NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.

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Designation: D4767 − 11

Standard Test Method for

Consolidated Undrained Triaxial Compression Test for
Cohesive Soils1
This standard is issued under the fixed designation D4767; 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* purposes only and are not considered standard. Reporting of

1.1 This test method covers the determination of 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 an intact, reconstituted, or remolded saturated cohesive 1.6.1 The gravitational system of inch-pound units is used
soil. Specimens are isotropically consolidated and sheared in when dealing with inch-pound units. In this system, the pound
compression without drainage at a constant rate of axial (lbf) represents a unit of force (weight), while the unit for mass
deformation (strain controlled). is slugs. The slug unit is not given, unless dynamic (F = ma)
calculations are involved.
1.2 This test method provides for the calculation of total and 1.6.2 It is common practice in the engineering/construction
effective stresses, and axial compression by measurement of profession to concurrently use pounds to represent both a unit
axial load, axial deformation, and pore-water pressure. of mass (lbm) and of force (lbf). This implicitly combines two
1.3 This test method provides data useful in determining separate systems of units; that is, the absolute system and the

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strength and deformation properties of cohesive soils such as
Mohr strength envelopes and Young’s modulus. Generally,
gravitational system. It is scientifically undesirable to combine
the use of two separate sets of inch-pound units within a single
standard. As stated, this standard includes the gravitational
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three specimens are tested at different effective consolidation
stresses to define a strength envelope. system of inch-pound units and does not use/present the slug
1.4 The determination of strength envelopes and the devel- unit for mass. However, the use of balances or scales recording
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opment of relationships to aid in interpreting and evaluating
test results are beyond the scope of this test method and must
pounds of mass (lbm) or recording density in lbm/ft3 shall not
be regarded as nonconformance with this standard.
be performed by a qualified, experienced professional. 1.6.3 The terms density and unit weight are often used
interchangeably. Density is mass per unit volume whereas unit
ASTM
1.5 All observed and calculated values shall conform D4767-11
to the weight is force per unit volume. In this standard density is
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guidelines for significant digits and rounding established in given only in SI units. After the density has been determined,
Practice D6026. the unit weight is calculated in SI or inch-pound units, or both.
1.5.1 The methods used to specify how data are collected,
1.7 This standard does not purport to address all of the
calculated, or recorded in this standard are regarded as the
safety concerns, if any, associated with its use. It is the
industry standard. In addition, they are representative of the
responsibility of the user of this standard to establish appro-
significant digits that generally should be retained. The proce-
priate safety and health practices and determine the applica-
dures used do not consider material variation, purpose for
bility of regulatory limitations prior to use.
obtaining the data, special purpose studies or any consideration
of end use. It is beyond the scope of this test method to
2. Referenced Documents
consider significant digits used in analysis methods for engi-
neering design. 2.1 ASTM Standards:2
D422 Test Method for Particle-Size Analysis of Soils
1.6 Units—The values stated in SI units are to be regarded
D653 Terminology Relating to Soil, Rock, and Contained
as standard. The inch-pound units given in parentheses are
Fluids
mathematical conversions which are provided for information
D854 Test Methods for Specific Gravity of Soil Solids by
Water Pycnometer
1
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
2
Compressibility of Soils. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Jan. 15, 2011. Published February 2011. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1988. Last previou edition approved in 2004 as D4767–04. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D4767-11. the ASTM website.

