ASTM D2850-23

Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils

SIGNIFICANCE AND USE
5.1 In this test method, the compressive strength of a soil is determined in terms of the total stress, therefore, the resulting strength depends on the pressure developed in the pore fluid during loading. In this test method, fluid flow is not permitted from or into the soil specimen as the load is applied, therefore the resulting pore pressure, and hence strength, differs from that developed in the case where drainage can occur.  
5.2 If the test specimens is 100 % saturated, consolidation cannot occur when the confining pressure is applied nor during the shear portion of the test since drainage is not permitted. Therefore, if several specimens of the same material are tested, and if they are all at approximately the same water content and void ratio when they are tested, they will have approximately the same unconsolidated-undrained shear strength.  
5.3 If the test specimens are partially saturated, or compacted/reconstituted specimens, where the degree of saturation is less than 100 %, consolidation may occur when the confining pressure is applied and during application of axial load, even though drainage is not permitted. Therefore, if several partially saturated specimens of the same material are tested at different confining stresses, they will not have the same unconsolidated-undrained shear strength.  
5.4 Mohr failure envelopes may be plotted from a series of unconsolidated undrained triaxial tests. The Mohr’s circles at failure based on total stresses are constructed by plotting a half circle with a radius of half the principal stress difference (deviator stress) beginning at the axial stress (major principal stress) and ending at the confining stress (minor principal stress) on a graph with principal stresses as the abscissa and shear stress as the ordinate and equal scale in both directions. The failure envelopes will usually be a horizontal line for saturated specimens and a curved line for partially saturated specimens.  
5.5 The unconsolidated-u...
SCOPE
1.1 This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of either intact, compacted, or remolded cohesive soil. Specimens are subjected to a confining fluid pressure in a triaxial chamber. No drainage of the specimen is permitted during the application of the confining fluid pressure or during the compression phase of the test. The specimen is axially loaded at a constant rate of axial deformation (strain controlled).  
1.2 This test method provides data for determining undrained strength properties and stress-strain relations for soils. This test method provides for the measurement of the total stresses applied to the specimen, that is, the stresses are not corrected for pore-water pressure.
Note 1: The determination of the unconfined compressive strength of cohesive soils is covered by Test Method D2166/D2166M.
Note 2: The determination of the consolidated, undrained strength of cohesive soils with pore pressure measurement is covered by Test Method D4767.  
1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.  
1.3.1 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.  
1.4 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are mathemat...

General Information

• Status: Published
• Publication Date: 31-Jan-2023
• 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 D4753-24 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-Feb-2024
• 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 D3740-23 - 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 D4767-11(2020) - Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soils
• Effective Date: 01-Apr-2020
• 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 D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17e1 - 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 D1587/D1587M-15 - Standard Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes (Withdrawn 2024)
• Effective Date: 15-Nov-2015
• Refers: ASTM D4753-15 - Standard Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction Materials Testing
• Effective Date: 01-May-2015
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014
• Refers: ASTM D2166/D2166M-13 - Standard Test Method for Unconfined Compressive Strength of Cohesive Soil
• Effective Date: 15-May-2013

Overview

ASTM D2850-23, titled "Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils," is a widely recognized standard developed by ASTM International. It provides a method for determining the strength and stress-strain relationship of cylindrical specimens of cohesive soil-whether intact, compacted, or remolded-when subjected to axial loading without allowing drainage. This test method is fundamental in geotechnical engineering for assessing the undrained shear strength and total stress characteristics of soils, which are critical for construction and engineering projects involving rapid loading or short-term stability analysis.

Key Topics

• Scope and Purpose:

  • Applies to cylindrical soil specimens subjected to confining fluid pressure in a triaxial chamber, with axial loading at a constant rate and no drainage permitted.
  • Focuses on measuring undrained strength and stress-strain response, using total stress without correcting for pore-water pressure.
  • Provides guidelines for specimen preparation, apparatus, testing procedures, calculation methods, and reporting requirements.

• Significance and Use:

  • The test measures compressive strength in terms of total stress, affected by pore pressure developed during loading due to the prohibition of drainage.
  • Useful for evaluating conditions where loading occurs so quickly that there is no time for pore-water pressure to dissipate (e.g., seismic events, rapid foundation loading).
  • Results enable plotting of Mohr failure envelopes to distinguish behaviors for fully saturated vs partially saturated soils.

• Test Applicability:

  • Applies to both field-collected, undisturbed (intact), laboratory-compacted, or remolded cohesive soil specimens.
  • Particularly valuable for soils below groundwater level or in short-term loading scenarios.

