ASTM D2850-03a(2007)
(Test Method)Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils
Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test 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 D 2166. Note 2
The determination of the consolidated, undrained strength of cohesive soils with pore pressure measurement is covered by Test Method D 4767.
1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D 6026.
1.3.1 The method used to specify how data are collected, calculated, or recorded in this standard is not directly related to the accuracy to which the data can be applied in design or other uses, or both. How one applies the results obtained using this standard is beyond its scope.
1.4 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.
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.
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Designation: D2850 − 03a(Reapproved 2007)
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.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers determination of the strength
and stress-strain relationships of a cylindrical specimen of D422Test Method for Particle-Size Analysis of Soils
D653Terminology Relating to Soil, Rock, and Contained
either undisturbed or remolded cohesive soil. Specimens are
subjectedtoaconfiningfluidpressureinatriaxialchamber.No Fluids
D854Test Methods for Specific Gravity of Soil Solids by
drainage of the specimen is permitted during the test. The
specimen is sheared in compression without drainage at a Water Pycnometer
D1587Practice for Thin-Walled Tube Sampling of Soils for
constant rate of axial deformation (strain controlled).
Geotechnical Purposes
1.2 This test method provides data for determining
D2166Test Method for Unconfined Compressive Strength
undrained strength properties and stress-strain relations for
of Cohesive Soil
soils. This test method provides for the measurement of the
D2216TestMethodsforLaboratoryDeterminationofWater
total stresses applied to the specimen, that is, the stresses are
(Moisture) Content of Soil and Rock by Mass
not corrected for pore-water pressure.
D2487Practice for Classification of Soils for Engineering
NOTE 1—The determination of the unconfined compressive strength of
Purposes (Unified Soil Classification System)
cohesive soils is covered by Test Method D2166.
D2488Practice for Description and Identification of Soils
NOTE 2—The determination of the consolidated, undrained strength of
(Visual-Manual Procedure)
cohesivesoilswithporepressuremeasurementiscoveredbyTestMethod
D3740Practice for Minimum Requirements for Agencies
D4767.
Engaged in Testing and/or Inspection of Soil and Rock as
1.3 All observed and calculated values shall conform to the
Used in Engineering Design and Construction
guidelines for significant digits and rounding established in
D4220 Practices for Preserving and Transporting Soil
Practice D6026.
Samples
1.3.1 The method used to specify how data are collected,
D4318Test Methods for Liquid Limit, Plastic Limit, and
calculated,orrecordedinthisstandardisnotdirectlyrelatedto
Plasticity Index of Soils
theaccuracytowhichthedatacanbeappliedindesignorother
D4753Guide for Evaluating, Selecting, and Specifying Bal-
uses, or both. How one applies the results obtained using this
ances and Standard Masses for Use in Soil, Rock, and
standard is beyond its scope.
Construction Materials Testing
1.4 The values stated in SI units are to be regarded as the D4767Test Method for Consolidated Undrained Triaxial
standard. The values stated in inch-pound units and given in Compression Test for Cohesive Soils
parentheses are approximate. D6026Practice for Using Significant Digits in Geotechnical
Data
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions—The definitions of terms used in this test
priate safety and health practices and determine the applica-
method shall be in accordance with Terminology D653.
bility of regulatory limitations prior to use.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 failure—the stress condition at failure for a test speci-
men. Failure is often taken to correspond to the maximum
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
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 Sept. 15, 2007. Published October 2007. Originally contact Customer Service at service@astm.org. For Annual Book of ASTM Stan-
approved in 1970. Last previous edition approved in 2003 as D2850–03a. DOI: dardsvolume information, refer to the standard’s Document Summary page on the
10.1520/D2850-03AR07. ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2850 − 03a (2007)
principal stress difference (deviator stress) attained or the selected value. Vibrations due to the operation of the loading
principalstressdifference(deviatorstress)at15%axialstrain, device shall be sufficiently small to not cause dimensional
whichever is obtained first during the performance of a test. changes in the specimen.
3.2.2 unconsolidated-undrained compressive strength—the
NOTE 4—A loading device may be said to provide sufficiently small
value of the principal stress difference (deviator stress) at
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
failure.
is performed.
