ASTM D8296-19

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: D8296 − 19
Standard Test Method for
Consolidated Undrained Cyclic Direct Simple Shear Test
under Constant Volume with Load Control or Displacement
Control
This standard is issued under the fixed designation D8296; 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 and into the specimen) can be performed using some simple
shear devices, but is beyond the scope of this standard.
1.1 This test method defines equipment specifications and
1.6 The cyclic strength of a soil is determined based on the
testing procedures for the measurement of cyclic strength,
number of cycles required to reach a limiting double amplitude
number of cycles to liquefaction or cyclic properties (Modulus
shear strain or a single amplitude shear strain, while liquefac-
and Damping) of soils, after one-dimensional consolidation
tion is more commonly defined as 100 % change in vertical
using a cyclic mode of loading.
stress ratio (change in effective vertical stress during shearing
1.2 The cyclic shearing can be applied using load control or
divided by effective vertical stress at end of primary consoli-
displacement control. It shall be the responsibility of the
dation). The change in vertical stress ratio in constant volume
agency requesting this test to specify the magnitude and
shearing is equivalent to the excess pore pressure ratio (excess
frequency of the cyclic loading. Other loading histories may be
pore pressure during shearing divided by effective vertical
used if required by the agency requesting the testing.
stress at end of primary consolidation) under undrained con-
ditions.Thestraincriterionisonlyapplicablewhenperforming
1.3 This test method is written specifically for devices that
load controlled tests; 100 % change in vertical stress ratio can
test cylindrical specimens enclosed in a wire-reinforced mem-
be used for both, load and displacement control. For displace-
brane or a soft membrane within a stack of rigid rings (this test
ment control testing, the criterion to stop the test could be a
method applies to Teflon coated rigid rings as well). Other
specified number of cycles.
typesofsheardevicesarebeyondthescopeofthistestmethod.
1.7 This test method is applicable to testing intact,
1.4 This test method can be used for testing cohesionless
reconstituted, or compacted specimens; however, it does not
free draining soils or fine grained soils. However, this test
include specific guidance for preparing, reconstituting or com-
method may be followed when testing most soil types if care is
pacting test specimens.
taken to ensure that any special considerations required for
1.8 It shall be the responsibility of the agency requesting
such soils are accounted for.
this test to specify the magnitude of the consolidation stress
1.5 The shearing phase of this test is conducted under
priortoshearand,ifassigned,anunloadingconsolidationstage
constant volume conditions. Since the lateral confinement
may be required for over-consolidating the specimen.
system prevents radial specimen strains, the constant volume
1.9 All recorded and calculated values shall conform to the
condition is accomplished by preventing specimen height
guide for significant digits and rounding established in Practice
change during shear. Shearing under constant volume can be
D6026.
performed on dry or saturated specimens.The constant volume
1.9.1 Theproceduresusedtospecifyhowdataarecollected/
condition is equivalent to the undrained condition for fully
recorded and calculated in this test method are regarded as the
saturated specimens. Cyclic direct simple shear testing with
industry standard. In addition, they are representative of the
truly undrained conditions (restricting pore water flow from
significant digits that shall generally be retained. The proce-
dures used do not consider material variation, purpose for
obtaining the data, special purpose studies, or any consider-
ations for the user’s objectives; it is common practice to
increase or reduce significant digits of reported data to be
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.09 on Cyclic and
Dynamic Properties of Soils. Testsshearedundertrulyundrainedconditionsshouldbeperformedexclusively
Current edition approved Nov. 1, 2019. Published November 2019. DOI: on saturated specimens. Therefore, backpressure saturation is required to ensure
10.1520/D8296-19 complete saturation of test specimen.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8296 − 19
commensuratewiththeseconsiderations.Itisbeyondthescope Used in Engineering Design and Construction
of this test method to consider significant digits used in D4186/D4186M TestMethodforOne-DimensionalConsoli-
analysis methods for engineering design. dation Properties of Saturated Cohesive Soils Using
1.9.2 Measurements made to more significant digits or Controlled-Strain Loading
better sensitivity than specified in this standard shall not be D4220/D4220M Practices for Preserving and Transporting
regarded as nonconformance with this standard. Soil Samples
D4318 Test Methods for Liquid Limit, Plastic Limit, and
1.10 Units—The values stated in SI units are to be regarded
Plasticity Index of Soils
as the standard. Reporting test results in units other than SI
D4452 Practice for X-Ray Radiography of Soil Samples
shall be regarded as conformance with this test method. In the
D6026 Practice for Using Significant Digits in Geotechnical
engineering profession it is customary practice to use,
Data
interchangeably, units representing both mass and force, unless
D6528 Test Method for Consolidated Undrained Direct
dynamic calculations (F=Ma) are involved. This implicitly
Simple Shear Testing of Fine Grain Soils
combines two separate systems of units, that is, the absolute
D6913/D6913M Test Methods for Particle-Size Distribution
system and the gravimetric system. It is scientifically undesir-
(Gradation) of Soils Using Sieve Analysis
able to combine two separate systems within a single standard.