• Procedural Highlights:

  • Preparation includes precise dimensions and mass documentation, water content determination, and careful handling to minimize disturbance.
  • Test involves measuring deformation, applied load, and chamber pressure, then calculating stress-strain relationships and undrained shear strength.

Applications

• Geotechnical Site Investigation:

  • Determines undrained shear strength, a key parameter for short-term slope stability, earthworks, foundation, embankment, and retaining structure design.
  • Assesses soil behavior under conditions such as rapid loading or construction staging, where consolidation and drainage cannot occur.

• Construction and Design:

  • Used by geotechnical engineers to inform designs that are sensitive to soil strength under undrained conditions, especially for infrastructure built on or involving cohesive soils.
  • Supports risk assessment for construction activities and strategies for managing soil stability in the presence of water.

• Quality Control and Research:

  • Facilitates comparison between soils of differing origins, compaction states, or degrees of saturation.
  • Useful for research in soil mechanics, material modeling, and validation of analytical or numerical predictions regarding undrained soil response.

Related Standards

• ASTM D2166/D2166M:
  Standard test method for unconfined compressive strength of cohesive soils.

• ASTM D4767:
  Standard test method for consolidated undrained triaxial compression test on cohesive soils with measurement of pore water pressure.

• ASTM D2216:
  Test methods for laboratory determination of water content of soil and rock by mass.

• ASTM D7012:
  Test methods related to compressive strength and elastic properties of rock.

• ASTM D6026:
  Practice for using significant digits and data records in geotechnical data.

Practical Value

Using ASTM D2850-23 ensures that soil strength data are generated reliably and consistently, which is critical for responsible and safe geotechnical design and construction practices worldwide. By following this standard, engineers and laboratories can provide results that are trusted and comparable across projects, enhancing overall quality and safety in geotechnical engineering.

