5.1 There are many underground structures that are constructed for permanent or long-term use. Often, these structures are subjected to a relatively constant load. Creep tests provide quantitative parameters for stability analysis of these structures.

5.2 The deformation and strength properties of rock cores measured in the laboratory usually do not accurately reflect large-scale in situ properties, because the latter are strongly influenced by joints, faults, inhomogeneities, weakness planes, and other factors. Therefore, laboratory test results of intact specimens shall be utilized with proper judgment in engineering applications.

Note 1: The statements on precision and bias contained in this test method; the precision of this test method is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D3740 does not in itself assure reliable testing. Reliable testing depends on many factors; Practice D3740 provides a means of evaluating some of these factors.

1.1 These test methods cover the creep behavior of intact weak and hard rock core in fixed states of stress at ambient (room) or elevated temperatures. For creep behavior at lower temperatures refer to Test Method D5520. The methods specify the apparatus, instrumentation, and procedures necessary to determine the strain as a function of time under sustained load at constant temperature and when applicable, constant humidity.

1.1.1 Hard rocks are considered those with a maximum axial strain at failure of less than 2 %. Weak rocks include such materials as salt, potash, shale, and weathered rock, which often exhibit very large strain at failure.

1.2 This standard consists of three methods that cover the creep capacity of core specimens.

1.2.1 Method A—Creep of Hard Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature.

1.2.2 Method B—Creep of Weak Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature.

1.2.3 Method C—Creep of Rock Core Specimens in Triaxial Compression at Ambient or Elevated Temperature.

1.3 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.4 The procedures used to specify how data are collected/recorded and calculated in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should be retained. The procedures used do not consider material variation, purpose for obtaining data, special purpose studies, or any considerations for the user’s objectives; and it is common practice to increase or reduce significant digits of reported data to commensurate with these considerations. It is beyond the scope of these test methods to consider significant digits used in analysis methods for engineering design.

1.5 Units—The values stated in SI units are to be regarded as the standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.

1.6 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 to determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see Section 7.