ASTM D7608-18e1

Standard Test Method for Torsional Ring Shear Test to Measure Drained Fully Softened Shear Strength and Stress Dependent Strength Envelope of Fine-Grained Soils

SIGNIFICANCE AND USE
5.1 The ring shear apparatus maintains the cross-sectional area of the shear surface constant during shear and shears the specimen continuously in one rotational direction for any magnitude of shear displacement and along the entire specimen cross-sectional area.  
5.2 The ring shear apparatus allows a reconstituted specimen to be consolidated at the desired normal stress prior to drained shearing. This simulates the field conditions under which complete softening develops in overconsolidated clays, claystones, mudstones, and shales that do not have a pre-existing shear surface, sheared bedding planes, joints, or faults as described by Skempton (19702 and 19773) and unfailed compacted fill slopes (Gamez and Stark 20144) because the fully softened strength corresponds to the peak shear strength of a normally consolidated fine-grained soil. The fully softened strength is only applicable to the soil zones that are subject to the environmental deterioration and applied shear stresses that lead to soil softening, deterioration of soil fabric, and strength loss, which may not be relevant to all slopes and all depths. The fully softened strength should be used in an effective stress/drained stability analysis using a stress dependent strength envelope for slopes with no prior shearing.  
5.3 The ring shear test is suited to the determination of the drained fully softened shear strength because of the short drainage path through the thin specimen, small post-peak strength loss in a normally consolidated specimen, and the constant cross-sectional area.  
5.4 The ring shear test specimen is annular so the angular displacement differs from the inner radius to the outer radius. This is not significant because a normally consolidated specimen does not exhibit a large post-peak strength loss so the difference in peak shear resistance at the inner radius and outer radius at different displacements is not significant and the ratio of the inner to outer radii of the ring is great...
SCOPE
1.1 This test method provides a procedure for performing a torsional ring shear test under a drained condition to measure the fully softened shear strength and stress dependent strength envelope of fine-grained soils (using a reconstituted normally consolidated specimen). The fully softened strength and the corresponding stress dependent effective stress strength envelope are used to evaluate the stability of slopes that do not have a pre-existing shear surface but have been subjected to environmental conditions and shear stresses that lead to soil softening, deterioration of the soil fabric, and strength loss. It has been shown (Skempton 19702 and 19773) that under these conditions and within the depth zones that have undergone softening, first-time slope failures can occur at effective stress levels that correspond to a fully softened strength envelope. It has also been shown empirically (Skempton 19702 and 19773) that fully softened strength of fine grained soils can be approximated by the peak strength of a reconstituted and normally consolidated specimen. In this test method, reconstituted and normally consolidated specimens are sheared at a controlled and constant displacement rate until the peak shear resistance has been obtained. Generally, the drained fully softened failure envelope is determined at three or more effective normal stresses. A separate test specimen must be used for each normal stress to measure the fully softened strength otherwise a post-peak or even drained residual strength will be measured if the same specimen is used at the same or at another effective normal stress because of the existence of a prior shear surface.  
1.2 The ring shear apparatus allows a reconstituted specimen to be normally consolidated at the desired normal stress prior to drained shearing. The test results closely simulate the fully softened strength of stiff natural fine-grained soils (Skempton 19702 and 19773) and com...

General Information

• Status: Published
• Publication Date: 31-May-2018
• ICS: 13.080.20 - Physical properties of soils
• Technical Committee: D18 - Soil and Rock
• Drafting Committee: D18.05 - Strength and Compressibility of Soils

Relations

• Refers: ASTM D3740-23 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Nov-2023
• Refers: ASTM D854-23 - Standard Test Methods for Specific Gravity of Soil Solids by the Water Displacement Method
• Effective Date: 01-Nov-2023
• Refers: ASTM D2974-20 - Standard Test Methods for Determining the Water (Moisture) Content, Ash Content, and Organic Material of Peat and Other Organic Soils
• Effective Date: 15-Jan-2020
• Refers: ASTM D2974-20e1 - Standard Test Methods for Determining the Water (Moisture) Content, Ash Content, and Organic Material of Peat and Other Organic Soils
• Effective Date: 15-Jan-2020
• Refers: ASTM D3740-19 - Standard Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction
• Effective Date: 01-Oct-2019
• Refers: ASTM D2216-19 - Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass
• Effective Date: 01-Mar-2019
• Refers: ASTM D2487-17 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2487-17e1 - Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)
• Effective Date: 15-Dec-2017
• Refers: ASTM D2488-17 - Standard Practice for Description and Identification of Soils (Visual-Manual Procedures)
• Effective Date: 15-Jul-2017
• Refers: ASTM D4318-17e1 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D4318-17 - Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils
• Effective Date: 01-Jun-2017
• Refers: ASTM D7928-16 - Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
• Effective Date: 01-May-2016
• Refers: ASTM D7928-16e1 - Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis
• Effective Date: 01-May-2016
• Refers: ASTM D2974-14 - Standard Test Methods for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils
• Effective Date: 01-Nov-2014
• Refers: ASTM D653-14 - Standard Terminology Relating to Soil, Rock, and Contained Fluids
• Effective Date: 01-Aug-2014

