ASTM D5321/D5321M-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D5321/D5321M − 20 D5321/D5321M − 21
Standard Test Method for
Determining the Shear Strength of Soil-Geosynthetic and
Geosynthetic-Geosynthetic Interfaces by Direct Shear
This standard is issued under the fixed designation D5321/D5321M; 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
1.1 This test method covers a procedure for determining the shear resistance of a geosynthetic against soil, or a geosynthetic
against another geosynthetic, under a constant rate of deformation.
1.1.1 The test method is intended to indicate the performance of the selected specimen by attempting to model certain field
conditions. Results obtained from this method may be limited in their applicability to the specific conditions considered in the
testing.
1.2 The test method is applicable for all geosynthetics, with the exception of geosynthetic clay liners (GCLs), which are addressed
in Test Method D6243/D6243M.
1.3 The test method is not suited for the development of exact stress-strain relationships for the test specimen due to the
nonuniform distribution of shearing forces and displacement.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the
two systems may result in nonconformance with the standard.
1.5 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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D653 Terminology Relating to Soil, Rock, and Contained Fluids
3 3
D698 Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft (600 kN-m/m ))
D1557 Test Methods for Laboratory Compaction Characteristics of Soil Using Modified Effort (56,000 ft-lbf/ft (2,700
kN-m/m ))
This test method is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.01 on Mechanical Properties.
Current edition approved Feb. 15, 2020June 1, 2021. Published March 2020June 2021. Originally approved in 1992. Last previous edition approved in 20192020 as
D5321/D5321M – 19.D5321/D5321M – 20. DOI: 10.1520/D5321_D5321M-20.10.1520/D5321_D5321M-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D5321/D5321M − 21
D2435/D2435M Test Methods for One-Dimensional Consolidation Properties of Soils Using Incremental Loading
D2487 Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
D3080/D3080M Test Method for Direct Shear Test of Soils Under Consolidated Drained Conditions (Withdrawn 2020)
D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in
Engineering Design and Construction
D4354 Practice for Sampling of Geosynthetics and Rolled Erosion Control Products (RECPs) for Testing
D4439 Terminology for Geosynthetics
D6243/D6243M Test Method for Determining the Internal and Interface Shear Strength of Geosynthetic Clay Liner by the Direct
Shear Method
D7005/D7005M Test Method for Determining the Bond Strength (Ply Adhesion) of Geocomposites
D7466/D7466M Test Method for Measuring Asperity Height of Textured Geomembranes
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms relating to soil and rock, refer to Terminology D653. For definitions of terms relating to
geosynthetics, refer to Terminology D4439.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 adhesion, c , n—the y-intercept of the Mohr-Coulomb strength envelope.
a
3.2.2 atmosphere for testing geosynthetics, n—air maintained at a relative humidity between 50 and 70 % and a temperature of
21 6 2 °C [70 6 4 °F].
3.2.3 Mohr-Coulomb friction angle, δ, n—(angle of friction of a material or between two materials, °) the angle defined by the
least-squares, “best-fit” straight line through a defined section of the shear strength-normal stress failure envelope; the component
of the shear strength indicated by the term δ, in Coulomb’s equation, τ = c + σ * tan (δ) (see 12.6).
a n
3.2.3.1 Discussion—
The end user is cautioned that some organizations (for example, FHWA, AASHTO, along with state agencies who use these
documents) are currently using the Greek letter, Delta (δ), to designate wall-backfill interface friction angle and the Greek letter,
4,5
Rho (ρ), to designate the interface friction angle between geosynthetics and soil.
3.2.4 Mohr-Coulomb shear strength envelope, n—the least squares, “best fit” straight line through a defined section of the shear
strength-normal stress failure envelope described by the equation, τ = c + σ * tan (δ) (see 12.6). The envelope can be described
a n
for any chosen shear failure mode (example, peak or post-peak).
3.2.5 secant friction angle, δ , n—(angle of friction of a material or between two materials, °) the angle defined by a line drawn
sec
from the origin to a data point on the shear strength-normal stress failure envelope. Intended to be used only for the normal stress
on the shearing plane for which it is defined.
3.2.6 shear strength, τ, n—the shear force on a given failure plane. In the direct shear test, it is always stated in relation to the
normal stress acting on the failure plane. Two different types of shear strengths are often estimated and used in standard practice:
3.2.6.1 peak shear strength—the largest value of shear resistance experienced during the test under a given normal stress.
