ASTM D2850-95(1999)
(Test Method)Standard Test Method for Unconsolidated-Undrained Triaxial CompressionTest on Cohesive Soils
Standard Test Method for Unconsolidated-Undrained Triaxial CompressionTest on Cohesive Soils
SCOPE
1.1 This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of either undisturbed 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 test. The specimen is sheared in compression without drainage 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.
Note 2--The determination of the consolidated, undrained strength of cohesive soils with pore pressure measurement is covered by Test Method D4767.
1.3 The values stated in SI units are to be regarded as the standard. The values stated in inch-pound units and given in parentheses are approximate.
1.4 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 health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: D 2850 – 95 (Reapproved 1999)
Standard Test Method for
Unconsolidated-Undrained Triaxial Compression Test on
Cohesive Soils
This standard is issued under the fixed designation D 2850; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope * D 2487 Classification of Soils for Engineering Purposes
D 2488 Practice for Description and Identification of Soils
1.1 This test method covers determination of the strength
(Visual-Manual Procedure)
and stress-strain relationships of a cylindrical specimen of
D 3740 Practice for Evaluation of Agencies Engaged in the
either undisturbed or remolded cohesive soil. Specimens are
Testing and/or Inspection of Soil and Rock as Used in
subjected to a confining fluid pressure in a triaxial chamber. No
Engineering Design and Construction
drainage of the specimen is permitted during the test. The
D 4220 Practices for Preserving and Transporting Soil
specimen is sheared in compression without drainage at a
Samples
constant rate of axial deformation (strain controlled).
D 4318 Test Method for Liquid Limit, Plastic Limit, and
1.2 This test method provides data for determining und-
Plasticity Index of Soils
rained strength properties and stress-strain relations for soils.
D 4753 Specification for Evaluating, Selecting, and Speci-
This test method provides for the measurement of the total
fying Balances and Scales for Use in Testing Soil and
stresses applied to the specimen, that is, the stresses are not
Rock, and Related Construction Materials
corrected for pore-water pressure.
D 4767 Test Method for Consolidated-Undrained Triaxial
NOTE 1—The determination of the unconfined compressive strength of 2
Compression Test on Cohesive Soils
cohesive soils is covered by Test Method D 2166.
NOTE 2—The determination of the consolidated, undrained strength of
3. Terminology
cohesive soils with pore pressure measurement is covered by Test Method
3.1 Definitions—The definitions of terms used in this test
D 4767.
method shall be in accordance with Terminology D 653.
1.3 The values stated in SI units are to be regarded as the
3.2 Definitions of Terms Specific to This Standard:
standard. The values stated in inch-pound units and given in
3.2.1 failure—the stress condition at failure for a test
parentheses are approximate.
specimen. Failure is often taken to correspond to the maximum
1.4 This standard does not purport to address all of the
principal stress difference (deviator stress) attained or the
safety concerns, if any, associated with its use. It is the
principal stress difference (deviator stress) at 15 % axial strain,
responsibility of the user of this standard to establish appro-
whichever is obtained first during the performance of a test.
priate safety and health practices and determine the applica-
3.2.2 unconsolidated-undrained compressive strength—the
bility of regulatory limitations prior to use.
value of the principal stress difference (deviator stress) at
failure.
2. Referenced Documents
2.1 ASTM Standards:
4. Significance and Use
D 422 Method for Particle-Size Analysis of Soils
4.1 In this test method, the compressive strength of a soil is
D 653 Terminology Relating to Soil, Rock, and Contained
determined in terms of the total stress, therefore, the resulting
Fluids
strength depends on the pressure developed in the pore fluid
D 854 Test Method for Specific Gravity of Soils
during loading. In this test method, fluid flow is not permitted
D 1587 Method for Thin-Walled Tube Sampling of Soils
from or into the soil specimen as the load is applied, therefore
D 2166 Test Methods for Unconfined Compressive Strength
the resulting pore pressure, and hence strength, differs from
of Cohesive Soil
that developed in the case where drainage can occur.
D 2216 Test Method for Laboratory Determination of Water
4.2 If the test specimens are 100 % saturated, consolidation
(Moisture) Content of Soil and Rock
cannot occur when the confining pressure is applied nor during
the shear portion of the test since drainage is not permitted.