*A Summary of Changes section appears at the end of this standard

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

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 D4767 − 11
D1587 Practice for Thin-Walled Tube Sampling of Soils for consolidated during testing prior to shear, refer to Test Method D2850 or
Geotechnical Purposes Test Method D2166.
D2166 Test Method for Unconfined Compressive Strength 4.3 Using the pore-water pressure measured during the test,
of Cohesive Soil the shear strength determined from this test method can be
D2216 Test Methods for Laboratory Determination of Water expressed in terms of effective stress. This shear strength may
(Moisture) Content of Soil and Rock by Mass be applied to field conditions where full drainage can occur
D2435 Test Methods for One-Dimensional Consolidation (drained conditions) or where pore pressures induced by
Properties of Soils Using Incremental Loading loading can be estimated, and the field stress conditions are
D2850 Test Method for Unconsolidated-Undrained Triaxial similar to those in the test method.
Compression Test on Cohesive Soils 4.4 The shear strength determined from the test expressed in
D3740 Practice for Minimum Requirements for Agencies terms of total stresses (undrained conditions) or effective
Engaged in Testing and/or Inspection of Soil and Rock as stresses (drained conditions) is commonly used in embankment
Used in Engineering Design and Construction stability analyses, earth pressure calculations, and foundation
D4220 Practices for Preserving and Transporting Soil design.
Samples
D4318 Test Methods for Liquid Limit, Plastic Limit, and NOTE 2—Notwithstanding the statements on precision and bias con-
Plasticity Index of Soils tained in this test method. The precision of this test method is dependent
on the competence of the personnel performing it and the suitability of the
D4753 Guide for Evaluating, Selecting, and Specifying Bal- equipment and facilities used. Agencies which meet the criteria of Practice
ances and Standard Masses for Use in Soil, Rock, and D3740 are generally considered capable of competent testing. Users of
Construction Materials Testing this test method are cautioned that compliance with Practice D3740 does
D6026 Practice for Using Significant Digits in Geotechnical not ensure reliable testing. Reliable testing depends on several factors;
Practice D3740 provides a means of evaluating some of those factors.
Data

3. Terminology 5. Apparatus
3.1 Definitions—For standard definitions of common tech- 5.1 The requirements for equipment needed to perform
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nical terms, refer to Terminology D653.
3.2 Definitions of Terms Specific to This Standard:
satisfactory tests are given in the following sections. See Fig.
1 and Fig. 2

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3.2.1 back pressure—a pressure applied to the specimen
pore-water to cause air in the pore space to compress and to
5.2 Axial Loading Device—The axial loading device shall
be a screw jack driven by an electric motor through a geared

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pass into solution in the pore-water thereby increasing the transmission, a hydraulic loading device, or any other com-
percent saturation of the specimen. pression device with sufficient capacity and control to provide
the rate of axial strain (loading) prescribed in 8.4.2. The rate of
3.2.2 effective consolidation stress—the difference between
advance of the loading device shall not deviate by more than
the cell pressure and the pore-water pressure prior to shearing
the specimen. ASTM D4767-11
61 % from the selected value. Vibration due to the operation
of the loading device shall be sufficiently small to not cause
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3.2.3 failure—a maximum-stress condition or stress at a dimensional changes in the specimen or to produce changes in
defined strain for a test specimen. Failure is often taken to pore-water pressure when the drainage valves are closed.
correspond to the maximum principal stress difference (maxi-
mum deviator stress) attained or the principal stress difference NOTE 3—A loading device may be judged to produce sufficiently small
vibrations if there are no visible ripples in a glass of water placed on the
(deviator stress) at 15 % axial strain, whichever is obtained first loading platform when the device is operating at the speed at which the
during the performance of a test. Depending on soil behavior test is performed.
and field application, other suitable failure criteria may be
5.3 Axial Load-Measuring Device—The axial load-
defined, such as maximum effective stress obliquity, (σ1'/
measuring device shall be an electronic load cell, hydraulic
σ3')max, or the principal stress difference (deviator stress) at a
load cell, or any other load-measuring device capable of the
selected axial strain other than 15 %.
accuracy prescribed in this paragraph and may be a part of the
4. Significance and Use axial loading device. The axial load-measuring device shall be
capable of measuring the axial load to an accuracy of within
4.1 The shear strength of a saturated soil in triaxial com- 1 % of the axial load at failure. If the load-measuring device is
pression depends on the stresses applied, time of consolidation, located inside the triaxial compression chamber, it shall be
strain rate, and the stress history experienced by the soil. insensitive to horizontal forces and to the magnitude of the
4.2 In this test method, the shear characteristics are mea- chamber pressure.
sured under undrained conditions and is applicable to field 5.4 Triaxial Compression Chamber—The triaxial chamber
conditions where soils that have been fully consolidated under shall have a working chamber pressure equal to the sum of the
one set of stresses are subjected to a change in stress without effective consolidation stress and the back pressure. It shall
time for further consolidation to take place (undrained consist of a top plate and a base plate separated by a cylinder.
condition), and the field stress conditions are similar to those in The cylinder may be constructed of any material capable of
the test method. withstanding the applied pressures. It is desirable to use a
NOTE 1—If the strength is required for the case where the soil is not transparent material or have a cylinder provided with viewing

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 D4767 − 11

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FIG. 1 Schematic Diagram of a Typical Consolidated Undrained Triaxial Apparatus

