ASTM D2166-00

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation: D 2166 – 00
Standard Test Method for
Unconfined Compressive Strength of Cohesive Soil
This standard is issued under the fixed designation D 2166; 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* 1.7 This standard does not purport to address all of the
safety problems, if any, associated with its use. It is the
1.1 This test method covers the determination of the uncon-
responsibility of the user of this standard to establish appro-
fined compressive strength of cohesive soil in the undisturbed,
priate safety and health practices and determine the applica-
remolded, or compacted condition, using strain-controlled
bility of regulatory limitations prior to use.
application of the axial load.
1.2 This test method provides an approximate value of the
2. Referenced Documents
strength of cohesive soils in terms of total stresses.
2.1 ASTM Standards:
1.3 Thistestmethodisapplicableonlytocohesivematerials
D 422 Test Method for Particle-Size Analysis of Soils
which will not expel or bleed water (water expelled from the
D 653 Terminology Relating to Soil, Rock, and Contained
soil due to deformation or compaction) during the loading
Fluids
portion of the test and which will retain intrinsic strength after
D 854 Test Method for Specific Gravity of Soil Solids by
removal of confining pressures, such as clays or cemented
Water Pycnometer
soils. Dry and crumbly soils, fissured or varved materials, silts,
D 1587 Practice for Thin-Walled Tube Sampling of Soils
peats, and sands cannot be tested with this method to obtain
for Geotechnical Purposes
valid unconfined compression strength values.
D 2216 TestMethodforLaboratoryDeterminationofWater
NOTE 1—The determination of the unconsolidated, undrained strength
(Moisture) Content of Soil and Rock by Mass
of cohesive soils with lateral confinement is covered by Test Method
D 2487 Practice for Classification of Soils for Engineering
D 2850.
Purposes (Unified Soil Classification System)
1.4 This test method is not a substitute for Test Method
D 2488 Practice for Description and Identification of Soils
D 2850.
(Visual-Manual Procedure)
1.5 All observed and calculated values shall conform to the
D 2850 Test Method for Unconsolidated, Undrained Com-
guidelines for significant digits and rounding established in
pressive Strength of Cohesive Soils in Triaxial Compres-
Practice D 6026.
sion
1.5.1 Theproceduresusedtospecifyhowdataarecollected/
D 3740 Practice for Minimum Requirements for Agencies
recorded and calculated in this test method are regarded as the
Engaged in the Testing and/or Inspection of Soil and Rock
industry standard. In addition, they are representative of the
as Used in Engineering Design Construction
significant digits that should generally be retained. The proce-
D 4220 Practices for Preserving and Transporting Soil
dures used do not consider material variation, purpose for
Samples
obtaining the data, special purpose studies, or any consider-
D 4318 Test Method for Liquid Limit, Plastic Limit, and
ations for the user’s objectives; and it is common practice to
Plasticity Index of Soils
increase or reduce significant digits of reported data to com-
D 6026 Practice for Using Significant Digits in Geotechni-
mensurate with these considerations. It is beyond the scope of
cal Data
this test method to consider significant digits used in analysis
E 177 Practice for Use of the Terms Precision and Bias in
methods for engineering design.
ASTM Test Methods
1.6 The values stated in SI units are to be regarded as the
E 691 Practice for Conducting an Interlaboratory Study to
standard. The values stated in inch-pound units are approxi-
Determine the Precision of a Test Method
mate.
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.05 on Structural
Properties of Soils. Annual Book of ASTM Standards, Vol 04.08.
Current edition approved June 10, 2000. Published September 2000. Originally Annual Book of ASTM Standards, Vol 04.09.
published as D 2166 – 63T. Last previous edition D 2166 – 98a. Annual Book of ASTM Standards, Vol 14.02.
*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.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D 2166 – 00
3. Terminology the sample entered the tube, at a uniform rate, and with
negligible disturbance of the sample. Conditions at the time of
3.1 Definitions: Refer to Terminology D 653 for standard
sample removal may dictate the direction of removal, but the
definitions of terms.
principal concern is to keep the degree of disturbance negli-
3.2 Definitions of Terms Specific to This Standard:
gible.
