ASTM D2166/D2166M-16

Standard Test Method for Unconfined Compressive Strength of Cohesive Soil

SIGNIFICANCE AND USE
5.1 The primary purpose of the unconfined compression test is to quickly obtain a measure of compressive strength for those soils that possess sufficient cohesion to permit testing in the unconfined state.  
5.2 Samples of soils having slickensided or fissured structure, samples of some types of loess, very soft clays, dry and crumbly soils and varved materials, or samples containing significant portions of silt or sand, or both (all of which usually exhibit cohesive properties), frequently display higher shear strengths when tested in accordance with Test Method D2850. Also, unsaturated soils will usually exhibit different shear strengths when tested in accordance with Test Method D2850.  
5.3 If tests on the same sample in both its intact and remolded states are performed, the sensitivity of the material can be determined. This method of determining sensitivity is suitable only for soils that can retain a stable specimen shape in the remolded state.
Note 2: For soils that will not retain a stable shape, a vane shear test or Test Method D2850 can be used to determine sensitivity.
Note 3: The quality of the result produced by this standard is dependent on the competence of the personnel 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. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
SCOPE
1.1 This test method covers the determination of the unconfined compressive strength of cohesive soil in the intact, remolded, or reconstituted condition, using strain-controlled application of the axial load.  
1.2 This test method provides an approximate value of the strength of cohesive soils in terms of total stresses.  
1.3 This test method is applicable only to cohesive materials which will not expel or bleed water (water expelled from the soil due to deformation or compaction) during the loading portion of the test and which will retain intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with this method to obtain valid unconfined compression strength values.  
Note 1: The determination of the unconsolidated, undrained strength of cohesive soils with lateral confinement is covered by Test Method D2850.  
1.4 This test method is not a substitute for Test Method D2850.  
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.  
1.5.1 The procedures used to specify how data are collected/recorded and calculated in this test method are regarded as the industry standard. In addition, they are representative of the significant digits that should generally 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 commensurate with these considerations. It is beyond the scope of this test method to consider significant digits used in analysis methods for engineering design.  
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.6.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf)...

General Information

• Status: Published
• Publication Date: 30-Jun-2016
• ICS: 93.020 - Earthworks. Excavations. Foundation construction. Underground works
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.05 - Strength and Compressibility of Soils

Relations

• 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 D854-23 - Standard Test Methods for Specific Gravity of Soil Solids by the Water Displacement Method
• 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 D7263-09(2018)e1 - Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
• Effective Date: 15-Feb-2018
• Refers: ASTM D7263-09(2018) - Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
• Effective Date: 15-Feb-2018
• 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 D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM E177-13 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2013
• Refers: ASTM D1587-08(2012)e1 - Standard Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes
• Effective Date: 15-May-2012
• Refers: ASTM D3740-12a - 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-May-2012

Overview

ASTM D2166/D2166M-16 is an internationally recognized standard developed by ASTM International for determining the unconfined compressive strength of cohesive soils. This test method provides a straightforward means to evaluate the compressive strength of soils that exhibit sufficient cohesion to be tested in an unconfined (no lateral support) state. The method applies to intact, remolded, or reconstituted specimens of soils such as clays and cemented soils, which do not expel or bleed water during testing and maintain strength after removal of confining pressures. The results of this test are widely used in geotechnical engineering to inform soil stability, construction suitability, and foundation design.

Key Topics

• Unconfined Compressive Strength: The maximum axial compressive stress that a cylindrical soil specimen can withstand before failure, without lateral confinement.
• Cohesive Soil Testing: Applicable to soils exhibiting cohesion, such as clays and cemented materials; not suitable for dry, crumbly soils, fissured or varved materials, silts, peats, or sands.
• Strain-Controlled Loading: The axial load is applied under a controlled strain rate, typically ranging from 0.5% to 2% per minute until the specimen fails or reaches 15% strain.
• Sensitivity Assessment: By testing both intact and remolded specimens, the sensitivity of the soil (change in strength due to disturbance) can be evaluated for cohesive soils retaining shape after remolding.
• Significance of Results: Findings are approximate and relate to total stresses. The test provides quick strength assessments valuable for preliminary site investigation, construction planning, and design.