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ASTM D4767-11
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FIG. 2 Filter Strip Cage

ports so the behavior of the specimen may be observed. The top load at failure and so there is negligible lateral bending of the
plate shall have a vent valve such that air can be forced out of piston during loading.
the chamber as it is filled. The baseplate shall have an inlet
NOTE 4—The use of two linear ball bushings to guide the piston is
through which to fill the chamber, and inlets leading to the recommended to minimize friction and maintain alignment.
specimen base and to the cap to allow saturation and drainage NOTE 5—A minimum piston diameter of 1⁄6 the specimen diameter has
of the specimen when required. The chamber shall provide a been used successfully in many laboratories to minimize lateral bending.
connection to the cap. 5.6 Pressure and Vacuum-Control Devices—The chamber
5.5 Axial Load Piston—The piston passing through the top pressure and back pressure control devices shall be capable of
of the chamber and its seal must be designed so the variation applying and controlling pressures to within 62 kPa (0.25
in axial load due to friction does not exceed 0.1 % of the axial lb/in.2) for effective consolidation pressures less than 200 kPa

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 D4767 − 11
(28 lbf/in.2) and to within 61 % for effective consolidation meeting the accuracy requirement. The device must be able to
pressures greater than 200 kPa. The vacuum-control device withstand the maximum back pressure.
shall be capable of applying and controlling partial vacuums to
5.10 Deformation Indicator—The vertical deformation of
within 62 kPa. The devices shall consist of pressure/volume
the specimen is usually determined from the travel of the piston
controllers pneumatic pressure regulators, combination pneu-
acting on the top of the specimen. The piston travel shall be
matic pressure and vacuum regulators, or any other device
measured with an accuracy of at least 0.25 % of the initial
capable of applying and controlling pressures or partial vacu-
specimen height. The deformation indicator shall have a range
ums to the required tolerances. These tests can require a test
of at least 15 % of the initial height of the specimen and may
duration of several day. Therefore, an air/water interface is not
be a dial indicator or other measuring device meeting the
recommended for either the chamber pressure or back pressure
requirements for accuracy and range.
systems, unless isolated from the specimen and chamber (e.g.
by long tubing). 5.11 Specimen Cap and Base—The specimen cap and base
5.7 Pressure- and Vacuum-Measurement Devices—The shall be designed to provide drainage from both ends of the
chamber pressure-, back pressure-, and vacuum-measuring specimen. They shall be constructed of a rigid, noncorrosive,
devices shall be capable of measuring pressures or partial impermeable material, and each shall, except for the drainage
vacuums to the tolerances given in 5.6. They may consist of provision, have a circular plane surface of contact with the
electronic pressure transducers, or any other device capable of porous disks and a circular cross section. It is desirable for the
measuring pressures, or partial vacuums to the stated toler- mass of the specimen cap and top porous disk to be as minimal
ances. If separate devices are used to measure the chamber as possible. However, the mass may be as much as 10 % of the
pressure and back pressure, the devices must be calibrated axial load at failure. If the mass is greater than 0.5 % of the
simultaneously and against the same pressure source. Since the applied axial load at failure and greater than 50 g, the axial load
chamber and back pressure are the pressures taken at the must be corrected for the mass of the specimen cap and top
mid-height of the specimen, it may be necessary to adjust the porous disk. The diameter of the cap and base shall be equal to
calibration of the devices to reflect the hydraulic head of fluids the initial diameter of the specimen. The specimen base shall
in the chamber and back pressure control systems. be connected to the triaxial compression chamber to prevent
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5.8 Pore-Water Pressure-Measurement Device—The speci-
lateral motion or tilting, and the specimen cap shall be
designed such that eccentricity of the piston-to-cap contact
men pore-water pressure shall also be measured to the toler-
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ances given in 5.6. During undrained shear, the pore-water
pressure shall be measured in such a manner that as little water
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
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as possible is allowed to go into or out of the specimen. To
achieve this requirement, a very stiff electronic pressure
the test is minimal. The cylindrical surface of the specimen
base and cap that contacts the membrane to form a seal shall be
transducer or null-indicating device must be used. With an smooth and free of scratches.
electronic pressure transducer the pore-water pressure is read
directly. With a null-indicating device a pressureASTMcontrol D4767-11
is 5.12 Porous Discs—Two rigid porous disks shall be used to
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continuously adjusted to maintain a constant level of the provide drainage at the ends of the specimen. The coefficient of
water/mercury interface in the capillary bore of the device. The permeability of the disks shall be approximately equal to that
pressure required to prevent movement of the water is equal to of fine sand (1 × 10−4 cm/s (4 × 10−5 in./s)). The disks shall be
the pore-water pressure. Both measuring devices shall have a regularly cleaned by ultrasonic or boiling and brushing and
compliance of all the assembled parts of the pore-water checked to determine whether they have become clogged.
pressure-measurement system relative to the total volume of 5.13 Filter-Paper Strips and Disks— Filter-paper strips are
the specimen, satisfying the following requirement: used by many laboratories to decrease the time required for
~ ∆V/V ! /∆u,3.2 3 1026 m 2 /kN ~ 2.2 3 1025 in. 2 /lb! (1) testing. Filter-paper disks of a diameter equal to that of the
specimen may be placed between the porous disks and speci-
where:
men to avoid clogging of the porous disks. If filter strips or
∆V = change in volume of the pore-water measurement disks are used, they shall be of a type that does not dissolve in
system due to a pore pressure change, mm3 (in.3), water. The coefficient of permeability of the filter paper shall
V = total volume of the specimen, mm3 (in. 3), and not be less than 1 × 10−5 cm/s (4 × 10−6 in./s) for a normal
∆u = change in pore pressure, kPa (lbf/in.2).
pressure of 550 kPa (80 lbf/in.2). To avoid hoop tension, filter
NOTE 6—To meet the compliance requirement, tubing between the
specimen and the measuring device should be short and thick-walled with strips should cover no more than 50 % of the specimen
small bores. Thermoplastic, copper, and stainless steel tubing have been periphery. Filter-strip cages have been successfully used by
used successfully. To measure this compliance, assemble the triaxial cell many laboratories. An equation for correcting the principal
without a specimen. Then, open the appropriate valves, increase the stress difference (deviator stress) for the effect of the strength
pressure, and record the volume change.
of vertical filter strips is given in 10.4.3.1.
5.9 Volume Change Measurement Device— The volume of
water entering or leaving the specimen shall be measured with NOTE 7—Grade No. 54 Filter Paper has been found to meet the
permeability and durability requirements.
an accuracy of within 60.05 % of the total volume of the
specimen. The volume measuring device is usually a burette 5.14 Rubber Membrane—The rubber membrane used to
connected to the back pressure but may be any other device encase the specimen shall provide reliable protection against