D7928 Test Method for Particle-Size Distribution (Grada-
This test method has been written using SI units; however,
tion) of Fine-Grained Soils Using the Sedimentation
inch-pound conversions are given in the gravimetric system,
(Hydrometer) Analysis
where the pound (lbf) represents a unit of force (weight). The
use of balances or scales recording pounds of mass (lbm), or
3. Terminology
the recording of density in lb/ft shall not be regarded as
nonconformance with this test method. 3.1 Definitions:
3.1.1 The terms used in this test method are in accordance
1.11 This standard does not purport to address all of the
with Terminology D653.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2 Definitions:
priate safety, health, and environmental practices and deter-
3.2.1 liquefaction, n—the act or process of transforming any
mine the applicability of regulatory limitations prior to use.
soil response to loading from a solid-like response to a
1.12 This international standard was developed in accor-
liquid-like response, usually as a result of increased pore
dance with internationally recognized principles on standard-
pressure leading to a reduced shearing resistance.
ization established in the Decision on Principles for the
3.2.2 pore pressure ratio, n—the ratio, expressed as a
Development of International Standards, Guides and Recom-
percentage, of the change in the pore pressure during cyclic
mendations issued by the World Trade Organization Technical
loading, ∆u, to the effective vertical stress, σ’ , at the end of
nc
Barriers to Trade (TBT) Committee.
consolidation.
3.2.3 full or 100% pore pressure ratio, n—a condition in
2. Referenced Documents
which ∆u equals σ’ (also referred to as initial liquefaction
nc
2.1 ASTM Standards:
when it first occurs during the test).
D653 Terminology Relating to Soil, Rock, and Contained
3.3 Definitions of Terms Specific to This Standard:
Fluids
3.3.1 active height control, n—a method of keeping the
D854 Test Methods for Specific Gravity of Soil Solids by
height of the specimen constant during the shearing process in
Water Pycnometer
which the vertical displacement control mechanism is physi-
D1587/D1587M Practice for Thin-Walled Tube Sampling of
cally adjusted in response to the axial displacement measure-
Fine-Grained Soils for Geotechnical Purposes
ment.
D2216 Test Methods for Laboratory Determination of Water
(Moisture) Content of Soil and Rock by Mass
3.3.2 passive height control, n—a method of keeping the
D2435/D2435M Test Methods for One-Dimensional Con-
height of the specimen constant during the shearing process in
solidation Properties of Soils Using Incremental Loading
which the vertical load application components of the device
D2487 Practice for Classification of Soils for Engineering
are clamped by a mechanism that is much stiffer than the
Purposes (Unified Soil Classification System)
specimen.
D2488 Practice for Description and Identification of Soils
3.3.3 change in vertical stress ratio, n—the ratio, expressed
(Visual-Manual Procedures)
as a percentage, of the change in effective vertical stress during
D3550/D3550M Practice for Thick Wall, Ring-Lined, Split
cyclic loading, ∆σ’ , to the vertical effective stress, σ’ ,atthe
n nc
Barrel, Drive Sampling of Soils
end of last stage of consolidation.
