution (Grada-
dependent on the competence of the personal performing it, and the
tion) of Fine-Grained Soils Using the Sedimentation
suitability of the equipment and facilities used. Agencies that meet the
criteria of Practice D3740 are generally considered capable of competent
(Hydrometer) Analysis
and objective testing/sampling/inspection/etc. Users of this standard are
3. Terminology cautioned that compliance with Practice D3740 does not in itself assure
reliable results. Reliable results depends on many factors; Practice D3740
3.1 Definitions:
provides a means of evaluating some of those factors.
3.1.1 For definitions of common technical terms used in this
6. Apparatus
standard, refer to Terminology D653.
6.1 Section 6 of Test Method D7928 describes the equip-
3.2 Definitions of Terms Specific to This Standard:
ment and tools needed for performing the sedimentation
3.2.1 dispersive clays, n—soils that deflocculate easily and
(hydrometer) analysis portion of this standard.
rapidly without significant mechanical assistance in water of
low-salt concentration.
6.2 Container—An airtight, glass or equivalent inert con-
3.2.1.1 Discussion—Such soils usually have a high propor-
tainerwithenoughcapacitytoholdtheminusNo.10(2.0-mm)
tion of their adsorptive capacity saturated with sodium cation
specimen(s).
althoughadsorbedlithiumandmagnesiummayalsoplayarole
6.3 Filtering Flask—A 500-mL filtering flask with a rubber
(6). Such soils also generally have a high shrink-swell
stopper and a side tube capable of withstanding a vacuum.
potential, have low resistance to erosion, and have low
permeability in an intact state. 6.4 Vacuum System—A vacuum pump or water aspirator
capable of producing a vacuum between 508 and 635 mm of
4. Summary of Test Method
Hg on the vacuum gauge.
4.1 This test method is used to determine the percent
7. Reagents
dispersionofasoil.Inordertocalculatethepercentdispersion,
two similar specimens are obtained from a representative
7.1 Section 7 of Test Method D7928 describes the reagents
sample and then a sedimentation (hydrometer) analysis is
needed for performing the mechanically and chemically dis-
performed on each specimen to determine the amount of
persed sedimentation (hydrometer) analysis portion of this
particles finer than 2-µm. The sedimentation analysis is per-
standard.
formed following Test Method D7928 for both specimens,
7.2 Distilled Water—Distilledordemineralizedwaterwitha
except that one of the specimens is de-aired and is not
pH between 5.5 and 7 is the only permissible test fluid for use
mechanically or chemically dispersed.
in the sedimentation portion of the test. The use of tap water is
4.2 The percent dispersion is calculated by dividing the
not permitted.
percent passing the 2-µm size from the de-aired, not dispersed
8. Sampling
specimen by the percent passing the 2-µm size from the
specimen that was dispersed and by multiplying the result by
8.1 General—This test method does not address, in any
100.
detail, procurement of the sample. It is assumed the sample is
obtainedusingappropriatemethodsandisrepresentativeofthe
5. Significance and Use
materialunderevaluation.Thetestingagencymustpreserveall
5.1 Dispersive clays are those which normally deflocculate
samples in accordance with Practice D4220/D4220M, Group
when exposed to water of low-salt concentration, the opposite
B, except if the as-received sample does not meet those
of aggregated clays that would remain flocculated in the same
requirements. In which case, the water content of the sample
soil-water system (3, 4, 7). Generally, dispersive clays are
does not have to be maintained. Section 9 of Test Method
highly erosive, possibly subject to high shrink-swell potential,
D6913 gives additional information regarding sampling from
may have lower shear strength, and have lower permeability
different sources.
rates than aggregated clays.
8.2 Follow the steps given in 8.4 of Test Method D7928,
5.2 When the percent dispersion equals 100, it indicates a
including the mass requirements given in Table 1 of that
completely dispersive clay-size fraction. When the percent
standard, to obtain the reduced sample from which the test
dispersion equals 0, it indicates completely nondispersive
specimens are to be obtained.
clay-size fraction.