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 D4767 − 11
leakage. Membranes shall be carefully inspected prior to use temperature fluctuations are less than 64°C (67.2°F) and there
and if any flaws or pinholes are evident, the membrane shall be is no direct contact with sunlight.
discarded. To offer minimum restraint to the specimen, the 5.22 Miscellaneous Apparatus—Specimen trimming and
unstretched membrane diameter shall be between 90 and 95 % carving tools including a wire saw, steel straightedge, miter
of that of the specimen. The membrane thickness shall not box, vertical trimming lathe, apparatus for preparing reconsti-
exceed 1 % of the diameter of the specimen. The membrane tuted specimens, membrane and O-ring expander, water con-
shall be sealed to the specimen cap and base with rubber tent cans, and data sheets shall be provided as required.
O-rings for which the unstressed inside diameter is between 75
and 85 % of the diameter of the cap and base, or by other 6. Test Specimen Preparation
means that will provide a positive seal. An equation for 6.1 Specimen Size—Specimens shall be cylindrical and have
correcting the principal stress difference (deviator stress) for a minimum diameter of 33 mm (1.3 in.). The average height-
the effect of the stiffness of the membrane is given in 10.4.3.2. to-average diameter ratio shall be between 2 and 2.5. The
5.15 Valves—Changes in volume due to opening and closing largest particle size shall be smaller than 1⁄6 the specimen
valves may result in inaccurate volume change and pore-water diameter. If, after completion of a test, it is found based on
pressure measurements. For this reason, valves in the specimen visual observation that oversize particles are present, indicate
drainage system shall be of the type that produce minimum this information in the report of test data (11.2.23).
volume changes due to their operation. A valve may be NOTE 10—If oversize particles are found in the specimen after testing,
assumed to produce minimum volume change if opening or a particle-size analysis may be performed on the tested specimen in
closing the valve in a closed, saturated pore-water pressure accordance with Test Method D422 to confirm the visual observation and
system does not induce a pressure change of greater than 0.7 the results provided with the test report (11.2.4).
kPa (60.1 lbf/in.2). All valves must be capable of withstanding 6.2 Intact Specimens—Prepare intact specimens from large
applied pressures without leakage. intact samples or from samples secured in accordance with
Practice D1587 or other acceptable intact tube sampling
NOTE 8—Ball valves have been found to provide minimum volume-
change characteristics; however, any other type of valve having suitable
procedures. Samples shall be preserved and transported in