Applications

The ASTM D2166/D2166M-16 Test Method is essential for:

• Site Investigation and Soil Characterization
  Offers rapid assessment of compressive strength for cohesive soils, aiding in geotechnical site characterization and risk evaluation.

• Foundation and Embankment Design
  Used to estimate the bearing capacity and stability of soils supporting structures, embankments, and earthworks.

• Comparative Soil Analysis
  Provides a standardized way to compare the strength of different cohesive soils or the impact of soil treatment procedures (such as remolding or compaction).

• Construction Quality Assurance
  Assists in verifying soil properties during and after construction, ensuring compliance with design specifications.

• Assessment of Soil Sensitivity
  Determines how soil strength changes when disturbed, informing safe handling and best practices for excavation and building.

Related Standards

Several ASTM standards complement or relate to ASTM D2166/D2166M-16, ensuring comprehensive soil analysis and data reliability:

• ASTM D2850: Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils - for soils requiring lateral confinement or where water expulsion is significant.
• ASTM D653: Terminology Relating to Soil, Rock, and Contained Fluids.
• ASTM D2216: Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass.
• ASTM D2488: Practice for Description and Identification of Soils (Visual-Manual Procedure).
• ASTM D3740: Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction.
• ASTM D6913: Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis.
• ASTM D7263: Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens.

For a comprehensive and reliable soil testing regimen, these related standards should be considered in tandem with ASTM D2166/D2166M-16.

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Keywords: unconfined compressive strength, ASTM D2166, cohesive soils, soil testing, geotechnical site investigation, compressive strength test, soil sensitivity, laboratory soil test standards, foundation design, soil mechanics.