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: D2850 − 23
Standard Test Method for
Unconsolidated-Undrained Triaxial Compression Test on
Cohesive Soils
This standard is issued under the fixed designation D2850; 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* cal conversions to inch-pound units, which are provided for
information only and are not considered standard. Reporting of
1.1 This test method covers determination of the strength
test results in units other than SI shall not be regarded as
and stress-strain relationships of a cylindrical specimen of
nonconformance with this test method.
either intact, compacted, or remolded cohesive soil. Specimens
1.4.1 The converted inch-pound units use the gravitational
are subjected to a confining fluid pressure in a triaxial chamber.
system of units. In this system, the pound (lbf) represents a unit
No drainage of the specimen is permitted during the applica-
of force (weight), while the unit for mass is slugs. The slug unit
tion of the confining fluid pressure or during the compression
is not given, unless dynamic (F = ma) calculations are
phase of the test. The specimen is axially loaded at a constant
involved.
rate of axial deformation (strain controlled).
1.5 This standard does not purport to address all of the
1.2 This test method provides data for determining und-
safety concerns, if any, associated with its use. It is the
rained strength properties and stress-strain relations for soils.
responsibility of the user of this standard to establish appro-
This test method provides for the measurement of the total
priate safety, health, and environmental practices and deter-
stresses applied to the specimen, that is, the stresses are not
mine the applicability of regulatory limitations prior to use.
corrected for pore-water pressure.
1.6 This international standard was developed in accor-
NOTE 1—The determination of the unconfined compressive strength of
dance with internationally recognized principles on standard-
cohesive soils is covered by Test Method D2166/D2166M.
ization established in the Decision on Principles for the
NOTE 2—The determination of the consolidated, undrained strength of
Development of International Standards, Guides and Recom-
cohesive soils with pore pressure measurement is covered by Test Method
mendations issued by the World Trade Organization Technical
D4767.
Barriers to Trade (TBT) Committee.
1.3 All observed and calculated values shall conform to the
guidelines for significant digits and rounding established in
2. Referenced Documents
Practice D6026.
1.3.1 The procedures used to specify how data are collected/ 2.1 ASTM Standards:
D422 Test Method for Particle-Size Analysis of Soils (With-
recorded or calculated in this standard are regarded as the
industry standard. In addition, they are representative of the drawn 2016)
D653 Terminology Relating to Soil, Rock, and Contained
significant digits that generally should be retained. The proce-
dures used do not consider material variation, purpose for Fluids
D854 Test Methods for Specific Gravity of Soil Solids by
obtaining the data, special purpose studies, or any consider-
ations for the user’s objectives; and it is common practice to Water Pycnometer
D1587/D1587M Practice for Thin-Walled Tube Sampling of
increase or reduce significant digits of reported data to be
commensurate with these considerations. It is beyond the scope Fine-Grained Soils for Geotechnical Purposes
D2166/D2166M Test Method for Unconfined Compressive
of this standard to consider significant digits used in analysis
methods for engineering design. Strength of Cohesive Soil
D2216 Test Methods for Laboratory Determination of Water
1.4 Units—The values stated in SI units are to be regarded
(Moisture) Content of Soil and Rock by Mass
as the standard. The values given in parentheses are mathemati-
1 2
This test method is under the jurisdiction of ASTM Committee D18 on Soil and For referenced ASTM Standards, visit the ASTM website, www.astm.org, or
Rock and is the direct responsibility of Subcommittee D18.05 on Strength and contact Customer Service at [e-mail]. For Annual Book of ASTM Stan-
Compressibility of Soils. dardsvolume information, refer to the standard’s Document Summary page on the
Current edition approved Feb. 1, 2023. Published February 2023. Originally ASTM website.
approved in 1970. Last previous edition approved in 2015 as D2850 – 15. DOI: The last approved version of this historical standard is referenced on www.ast-
10.1520/D2850-23. m.org.
*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
D2850 − 23
D2487 Practice for Classification of Soils for Engineering strength depends on the pressure developed in the pore fluid
Purposes (Unified Soil Classification System) during loading. In this test method, fluid flow is not permitted
D2488 Practice for Description and Identification of Soils from or into the soil specimen as the load is applied, therefore
(Visual-Manual Procedures) the resulting pore pressure, and hence strength, differs from
D3740 Practice for Minimum Requirements for Agencies that developed in the case where drainage can occur.
Engaged in Testing and/or Inspection of Soil and Rock as
5.2 If the test specimens is 100 % saturated, consolidation
Used in Engineering Design and Construction
cannot occur when the confining pressure is applied nor during
D4220/D4220M Practices for Preserving and Transporting
the shear portion of the test since drainage is not permitted.
Soil Samples (Withdrawn 2023)
Therefore, if several specimens of the same material are tested,
D4318 Test Methods for Liquid Limit, Plastic Limit, and
and if they are all at approximately the same water content and
Plasticity Index of Soils
void ratio when they are tested, they will have approximately
D4753 Guide for Evaluating, Selecting, and Specifying Bal-
the same unconsolidated-undrained shear strength.
ances and Standard Masses for Use in Soil, Rock, and
5.3 If the test specimens are partially saturated, or
Construction Materials Testing
compacted/reconstituted specimens, where the degree of satu-
D4767 Test Method for Consolidated Undrained Triaxial