9. Preparation of the Test Specimens
5.3 Available data (1) indicates that the test method has
about 85 % reliance in predicting dispersive performance 9.1 Specimen Procurement—This standard presents two
(85 % of dispersive clays show more than 35 % dispersion). preparation methods to obtain the sedimentation specimens:
D4221 − 18
moist and air-dried. Moist and air-dried refers to the condition where:
of the sample as it is being reduced to an appropriate particle
M = mass of moist soil, nearest 0.01 g,
m
size and mass. The test shall not be performed on oven-dried
M = mass of dry soil, nearest 0.01 g, and
d
soil. The air-dried method shall only be used on samples w = water content, nearest 0.1 %.
c
receivedintheair-driedstate(Note2).Sincesomefine-grained
10.2.2 Place approximately 125 mLof distilled water in the
air-dried soils aggregate, a mortar and rubber covered pestle is
filtering flask.
used to break up aggregations. Care must be taken to avoid
10.2.3 Using one of the specimens stored in one of the
disintegration or reduction of individual particles. Use only
containers, take the moist mass, M , amount as determined in
enoughforceasnecessarytobreakuptheaggregationswithout
m
10.2.1, and place it into the filtering flask with the distilled
destroying the individual particles. Additional guidance for
water.
splitting materials to obtain a representative specimen is given
in Test Method D6913, Annex A2.
10.2.4 Place a rubber stopper into the mouth of the filtering
flask and connect the flask to the vacuum pump. If the soil was
9.2 See 9.2 and 9.3 ofTest Method D7928 for the moist and
received in the air-dried st
...

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: D4221 − 17 D4221 − 18
Standard Test Method for
Dispersive Characteristics of Clay Soil by Double
Hydrometer
This standard is issued under the fixed designation D4221; 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 provides an indication of the natural dispersive characteristics of clay soils by comparing the amount of
particles finer than 2-μm as determined by this method compared to the amount of particles finer than 2-μm as determined by Test
Method D7928(1). In order to do this comparison, two similar specimens must be obtained from the sample.
1.2 This test method follows the procedure given in Test Method D7928 with the exception that the soil slurry is not
mechanically dispersed and no dispersing agent is added.
1.3 This test method is applicable only to soils where the position of the plasticity index versus liquid limit plots (Test Methods
D4318) falls on or above the “A” line (Practice D2487) and more than 12 % of the soil fraction is finer than 2-μm as determined
in accordance with Test Method D7928(2).
1.4 Since this test method may not identify all dispersive clay soils, other tests such as, pinhole dispersion (Test Methods
D4647/D4647M), crumb (Test Methods D6572) (3-5) and the analysis of pore water extraction (Test Methods D4542) (4-7) may
be performed individually or used together to help verify dispersion.
1.5 Units—The values stated in SI units are to be regarded as the standard. Reporting of test results in units other than SI shall
not be regarded as nonconformance with this test method.
1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.6.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as the industry
standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not
consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user’s objectives;
and it is common practice to increase or reduce significant digits of reported data to be commensurate with these considerations.
It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
D2488 Practice for Description and Identification of Soils (Visual-Manual Procedures)
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.06 on Physical-Chemical
Interactions of Soil and Rock.
Current edition approved July 1, 2017Jan. 1, 2018. Published July 2017February 2018. Originally approved in 1983. Last previous edition approved in 20112017 as
D4221–11.–17. DOI: 10.1520/D4221-17.10.1520/D4221-18.
The boldface numbers in parentheses refer to the list of references appended to this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D4221 − 18
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4220/D4220M Practices for Preserving and Transporting Soil Samples
D4318 Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
D4542 Test Methods for Pore Water Extraction and Determination of the Soluble Salt Content of Soils by Refractometer
D4647/D4647M Test Methods for Identification and Classification of Dispersive Clay Soils by the Pinhole Test
D6026 Practice for Using Significant Digits in Geotechnical Data
D6572 Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test
D6913 Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
D7928 Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer)
Analysis
3. Terminology
3.1 Definitions:
3.1.1 For definitions of common technical terms used in this standard, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 dispersive clays, n—soils that deflocculate easily and rapidly without significant mechanical assistance in water of low-salt
concentration.
3.2.1.1 Discussion—
Such soils usually have a high proportion of their adsorptive capacity saturated with sodium cation although adsorbed lithium and
magnesium may also play a role (6). Such soils also generally have a high shrink-swell potential, have low resistance to erosion,
and have low permeability in an intact state.
4. Summary of Test Method
4.1 This test method is used to determine the percent dispersion of a soil. In order to calculate the percent dispersion, two similar
specimens are obtained from a representative sample and then a sedimentation (hydrometer) analysis is performed on each
specimen to determine the amount of particles finer than 2-μm. The sedimentation analysis is performed following Test Method
D7928 for both specimens, except that one of the specimens is de-aired and is not mechanically or chemically dispersed.