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:D2166/D2166M −16
Standard Test Method for
Unconfined Compressive Strength of Cohesive Soil
This standard is issued under the fixed designation D2166/D2166M; 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* each system may not be exact equivalents; therefore, each
system shall be used independently of the other. Combining
1.1 This test method covers the determination of the uncon-
values from the two systems may result in non-conformance
fined compressive strength of cohesive soil in the intact,
with the standard.
remolded, or reconstituted condition, using strain-controlled
1.6.1 The gravitational system of inch-pound units is used
application of the axial load.
when dealing with inch-pound units. In this system, the pound
1.2 This test method provides an approximate value of the
(lbf) represents a unit of force (weight), while the unit for mass
strength of cohesive soils in terms of total stresses.
is slugs.The rationalized slug unit is not given, unless dynamic
1.3 Thistestmethodisapplicableonlytocohesivematerials (F = ma) calculations are involved.
1.6.2 It is common practice in the engineering/construction
which will not expel or bleed water (water expelled from the
soil due to deformation or compaction) during the loading profession to concurrently use pounds to represent both a unit
of mass (lbm) and of force (lbf). This implicitly combines two
portion of the test and which will retain intrinsic strength after
removal of confining pressures, such as clays or cemented separate systems of units; that is, the absolute system and the
gravitational system. It is scientifically undesirable to combine
soils. Dry and crumbly soils, fissured or varved materials, silts,
peats, and sands cannot be tested with this method to obtain the use of two separate sets of inch-pound units within a single
standard. As stated, this standard includes the gravitational
valid unconfined compression strength values.
system of inch-pound units and does not use/present the slug
NOTE 1—The determination of the unconsolidated, undrained strength
unit for mass. However, the use of balances or scales recording
of cohesive soils with lateral confinement is covered by Test Method
pounds of mass (lbm) or recording density in lbm/ft shall not
D2850.
be regarded as nonconformance with this standard.
1.4 This test method is not a substitute for Test Method
1.7 This standard does not purport to address all of the
D2850.
safety problems, if any, associated with its use. It is the
1.5 All observed and calculated values shall conform to the
responsibility of the user of this standard to establish appro-
guidelines for significant digits and rounding established in
priate safety and health practices and determine the applica-
Practice D6026, unless superseded by this standard.
bility of regulatory limitations prior to use.
1.5.1 Theproceduresusedtospecifyhowdataarecollected/
recorded and calculated in this test method are regarded as the
2. Referenced Documents
industry standard. In addition, they are representative of the
2.1 ASTM Standards:
significant digits that should generally be retained. The proce-
D653 Terminology Relating to Soil, Rock, and Contained
dures used do not consider material variation, purpose for
Fluids
obtaining the data, special purpose studies, or any consider-
D854 Test Methods for Specific Gravity of Soil Solids by
ations for the user’s objectives; and it is common practice to
Water Pycnometer
increase or reduce significant digits of reported data to com-
D1587 Practice for Thin-Walled Tube Sampling of Fine-
mensurate with these considerations. It is beyond the scope of
Grained Soils for Geotechnical Purposes
this test method to consider significant digits used in analysis
D2216 Test Methods for Laboratory Determination of Water
methods for engineering design.
(Moisture) Content of Soil and Rock by Mass
1.6 The values stated in either SI units or inch-pound units
D2488 Practice for Description and Identification of Soils
are to be regarded separately as standard. The values stated in
(Visual-Manual Procedure)
Thistestmethodisunder the jurisdiction ofASTM CommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
Compressibility of Soils. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2016. Published July 2016. Originally approved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 1963. Last previous edition approved in 2013 as D2166 – 13. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D2166_D2166M-16. 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
D2166/D2166M−16
D2850 Test Method for Unconsolidated-Undrained Triaxial 5.3 If tests on the same sample in both its intact and
Compression Test on Cohesive Soils remolded states are performed, the sensitivity of the material
D3740 Practice for Minimum Requirements for Agencies can be determined. This method of determining sensitivity is
Engaged in Testing and/or Inspection of Soil and Rock as suitable only for soils that can retain a stable specimen shape
Used in Engineering Design and Construction in the remolded state.
D4220 Practices for Preserving and Transporting Soil
NOTE 2—For soils that will not retain a stable shape, a vane shear test
Samples
or Test Method D2850 can be used to determine sensitivity.
D4318 Test Methods for Liquid Limit, Plastic Limit, and
NOTE 3—The quality of the result produced by this standard is
dependent on the competence of the personnel performing it, and the
Plasticity Index of Soils
suitability of the equipment and facilities used. Agencies that meet the
D6026 Practice for Using Significant Digits in Geotechnical
criteria of Practice D3740 are generally considered capable of competent
Data
and objective testing/sampling/inspection. Users of this standard are
D6913 Test Methods for Particle-Size Distribution (Grada-
cautioned that compliance with Practice D3740 does not in itself ensure