ration is less than 100 %, consolidation may occur when the
Compression Test for Cohesive Soils
confining pressure is applied and during application of axial
D6026 Practice for Using Significant Digits and Data Re-
load, even though drainage is not permitted. Therefore, if
cords in Geotechnical Data
several partially saturated specimens of the same material are
D6913/D6913M Test Methods for Particle-Size Distribution
tested at different confining stresses, they will not have the
(Gradation) of Soils Using Sieve Analysis
same unconsolidated-undrained shear strength.
3. Terminology
5.4 Mohr failure envelopes may be plotted from a series of
unconsolidated undrained triaxial tests. The Mohr’s circles at
3.1 Definitions—For definitions of common technical terms
failure based on total stresses are constructed by plotting a half
in this standard, refer to Terminology D653.
circle with a radius of half the principal stress difference
3.2 Definitions of Terms Specific to This Standard:
(deviator stress) beginning at the axial stress (major principal
3.2.1 failure—a stress condition selected to represent the
stress) and ending at the confining stress (minor principal
maximum stress supported by a test specimen.
stress) on a graph with principal stresses as the abscissa and
3.2.1.1 Discussion—Failure is often taken to correspond to
shear stress as the ordinate and equal scale in both directions.
the maximum principal stress difference (deviator stress) at-
The failure envelopes will usually be a horizontal line for
tained or the principal stress difference (deviator stress) at
saturated specimens and a curved line for partially saturated
15 % axial strain, whichever is obtained first during the
specimens.
performance of a test.
5.5 The unconsolidated-undrained shear strength is appli-
3.2.2 unconsolidated-undrained compressive strength—the
cable to situations where the loads are assumed to take place so
value of the principal stress difference (deviator stress) at
rapidly that there is insufficient time for the induced pore-water
failure.
pressure to dissipate and for consolidation to occur during the
3.2.3 unconsolidated-undrained shear strength—the value
loading period (that is, drainage does not occur).
of the principal stress difference (deviator stress) at failure
5.6 Compressive strengths determined using this procedure
divided by two.
may not apply in cases where the loading conditions in the field
differ significantly from those used in this test method.
4. Summary of Test Method
NOTE 3—The quality of the results produced by this standard is
4.1 A cylindrical soil specimen with known dimensions and
dependent on the competence of the personnel performing it, and the
mass is sealed between loading platens inside the chamber
suitability of the equipment and facilities used. Agencies that meet the
using a flexible membrane. A confining pressure is applied to
criteria of Practice D3740 are generally considered capable of competent
the specimen in the chamber and the specimen is given time to testing. Users of this test method are cautioned that compliance with
Practice D3740 does not ensure reliable results. Reliable results depend on
equalize without consolidation, as drainage of the specimen
several factors; Practice D3740 provides a means of evaluating some of
pore water is not allowed at any time during the test. The
those factors.
specimen is then loaded axially using a strain rate between 0.3
and 1 % ⁄min such that the time to failure does not exceed 6. Apparatus
approximately 15 min. During the shearing phase of the test,
6.1 Axial Loading Device—The axial loading device shall
measurements of elapsed time, axial deformation, axial load,
be screw jack driven by an electric motor through a geared
and chamber pressure are taken. Based on these data, the soil
transmission, a hydraulic loading device, or any other com-
specimen unconsolidated-undrained compressive strength and
pression device with sufficient capacity and control to provide
unconsolidated-undrained shear strength are determined.
the rate of loading prescribed in 8.5. The rate of advance of the
loading device shall not deviate by more than 65 % from the
5. Significance and Use
selected value. Vibrations due to the operation of the loading
5.1 In this test method, the compressive strength of a soil is device shall be sufficiently small to not cause dimensional
determined in terms of the total stress, therefore, the resulting changes in the specimen.
D2850 − 23
NOTE 4—A loading device may be said to provide sufficiently small
vertical axis of the specimen does not exceed 1.3 mm (0.05
vibrations if there are no visible ripples in a glass of water placed on the
in.). The end of the piston and specimen cap contact area shall
loading platen when the device is operating at the speed at which the test
be designed so that tilting of the specimen cap during the test
is performed.
is minimal. The cylindrical surface of the specimen base and
6.2 Axial Load-Measuring Device—The axial load-
cap that contacts the membrane to form a seal shall be smooth
measuring device shall be capable of measuring the axial load
and free of scratches.
to at least three significant digits (readability); have a full scale
NOTE 7—To determine the axial stress from the top cap, measure the
accuracy not to exceed 0.25 %; and a capacity that is not
mass of the top cap in grams and area of the top cap in cm . The stress
greater than four times the axial load at failure. Commonly, an
from the top cap, in kN/m (= kPa), is equal to the mass in grams times
2 2
electronic load cell is used and may be integrated with the axial
the acceleration due to gravity (9.8087 m/sec ) divided by the area in cm
2 2
loading device.
times 10,000 cm /m divided by 1000 N/kN and 1000 g/kg.
6.7 Deformation Indicator—The vertical deformation of the
6.3 Triaxial Compression Chamber—The triaxial chamber
shall consist of a top plate and a baseplate separated by a specimen is usually determined from the travel of the piston
acting on the top of the specimen. The piston travel shall be
cylinder. The cylinder shall be constructed of any material