Overview

ASTM D7608-18e1 defines a standardized test method for conducting torsional ring shear tests to measure the drained, fully softened shear strength and stress dependent strength envelope of fine-grained soils. Developed by ASTM International, this procedure is essential in geotechnical engineering, particularly for slope stability analysis of natural and manmade earth structures, such as embankments and levees, where fine-grained soils are prone to softening and strength loss due to environmental exposure and loading. The standard details the apparatus, specimen preparation, test process, data interpretation, and relevant reporting requirements, ensuring reliable results for use in engineering design and risk assessment.

Key Topics

• Torsional Ring Shear Test Method
  The method utilizes a ring shear apparatus that maintains a constant cross-sectional area during testing. It rotates the soil specimen continuously in one direction under controlled normal stress and drainage conditions, simulating realistic field scenarios for slope failures in softened soils.

• Fully Softened Shear Strength
  This term refers to the maximum shear resistance of a normally consolidated, reconstituted specimen before strength starts to decrease, providing a crucial parameter for evaluating the stability of first-time slope failures in overconsolidated and natural fine-grained soils.

• Stress Dependent Strength Envelope
  The procedure generates a shear strength envelope that shows how the fully softened strength varies with applied effective normal stress. The envelope is used in effective stress/drained stability analyses of slopes without existing shear surfaces.

• Specimen Preparation and Test Conditions
  The test requires reconstituted, normally consolidated fine-grained soil specimens. Careful preparation ensures the soil matches field conditions, including rehydration and consolidation at target normal stresses, which is essential for meaningful results.

• Reporting and Data Interpretation
  The standard provides guidance on data precision, specimen identification, soil properties, device details, and graphical representation of results, underpinning traceability, accuracy, and engineering application.

Applications

• Slope Stability Analysis
  ASTM D7608-18e1 is primarily used to assess the drained, fully softened shear strength required for effective stress analyses of earth slopes, embankments, levees, and dams constructed with or on fine-grained soils.

• Design of Earth Structures
  The results directly inform the design and safety evaluation of new earth structures or the assessment of existing slopes where environmental action may lead to soil softening but no prior failure or shearing has occurred.

• Geotechnical Risk Assessment
  Engineers use the fully softened strength values and stress envelopes obtained from this method for risk analysis of potential slope failures, especially in soil zones affected by environmental degradation, construction activities, or changes in groundwater conditions.

• Material Characterization
  The procedure supports the classification and comparison of fine-grained soils, particularly when studying the effects of soil composition, compaction, and environmental history on shear strength.

Related Standards

• ASTM D653 - Terminology relating to soil, rock, and contained fluids
• ASTM D2216 - Laboratory determination of water (moisture) content of soil and rock
• ASTM D2435 - One-dimensional consolidation properties of soils
• ASTM D2487 / D2488 - Soil classification and identification for engineering purposes
• ASTM D2974 - Determining water, ash, and organic content of soils
• ASTM D4318 - Atterberg limits and plasticity index of soils
• ASTM D6467 - Torsional ring shear test for drained residual shear strength
• ASTM D7928 - Particle-size distribution (hydrometer analysis) of fine-grained soils

These standards ensure consistency in terminology, sample preparation, companion test methods, and the broader geotechnical investigation process, enhancing the value and applicability of ASTM D7608-18e1 in engineering practice.

Keywords: ASTM D7608-18e1, torsional ring shear test, fully softened shear strength, fine-grained soils, drained strength, stress envelope, slope stability, geotechnical engineering, soil testing, earth embankment design.

