ASTM D7608-18e1
(Test Method)Standard Test Method for Torsional Ring Shear Test to Measure Drained Fully Softened Shear Strength and Stress Dependent Strength Envelope of Fine-Grained Soils
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
Relations
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
1
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.
1
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
4
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-
1
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
2
Skempton, A. (1970). “Fir
...
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