3.2.6.2 post-peak shear strength—the minimum, or steady-state value of shear resistance that occurs after the peak shear
strength is experienced.
3.2.6.3 Discussion—
The end user is cautioned that the reported value of post-peak shear strength (regardless how defined) is not necessarily the residual
shear strength. In some instances, a post-peak shear strength may not be defined before the limit of horizontal displacement is
reached.
3.2.7 shear strength envelope, n—curvi-linear line on the shear stress-normal stress plot representing the combination of shear and
normal stresses that define a selected shear failure mode (for example, peak and post-peak).
The last approved version of this historical standard is referenced on www.astm.org.
LRFD Bridge Design Specifications, 5th Edition, American Association of State Highway and Transportation Officials (AASHTO), Washington, DC, 2010.
“Mechanically Stabilized Earth Walls and Reinforced Soil Slopes, Design and Construction Guidelines,” FHWA GEC 011, FHWA NHI-10-024, Vol I, and FHWA
NHI-10-025, Vol II, U.S. Department of Transportation, Federal Highway Administration (FHWA), Washington, DC, 2009.
D5321/D5321M − 21
4. Summary of Test Method
4.1 The shear resistance between a geosynthetic and a soil, or other material selected by the user, is determined by placing the
geosynthetic and one or more contact surfaces, such as soil, within a direct shear box. A constant normal stress representative of
design stresses is applied to the specimen, and a tangential (shear) force is applied to the apparatus so that one section of the box
moves in relation to the other section. The shear force is recorded as a function of the shear displacement of the moving section
of the shear box.
4.2 To define a Mohr-Coulomb shear strength envelope, it is recommended that a minimum of three test points be performed at
different normal stresses, selected by the user, to model appropriate field conditions. However, there may be instances where fewer
test points are desired (see Note 1). The peak shear stresses, or shear stresses at some post-peak displacement, or both, are plotted
against the applied normal stresses used for testing. The test data are generally represented by a best-fit straight line through the
peak strength values whose slope is the Mohr-Coulomb friction angle for peak strength between the two materials where the
shearing occurred. The y-intercept of the straight line is the adhesion intercept. A straight line fit for shear stresses at some
post-peak displacement is the post-peak interface strength between the two materials where the shearing occurred.
NOTE 1—There may be some investigative cases where only a single test point is desired. If the field design conditions will experience a range of normal
stresses, it is standard industry practice to bracket the normal stress range with tests on both sides of the range, as it is unconservative to extrapolate results
outside of the normal stress range tested. When defining a Mohr-Coulomb shear strength envelope over a range of normal stresses, standard industry
practice is to use a minimum of three test points. Attempting to define a single linear Mohr-Coulomb shear strength envelope over too large of a normal
stress range may prove to be problematic in many cases because most failure envelopes exhibit significant curvature over such a large range, particularly
at low normal stresses on the shearing plane.
5. Significance and Use
5.1 The procedure described in this test method for determination of the shear resistance of the soil and geosynthetic or
geosynthetic and geosynthetic interface is intended as a performance test to provide the user with a set of design values for the
test conditions examined. The test specimens and conditions, including normal stresses, are generally selected by the user.
5.2 This test method may be used for acceptance testing of commercial shipments of geosynthetics, but caution is advised as
outlined in 5.2.1.
5.2.1 The shear resistance can be expressed only in terms of actual test conditions (see Notes 2 and 3). The determined value may
be a function of the applied normal stress, material characteristics (for example, of the geosynthetic), soil properties, size of sample,
moisture content, drainage conditions, displacement rate, magnitude of displacement, and other parameters.
NOTE 2—In the case of acceptance testing requiring the use of soil, the user must furnish the soil sample, soil parameters, and direct shear test parameters.
The method of test data interpretation for purposes of acceptance should be mutually agreed to by the users of this test method.
NOTE 3—Testing under this test method should be performed by laboratories qualified in the direct shear testing of soils and meeting the requirements
of Practice D3740, especially since the test results may depend on site-specific and test conditions.
5.2.2 This test method measures the total resistance to shear between a geosynthetic and a supporting material (substratum) or a
geosynthetic and an overlying material (superstratum). The total shear resistance may be a combination of sliding, rolling, and
interlocking of material components.