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volume-change characteristics may be used. accordance with the practices for Group C samples in Practices
D4220. Specimens obtained by tube sampling may be tested
5.16 Specimen-Size Measurement Devices— Devices used without trimming except for cutting the end surfaces plane and
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to determine the height and diameter of the specimen shall
measure the respective dimensions to four significant digits and
perpendicular to the longitudinal axis of the specimen, pro-
vided soil characteristics are such that no significant distur-
shall be constructed such that their use will not disturb/deform
the specimen. Document Preview bance results from sampling. Handle specimens carefully to
minimize disturbance, changes in cross section, or change in
water content. If compression or any type of noticeable
NOTE 9—Circumferential measuring tapes are recommended over
calipers for measuring the diameter. disturbance would be caused by the extrusion device, split the
ASTM D4767-11 sample tube lengthwise or cut the tube in suitable sections to
5.17 Sample Extruder—The sample extruder shall be ca-
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pable of extruding the soil core from the sampling tube at a facilitate removal of the specimen with minimum disturbance.
uniform rate in the same direction of travel as the sample Prepare trimmed specimens, in an environment such as a
entered the tube and with minimum disturbance of the sample. controlled high-humidity room where soil water content
If the soil core is not extruded vertically, care should be taken change is minimized. Where removal of pebbles or crumbling
to avoid bending stresses on the core due to gravity. Conditions resulting from trimming causes voids on the surface of the
at the time of sample removal may dictate the direction of specimen, carefully fill the voids with remolded soil obtained
removal, but the principal concern is to minimize the degree of from the trimmings. If the sample can be trimmed with
disturbance. minimal disturbance, a vertical trimming lathe may be used to
reduce the specimen to the required diameter. After obtaining
5.18 Timer—A timing device indicating the elapsed testing the required diameter, place the specimen in a miter box, and
time to the nearest 1 s shall be used to obtain consolidation data cut the specimen to the final height with a wire saw or other
(8.3.3). suitable device. Trim the surfaces with the steel straightedge.
5.19 Balance—A balance or scale conforming to the re- Perform one or more water content determinations on material
quirements of Specification D4753 readable to four significant trimmed from the specimen in accordance with Test Method
digits. D2216.
6.3 Reconsituted Specimens—Soil required for reconstituted
5.20 Water Deaeration Device—The amount of dissolved
specimens shall be thoroughly mixed with sufficient water to
gas (air) in the water used to saturate the specimen shall be
produce the desired water content. If water is added to the soil,
decreased by boiling, by heating and spraying into a vacuum,
store the material in a covered container for at least 16 h prior
or by any other method that will satisfy the requirement for
to compaction. Reconsituted specimens may be prepared by
saturating the specimen within the limits imposed by the
compacting material in at least six layers using a split mold of
available maximum back pressure and time to perform the test.
circular cross section having dimensions meeting the require-
5.21 Testing Environment—The consolidation and shear ments enumerated in 6.1. Specimens may be reconstituted to
portion of the test shall be performed in an environment where the desired density by either: (1) kneading or tamping each