D3740 Practice for Minimum Requirements for Agencies
3.3.4 equivalent excess pore pressure, n—the change in
Engaged in Testing and/or Inspection of Soil and Rock as
effective vertical stress during cyclic loading.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 4. Summary of Test Method
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.1 In this test method a specimen of soil is constrained
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. axially between two parallel, rigid platens and laterally by
D8296 − 19
reinforced membrane or stack of rings, such that the cross 5. Significance and Use
sectional area remains constant.
5.1 Cyclic direct simple shear strength test results are used
4.2 The specimen is loaded axially and allowed to consoli-
most often for evaluating the ability of a soil to resist shear
date one-dimensionally. Each vertical load increment is main-
stresses induced in a soil mass during earthquake loading,
tained until excess pore water pressures are essentially dissi-
offshore storm loading, etc.
pated. The final vertical load increment is maintained until the
5.2 In this test, the cyclic strength is measured under
completion of one log cycle of secondary compression or a
constant volume conditions that are equivalent to undrained
minimum of 120 minutes (mostly for sandy specimens),
conditions; hence, the test is applicable to field conditions in
whichever is longer. It is common practice to maintain the final
whichthesoilshaveconsolidatedunderonesetofstresses,and
vertical loading increment till the next day for specimens that
then are subjected to changes in stress/strain without time for
complete a log-cycle of secondary consolidation within the
further drainage to take place.
same day of starting the loading stage.
5.3 The cyclic strength is a function of many factors
4.3 The specimen is sheared by displacing one platen
including density, confining pressure, stress history, grain
horizontally relative to the other at a cyclic rate under either
structure, specimen preparation procedure, frequency, and
displacement or load control and measuring the shear and
characteristics of the cyclic loading applied. Therefore, test
vertical forces and displacements. Other loading histories may
factors shall be considered during evaluation of test results.
be used if required by the agency requesting the testing. The
platens are constrained against rotation throughout shear.
5.4 The state of stress within the direct simple shear
specimen is not sufficiently defined nor uniform enough to
4.4 The cyclic loading is run under a constant volume
allow rigorous interpretation of the results. Expressing the data
during shear to simulate undrained conditions. Constant vol-
in terms of the shear stress and vertical effective stress on the
ume is achieved either by active (constant) height control or by
horizontal plane is useful for engineering purposes. Some
fixing the top platen against vertical movement (passive height
effective stress parameters that could be derived from a cyclic
control). The change in vertical effective stress is monitored
direct simple shear test shall not be confused with correspond-
during shearing. Since the actual pore pressure in a constant
ing parameters derived from other shear tests having better
volume test is zero through shear, the change in vertical stress
defined states of stress (that is, cyclic triaxial tests).
is equal to the change in effective stress and assumed to be
equal to the change in pore water pressure that would occur in
5.5 The values of settlement in saturated soil after cyclic
a sealed saturated specimen.
loading can be assessed from the test results by allowing
NOTE 1—The quality of the result produced by this test method is
volume change at the end of the shearing to achieve same
dependent on the competence of the personnel performing it, and the
vertical effective stresses as at end of primary consolidation.
suitability of the equipment and facilities. Agencies that meet the criteria
of Practice D3740 generally are considered capable of competent and
5.6 The data from the consolidation portion of this test are
objective testing/sampling/inspection/etc. Users of this test method are
comparable to results obtained using Test Method D2435/
cautioned that compliance with Practice D3740 does not in itself assure
D2435M provided that the more rigorous consolidation proce-
reliable results. Reliable results depend on many factors; Practice D3740
provides a means of evaluating some of those factors. dure of Test Method D2435/D2435M is followed.