5.2.3 This test method does not distinguish between individual mechanisms, which may be a function of the soil and geosynthetic
used, method of material placement and hydration, normal and shear stresses applied, means used to hold the geosynthetic in place,
rate of shear displacement, and other factors. Every effort should be made to identify, as closely as practicable, the sheared area
and failure mode of the specimen. Care should be taken, including close visual inspection of the specimen after testing, to ensure
that the testing conditions are representative of those being investigated.
5.2.4 Information on precision among laboratories is incomplete. In cases of dispute, comparative tests to determine whether a
statistical bias exists among laboratories may be advisable.
5.3 The test results can be used in the design of geosynthetic applications including, but not limited to: the design of liners and
caps for landfills, mining heap leach pads, tailings impoundments, cutoffs for dams and other hydraulic barriers, geosynthetic-
reinforced retaining walls, embankments, and base courses; in applications in which the geosynthetic is placed on a slope; for
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determination of geosynthetic overlap requirements; or in other applications in which sliding may occur between soil and a
geosynthetic or between two geosynthetic materials.
5.4 The displacement at which peak strength and post-peak strength occurs and the shape of the shear stress versus shear
displacement curve may differ considerably from one test device to another due to differences in specimen mounting, gripping
surfaces, and material preparation. The user of results from this test method is cautioned that results at a specified displacement
may not be reproducible across laboratories and that the relative shear displacement measured in this test at peak strength may not
match relative shear displacement at peak strength in a field condition.
6. Apparatus
6.1 Shear Device—A rigid device to hold the specimen securely and in such a manner that a uniform shear force without torque
can be applied to the tested interface. The device consists of both a stationary and moving container, each of which is capable of
containing dry or wet soil and is rigid enough to not distort during shearing of the specimen. The traveling container must be placed
on firm bearings and rack to ensure that the movement of the container is only in a direction parallel to that of the applied shear
force.
NOTE 4—The position of one of the containers should be adjustable in the normal direction to compensate for vertical deformation of the substrate and
geosynthetic.
6.1.1 Square or rectangular containers are recommended. They should have a minimum dimension that is the greatest of 300 mm
[12 in.], 15× the d of the coarser soil used in the test, or a minimum of 5× the maximum opening size (in plane) of the
geosynthetic tested. The depth of each container that contains soil must be a minimum of 50 mm [2 in.] or 6× the maximum particle
size of the coarser soil tested, whichever is greater.
NOTE 5—The minimum container dimensions given in 6.1.1 are guidelines based on requirements for testing most combinations of geosynthetics and
soils. Containers smaller than those specified in 6.1.1 can be used if it can be shown that data generated by the smaller devices contain no bias from scale
or edge effects when compared to the minimum-size devices specified in 6.1.1 for specific materials being tested. The user should conduct comparative
testing prior to the acceptance of data produced on smaller devices. For direct shear testing involving soils, competent geotechnical review is
recommended to evaluate the compatibility of the minimum and smaller direct shear devices.
6.2 Normal Stress Loading Device, capable of applying and maintaining a constant uniform normal stress on the specimen for the
duration of the test. Careful control and accuracy (62 %) of normal stress is important. Normal force loading devices include, but
are not limited to: weights, pneumatic or hydraulic bellows, or piston-applied stresses. For jacking systems, the tilting of loading
plates must be limited to 2° from the shear direction during shearing. The device must be calibrated to determine the normal stress
delivered to the shear plane.
6.3 Shear Force Loading Device, capable of applying a shearing force to the specimen at a constant rate of shear displacement.
The horizontal force measurement system must be calibrated, including provisions to measure and correct for the effects of friction
and tilting of the loading system. The rate of displacement should be controlled to an accuracy of 610 % over a range of at least
6.35 mm/min [0.25 in./min] to 0.025 mm ⁄min [0.001 in./min]. The system must allow constant measurement and readout of the
applied shear force. An electronic load cell or proving ring arrangement is generally used. The shear force loading device should
be connected to the test apparatus in such a fashion that the point of the load application to the traveling container is in the plane
of the shearing interface and remains the same for all tests. (See Note 6.)
NOTE 6—The operating range of normal and horizontal shear stresses for a device should be limited to between 10 % and 90 % of its calibrated range.
If a device is used outside this range, the report shall so state and give a discussion of the potential effect of uncertainties in normal stress on the measured
results.