4.2 The percent dispersion is calculated by dividing the percent passing the 2-μm size from the de-aired, not dispersed specimen
by the percent passing the 2-μm size from the specimen that was dispersed and by multiplying the result by 100.
5. Significance and Use
5.1 Dispersive clays are those which normally deflocculate when exposed to water of low-salt concentration, the opposite of
aggregated clays that would remain flocculated in the same soil-water system (3, 4, 7). Generally, dispersive clays are highly
erosive, possibly subject to high shrink-swell potential, may have lower shear strength, and have lower permeability rates than
aggregated clays.
5.2 When the percent dispersion equals 100, it indicates a completely dispersive clay-size fraction. When the percent dispersion
equals 0, it indicates completely nondispersive clay-size fraction.
5.3 Available data (1) indicates that the test method has about 85 % reliance in predicting dispersive performance (85 % of
dispersive clays show more than 35 % dispersion).
5.4 Since this test method may not identify all dispersive clays, design decisions based solely on this test method may not be
conservative. It is often run in conjunction with the crumb test (D6572) (4, 7), the pinhole test (D4647/D4647M), or the analysis
of the pore water extract (D4542) (4, 7), or combination thereof, to identify possible dispersive clay behavior.
NOTE 1—The quality of the result produced by this standard is dependent on the competence of the personal performing it, and the suitability of the
equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective
testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable
results depends on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Apparatus
6.1 Section 6 of Test Method D7928 describes the equipment and tools needed for performing the sedimentation (hydrometer)
analysis portion of this standard.
6.2 Container—An airtight, glass or equivalent inert container with enough capacity to hold the minus No. 10 (2.0-mm)
specimen(s).
6.3 Filtering Flask—A 500-mL filtering flask with a rubber stopper and a side tube capable of withstanding a vacuum.
D4221 − 18
6.4 Vacuum System—A vacuum pump or water aspirator capable of producing a vacuum between 508 and 635 mm of Hg on
the vacuum gauge.
7. Reagents
7.1 Section 7 of Test Method D7928 describes the reagents needed for performing the mechanically and chemically dispersed
sedimentation (hydrometer) analysis portion of this standard.
7.2 Distilled Water—Distilled or demineralized water with a pH between 5.5 and 7 is the only permissible test fluid for use in
the sedimentation portion of the test. The use of tap water is not permitted.
8. Sampling
8.1 General—This test method does not address, in any detail, procurement of the sample. It is assumed the sample is obtained
using appropriate methods and is representative of the material under evaluation. The testing agency must preserve all samples in
accordance with Practice D4220/D4220M, Group B, except if the as-received sample does not meet those requirements. In which
case, the water content of the sample does not have to be maintained. Section 9 of Test Method D6913 gives additional information
regarding sampling from different sources.
8.2 Follow the steps given in 8.4 of Test Method D7928, including the mass requirements given in Table 1 of that standard, to
obtain the reduced sample from which the test specimens are to be obtained.
9. Preparation of the Test Specimens
9.1 Specimen Procurement—This standard presents two preparation methods to obtain the sedimentation specimens: moist and
air-dried. Moist and air-dried refers to the condition of the sample as it is being reduced to an appropriate particle size and mass.
The test shall not be performed on oven-dried soil. The air-dried method shall only be used on samples received in the air-dried
state (Note 2). Since some fine-grained air-dried soils aggregate, a mortar and rubber covered pestle is used to break up
aggregations. Care must be taken to avoid disintegration or reduction of individual particles. Use only enough force as necessary
to break up the aggregations without destroying the individual particles. Additional guidance for splitting materials to obtain a
representative specimen is given in Test Method D6913, Annex A2.
9.2 See 9.2 and 9.3 of Test Method D7928 for the moist and air-dried preparation methods, respectively.
9.3 If the reduced sample contains particles larger than the No. 10 (2.0-mm) sieve, the soil must be separated using a No. 10
(2.0-mm) sieve. Process the entire reduced sample over the No. 10 (2.0-mm) sieve using a rubber scraper and, if needed, distilled
water to aid in working the soil through the sieve. Check that the soil retained on the sieve does not contain aggregations of finer
particles. Any aggregations should be broken and passed through the sieve. It is not necessary that the
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