FIG. 1 Schematic Diagram of Direct Simple Shear Components (water bath can be replaced with flexible tubing connecting the drain-
age lines to a burette)
D8296 − 19
6. Apparatus 6.7 Shear Loading Ram—The shear load ram must apply
horizontal displacement of the specimen with minimum eccen-
6.1 Fig. 1 presents a schematic diagram of the components
tricity in the horizontal direction (from the specimen centerline
for a typical apparatus, but other designs exist and perform
along direction of shearing).
well. The following sections specify the component require-
ments in more detail.
6.8 Lateral Confinement Device—The specimen shall be
constrained laterally such that the cross-sectional area at any
6.2 Vertical Loading Device—Asuitabledeviceforapplying
location does not change by more than 0.1% during any part of
axial vertical force to the specimen. The device must be
the test. In addition, the confinement must allow uniform shear
capable of maintaining constant force during the consolidation
deformation. Specimens are generally confined by a wire
phase of a test, permit quick application of force for consoli-
reinforced membrane or a standard membrane supported by
dationincrements,andallowcontinuousadjustmentofposition
stacked rigid rings. The thickness of the individual stacked
when using active height control or can be rigidly locked in
rings or plates must be less than ⁄10 of the specimen thickness
place when using passive height control. The vertical loading
in order to allow relatively uniform shear deformation. Rigid
device must maintain a constant vertical load within 62%of
rings shall have minimal friction when sliding on each other
the target load during consolidation and a constant height
during shearing (Teflon coating or similar methods shall be
within 60.05 % of the preshear specimen height (H ) during
ps
utilized to reduce friction, if needed). When the confining
shearing.
device is within a water bath, it shall be constructed of
6.3 Shear Loading Device—A device for applying shear
corrosion resistant material.
force/displacementtothespecimenwithsufficientcapacityand
6.8.1 Specimen Size Requirements:
control to load/deform the specimen at the required rate.
6.8.1.1 The minimum specimen diameter shall be 45 mm.
Application of load/displacement shall be smooth and continu-
ous. For cyclic loading, the loading device must be able to 6.8.1.2 The minimum specimen height shall be 12 mm.
maintain a constant amplitude at the selected frequency and
6.8.1.3 The height to diameter ratio shall not exceed 0.4.
shall be able to apply loads at a frequency range of at least 0.1
6.8.1.4 The specimen height shall not be less than ten times
to 1 Hz. The loading device must be able to maintain uniform
the maximum particle diameter (see 9.4).
cyclic loadings to at least failure conditions or 10 % peak-to-
6.8.2 Platens—The top and bottom platens of the apparatus
peak strains. Nonsymmetrical shapes of load peaks, non-
shall be constructed of corrosion resistant material and have a
uniformity of pulse duration, and “ringing” must be avoided.
circular cross-section to match the specimen. The platens shall
Cyclic load fall-off at large strains for load controlled testing
be designed to securely hold the porous disks and provide
must not exceed 5 % of the initial values (with the exception of
drainage from the specimen and transfer shear to the specimen
liquefaction testing where the fall off can be larger). The
without horizontal slippage.
equipment must also be able to apply the cyclic load superim-
6.8.3 Porous Disks—Theporousdisksshallbebrass,silicon
posed on an initial static shear load.
carbide, aluminum oxide, or similar rigid corrosion resistant
6.4 Force Measuring Devices—Two devices are required:
material. The disks shall be flat, fine enough to prevent
one for measuring vertical force and one for measuring shear
intrusion of the soil into the pores, and rough enough to
force. Each device shall have the necessary capacity, be
transfer the shear stress. The disks must be at least ten times
accurate to 61 % of the applied maximum force for a given
more permeable than the soil. Disks must cover at least 90 %
test and have a readability of at least 4 significant digits of the
of the specimen surface and when smaller than the specimen,
applied maximum force for a given test. The devices shall be
mustberecessedintotheplatensuchthatthesurfaceincontact
insensitive to eccentric loading or installed in a fashion to
with the soil is flush with the platen.
eliminate eccentric loading. The compressibility of the shear
NOTE 2—It is sometimes necessary to increase the surface roughness of
measuring device shall not cause the deviation in shear
the porous disks in order to prevent interface slippage. Short metallic pins
displacement rate to exceed 615 % of the average rate. When
cemented into the disks have been used successfully but can introduce
using passive height control the compressibility of the axial
uncertainty in the shear strain calculations.
measuring device together with other sources of false defor-
NOTE 3—Disks of ductile material, for example, brass, have been found
mations must satisfy the deflection requirement of 6.10.
to warp due to the shear stress and need to be flattened on a regular basis.