6.4 Displacement Indicators, for providing continuous readout of the horizontal shear displacement, and if desired, vertical
displacement of the specimen during the consolidation or shear phase, or both. Displacement indicators such as dial indicators, or
linear variable differential transformers (LVDTs), capable of measuring a displacement of at least 75 mm [3 in.] for shear
displacement and 25 mm [1 in.] for vertical displacement are recommended. The sensitivity of displacement indicators should be
0.02 mm [0.001 in.] for measuring shear displacement and 0.002 mm [0.0001 in.] for measuring vertical displacement.
6.5 Geosynthetic Clamping Devices, required for fixing geosynthetic specimens to the stationary section or container, the traveling
container, or both, during shearing of the specimen. Clamps and grips shall not interfere with the shearing surfaces within the shear
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box and must keep the geosynthetic specimens flat during testing. Gripping surfaces must develop sufficient shear resistance to
prevent nonuniform displacement of the geosynthetic and adjacent geosynthetics. Gripping surfaces must develop sufficient shear
resistance to prevent tensile failure within any geosynthetics material outside the specimen area subjected to normal stress. Flat,
jaw-like clamping devices are normally sufficient. Textured surfaces or soil must be used to support the top or bottom, or both,
of the geosynthetic. These surfaces must permit flow of water into and out of the test specimen. Work is still in progress to define
the best type of textured surfaces. Selection of the type of textured surface should be based on the following criteria:
6.5.1 The gripping surface should be able to fully mobilize the friction between the gripping surface and the outside surfaces of
the geosynthetic. The rough surfaces must be able to prevent slip between the geosynthetic and the gripping surface to prevent
tensile failure in the geosynthetic.
6.5.2 The gripping surface must be able to completely transfer the applied shear force through the outside surfaces into the
geosynthetic.
6.5.3 The gripping surface must not damage the geosynthetic and should not influence the shear strength behavior of the
geosynthetic.
NOTE 7—The selection of specimen substrate may influence the test results. For instance, a test performed using a rigid substrate, such as a wood or metal
plate, may not simulate field conditions as accurately as that using a soil substrate. However, use of compressible soils as a substrate is not recommended
due to the possibility that these soils may compress under the applied normal load to the extent that the intended shear plane is no longer level with the
gap between the two halves of the shear box. The user should be aware of the influence of substrate on direct shear resistance data. Accuracy,
reproducibility, and relevance to field conditions should be considered when selecting a substrate for testing.
NOTE 8—Gripping and clamping systems vary widely and can be different based on the geosynthetic material being tested. Several authors have
successfully used a multitude of systems.
6.6 Soil Preparation Equipment, for preparing or compacting bulk soil samples, as outlined in Test Methods D698, D1557, or
D3080/D3080M.
6.7 Miscellaneous Equipment, as required for preparing specimens. A timing device and equipment required for maintaining
saturation of the geosynthetic or soil samples, if desired.
7. Geosynthetic Sampling
7.1 Lot Sample—Divide the product into lots, and for any lot to be tested, take the lot sample as directed in Practice D4354 (see
Notes 9 and 10).
7.2 Laboratory Sample—Consider the units in the lot sample as the units in the laboratory sample for the lot to be tested. For a
laboratory sample, take a sample extending the full width of the geosynthetic production unit and of sufficient length so that the
requirements of 7.3 can be met. Take a sample that will exclude material from the outer edge.
7.3 Test Specimens—From each unit in the laboratory sample, remove three specimens (or fewer if specified by the user) as
outlined in 7.3.1.
7.3.1 Remove specimens for shearing in a direction parallel to the machine, or roll, direction of the laboratory sample and
specimens for shearing in a direction parallel to the cross-machine, or cross-roll, direction, if required (see Notes 9 and 10). All
specimens should be sufficiently large to fit snugly in the container described in 6.1.1, and they should be of sufficient size to
facilitate clamping. All specimens should be free of surface defects, etc., that are not typical of the laboratory sample. Space the
specimens along a diagonal of the unit of the laboratory sample. Take no specimens nearer the edge of the geosynthetic production
unit than one tenth the width of the unit.
NOTE 9—Lots for geosynthetics usually are designated by the producer during manufacturing. While the test method does not attempt to establish a
frequency of testing for the determination of design-oriented data, the lot number of the laboratory sample should be identified. The lot number should
be unique to the raw material and manufacturing process for a specific number of units, for example, rolls, panels, etc., designated by the producer.
Fox et al., 1997; Pavlik, 1997; Trauger, et al., 1997; Fox, et al., 1998; Zanzinger and Alexiew, 2000; Olsta and Swan, 2001; Triplett and Fox, 2001; Marr, 2002; Koerner
and Lacy, 2005; Fox, et al., 2006; and Allen and Fox, 2007.