3.2.1 unconfined compressive strength (q )—the compres-
u
5.3 Deformation Indicator—The deformation indicator
sive stress at which an unconfined cylindrical specimen of soil
shall be a dial indicator graduated to 0.03 mm (0.001 in.) or
will fail in a simple compression test. In this test method,
better and having a travel range of at least 20 % of the length
unconfinedcompressivestrengthistakenasthemaximumload
of the test specimen, or some other measuring device, such as
attained per unit area or the load per unit area at 15 % axial
an electronic deformation measuring device, meeting these
strain, whichever is secured first during the performance of a
requirements.
test.
5.4 Dial Comparator, or other suitable device, for measur-
3.2.2 shear strength (s )—for unconfined compressive
u
ing the physical dimensions of the specimen to within 0.1 % of
strength test specimens, the shear strength is calculated to be
1 the measured dimension.
⁄2 of the compressive stress at failure, as defined in 3.2.1.
NOTE 4—Vernier calipers are not recommended for soft specimens,
4. Significance and Use
which will deform as the calipers are set on the specimen.
4.1 The primary purpose of the unconfined compression test
5.5 Timer—A timing device indicating the elapsed testing
is to quickly obtain the approximate compressive strength of
timetothenearestsecondshallbeusedforestablishingtherate
soils that possess sufficient cohesion to permit testing in the
of strain application prescribed in 7.1.
unconfined state.
5.6 Balance—The balance used to weigh specimens shall
4.2 Samples of soils having slickensided or fissured struc-
determine the mass of the specimen to within 0.1 % of its total
ture, samples of some types of loess, very soft clays, dry and
mass.
crumbly soils and varved materials, or samples containing
5.7 Equipment, as specified in Test Method D 2216.
significant portions of silt or sand, or both (all of which usually
5.8 Miscellaneous Apparatus, including specimen trimming
exhibit cohesive properties), frequently display higher shear
and carving tools, remolding apparatus, remove the water
strengths when tested in accordance with Test Method D 2850.
content cans, and data sheets, as required.
Also, unsaturated soils will usually exhibit different shear
strengths when tested in accordance with Test Method D 2850.
6. Preparation of Test Specimens
4.3 If both an undisturbed and a remolded test are per-
6.1 Specimen Size—Specimens shall have a minimum di-
formed on the same sample, the sensitivity of the material can
ameter of 30 mm (1.3 in.) and the largest particle contained
be determined. This method of determining sensitivity is
within the test specimen shall be smaller than one tenth of the
suitable only for soils that can retain a stable specimen shape
specimen diameter. For specimens having a diameter of 72 mm
in the remolded state.
(2.8 in.) or larger, the largest particle size shall be smaller than
one sixth of the specimen diameter. If, after completion of a
NOTE 2—For soils that will not retain a stable shape, a vane shear test
or Test Method D 2850 can be used to determine sensitivity. test on an undisturbed specimen, it is found, based on visual
observation, that larger particles than permitted are present,
NOTE 3—The quality of the result produced by this standard is
indicate this information in the remarks section of the report of
dependent on the competence of the personnel performing it, and the
test data (Note 5). The height-to-diameter ratio shall be
suitability of the equipment and facilities used. Agencies that meet the
criteria of Practice D 3740 are generally considered capable of competent between 2 and 2.5. Determine the average height and diameter
and objective testing/sampling/inspection. Users of this standard are
of the test specimen using the apparatus specified in 5.4. Take
cautioned that compliance with Practice D 3740 does not in itself ensure
a minimum of three height measurements (120° apart), and at
reliable results. Reliable results depend on many factors; Practice D 3740
least three diameter measurements at the quarter points of the
provides a means of evaluating some of those factors.
height.