capable of withstanding the applied pressure. It is desirable to measured using a deformation indicator with a range of at least
20 % of the initial height of the specimen and an accuracy not
use a transparent material or have a cylinder provided with
viewing ports so the behavior of the specimen may be to exceed 0.25 % of the initial specimen height. The deforma-
tion indicator is commonly a linear variable differential trans-
observed. The top plate shall have a vent valve such that air can
be forced out of the chamber as it is filled. The base plate shall former (LVDT) or other measuring device meeting the require-
ments for accuracy and range.
have an inlet to fill the chamber.
6.4 Axial Load Piston—The piston passing through the top 6.8 Rubber Membrane—The rubber membrane used to en-
case the specimen shall provide reliable protection against
of the chamber and its seal must be designed so the variation
in axial load due to friction does not exceed 0.1 % of the axial leakage. Membranes shall be carefully inspected prior to use,
and if any flaws or pinholes are evident, the membrane shall be
load at failure as measured in 9.6 and so there is negligible
lateral bending of the piston during loading. discarded. To offer minimum restraint to the specimen, the
unstretched membrane diameter shall be between 90 and 95 %
NOTE 5—The use of two linear ball bushings to guide the piston is
of that of the specimen. The membrane thickness shall not
recommended to reduce the friction and maintain alignment.
exceed 1 % of the diameter of the specimen. The membrane
NOTE 6—A minimum piston diameter of one sixth the specimen
diameter has been used successfully in many laboratories to minimize shall be sealed to the specimen base and cap with rubber
lateral bending.
O-rings for which the unstressed inside diameter is between 75
and 85 % of the diameter of the cap and base, or by any method
6.5 Pressure-maintaining and Measurement Devices—The
that will produce a positive seal. An equation for correcting the
pressure-maintaining and measurement devices shall be ca-
principal stress difference (deviator stress) for the effect of the
pable of applying, controlling, and measuring the chamber
strength of the membrane is given in 9.8.
pressure to within 62 kPa (0.3 psi) for pressures less than 200
kPa (29 psi) and to within 61 % for pressures greater than 200
6.9 Sample Extruder—The sample extruder shall be capable
kPa (29 psi).
of extruding the soil core from the sampling tube in the same
6.5.1 A pressure transducer measuring the applied chamber
direction of travel in which the sample entered the tube and
pressure shall have an accuracy not to exceed 60.25 % of full
with minimum disturbance of the sample. If the soil core is not
range, a capacity in excess of the applied chamber pressure,
extruded vertically, care should be taken to avoid bending
and a readability equivalent to at least three significant digits at
stresses on the core due to gravity. Conditions at the time of
the maximum applied chamber pressure. This device com-
sample removal may dictate the direction of removal, but the
monly consists of a reservoir connected to the triaxial chamber
principal concern is to keep the degree of disturbance minimal.
and partially filled with the chamber fluid (usually water), with
6.10 Specimen-Size Measurement Devices—Devices used to
the upper part of the reservoir connected to a compressed gas
measure the height and diameter of the specimen to three or
supply; the gas pressure being controlled by a pressure
more significant digits (readability) with an accuracy not to
regulator and measured by an electronic pressure transducer.
exceed 0.25 % of its full range. The devices shall be con-
6.6 Specimen Cap and Base—An impermeable rigid cap
structed such that during use the specimen is not disturbed or
and base shall be used to prevent drainage of the specimen. The
deformed.
specimen cap and base shall be constructed of a noncorrosive
NOTE 8—Circumferential measuring tapes are recommended over
impermeable material, and each shall have a circular plane
calipers for measuring the diameter.
surface of contact with the specimen and a circular cross
6.11 Timer—A timing device indicating the elapsed testing
section. The mass of the specimen cap shall produce an axial
time to the nearest 1 s shall be used for establishing the rate of
stress on the specimen of less than 1 kPa (0.1 psi). The
strain application prescribed in 8.5 and recording the time
diameter of the cap and base shall be equal to the initial
during specimen compression as required in 8.6.
diameter of the specimen. The specimen base shall be con-
nected to the triaxial compression chamber to prevent lateral 6.12 Balances—A balance or scale conforming to the re-
motion or tilting, and the specimen cap shall be designed such quirements of Specification D4753 readable (with no estima-
that eccentricity of the piston-to-cap contact relative to the tion) to 0.1 % of the test mass, or better.
D2850 − 23
6.13 Miscellaneous Apparatus—Specimen trimming and terial in at least six layers using a split mold of circular cross
carving tools including a wire saw, steel straightedge, miter section having dimensions meeting the requirements enumer-
box and vertical trimming lathe, apparatus for preparing ated in 7.1. Specimens may be compacted/reconstituted to the
remolded specimens, membrane and O-ring expander, water desired density by either: (1) kneading or tamping each layer
content containers, and data sheets shall be provided as until the accumulative mass of the soil placed in the mold is
required. compacted/reconstituted to a known volume; or (2) by adjust-
ing the number of layers, the number of tamps per layer, and
7. Test Specimens
the force per tamp. The top of each layer shall be scarified prior
to the addition of material for the next layer. The tamper used
7.1 Specimen Size—Specimens shall be cylindrical and have
to compact the material shall have a diameter equal to or less
a minimum diameter of 33 mm (1.3 in.). The average height-
than one half the diameter of the mold. After a specimen is
to-average diameter ratio shall be between 2 and 2.5. The
formed,
...