Standards Content (Sample)

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.
´1
Designation: D7608 − 18
Standard Test Method for
Torsional Ring Shear Test to Measure Drained Fully
Softened Shear Strength and Stress Dependent Strength
Envelope of Fine-Grained Soils
This standard is issued under the fixed designation D7608; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The standard was editorially updated in January 2022.
1. Scope 1.2 The ring shear apparatus allows a reconstituted speci-
men to be normally consolidated at the desired normal stress
1.1 This test method provides a procedure for performing a
prior to drained shearing. The test results closely simulate the
torsional ring shear test under a drained condition to measure
fully softened strength of stiff natural fine-grained soils
the fully softened shear strength and stress dependent strength
2 3
(Skempton 1970 and 1977 ) and compacted fills of fine-
envelope of fine-grained soils (using a reconstituted normally
grained soils (Gamez and Stark 2014 ). This simulates the
consolidated specimen). The fully softened strength and the
mobilized shear strength in overconsolidated clays, claystones,
corresponding stress dependent effective stress strength enve-
mudstones, and shales in natural slopes and compacted fill in
lopeareusedtoevaluatethestabilityofslopesthatdonothave
manmade slopes, such as, dams, levees, and highway
a pre-existing shear surface but have been subjected to envi-
embankments, after the soil has fully softened and attained the
ronmental conditions and shear stresses that lead to soil
fully softened strength condition.
softening, deterioration of the soil fabric, and strength loss. It
2 3
has been shown (Skempton 1970 and 1977 ) that under these 1.3 A shear stress-displacement relationship may be ob-
conditions and within the depth zones that have undergone tained from this test method. However, a shear stress-strain
softening, first-time slope failures can occur at effective stress relationship or any associated quantity, such as modulus,
cannot be determined from this test method because defining
levels that correspond to a fully softened strength envelope. It
2 3
has also been shown empirically (Skempton 1970 and 1977 ) the height of the shear zone is difficult and needed in the shear
strain calculations.As a result, the height of this shear zone is
that fully softened strength of fine grained soils can be
approximated by the peak strength of a reconstituted and unknown, so an accurate or representative shear strain can
normally consolidated specimen. In this test method, reconsti- therefore not be determined.
tuted and normally consolidated specimens are sheared at a
1.4 The selection of normal stresses and final determination
controlled and constant displacement rate until the peak shear
of the shear strength envelope for design analyses and the
resistance has been obtained. Generally, the drained fully
criteria to interpret and evaluate the test results are the
softened failure envelope is determined at three or more
responsibility of the engineer or entity requesting the test.
effective normal stresses. A separate test specimen must be
1.5 Units—The values stated in SI units are to be regarded
used for each normal stress to measure the fully softened
asthestandard.Thevaluesgiveninparenthesesaremathemati-
strength otherwise a post-peak or even drained residual
cal conversions to inch-pound units that are provided for
strength will be measured if the same specimen is used at the
information only and are not considered standard.
same or at another effective normal stress because of the
1.6 This standard does not purport to address all of the
existence of a prior shear surface.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
priate safety, health, and environmental practices and deter-
Rock and is the direct responsibility of Subcommittee D18.05 on Strength and
mine the applicability of regulatory limitations prior to use.
Compressibility of Soils.
1.7 This international standard was developed in accor-
CurrenteditionapprovedJune1,2018.PublishedJuly2018.Originallyapproved
in 2010. Last previous edition approved in 2010 as D7263–10. DOI: 10.1520/
dance with internationally recognized principles on standard-
D7608–18E01.
ization established in the Decision on Principles for the
Skempton, A. (1970). “First-time slides in over-consolidated clays.”
Géotechnique, 20(3), 320–324.
Skempton,A. (1977). “Slope stability of cutting in brown London clay.” Proc. Gamez, J. and Stark, T.D. (2014). “Fully Softened Shear Strength at Low
9th Int. Conf. on Soil Mechanics and Foundation Engineering, Society of Soil Stresses for Levee and Embankment Design” ASCE Journal of Geotechnical and
Mechanics and Foundation Engineering, Tokyo, 261–270. Geoenvironmental Engineering, June, 140(9), 06014010-1-06014010-6.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
´1
D7608 − 18
Development of International Standards, Guides and Recom- 4. Summary of Test Method
mendations issued by the World Trade Organization Technical
4.1 This test method consists of placing the soft reconsti-
Barriers to Trade (TBT) Committee.
tuted specimen (paste) in the annular specimen container of a
ring shear device, applying a predetermined normal stress