5. Apparatus
NOTE 5—If large soil particles are found in the specimen after testing,
5.1 Compression Device—The compression device may be a particle-size analysis performed in accordance with Method D 422 may
be performed to confirm the visual observation and the results provided
a platform weighing scale equipped with a screw-jack-
with the test report.
activated load yoke, a hydraulic loading device, or any other
compression device with sufficient capacity and control to 6.2 Undisturbed Specimens—Prepare undisturbed speci-
provide the rate of loading prescribed in 7.1. For soil with an mens from large undisturbed samples or from samples secured
unconfined compressive strength of less than 100 kPa (1.0 in accordance with Practice D 1587 and preserved and trans-
ton/ft ) the compression device shall be capable of measuring ported in accordance with the practices for Group C samples in
the compressive stress to within 1 kPa (0.01 ton/ft ). For soil Practices D 4220. Tube specimens may be tested without
with an unconfined compressive strength of 100 kPa (1.0 trimming except for the squaring of ends, if conditions of the
ton/ft ) or greater, the compression device shall be capable of sample justify this procedure. Handle specimens carefully to
measuring the compressive stress to the nearest 5 kPa (0.05 prevent disturbance, changes in cross section, or loss of water
ton/ft ). content. If compression or any type of noticeable disturbance
5.2 Sample Extruder, capable of extruding the soil core would be caused by the extrusion device, split the sample tube
from the sampling tube in the same direction of travel in which lengthwise or cut it off in small sections to facilitate removal of
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D 2166 – 00
the specimen without disturbance. Prepare carved specimens the time to failure does not exceed about 15 min (Note 7).
without disturbance, and whenever possible, in a humidity- Continueloadinguntiltheloadvaluesdecreasewithincreasing
controlled room. Make every effort to prevent any change in strain,oruntil15 %strainisreached.Therateofstrainusedfor
water content of the soil. Specimens shall be of uniform testing sealed specimens may be decreased if deemed desirable
circular cross section with ends perpendicular to the longitu- for better test results. Indicate the rate of strain in the report of
dinal axis of the specimen. When carving or trimming, remove the test data, as required in 9.1.7. Determine the water content
any small pebbles or shells encountered. Carefully fill voids on of the test specimen using the entire specimen, unless repre-
the surface of the specimen with remolded soil obtained from sentativetrimmingsareobtainedforthispurpose,asinthecase
the trimmings. When pebbles or crumbling result in excessive of undisturbed specimens. Indicate on the test report whether
irregularity at the ends, cap the specimen with a minimum the water content sample was obtained before or after the shear
thickness of plaster of paris, hydrostone, or similar material. test, as required in 9.1.2.
When sample condition permits, a vertical lathe that will
NOTE 7—Softer materials that will exhibit larger deformation at failure
accommodatethetotalsamplemaybeusedasanaidincarving
should be tested at a higher rate of strain. Conversely, stiff or brittle
the specimen to the required diameter.Where prevention of the
materials that will exhibit small deformations at failure should be tested at
development of appreciable capillary forces is deemed impor- a lower rate of strain.
tant, seal the specimen with a rubber membrane, thin plastic
7.2 Make a sketch, or take a photo, of the test specimen at
coatings, or with a coating of grease or sprayed plastic
failure showing the slope angle of the failure surface if the
immediately after preparation and during the entire testing
angle is measurable.
cycle. Determine the mass and dimensions of the test speci-
7.3 Acopy of a example data sheet is included inAppendix
men. If the specimen is to be capped, its mass and dimensions
X1.Any data sheet can be used, provided the form contains all
should be determined before capping. If the entire test speci-
the required data.
menisnottobeusedfordeterminationofwatercontent,secure
a representative sample of trimmings for this purpose, placing
8. Calculation
them immediately in a covered container. The water content
8.1 Calculate the axial strain, e , to the nearest 0.1 %, for a
determination shall be performed in accordance with Test
given applied load, as follows:
Method D 2216.
e 5DL/L
1 0
6.3 Remolded Specimens—Specimens may be prepared ei-
ther from a failed undisturbed specimen or from a disturbed
where:
sample, providing it is representative of the failed undisturbed
DL = length change of specimen as read from deformation
specimen. In the case of failed undisturbed specimens, wrap
indicator, mm (in.), and
the material in a thin rubber membrane and work the material L = initial length of test specimen, mm (in).
thoroughly with the fingers to assure complete remolding. 8.2 Calculatetheaveragecross-sectionalarea, A,foragiven
Avoid entrapping air in the specimen. Exercise care to obtain a
applied load, as follows:
uniform density, to remold to the same void ratio as the
A
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