Standard Test Method for Splitting Tensile Strength of Intact Rock Core Specimens

SCOPE
1.1 This test method covers testing apparatus, specimen preparation, and testing procedures for determining the splitting tensile strength of rock by diametral line compression of a disk.
Note 1—The tensile strength of rock determined by tests other than the straight pull test is designated as the "indirect" tensile strength and, specifically, the value obtained in Section 8 of this test is termed the "splitting" tensile strength.
1.2 The values stated in SI units are to be regarded as the standard.
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.

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Historical
Publication Date
31-Oct-2004
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Drafting Committee
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ASTM D3967-95a(2004) - Standard Test Method for Splitting Tensile Strength of Intact Rock Core Specimens
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D3967–95a (Reapproved 2004)
Standard Test Method for
Splitting Tensile Strength of Intact Rock Core Specimens
This standard is issued under the fixed designation D 3967; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope method is needed for data to be comparable. A uniform test is
also needed to insure positively that the disk specimens break
1.1 This test method covers testing apparatus, specimen
diametrally due to tensile pulling along the loading diameter.
preparation, and testing procedures for determining the split-
ting tensile strength of rock by diametral line compression of a
4. Apparatus
disk.
4.1 Loading Device, to apply and measure axial load on the
NOTE 1—The tensile strength of rock determined by tests other than the
specimen, of sufficient capacity to apply the load at a rate
straight pull test is designated as the “indirect” tensile strength and,
conforming to the requirements in 7.3. It shall be verified at
specifically, the value obtained in Section 8 of this test is termed the
suitable time intervals in accordance with Practices E4 and
“splitting” tensile strength.
shall comply with the requirements prescribed therein.
1.2 The values stated in SI units are to be regarded as the
4.2 Bearing Surfaces—The testing machine shall be
standard.
equipped with two steel bearing blocks having a Rockwell
1.3 This standard does not purport to address all of the
hardness of not less than 58 HRC (see Note 2).
safety concerns, if any, associated with its use. It is the
NOTE 2—False platens, with bearing faces conforming to the require-
responsibility of the user of this standard to establish appro-
ments of this standard, may be used. These shall be oil hardened to more
priate safety and health practices and determine the applica-
than 58 HRC, and surface ground. With abrasive rocks these platens tend
bility of regulatory limitations prior to use.
to roughen after a number of specimens have been tested, and hence need
to be surfaced from time to time.
2. Referenced Documents
4.2.1 Flat Bearing Blocks—During testing the specimen
2.1 ASTM Standards:
can be placed in direct contact with the machine bearing plates
E4 Practices for Force Verification of Testing Machines
(or false platens, if used) (see Fig. 1). The bearing faces shall
E 691–92 Practice for Conducting an Interlaboratory Study
not depart from a plane by more than 0.0125 mm when the
to Determine the Precision of a Test Method
platens are new and shall be maintained within a permissible
variation of 0.025 mm. The bearing block diameter shall be at
3. Significance and Use
least as great as the specimen thickness.
3.1 By definition the tensile strength is obtained by the
4.2.2 Curved Bearing Blocks, may be used to reduce the
direct uniaxial tensile test. But the tensile test is difficult and
contact stresses. The radius of curvature of the supplementary
expensive for routine application. The splitting tensile test
bearingplatesshallbesodesignedthattheirarcofcontactwith
appears to offer a desirable alternative, because it is much
the specimen will in no case exceed 15° or that the width of
simpler and inexpensive. Furthermore, engineers involved in
contact is less than D/6, where D is the diameter of the
rock mechanics design usually deal with complicated stress
specimen.
fields, including various combinations of compressive and
tensile stress fields. Under such conditions, the tensile strength
NOTE 3—Since the equation used in 8.1 for splitting tensile strength is
derived based on a line load, the applied load shall be confined to a very
shouldbeobtainedwiththepresenceofcompressivestressesto
narrow strip if the splitting tensile strength test is to be valid. But a line
be representative of the field conditions. The splitting tensile
load creates extremely high contact stresses which cause premature
strength test is one of the simplest tests in which such stress
cracking. A wider contact strip can reduce the problems significantly.
fields occur. Since it is widely used in practice, a uniform test
Investigationsshowthatanarcofcontactsmallerthan15°causesnomore
than 2 % of error in principal tensile stress while reducing the incidence
of premature cracking greatly.
ThistestmethodisunderthejurisdictionofASTMCommitteeD18onSoiland
Rock and is the direct responsibility of Subcommittee D18.12 on Rock Mechanics. 4.2.3 Spherical Seating—One of the bearing surfaces
Current edition approved Nov. 1, 2004. Published December 2004. Originally
should be spherically seated and the other a plain rigid block.
approved in 1981. Last previous edition approved in 2001 as D 3967 – 95a(2001).
The diameter of the spherical seat shall be at least as large as
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
that of the test specimen, but shall not exceed twice the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standardsvolume 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.
D3967–95a (2004)
can be achieved by visual observations of mineral constituents,
grain sizes and shape, partings, and defects such as pores and
fissures.
6. Test Specimens
6.1 Dimensions—The test specimen shall be a circular disk
with a thickness-to-diameter ratio ( t/D) between 0.2 and 0.75.
The diameter of the specimen shall be at least 10 times greater
thanthelargestmineralgrainconstituent.Adiameterof50mm
(1 ⁄16 in.) (NX wireline core) will generally satisfy this
criterion.
NOTE 5—When cores smaller than the specified minimum must be
tested because of the unavailability of material, notation of the fact shall
be made in the test report.
NOTE 6—If the specimen shows apparent anisotropic features such as
bedding or schistosity, care shall be exercised in preparing the specimen
so that the orientation of the loading diameter relative to anisotropic
features can be determined precisely.
6.2 Number of specimens—At least ten specimens shall be
tested to obtain a meaningful average value. If the reproduc-
ibility of the test results is good (coefficient of variation less
than 5 %), a smaller number of specimens is acceptable.
6.3 The circumferential surface of the specimen shall be
smooth and straight to 0.50 mm (0.020 in.).
6.4 Cut the ends of the specimen parallel to each other and
at right angles to the longitudinal axis. The ends of the
specimen shall not deviate from perpendicular to the core axis
by more than 0.5°. This requirement can be generally met by
cutting the specimen with a precision diamond saw.
FIG. 1 One Proposed Testing Setup for Splitting Tensile Strength
6.5 Determine the diameter of the specimen to the nearest
0.25 mm (0.01 in.) by taking the average of at least three
measurements, one of which shall be along the loading
diameter of the test specimen. The center of the sphere in the
diameter.
spherical seat shall coincide with the center of the loaded side
6.6 Determine the thickness of the specimen to the nearest
ofthespecimen.Thesphericalseatshallbelubricatedtoassure
0.25 mm (0.01 in.) by taking the average of at least three
freemovement.Themovableportionoftheplatenshallbeheld
...

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