ASTM D7070-08

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

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 values for intact specimens must be employed with proper judgment in engineering applications.

Note 1—Notwithstanding 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 D 3740 are generally considered capable of competent and objective testing. Users of this test method are cautioned that compliance with Practice D 3740 does not in itself assure reliable testing. Reliable testing depends on many factors; Practice D 3740 provides a means of evaluating some of these factors.

1.1 These test methods cover the creep behavior of intact soft and hard rock core in fixed states of stress and temperature. They specify the apparatus, instrumentation, and procedures for determining the strain as a function of time under sustained load. Hard rocks are those with a maximum axial strain at failure of less than 2 %. Soft rocks include such materials as salt and potash, which often exhibit very large strain at failure.

1.2 This standard replaces and combines the following Standard Test Methods now to be referred to as Methods:

Method ‘A’ (D 5341 Creep of Hard Rock Core Specimens in Uniaxial Compression at Ambient/Elevated Temperatures);

Method ‘B’ (D 4405 Creep of Soft Rock Core Specimens in Uniaxial Compression at Ambient or Elevated Temperature); and

Method ‘C’ (D 4406 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 D 6026.

1.3.1 The method used to specify how data are collected, calculated, or recorded in this standard is not directly related to the accuracy to which the data can be applied in design or other uses, or both. How one applies the results obtained using this standard is beyond its scope.

1.4 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.

1.5 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 and health practices and to determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see Section 7.