This test method is under the jurisdiction of ASTM Committee D18 on Soil and
Therefore, if several specimens of the same material are tested,
Rock and is the direct responsibility of Subcommittee D18.05 on Structural
and if they are all at approximately the same water content and
Properties of Soils.
void ratio when they are tested, they will have approximately
Current edition approved May 15, 1995. Published July 1995. Originally
e1
published as D 2850 – 70. Last previous edition D 2850 – 87 .
the same undrained shear strength. The Mohr failure envelope
Annual Book of ASTM Standards, Vol 04.08.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2850
will usually be a horizontal straight line over the entire range of the chamber and its seal must be designed so the variation
of confining stresses applied to the specimens if the specimens in axial load due to friction does not exceed 0.1 % of the axial
are fully saturated. load at failure as measured in 8.4.1.3 and so there is negligible
4.3 If the test specimens are partially saturated or com- lateral bending of the piston during loading.
pacted specimens, where the degree of saturation is less than
NOTE 5—The use of two linear ball bushings to guide the piston is
100 %, consolidation may occur when the confining pressure is
recommended to minimize friction and maintain alignment.
applied and during shear, even though drainage is not permit-
NOTE 6—A minimum piston diameter of one sixth the specimen
ted. Therefore, if several partially saturated specimens of the
diameter has been used successfully in many laboratories to minimize
same material are tested at different confining stresses, they
lateral bending.
will not have the same undrained shear strength. Thus, the
5.5 Pressure Control Device—The chamber pressure con-
Mohr failure envelope for unconsolidated undrained triaxial
trol device shall be capable of applying and controlling the
tests on partially saturated soils is usually curved.
chamber pressure to within 62 kPa (0.25 psi) for pressures less
4.4 The unconsolidated undrained triaxial strength is appli-
than 200 kPa (28 psi) and to within 61 % for pressures greater
cable to situations where the loads are assumed to take place so
than 200 kPa (28 psi). This device may consist of a reservoir
rapidly that there is insufficient time for the induced pore-water
connected to the triaxial chamber and partially filled with the
pressure to dissipate and for consolidation to occur during the
chamber fluid (usually water), with the upper part of the
loading period (that is, drainage does not occur).
reservoir connected to a compressed gas supply; the gas
4.5 Compressive strengths determined using this procedure
pressure being controlled by a pressure regulator and measured
may not apply in cases where the loading conditions in the field
by a pressure gage, electronic pressure transducer, or any other
differ significantly from those used in this test method.
device capable of measuring to the prescribed tolerance.
NOTE 3—Notwithstanding the statements on precision and bias con-
However, a hydraulic system pressurized by deadweight acting
tained in this test method: The precision of this test method is dependent
on a piston or any other pressure-maintaining and measurement
on the competence of the personnel performing it and the suitability of the
device capable of applying and controlling the chamber pres-
equipment and facilities used. Agencies which meet the criteria of Practice
sure to the tolerance prescribed in this section may be used.
D 3740 are generally considered capable of competent testing. Users of
5.6 Specimen Cap and Base—An impermeable rigid cap
this test method are cautioned that compliance with Practice D 3740 does
not ensure reliable testing. Reliable testing depends on several factors; and base shall be used to prevent drainage of the specimen. The
Practice D 3740 provides a means of evaluating some of those factors.
specimen cap and base shall be constructed of a noncorrosive
impermeable material, and each shall have a circular plane
5. Apparatus
surface of contact with the specimen and a circular cross
5.1 Axial Loading Device—The axial loading device may
section. The weight of the specimen cap shall produce an axial
be screw jack driven by an electric motor through a geared
stress on the specimen of less than 1 kN/m . The diameter of
transmission, a hydraulic loading device, or any other com-
the cap and base shall be equal to the initial diameter of the
pression device with sufficient capacity and control to provide
specimen. The specimen base shall be connected to the triaxial
the rate of loading prescribed in 7.5. The rate of advance of the
compression chamber to prevent lateral motion or tilting and
loading device should not deviate by more than 65 % from the
the specimen cap shall be designed such that eccentricity of the
selected value. Vibrations due to the operation of the loading
piston to cap contact relative to the vertical axis of the
device shall be sufficiently small to not cause dimensional
specimen does not exceed 1.3 mm (0.05 in.). The end of the
changes in the specimen.
piston and specimen cap contact area shall be designed so that
tilting of the specimen cap during the test is minimal. The
NOTE 4—A loading device may be said to provide sufficiently small
cylindrical surface of the specimen base and cap that contacts
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 the membrane to form a seal shall be smooth and free of
is performed.
scratches.