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: D2850 − 15 D2850 − 23
Standard Test Method for
Unconsolidated-Undrained Triaxial Compression Test on
Cohesive Soils
This standard is issued under the fixed designation D2850; 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 determination of the strength and stress-strain relationships of a cylindrical specimen of either intact,
compacted, or remolded cohesive soil. Specimens are subjected to a confining fluid pressure in a triaxial chamber. No drainage
of the specimen is permitted during the application of the confining fluid pressure or during the compression phase of the test. The
specimen is axially loaded at a constant rate of axial deformation (strain controlled).
1.2 This test method provides data for determining undrained strength properties and stress-strain relations for soils. This test
method provides for the measurement of the total stresses applied to the specimen, that is, the stresses are not corrected for
pore-water pressure.
NOTE 1—The determination of the unconfined compressive strength of cohesive soils is covered by Test Method D2166/D2166M.
NOTE 2—The determination of the consolidated, undrained strength of cohesive soils with pore pressure measurement is covered by Test Method D4767.
1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice
D6026.
1.3.1 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.
1.4 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are mathematical
conversions to inch-pound units, which are provided for information only and are not considered standard. Reporting of test results
in units other than SI shall not be regarded as nonconformance with this test method.
1.4.1 The converted inch-pound units use the gravitational system of units. In this system, the pound (lbf) represents a unit of force
(weight), while the unit for mass is slugs. The slug unit is not given, unless dynamic (F = ma) calculations are involved.
1.5 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 and healthsafety, health, and environmental practices and determine
the applicability of regulatory limitations prior to use.
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 Nov. 15, 2015Feb. 1, 2023. Published December 2015February 2023. Originally approved in 1970. Last previous edition approved in 20072015
as D2850 – 03a (2007).D2850 – 15. DOI: 10.1520/D2850-15.10.1520/D2850-23.
*A Summary of Changes section appears at the end of this standard
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1.6 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:
D422 Test Method for Particle-Size Analysis of Soils (Withdrawn 2016)
D653 Terminology Relating to Soil, Rock, and Contained Fluids
D854 Test Methods for Specific Gravity of Soil Solids by Water Pycnometer
D1587D1587/D1587M Practice for Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes
D2166/D2166M Test Method for Unconfined Compressive Strength of Cohesive Soil
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)
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 (Withdrawn 2023)
D4318 Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
D4753 Guide for Evaluating, Selecting, and Specifying Balances and Standard Masses for Use in Soil, Rock, and Construction
Materials Testing
D4767 Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soils
D6026 Practice for Using Significant Digits and Data Records in Geotechnical Data
D6913D6913/D6913M Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis
3. Terminology
3.1 Definitions—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 failure—a stress condition selected to represent the maximum stress supported by a test specimen.
3.2.1.1 Discussion—
Failure is often taken to correspond to the maximum principal stress difference (deviator stress) attained or the principal stress
difference (deviator stress) at 15 % axial strain, whichever is obtained first during the performance of a test.
3.2.2 unconsolidated-undrained compressive strength—the value of the principal stress difference (deviator stress) at failure.
3.2.3 unconsolidated-undrained shear strength—the value of the principal stress difference (deviator stress) at failure divided by
two.
4. Summary of Test Method
4.1 A cylindrical soil specimen with known dimensions and mass is sealed between loading platens inside the chamber using a
flexible membrane. A confining pressure is applied to the specimen in the chamber and the specimen is given time to equalize
without consolidation, as drainage of the specimen pore water is not allowed at any time during the test. The specimen is then
loaded axially using a strain rate between 0.3 and 1 % ⁄min such that the time to failure does not exceed approximately 15 min.
During the shearing phase of the test, measurements of elapsed time, axial deformation, axial load, and chamber pressure are taken.
Based on these data, the soil specimen unconsolidated-undrained compressive strength and unconsolidated-undrained shear
strength are determined.
5. Significance and Use
5.1 In this test method, the compressive strength of a soil is determined in terms of the total stress, therefore, the resulting strength
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information, refer to the standard’s Document Summary page on the ASTM website.
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depends on the pressure developed in the pore fluid during loading. In this test method, fluid flow is not permitted from or into
the soil specimen as the load is applied, therefore the resulting pore pressure, and hence strength, differs from that developed in