6.5 Axial Loading Ram—The axial loading ram must hold
6.9 Displacement Indicators—Two devices are required:
one platen parallel to the other while allowing axial displace-
one to measure the change in specimen height and one for the
ment of the specimen. If the piston resists the shear force, it
shear deformation (axial and lateral movement of top platen
must do so with negligible rotation of the platen.
relative to bottom platen). These devices shall have a range of
6.6 Shear Slide Table—The shear slide table must hold the at least 20 % of the initial height of the specimen and shall
platens parallel to each other and allow shear displacement of have an accuracy of at least 0.25 % of full range and a
the specimen. When using passive height control and the slide readability of at least 4 significant digits of the initial specimen
table is within the height control boundaries, its compressibil- height. If a displacement measurement device is situated
ity together with other sources of false deformation must somewhere on the apparatus where its’ measurement will be
satisfy the deflection requirement of 6.10. The slide table shall affected by false deformations, this must be corrected/
allow a sufficient displacement to provide a minimum of accounted for. The placement of the two displacement indica-
615 % shear strain. tors must allow for measuring the relative movement between
D8296 − 19
the top and bottom platens regardless whether active or passive 7.1.1 Intact samples having satisfactory quality for testing
volume control is being used. by this method may be obtained using procedures and appara-
tus described by Practices D1587/D1587M. Specimens also
6.10 Volume Control Equipment—This applies to the con-
may be trimmed from large intact block samples obtained and
stantvolume(undrained)shearphaseofthetest.Passiveheight
sealed in the field.
control requires a mechanism to lock the axial loading ram in
7.1.2 Intact samples to be tested by this method shall be
place during shear. The vertical force transducer must be
preserved, handled and transported in accordance with the
moment insensitive and located between the specimen and the
practices for Groups C and D samples in Practice D4220/
clamp or the specimen and the slide base.Active height control
D4220M.
is accomplished by continuously measuring the specimen
7.1.3 Intact samples shall be sealed and stored such that no
height and using a system that controls the axial loading ram to
moisture is lost or gained between sampling and testing.
keep the specimen height constant throughout. In either case,
Storage time and temperature fluctuations shall be minimized.
the device shall not allow the specimen change in height to
7.1.4 The quality of direct simple shear test results dimin-
exceed 0.05 % including the equipment deformation deter-
ishes greatly with sample disturbance. No sampling procedure
mined in 10.1.
can assure completely undisturbed samples; therefore, careful
6.11 Specimen Trimming Device—Atrimming turntable or a
examination of the sample and selection of the highest quality
cylindrical cutting ring may be used for cutting the cylindrical
material for testing is essential for reliable testing.
specimens to the proper diameter. The top and bottom of the
specimen may be rough trimmed with a wire saw. All flat
NOTE 4—Examination for sample disturbance, stones or other
inclusions, and selection of specimen location is greatly facilitated by
surfaces must be finish trimmed with a sharpened straight edge
X-ray radiography of the samples as described in Methods D4452.
and shall have a tolerance of 60.05 mm.