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 D4767 − 11
layer until the accumulative mass of the soil placed in the mold 7.2.1.2 Saturate the porous disks by boiling them in water
is reconstituted to a known volume; or (2) by adjusting the for at least 10 min and allow to cool to room temperature.
number of layers, the number of tamps per layer, and the force 7.2.1.3 If filter-paper disks are to be placed between the
per tamp. The top of each layer shall be scarified prior to the porous disks and specimen, saturate the paper with water prior
addition of material for the next layer. The tamper used to to placement.
compact the material shall have a diameter equal to or less than 7.2.1.4 Place a saturated porous disk on the specimen base
1⁄2 the diameter of the mold. After a specimen is formed, with and wipe away all free water on the disk. If filter-paper disks
the ends perpendicular to the longitudinal axis, remove the are used, placed on the porous disk. Place the specimen on the
mold and determine the mass and dimensions of the specimen disk. Next, place another filter-paper disk (if used), porous disk
using the devices described in 5.16 and 5.19. Perform one or and the specimen cap on top of the specimen. Check that the
more water content determinations on excess material used to specimen cap, specimen, filter-paper disks (if used) and porous
prepare the specimen in accordance with Test Method D2216. disks are centered on the specimen base.
6.4 Determine the mass and dimensions of the specimen 7.2.1.5 If filter-paper strips or a filter-paper cage are to be
using the devices described in 5.16 and 5.19. A minimum of used, saturate the paper with water prior to placing it on the
three height measurements (120° apart) and at least three specimen. To avoid hoop tension, do not cover more than 50 %
diameter measurements at the quarter points of the height shall of the specimen periphery with vertical strips of filter paper.
be made to determine the average height and diameter of the 7.2.1.6 Proceed with 7.3.
specimen. An individual measurement of height or diameter 7.2.2 Dry Mounting Method:
shall not vary from average by more than 5 %. 7.2.2.1 Dry the specimen drainage system. This may be
NOTE 11—It is common for the density or unit weight of the specimen
accomplished by allowing dry air to flow through the system
after removal from the mold to be less than the value based on the volume prior to mounting the specimen.
of the mold. This occurs as a result of the specimen swelling after removal 7.2.2.2 Dry the porous disks in an oven and then place the
of the lateral confinement due to the mold. disks in a desiccator to cool to room temperature prior to
mounting the specimen.
7. Mounting Specimen 7.2.2.3 Place a dry porous disk on the specimen base and
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7.1 Preparations—Before mounting the specimen in the
triaxial chamber, make the following preparations:
place the specimen on the disk. Next, place a dry porous disk
and the specimen cap on the specimen. Check that the

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7.1.1 Inspect the rubber membrane for flaws, pinholes, and
leaks.
specimen cap, porous disks, and specimen are centered on the
specimen base.

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7.1.2 Place the membrane on the membrane expander or, if
it is to be rolled onto the specimen, roll the membrane on the
NOTE 13—If desired, dry filter-paper disks may be placed between the
porous disks and specimen.
cap or base. 7.2.2.4 If filter-paper strips or a filter-paper cage are to be
7.1.3 Check that the porous disks and specimen drainage used, the cage or strips may be held in place by small pieces of
tubes are not obstructed by passing air or water through ASTM the D4767-11
tape at the top and bottom.
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appropriate lines. 7.3 Place the rubber membrane around the specimen and
7.1.4 Attach the pressure-control and volume-measurement seal it at the cap and base with two rubber O-rings or other
system and a pore-pressure measurement device to the cham- positive seal at each end. A thin coating of silicon grease on the
ber base. vertical surfaces of the cap and base will aid in sealing the
7.2 Depending on whether the saturation portion of the test membrane. If filter-paper strips or a filter-paper cage are used,
will be initiated with either a wet or dry drainage system, do not apply grease to surfaces in contact with the filter-paper.
mount the specimen using the appropriate method, as follows 7.4 Attach the top drainage line and check the alignment of
in either 7.2.1 or 7.2.2. The dry mounting method is strongly the specimen and the specimen cap. If the dry mounting
recommended for specimens with initial saturation less than method has been used, apply a partial vacuum of approxi-
90 %. The dry mounting method removes air prior to adding mately 35 kPa (5 lbf/in.2) (not to exceed the consolidation
backpressure and lowers the backpressure needed to attain an stress) to the specimen through the top drainage line prior to
adequate percent saturation. checking the alignment. If there is any eccentricity, release the
NOTE 12—It is recommended that the dry mounting method be used for partial vacuum, realign the specimen and cap, and then reapply
specimens of soils that swell appreciably when in contact with water. If the partial vacuum. If the wet mounting method has been used,
the wet mounting method is used for such soils, it will be necessary to the alignment of the specimen and the specimen cap may be
obtain the specimen dimensions after the specimen has been mounted. In checked and adjusted without the use of a partial vacuum.
such cases, it will be necessary to determine the double thickness of the
membrane, the double thickness of the wet filter paper strips (if used), and
the combined height of the cap, base, and porous disks (including the 8. Procedure
thickness of filter disks if they are used) so that the appropriate values may 8.1 Prior to Saturation—After assembling the triaxial
be subtracted from the measurements.
chamber, perform the following operations:
7.2.1 Wet Mounting Method: 8.1.1 Bring the axial load piston into contact with the
7.2.1.1 Fill the specimen drainage lines and the pore-water specimen cap several times to permit proper seating and
pressure measurement device with deaired water. alignment of the piston with the cap. During this procedure,