the case where drainage can occur.
5.2 If the test specimens is 100 % saturated, consolidation cannot occur when the confining pressure is applied nor during the shear
portion of the test since drainage is not permitted. Therefore, if several specimens of the same material are tested, and if they are
all at approximately the same water content and void ratio when they are tested, they will have approximately the same
unconsolidated-undrained shear strength.
5.3 If the test specimens are partially saturated, or compacted/reconstituted specimens, where the degree of saturation is less than
100 %, consolidation may occur when the confining pressure is applied and during application of axial load, even though drainage
is not permitted. Therefore, if several partially saturated specimens of the same material are tested at different confining stresses,
they will not have the same unconsolidated-undrained shear strength.
5.4 Mohr failure envelopes may be plotted from a series of unconsolidated undrained triaxial tests. The Mohr’s circles at failure
based on total stresses are constructed by plotting a half circle with a radius of half the principal stress difference (deviator stress)
beginning at the axial stress (major principal stress) and ending at the confining stress (minor principal stress) on a graph with
principal stresses as the abscissa and shear stress as the ordinate and equal scale in both directions. The failure envelopes will
usually be a horizontal line for saturated specimens and a curved line for partially saturated specimens.
5.5 The unconsolidated-undrained shear strength is applicable to situations where the loads are assumed to take place so rapidly
that there is insufficient time for the induced pore-water pressure to dissipate and for consolidation to occur during the loading
period (that is, drainage does not occur).
5.6 Compressive strengths determined using this procedure may not apply in cases where the loading conditions in the field differ
significantly from those used in this test method.
NOTE 3—The quality of the results 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 testing. Users of this test
method are cautioned that compliance with Practice D3740 does not ensure reliable results. Reliable results depend on several factors; Practice D3740
provides a means of evaluating some of those factors.
6. Apparatus
6.1 Axial Loading Device—The axial loading device shall be screw jack driven by an electric motor through a geared transmission,
a hydraulic loading device, or any other compression device with sufficient capacity and control to provide the rate of loading
prescribed in 7.58.5. The rate of advance of the loading device shall not deviate by more than 65 % from the selected value.
Vibrations due to the operation of the loading device shall be sufficiently small to not cause dimensional changes in the specimen.
NOTE 4—A loading device may be said to provide sufficiently small vibrations if there are no visible ripples in a glass of water placed on the loading
platen when the device is operating at the speed at which the test is performed.
6.2 Axial Load-Measuring Device—The axial load-measuring device shall be capable of measuring the axial load to at least three
significant digits (readability); have a full scale accuracy not to exceed 0.25 %; and a capacity that is not greater than four times
the axial load at failure. Commonly, an electronic load cell is used and may be integrated with the axial loading device.
6.3 Triaxial Compression Chamber—The triaxial chamber shall consist of a top plate and a baseplate separated by a cylinder. The
cylinder shall be constructed of any material capable of withstanding the applied pressure. It is desirable to use a transparent
material or have a cylinder provided with viewing ports so the behavior of the specimen may be observed. The top plate shall have
a vent valve such that air can be forced out of the chamber as it is filled. The base plate shall have an inlet to fill the chamber.
6.4 Axial Load Piston—The piston passing through the top of the chamber and its seal must be designed so the variation in axial
load due to friction does not exceed 0.1 % of the axial load at failure as measured in 8.69.6 and so there is negligible lateral bending
of the piston during loading.
NOTE 5—The use of two linear ball bushings to guide the piston is recommended to reduce the friction and maintain alignment.
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NOTE 6—A minimum piston diameter of one sixth the specimen diameter has been used successfully in many laboratories to minimize lateral bending.
6.5 Pressure-maintaining and Measurement Devices—The pressure-maintaining and measurement devices shall be capable of
applying, controlling, and measuring the chamber pressure to within 62 kPa (0.3 psi) for pressures less than 200 kPa (29 psi) and
to within 61 % for pressures greater than 200 kPa (29 psi).
6.5.1 A pressure transducer measuring the applied chamber pressure shall have an accuracy not to exceed 60.25 % of full range,
a capacity in excess of the applied chamber pressure, and a readability equivalent to at least three significant digits at the maximum
applied chamber pressure. This device commonly consists of a reservoir connected to the triaxial chamber and partially filled with
the chamber fluid (usually water), with the upper part of the reservoir connected to a compressed gas supply; the gas pressure being
controlled by a pressure regulator and measured by an electronic pressure transducer.