2. Referenced Documents
through the top loading platen, providing for wetting and
2.1 ASTM Standards:
drainageofthespecimen;consolidatingthespecimenunderthe
D653Terminology Relating to Soil, Rock, and Contained
applied normal stress; applying a constant rate of shear
Fluids
deformation for fully drained condition; and measuring the
D854Test Methods for Specific Gravity of Soil Solids by
shearing force and angular shear displacement until a maxi-
Water Pycnometer
mum shear resistance is reached.
D2216Test Methods for Laboratory Determination ofWater
5. Significance and Use
(Moisture) Content of Soil and Rock by Mass
D2435Test Methods for One-Dimensional Consolidation
5.1 The ring shear apparatus maintains the cross-sectional
Properties of Soils Using Incremental Loading
area of the shear surface constant during shear and shears the
D2487Practice for Classification of Soils for Engineering
specimen continuously in one rotational direction for any
Purposes (Unified Soil Classification System)
magnitudeofsheardisplacementandalongtheentirespecimen
D2488Practice for Description and Identification of Soils
cross-sectional area.
(Visual-Manual Procedures)
5.2 The ring shear apparatus allows a reconstituted speci-
D2974Test Methods for Determining the Water (Moisture)
men to be consolidated at the desired normal stress prior to
Content, Ash Content, and Organic Material of Peat and
drained shearing. This simulates the field conditions under
Other Organic Soils
which complete softening develops in overconsolidated clays,
D3740Practice for Minimum Requirements for Agencies
claystones, mudstones, and shales that do not have a pre-
Engaged in Testing and/or Inspection of Soil and Rock as
existing shear surface, sheared bedding planes, joints, or faults
Used in Engineering Design and Construction
2 3
as described by Skempton (1970 and 1977 ) and unfailed
D4318Test Methods for Liquid Limit, Plastic Limit, and
compacted fill slopes (Gamez and Stark 2014 ) because the
Plasticity Index of Soils
fully softened strength corresponds to the peak shear strength
D6026Practice for Using Significant Digits and Data Re-
ofanormallyconsolidatedfine-grainedsoil.Thefullysoftened
cords in Geotechnical Data
strength is only applicable to the soil zones that are subject to
D6467Test Method for Torsional Ring Shear Test to Deter-
the environmental deterioration and applied shear stresses that
mine Drained Residual Shear Strength of Fine-Grained
lead to soil softening, deterioration of soil fabric, and strength
Soils
loss,whichmaynotberelevanttoallslopesandalldepths.The
D6913Test Methods for Particle-Size Distribution (Grada-
fully softened strength should be used in an effective stress/
tion) of Soils Using Sieve Analysis
drained stability analysis using a stress dependent strength
D7928Test Method for Particle-Size Distribution (Grada-
envelope for slopes with no prior shearing.
tion) of Fine-Grained Soils Using the Sedimentation
5.3 The ring shear test is suited to the determination of the
(Hydrometer) Analysis
drained fully softened shear strength because of the short
E11Specification forWovenWireTest Sieve Cloth andTest
drainage path through the thin specimen, small post-peak
Sieves
strength loss in a normally consolidated specimen, and the
constant cross-sectional area.
3. Terminology
5.4 The ring shear test specimen is annular so the angular
3.1 Definitions—For definitions of technical terms used in
displacement differs from the inner radius to the outer radius.
this test method, refer to Terminology D653.
This is not significant because a normally consolidated speci-
3.2 Definitions of Terms Specific to This Standard:
men does not exhibit a large post-peak strength loss so the
3.2.1 consolidated—soil specimen condition after primary
difference in peak shear resistance at the inner radius and outer
consolidation under a specific normal stress.
radius at different displacements is not significant and the ratio
3.2.2 fully softened shear force—the shear force being
of the inner to outer radii of the ring is greater than 0.5 in
applied to the specimen when the shear resistance begins to
accordance with Hvorslev (1936) .
decrease with continued shear displacement.
NOTE 1—Notwithstanding the statements on precision and bias con-
3.2.3 fully softened shear strength—the maximum shear
tained in this test method: The precision of this test method is dependent
resistanceofnormallyconsolidatedandnotpreshearedsoiland
onthecompetenceofthepersonnelperformingitandthesuitabilityofthe
equals the fully softened shear force divided by the cross- equipment and facilities used. Agencies that meet the criteria of Practice
D3740 are generally considered capable of competent testing. Users of
sectional area of the annular specimen.
this test method are cautioned that compliance with Practice D3740 does
not ensure reliable testing. Reliable testing depends on several factors;
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Hvorslev, M. J. (1936). “A ring shear apparatus for the determination of the
Standards volume information, refer to the standard’s Document Summary page on shearing resistance and plastic flow of soils.” Proceedings of the 1st International
the ASTM website. Conference on Soil Mechanics and Foundation Engineering, 2, 125–129.
´1
D7608 − 18