7.2 Laboratory Reconstituted and Compacted Specimens:
6.12 Specimen Setup Frame—A rigid frame to hold in
this sampling method is applicable to cohesionless and clayey
alignment the bottom platen, the specimen in the trimming
soils.
device, and expander/holder containing the confinement de-
7.2.1 Laboratory reconstituted and compacted specimens
vice. The frame must allow the trimmed specimen to be
may be prepared from bulk homogeneous material.
transferredfromthetrimmingdevicetotheconfinementdevice
7.2.2 Bulk material shall be handled and transported in
with a minimum of disturbance and with proper lateral contact.
accordancewiththepracticesforGroupBsamplesofPractices
6.13 Water Bath or Volume Change System—A method to
D4220/D4220M.
provide the specimen with free access to water at atmospheric
7.2.2.1 The material required for the specimen shall be
pressure and prevent specimen drying due to evaporation. The
batched by thoroughly mixing soil with sufficient water to
entire specimen and confinement device may be submerged in
produce the desired conditions. After batching, store the
a water bath or the end platens may be connected by flexible
material in a covered container for at least 16 hours prior to
tubing to a standpipe with a water level within the specimen
specimen preparation for fine grained soils. Other procedures
height. In either case, water must be available to both ends of
may be used for cohesionless soils.
thespecimenbymeansoftheporousdisks.Thisisonlyneeded
in case of running tests on saturated specimens.
8. Specimen Preparation
6.14 Miscellaneous Equipment—Including timing device
8.1 All reasonable precautions shall be taken to minimize
with one second readability, caliper, dial comparator, distilled
disturbance of the soil caused by vibration, distortion, and
or demineralized water, spatulas, knives, trimming blade and
compression.
wire saws.
8.2 Test specimens and soil processing shall be performed
6.15 Balances, in accordance with Test Method D2216.
in an environment that prevents moisture change.
6.16 Drying Oven, in accordance with Test Method D2216.
8.3 Intact Specimens—Trim the specimen to the lateral
6.17 Water Content Container, in accordance with Test
dimension of the lateral confinement device.
Method D2216.
8.3.1 Intact soil collected using sample tubes shall be at
6.18 Environment—Tests shall be performed in an environ-
least 2.5 mm larger in each dimension than the specimen
mentwheretemperaturefluctuationsarelessthan 62°Cduring
dimensionexceptasspecifiedin8.3.1.1and8.3.1.2.Trimaway
shear, and there is no direct exposure to sunlight.
the additional material using one of the following methods.
6.19 Trimming Environment—Trim the specimen in a way
NOTE 5—The degree of sample disturbance is known to increase
that the water content of the soil does not change during the
towards the perimeter of the tube sample, and therefore, it is better to use
process. This can be by working uninterrupted and covering larger diameter samples where possible.
exposed parts of the specimen or working in an environment
8.3.1.1 When using a trimming turntable and cylindrical
with high relative humidity.
specimens, make a complete perimeter cut, the width of the
blade, to reduce the soil diameter to that of the confinement
7. Sampling
ring. Gradually advance the specimen into the ring by the
7.1 Intact Samples—This sampling method is applicable to width of the blade. Repeat until the specimen protrudes from
clayey soils only. the bottom of the ring.
D8296 − 19
8.3.1.2 When using a cutting shoe, trim the soil to a gentle membrane. The area of the tamper footing shall be between 4
taper in front of the cutting surface with a knife or spatula. to 6 times less than the area of the sample.
After the taper is formed, advance the cutter a small distance to
8.13.3 Level the top of the specimen to be flat and perpen-
shaveofftheremainingsoilandformthefinaldiameter.Repeat dicular to the specimen sides (parallel to the face of the
the process until the specimen protrudes from the top of the
platens).
cutter.
8.13.4 Determine the initial dry mass of the specimen by
8.3.2 Fibrous soils, such as peats, and those soils that are
measuring the mass of the available sand before preparing the
damaged easily by trimming, may be transferred directly from
specimen and the remaining sand afterwards. The mass of the
the sampling tube to the confinement device, provided that the
specimen is determined as the difference between the two
device has the same dimensions as the sampling tube.
measurements. If the sand is not poured/tamped in the dry
state,thendryouttheremainingwetsandinaccordancetoTest
8.4 Laboratory Reconstituted and Compacted Specimens—
Method D2216 to determine the remaining amount of dry sand
The method of preparation and specification
...