tion) of Soils Using Sieve Analysis
reliable results. Reliable results depend on many factors; Practice D3740
provides a means of evaluating some of those factors.
D7263 Test Methods for Laboratory Determination of Den-
sity (Unit Weight) of Soil Specimens
6. Apparatus
E177 Practice for Use of the Terms Precision and Bias in
ASTM Test Methods 6.1 Compression Device—The compression device may be
E691 Practice for Conducting an Interlaboratory Study to a platform weighing scale equipped with a screw-jack-
Determine the Precision of a Test Method activated load yoke, a hydraulic loading device, or any other
compression device with sufficient capacity and control to
3. Terminology
provide the rate of loading prescribed in 8.1. The compression
3.1 Definitions: device shall be capable of measuring the compressive stress to
3.1.1 For definitions of common technical terms in this
three significant digits at the maximum stress, or within 1 kPa
standard, refer to Terminology D653. [0.01 ton/ft ], whichever is larger.
3.2 Definitions of Terms Specific to This Standard:
6.2 Sample Extruder,capableofextrudingthesoilcorefrom
3.2.1 unconfined compressive strength (q )—the compres- the sampling tube at a uniform rate in the same direction of
u
sive stress at which an unconfined cylindrical specimen of soil
travelinwhichthesampleenteredthetube,andwithnegligible
will fail in a simple compression test; in this test method, disturbance of the sample. Conditions at the time of sample
unconfinedcompressivestrengthistakenasthemaximumload
removal may dictate the direction of removal, but the principal
attained per unit area or the load per unit area at 15 % axial concern is to reduce the potential for additional disturbance
strain, whichever is secured first during the performance of a
beyond that incurred during initial sampling.
test.
6.3 Deformation Indicator—Thedeformationindicatorshall
3.2.2 shear strength (s )—for unconfined compressive
u be a dial indicator graduated to 0.03 mm [0.001 in.] or better
strength test specimens, the shear strength is calculated to be
and having a travel range of at least 20 % of the length of the
⁄2 of the compressive stress at failure, as defined in 3.2.1.
test specimen, or some other measuring device, such as an
electronic deformation measuring device, meeting these re-
4. Summary of Test Method
quirements.
4.1 In this test method, a cylindrical soil specimen is
6.4 Dial Comparator, or other suitable device, for measur-
unconfined laterally while loaded axially at an axial strain rate
ing the physical dimensions of the specimen to within 0.1 % of
between 0.5 to 2 %/min. Measurements are made of elapsed
the measured dimension.
time, axial deformation, and axial load. The unconfined com-
NOTE 4—Vernier calipers are not recommended for soft specimens,
pressive stress, q , is calculated as the compressive stress at
u
which will deform as the calipers are applied on the specimen.
failure. The shear strength, s , is one half of the unconfined
u
compressive strength. 6.5 Timer—A timing device indicating the elapsed testing
timetothenearestsecondshallbeusedforestablishingtherate
5. Significance and Use
of strain application prescribed in 8.1.
5.1 The primary purpose of the unconfined compression test
6.6 Balance—The balance used to weigh specimens shall
is to quickly obtain a measure of compressive strength for
determine the mass of the specimen to within 0.1 % of its total
those soils that possess sufficient cohesion to permit testing in
mass.
the unconfined state.
6.7 Equipment, as specified in Test Method D2216.
5.2 Samples of soils having slickensided or fissured
6.8 Miscellaneous Apparatus, including specimen trimming
structure, samples of some types of loess, very soft clays, dry
and carving tools, remolding apparatus, water content cans,
and crumbly soils and varved materials, or samples containing
and data sheets, as required.
significant portions of silt or sand, or both (all of which usually
exhibit cohesive properties), frequently display higher shear
7. Preparation of Test Specimens
strengths when tested in accordance with Test Method D2850.
Also, unsaturated soils will usually exhibit different shear 7.1 Specimen Size—Specimensshallhaveaminimumdiam-
strengths when tested in accordance with Test Method D2850. eter of 30 mm [1.3 in.] and the largest particle contained within
D2166/D2166M−16
the test specimen shall be smaller than one tenth of the remold to the same void ratio as the intact specimen, and to
specimendiameter.Forspecimenshavingadiameterof72mm preserve the natural water content of the soil. Form the
[2.8 in.] or larger, the largest particle size shall be smaller than disturbed material into a mold of circular cross section having
one sixth of the specimen diameter. If, after completion of a dimensions meeting the requirements of 7.1. After removal
test on an intact specimen, it is found, based on visual from the mold, determine the mass and dimensions of the test
observation, that larger particles than permitted are present, specimens.
indicate this information in the remarks section of the report of
7.4 Reconstituted Specimens—Specimens shall be prepared
test data (Note 5). The height-to-diameter ratio shall be
to the predetermined water content and density prescribed by
between 2 and 2.5. Determine the average height and diameter
the individual assigning the test (Note 6). After a specimen is
of the test specimen using the apparatus specified in 6.4. Take
formed, trim the ends perpendicular to the longitudinal axis,
a minimum of three height measurements (approximately 120°
removefromthemold,anddeterminethemassanddimensions
apart), and at least three diameter measurements at approxi-
of the test specimen.
mately the quarter points of the height.
NOTE6—Experienceindicatesthatitisdifficulttocompact,handle,and
NOTE 5—If large soil particles are found in the specimen after testing, obtain valid results with
...