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NOTE 10—The shear strength characteristics of some geosynthetics may depend on the direction tested. In many applications, it is necessary to perform
shear tests in only one direction that matches the direction of shear in the installation. In addition, it is often necessary to perform shear tests against a
specific side of the geosynthetic that matches the installation. The direction of shear and the side of the geosynthetic specimen(s) tested must be noted
clearly in the report for these cases.
NOTE 11—To help understand the shear strength characteristics of the geocomposite specimen(s),geosynthetic interface, it may be useful to conduct ply
adhesion tests pre-shear test nondestructive index testing (for example, thickness, asperity height, or mass per unit area) on the shear test specimen or
destructive index testing (for example, ply adhesion) on material adjacent in shear direction to the location where the on the laboratory sample from which
the shear test specimen was taken from the laboratory sample. Ply adhesion testingtaken. These tests should be conducted in general accordance with Test
Methodthe appropriate D7005/D7005M, but the ASTM test method though the number of specimens tested is at the discretion of the user.test specimens
or measurements may differ.
NOTE 12—To help understand the shear strength characteristics of the textured geomembrane specimen(s), it may be useful to measure the asperity height
of the shear test specimen(s) prior to shearing (and potentially after shearing). Asperity height measurements should be conducted in general accordance
with Test Method D7466/D7466M, but the number of measurements taken is at the discretion of the user.
8. Shear Device Calibration
8.1 The direct shear device must be calibrated to measure the internal resistance to shear inherent to the device. The inherent shear
resistance is a function of the geometry and mass of the traveling container, type and condition of the bearings, type of shear
loading system, and the applied normal stress. The calibration procedure described in this section is applicable to certain devices.
Other procedures may be required for specific devices. Refer to the manufacturer’s literature for recommended calibration
procedures. (See Note 1312.)
8.2 Assemble the shear device completely without placing a specimen inside it. If the design permits, apply a normal stress equal
to that for which friction is being measured. If applying a normal stress, some low-friction mechanism such as rollers must be used
to resist the normal stress without creating a shear resistance. Some boxes do not permit calibration with a normal stress. Adjust
the gap between the upper and lower box to the value used in shear testing. Apply the shear force to the traveling container at a
rate of 6.35 mm/min [0.25 in./min]. Record the shear force required to sustain movement of the traveling container for at least 75
mm [3 in.] total shear displacement. Record the applied shear force at 1-mm [0.05-in.] intervals. Determine the average shear force
over the 75 mm [3 in.] of displacement. Variations in shear force of more than 25 % of the average value may indicate damaged
or misaligned bearings, an eccentric application of the shear force, or a misaligned box. The equipment must be repaired if the
measured shear force varies by more than 25 % of the average value.
8.3 The maximum shear force recorded is the internal shear correction to be applied to shear force data after the testing of the
specimens. The internal shear correction for device friction should not exceed 10 % of the measured peak strength.
NOTE 12—Calibration of electronic equipment used in this method and calibration for device friction should be performed at least once per year using
traceable reference materials.
9. Conditioning
9.1 For tests on geosynthetics without soil, test specimens at the temperature specified in the standard atmosphere for testing
geosynthetics. Humidity control is normally not required for direct shear testing.
9.2 When soil is included in the test specimen, the method of conditioning is selected by the user or mutually agreed upon by the
user and the testing agency. Material required for the specimen shall be batched by thoroughly mixing soil with sufficient water
to produce the desired water content. Allow the soil to stand prior to compaction in accordance with the following guide:
Classification (by Practice D2487) Minimum Standing Time, h
SW, SP No Requirement
SM 3
SC, ML, CL 18
MH, CH 36
9.2.1 In the absence of specified conditioning criteria, as described in 9.3, the test should be performed at the temperature specified
in the standard atmosphere for testing geosynthetics. Relative humidity control should be performed when specified by the user.
9.3 The minimum user-specified test conditioning criteria include the following:
D5321/D5321M − 21
9.3.1 The test configuration, including all components from the top to the bottom (supporting substrates, soil, geosynthetics, and
gripping surfaces).
9.3.2 Type of clamping, gripping surfaces, or both.
9.3.3 Compaction criteria for soil(s), including dry unit weight, moisture content, and conditions for compacting the soil adjacent
to the geosynthetic material.
9.3.4 Sample conditioning, such as wetting and soaking/hydratio
...