6.6 Specimen Cap and Base—An impermeable rigid cap and base shall be used to prevent drainage of the specimen. The specimen
cap and base shall be constructed of a noncorrosive impermeable material, and each shall have a circular plane surface of contact
with the specimen and a circular cross section. The mass of the specimen cap shall produce an axial stress on the specimen of less
than 1 kPa (0.1 psi). The diameter of the cap and base shall be equal to the initial diameter of the specimen. The specimen base
shall be connected to the triaxial compression chamber to prevent lateral motion or tilting, and the specimen cap shall be designed
such that eccentricity of the piston-to-cap contact relative to the vertical axis of the specimen does not exceed 1.3 mm (0.05 in.).
The end of the piston and specimen cap contact area shall be designed so that tilting of the specimen cap during the test is minimal.
The cylindrical surface of the specimen base and cap that contacts the membrane to form a seal shall be smooth and free of
scratches.
NOTE 7—To determine the axial stress from the top cap, measure the mass of the top cap in grams and area of the top cap in cm . The stress from the
2 2 2
top cap, in kN/m (= kPa), is equal to the mass in grams times the acceleration due to gravity (9.8087 m/sec ) divided by the area in cm times 10,000
2 2
cm /m divided by 1000 N/kN and 1000 g/kg.
6.7 Deformation Indicator—The vertical deformation of the specimen is usually determined from the travel of the piston acting
on the top of the specimen. The piston travel shall be measured using a deformation indicator with a range of at least 20 % of the
initial height of the specimen and an accuracy not to exceed 0.25 % of the initial specimen height. The deformation indicator is
commonly a linear variable differential transformer (LVDT) or other measuring device meeting the requirements for accuracy and
range.
6.8 Rubber Membrane—The rubber membrane used to encase the specimen shall provide reliable protection against leakage.
Membranes shall be carefully inspected prior to use, and if any flaws or pinholes are evident, the membrane shall be discarded.
To offer minimum restraint to the specimen, the unstretched membrane diameter shall be between 90 and 95 % of that of the
specimen. The membrane thickness shall not exceed 1 % of the diameter of the specimen. The membrane shall be sealed to the
specimen base and cap with rubber O-rings for which the unstressed inside diameter is between 75 and 85 % of the diameter of
the cap and base, or by any method that will produce a positive seal. An equation for correcting the principal stress difference
(deviator stress) for the effect of the strength of the membrane is given in 8.89.8.
6.9 Sample Extruder—The sample extruder shall be capable of extruding the soil core from the sampling tube in the same direction
of travel in which the sample entered the tube and with minimum disturbance of the sample. If the soil core is not extruded
vertically, care should be taken to avoid bending stresses on the core due to gravity. Conditions at the time of sample removal may
dictate the direction of removal, but the principal concern is to keep the degree of disturbance minimal.
6.10 Specimen-Size Measurement Devices—Devices used to measure the height and diameter of the specimen to three or more
significant digits (readability) with an accuracy not to exceed 0.25 % of its full range. The devices shall be constructed such that
during use the specimen is not disturbed or deformed.
NOTE 8—Circumferential measuring tapes are recommended over calipers for measuring the diameter.
6.11 Timer—A timing device indicating the elapsed testing time to the nearest 1 s shall be used for establishing the rate of strain
application prescribed in 7.58.5 and recording the time during specimen compression as required in 7.68.6.
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6.12 Balances—A balance or scale conforming to the requirements of Specification D4753 readable (with no estimation) to 0.1 %
of the test mass, or better.
6.13 Miscellaneous Apparatus—Specimen trimming and carving tools including a wire saw, steel straightedge, miter box and
vertical trimming lathe, apparatus for preparing remolded specimens, membrane and O-ring expander, water content containers,
and data sheets shall be provided as required.
7. Test Specimens
7.1 Specimen Size—Specimens shall be cylindrical and have a minimum diameter of 33 mm (1.3 in.). The average
height-to-average diameter ratio shall be between 2 and 2.5. The largest particle size shall be smaller than one sixth the specimen
diameter. If, after completion of a test, it is found based on visual observation that oversize particles are present, indicate this
information in the report of test data (see 9.2.1410.2.14).
NOTE 9—If oversize particles are found in the specimen after testing, a particle-size analysis may be performed in accordance with Test Method D422
or D6913D6913/D6913M to confirm the visual observation and the results provided with the test report (see 9.2.410.2.4).
7.2 Intact Specimens—Prepare intact specimens from large intact samples or from samples secured in accordance with Practice
D1587D1587/D1587M or other acceptable intact tube sampling procedures. Samples shall be preserved and transported in
accordance with the practices for Group C samples in Practices D4220/D4220M. Specimens obtained by tube sampling may be
tested without trimming except for cutting the end surfaces plane and perpendicula
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