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: D2166/D2166M − 13 D2166/D2166M − 16
Standard Test Method for
Unconfined Compressive Strength of Cohesive Soil
This standard is issued under the fixed designation D2166/D2166M; 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 determination of the unconfined compressive strength of cohesive soil in the intact, remolded,
or reconstituted condition, using strain-controlled application of the axial load.
1.2 This test method provides an approximate value of the strength of cohesive soils in terms of total stresses.
1.3 This test method is applicable only to cohesive materials which will not expel or bleed water (water expelled from the soil
due to deformation or compaction) during the loading portion of the test and which will retain intrinsic strength after removal of
confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands
cannot be tested with this method to obtain valid unconfined compression strength values.
NOTE 1—The determination of the unconsolidated, undrained strength of cohesive soils with lateral confinement is covered by Test Method D2850.
1.4 This test method is not a substitute for Test Method D2850.
1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026, unless superseded by this standard.
1.5.1 The procedures used to specify how data are collected/recorded and calculated in this test method are regarded as the
industry standard. In addition, they are representative of the significant digits that should generally 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 commensurate with these
considerations. It is beyond the scope of this test method to consider significant digits used in analysis methods for engineering
design.
1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.6.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf)
represents a unit of force (weight), while the unit for mass is slugs. The rationalized slug unit is not given, unless dynamic (F =
ma) calculations are involved.
1.6.2 It is common practice in the engineering/construction profession to concurrently use pounds to represent both a unit of
mass (lbm) and of force (lbf). This implicitly combines two separate systems of units; that is, the absolute system and the
gravitational system. It is scientifically undesirable to combine the use of two separate sets of inch-pound units within a single
standard. As stated, this standard includes the gravitational system of inch-pound units and does not use/present the slug unit for
mass. However, the use of balances or scales recording pounds of mass (lbm) or recording density in lbm/ft shall not be regarded
as nonconformance with this standard.
1.7 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
This test method is under the jurisdiction of ASTM Committee D18 on Soil and Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
Compressibility of Soils.
Current edition approved May 15, 2013July 1, 2016. Published August 2013July 2016. Originally approved in 1963. Last previous edition approved in 20062013 as D2166
– 06.13. DOI: 10.1520/D2166_D2166M-13.10.1520/D2166_D2166M-16.
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
D2166/D2166M − 16
D854 Test Methods for Specific Gravity of Soil Solids by Water Pycnometer
D1587 Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes
D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
D2488 Practice for Description and Identification of Soils (Visual-Manual Procedure)
D2850 Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils
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 Practices for Preserving and Transporting Soil Samples
D4318 Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
D6026 Practice for Using Significant Digits in Geotechnical Data
D6913 Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
D7263 Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions:
3.1.1 For definitions of common technical terms in this standard, refer to Terminology D653.
3.1 Definitions:
3.1.1 For definitions of common technical terms in this standard, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 unconfined compressive strength (q )—the compressive stress at which an unconfined cylindrical specimen of soil will fail
u
in a simple compression test; in this test method, unconfined compressive strength is taken as the maximum load attained per unit
area or the load per unit area at 15 % axial strain, whichever is secured first during the performance of a test.
3.2.2 shear strength (s )—for unconfined compressive strength test specimens, the shear strength is calculated to be ⁄2 of the
u
compressive stress at failure, as defined in 3.2.1.
4. Summary of Test Method
4.1 In this test method, a cylindrical soil specimen is unconfined laterally while loaded axially at an axial strain rate between
0.5 to 2 %/min. Measurements are made of elapsed time, axial deformation, and axial load. The unconfined compressive stress,
q , is calculated as the compressive stress at failure. The shear strength, s , is one half of the unconfined compressive strength.
u u
5. Significance and Use
5.1 The primary purpose of the unconfined compression test is to quickly obtain a measure of compressive strength for those