4. Significance and Use
5.2 Axial Load-Measuring Device—The axial load-
4.1 In this test method, the compressive strength of a soil is measuring device shall be a load ring, electronic load cell,
determined in terms of the total stress, therefore, the resulting hydraulicloadcell,oranyotherload-measuringdevicecapable
strength depends on the pressure developed in the pore fluid
of measuring the axial load to an accuracy of 1% of the axial
during loading. In this test method, fluid flow is not permitted load at failure and may be a part of the axial loading device.
from or into the soil specimen as the load is applied, therefore
5.3 Triaxial Compression Chamber—The triaxial chamber
the resulting pore pressure, and hence strength, differs from
shall consist of a top plate and a baseplate separated by a
that developed in the case where drainage can occur.
cylinder. The cylinder shall be constructed of any material
4.2 If the test specimens are 100% saturated, consolidation
capable of withstanding the applied pressure. It is desirable to
cannotoccurwhentheconfiningpressureisappliednorduring
use a transparent material or have a cylinder provided with
the shear portion of the test since drainage is not permitted.
viewing ports so the behavior of the specimen may be
Therefore,ifseveralspecimensofthesamematerialaretested,
observed.Thetopplateshallhaveaventvalvesuchthataircan
andiftheyareallatapproximatelythesamewatercontentand
be forced out of the chamber as it is filled.The base plate shall
void ratio when they are tested, they will have approximately
have an inlet through which the pressure liquid is supplied to
the same undrained shear strength. The Mohr failure envelope
the chamber.
will usually be a horizontal straight line over the entire range
5.4 Axial Load Piston—The piston passing through the top
of confining stresses applied to the specimens if the specimens
of the chamber and its seal must be designed so the variation
are fully saturated.
in axial load due to friction does not exceed 0.1% of the axial
4.3 If the test specimens are partially saturated or com-
load at failure as measured in 8.4.1.3 and so there is negligible
pacted specimens, where the degree of saturation is less than
lateral bending of the piston during loading.
100%,consolidationmayoccurwhentheconfiningpressureis
NOTE 5—The use of two linear ball bushings to guide the piston is
applied and during shear, even though drainage is not permit-
recommended to minimize friction and maintain alignment.
ted. Therefore, if several partially saturated specimens of the
NOTE 6—A minimum piston diameter of one sixth the specimen
same material are tested at different confining stresses, they
diameter has been used successfully in many laboratories to minimize
will not have the same undrained shear strength. Thus, the
lateral bending.
Mohr failure envelope for unconsolidated undrained triaxial
5.5 Pressure Control Device—Thechamberpressurecontrol
tests on partially saturated soils is usually curved.
device shall be capable of applying and controlling the
4.4 The unconsolidated undrained triaxial strength is appli-
chamberpressuretowithin 62kPa(0.25psi)forpressuresless
cabletosituationswheretheloadsareassumedtotakeplaceso
than200kPa(28psi)andtowithin 61%forpressuresgreater
rapidlythatthereisinsufficienttimefortheinducedpore-water
than 200 kPa (28 psi). This device may consist of a reservoir
pressure to dissipate and for consolidation to occur during the
connected to the triaxial chamber and partially filled with the
loading period (that is, drainage does not occur).
chamber fluid (usually water), with the upper part of the
reservoir connected to a compressed gas supply; the gas
4.5 Compressive strengths determined using this procedure
pressurebeingcontrolledbyapressureregulatorandmeasured
maynotapplyincaseswheretheloadingconditionsinthefield
byapressuregage,electronicpressuretransducer,oranyother
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,ahydraulicsystempressurizedbydeadweightacting
tained in this test method: The precision of this test method is dependent
onapistonoranyotherpressure-maintainingandmeasurement
onthecompetenceofthepersonnelperformingitandthesuitabilityofthe
device capable of applying and controlling the chamber pres-
equipmentandfacilitiesused.AgencieswhichmeetthecriteriaofPractice
sure to the tolerance prescribed in this section may be used.