Practice D3740 provides a means of evaluating some of those factors.
penetrate into the specimen. The hydraulic conductivity of the
discs shall be substantially greater than that of the soil, but
6. Apparatus
shall be textured fine enough to prevent excessive intrusion of
6.1 Shear Device, to hold the specimen securely between
the soil into the pores of the porous disc. The outer and inner
two porous discs. The shear device shall provide a means for
diameters of the discs shall be 0.1 mm (0.004 in.) less, and
applying a normal stress to the faces of the specimen, for
greater than those of the specimen annular cavity, respectively.
measuringchangesinthicknessofthespecimen,forpermitting
The serration should have a depth of between 10 and 15% of
drainage of water through the porous discs at the top and
the specimen height before shearing.
bottom boundaries of the specimen, and for submerging the
NOTE 2—Exact criteria for porous disc texture and hydraulic conduc-
specimen in water. The device shall be capable of applying a
tivity have not been established. For normal soil testing, medium-grade
torque to the specimen along a shear surface parallel to the –4 –3
discs with a hydraulic conductivity of about 5.0 × 10 to 1.0 × 10 cm/s
facesofthespecimen.Anumberofdifferentringsheardevices
(0.5 to 1.0 × 10 ft/year) are appropriate for testing fine-grained soils.
are commercially available, in practice, or are being developed
6.5 Loading Devices:
so a general description of a ring shear device is presented
6.5.1 Device for Applying and Measuring the Normal
without schematic diagrams. The location of the shear surface
Force—The device shall be capable of rapidly applying and
depends on the configuration of the apparatus.As a result, the
maintaining the normal force to within 61% of the specified
shear surface may be located near a soil/porous disc interface
force.
or at the mid-height of the specimen if an upper ring can be
6.5.2 Device for Shearing the Specimen—This device shall
separated from a bottom ring as is done in a direct shear box.
be capable of shearing the specimen at a uniform rate of
The device shall have low friction along the inner and outer
displacement, without differences in shear displacement rate
walls of the specimen container during shearing. Friction may
due to friction. The rate to be applied depends upon the
be reduced by having the shear surface occur at the top of the
consolidation characteristics of the soil (see 8.5.1). The rate is
specimen container, modifying the specimen container walls
usually maintained with an electric motor and gear box
with low-friction material, or exposing the shear surface by
arrangement.
separating the top and bottom portions of the specimen
container. The frames that hold the specimen shall be suffi-
6.6 Shear Force Measurement Device, two proving rings,
ciently rigid to prevent their distortion during shearing. The
load cells, or a force or torque transducer with a readability/
various parts of the shear device shall be made of a material
sensitivity of 0.1 N-m (0.03 lbf-ft).
such as stainless steel, bronze, or coated aluminum that is not
6.7 Water Bath, container for the specimen container and
subject to corrosion by moisture or substances within the soil.
water needed to inundate the specimen.
Dissimilar metals, which may cause galvanic action, are not
6.8 Controlled High-Humidity Room—If required, for pre-
permitted.
paring the specimen, such that the water content gain or loss
6.2 Specimen Container—A device containing an annular
during specimen rehydration is minimized.
cavity for the soil specimen with an inside diameter not less
than 50 mm (2 in.) and an inside to outside diameter ratio not 6.9 Vertical Deformation Indicators, dial gauge, or other
suitable device, capable of measuring the change in thickness
lessthan0.5.Thecontainerhasprovisionsfordrainagethrough
the top and bottom. The initial specimen depth, before con- of the specimen, with a sensitivity of at least 0.0025 mm
(0.0001 in.).
solidationandpreshearing,isnotlessthan5mm(0.2in.)when
shearing occurs at the top soil/porous disc interface. The
6.10 Horizontal Deformation Indicator—Ring shear device
maximum particle size is limited to 10% of the initial
havinggaugeoretchedscaleoncircumferenceoftheringbase
specimen height as stated in the test specimen description.
to measure the degrees traveled, and thus the shear
6.3 Torque Arm/Loading Platen Assembly, may have differ- displacement, or other methods capable of obtaining a sensi-
ent bearing stops for the proving rings, load cells, or force or tivity of at least 1.0 mm or 1.5°.
torque transducers to provide different options for the torque
6.11 Equipment for Determination of Water Content, in
measurement.
accordance in Test Method D2216.
6.4 Porous Discs—Two bronze or stainless steel porous
6.12 Miscellaneous Equipment,includingtimingdevicethat
discs mounted on the top loading platen and the bottom of the
canbereadtoseconds,site-specific,distilled,ordemineralized
specimen container cavity to allow drainage from the soil
water, mortar, pestle, spatulas, spatula, razor blades,
specimen along the top and bottom boundaries. The discs
straightedge, data sheet or acquisition system to monitor the
should have good contact between the porous disc and
...