soils that possess sufficient cohesion to permit testing in the unconfined state.
5.2 Samples of soils having slickensided or fissured structure, samples of some types of loess, very soft clays, dry and crumbly
soils and varved materials, or samples containing significant portions of silt or sand, or both (all of which usually exhibit cohesive
properties), frequently display higher shear strengths when tested in accordance with Test Method D2850. Also, unsaturated soils
will usually exhibit different shear strengths when tested in accordance with Test Method D2850.
5.3 If tests on the same sample in both its intact and remolded states are performed, the sensitivity of the material can be
determined. This method of determining sensitivity is suitable only for soils that can retain a stable specimen shape in the remolded
state.
NOTE 2—For soils that will not retain a stable shape, a vane shear test or Test Method D2850 can be used to determine sensitivity.
NOTE 3—The quality of the result produced by this standard is dependent on the competence of the personnel 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. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable
results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.
6. Apparatus
6.1 Compression Device—The compression device may be a platform weighing scale equipped with a screw-jack-activated load
yoke, a hydraulic loading device, or any other compression device with sufficient capacity and control to provide the rate of loading
prescribed in 8.1. The compression device shall be capable of measuring the compressive stress to three significant digits at the
maximum stress, or within 1 kPa [0.01 ton/ft ], whichever is larger.
6.2 Sample Extruder, capable of extruding the soil core from the sampling tube at a uniform rate in the same direction of travel
in which the sample entered the tube, and with negligible disturbance of the sample. Conditions at the time of sample removal may
dictate the direction of removal, but the principal concern is to reduce the potential for additional disturbance beyond that incurred
during initial sampling.
D2166/D2166M − 16
6.3 Deformation Indicator—The deformation indicator shall be a dial indicator graduated to 0.03 mm [0.001 in.] or better and
having a travel range of at least 20 % of the length of the test specimen, or some other measuring device, such as an electronic
deformation measuring device, meeting these requirements.
6.4 Dial Comparator, or other suitable device, for measuring the physical dimensions of the specimen to within 0.1 % of the
measured dimension.
NOTE 4—Vernier calipers are not recommended for soft specimens, which will deform as the calipers are applied on the specimen.
6.5 Timer—A timing device indicating the elapsed testing time to the nearest second shall be used for establishing the rate of
strain application prescribed in 8.1.
6.6 Balance—The balance used to weigh specimens shall determine the mass of the specimen to within 0.1 % of its total mass.
6.7 Equipment, as specified in Test Method D2216.
6.8 Miscellaneous Apparatus, including specimen trimming and carving tools, remolding apparatus, water content cans, and
data sheets, as required.
7. Preparation of Test Specimens
7.1 Specimen Size—Specimens shall have a minimum diameter of 30 mm [1.3 in.] and the largest particle contained within the
test specimen shall be smaller than one tenth of the specimen diameter. For specimens having a diameter of 72 mm [2.8 in.] or
larger, the largest particle size shall be smaller than one sixth of the specimen diameter. If, after completion of a test on an intact
specimen, it is found, based on visual observation, that larger particles than permitted are present, indicate this information in the
remarks section of the report of test data (Note 5). The height-to-diameter ratio shall be between 2 and 2.5. Determine the average
height and diameter of the test specimen using the apparatus specified in 6.4. Take a minimum of three height measurements
(approximately 120° apart), and at least three diameter measurements at approximately the quarter points of the height.
NOTE 5—If large soil particles are found in the specimen after testing, a particle-size analysis performed in accordance with Test Method D6913 may
be performed to confirm the visual observation and the results provided with the test report.
7.2 Intact Specimens—Prepare intact specimens from large samples or from samples secured in accordance with Practice D1587
and preserved and transported in accordance with the practices for Group C samples in Practices D4220. Tube specimens may be
tested without trimming except for the squaring of ends, if conditions of the sample justify this procedure. Handle specimens
carefully to reduce the potential for additional disturbance, changes in cross section, or loss of water content. If compression or
any type of noticeable disturbance would be caused by the extrusion device, split the sample tube lengthwise or cut it off in small
sections to facilitate removal of the specimen with minimal disturbance. Prepare carved specimens with minimal disturbance, and
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