D3740 are generally considered capable of competent testing. Users of
this test method are cautioned that compliance with Practice D3740 does
5.6 Specimen Cap and Base—An impermeable rigid cap
not ensure reliable testing. Reliable testing depends on several factors;
andbaseshallbeusedtopreventdrainageofthespecimen.The
Practice D3740 provides a means of evaluating some of those factors.
specimen cap and base shall be constructed of a noncorrosive
5. Apparatus
impermeable material, and each shall have a circular plane
5.1 Axial Loading Device—The axial loading device shall surface of contact with the specimen and a circular cross
be screw jack driven by an electric motor through a geared section.The weight of the specimen cap shall produce an axial
transmission, a hydraulic loading device, or any other com- stress on the specimen of less than 1 kN/m . The diameter of
pression device with sufficient capacity and control to provide the cap and base shall be equal to the initial diameter of the
therateofloadingprescribedin7.5.Therateofadvanceofthe specimen.Thespecimenbaseshallbeconnectedtothetriaxial
loading device shall not deviate by more than 65% from the compression chamber to prevent lateral motion or tilting and
D2850 − 03a (2007)
thespecimencapshallbedesignedsuchthateccentricityofthe 6. Test Specimens
piston to cap contact relative to the vertical axis of the
6.1 Specimen Size—Specimensshallbecylindricalandhave
specimen does not exceed 1.3 mm (0.05 in.). The end of the
a minimum diameter of 3.3 cm (1.3 in.). The height-to-
piston and specimen cap contact area shall be designed so that
diameter ratio shall be between 2 and 2.5. The largest particle
tilting of the specimen cap during the test is minimal. The
size shall be smaller than one sixth the specimen diameter. If,
cylindrical surface of the specimen base and cap that contacts
after completion of a test, it is found based on visual observa-
the membrane to form a seal shall be smooth and free of
tion that oversize particles are present, indicate this informa-
scratches.
tion in the report of test data (see 9.2.12).
5.7 Deformation Indicator—Theverticaldeformationofthe
NOTE 8—If oversize particles are found in the specimen after testing, a
specimenshallbemeasuredwithanaccuracyofatleast0.03%
particle-size analysis may be performed in accordance with Test Method
D422 to confirm the visual observation and the results provided with the
of the specimen height.The deformation indicator shall have a
test report (see 9.2.4).
range of at least 20% of the height of the specimen, and may
be a dial indicator, linear variable differential transformer 6.2 Undisturbed Specimens—Prepare undisturbed speci-
(LVDT), extensiometer or other measuring device meeting the mens from large undisturbed samples or from samples secured
requirements for accuracy and range. in accordance with Practice D1587 or other acceptable undis-
turbed tube sampling procedures. Samples shall be preserved
5.8 Rubber Membrane—The rubber membrane used to en-
and transported in accordance with the practices for Group C
case the specimen shall provide reliable protection against
samples in Practices D4220. Specimens obtained by tube
leakage. Membranes shall be carefully inspected prior to use,
samplingmaybetestedwithouttrimmingexceptforcuttingthe
andifanyflawsorpinholesareevident,themembraneshallbe
endsurfacesplaneandperpendiculartothelongitudinalaxisof
discarded. To offer minimum restraint to the specimen, the
the specimen, provided soil characteristics are such that no
unstretched membrane diameter shall be between 90 and 95%
significant disturbance results from sampling. Handle speci-
of that of the specimen. The membrane thickness shall not
mens carefully to minimize disturbance, changes in cross
exceed 1% of the diameter of the specimen. The membrane
section,orchangeinwatercontent.Ifcompressionoranytype
shall be sealed to the specimen base and cap with rubber
of noticeable disturbance would be caused by the extrusion
O-ringsforwhichtheunstressedinsidediameterisbetween75
device, split the sample tube lengthwise or cut the tube in
and85%ofthediameterofthecapandbaseorbyanymethod
suitable sections to facilitate removal of the specimen with
thatwillproduceapositiveseal.Anequationforcorrectingthe
minimum disturbance. Prepare trimmed specimens, in an
principal stress difference (deviator stress) for the effect of the
environment such as a controlled high-humidity room where
stiffness of the membrane is given in 8.7.
soil water content change is minimized. Where removal of
5.9 Sample Extruder—Thesampleextrudershallbecapable pebbles or crumbling resulting from trimming causes voids on
of extruding the soil core from the sampling tube in the same the surface of the specimen, carefully fill the voids with
direction of travel in which the sample entered the tube and remolded soil obtained from the trimmings. When the sample
withminimumdisturbanceofthesample.Ifthesoilcoreis
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