5.7 Deformation Indicator—The vertical deformation of the
5.2 Axial Load-Measuring Device—The axial load-
specimen shall be measured with an accuracy of at least 0.03 %
measuring device shall be a load ring, electronic load cell,
of the specimen height. The deformation indicator shall have a
hydraulic load cell, or any other load-measuring device capable
range of at least 20 % of the height of the specimen, and may
of measuring the axial load to an accuracy of 1 % of the axial
be a dial indicator, linear variable differential transformer
load at failure and may be a part of the axial loading device.
(LVDT), extensiometer or other measuring device meeting the
5.3 Triaxial Compression Chamber—The triaxial chamber
requirements for accuracy and range.
shall consist of a top plate and a baseplate separated by a
cylinder. The cylinder may be constructed of any material 5.8 Rubber Membrane—The rubber membrane used to
capable of withstanding the applied pressure. It is desirable to encase the specimen shall provide reliable protection against
use a transparent material or have a cylinder provided with leakage. Membranes shall be carefully inspected prior to use,
viewing ports so the behavior of the specimen may be and if any flaws or pinholes are evident, the membrane shall be
observed. The top plate shall have a vent valve such that air can discarded. To offer minimum restraint to the specimen, the
be forced out of the chamber as it is filled. The base plate shall unstretched membrane diameter shall be between 90 and 95 %
have an inlet through which the pressure liquid is supplied to of that of the specimen. The membrane thickness shall not
the chamber. exceed 1 % of the diameter of the specimen. The membrane
5.4 Axial Load Piston—The piston passing through the top shall be sealed to the specimen base and cap with rubber
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
D 2850
O-rings for which the unstressed inside diameter is between 75 suitable sections to facilitate removal of the specimen with
and 85 % of the diameter of the cap and base or by any method minimum disturbance. Prepare trimmed specimens, in an
that will produce a positive seal. An equation for correcting the environment such as a controlled high-humidity room where
principal stress difference (deviator stress) for the effect of the soil water content change is minimized. Where removal of
stiffness of the membrane is given in 8.6. pebbles or crumbling resulting from trimming causes voids on
5.9 Sample Extruder—The sample extruder shall be capable the surface of the specimen, carefully fill the voids with
of extruding the soil core from the sampling tube in the same remolded soil obtained from the trimmings. When the sample
direction of travel in which the sample entered the tube and condition permits, a vertical trimming lathe may be used to
with minimum disturbance of the sample. If the soil core is not reduce the specimen to the required diameter. After obtaining
extruded vertically, care should be taken to avoid bending the required diameter, place the specimen in a miter box and
stresses on the core due to gravity. Conditions at the time of cut the specimen to the final height with a wire saw or other
sample removal may dictate the direction of removal, but the suitable device. Trim the surfaces with the steel straightedge.
principal concern is to keep the degree of disturbance minimal. Perform one or more water content determinations on material
5.10 Specimen Size Measurement Devices— Devices used trimmed from the specimen in accordance with Test Method
to measure the height and diameter of the specimen shall be D 2216. Determine the mass and dimensions of the specimen
capable of measuring the desired dimension to within 0.1 % of using the devices described in 5.11 and 5.9. A minimum of
its actual length and shall be constructed such that their use will three height measurements (120° apart) and at least three
not disturb the specimen. diameter measurements at the quarter points of the height shall
be made to determine the average height and diameter of the
NOTE 7—Circumferential measuring tapes are recommended over cali-
specimen.
pers for measuring the diameter.
6.3 Compacted Specimens—Soil required for compacted
5.11 Timer—A timing device indicating the elapsed testing
specimens shall be thoroughly mixed with sufficient water to
time to the neares
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