ASTM D7012 - 13

    Standard Test Methods for Compressive Strength and Elastic Moduli of Intact Rock Core Specimens under Varying States of Stress and Temperatures

    Active Standard ASTM D7012 | Developed by Subcommittee: D18.12

    Book of Standards Volume: 04.09

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    ASTM D7012

    Significance and Use

    5.1 The parameters obtained from Methods A and B are in terms of undrained total stress (as already mentioned in 1.1). However, there are some cases where either the rock type or the loading condition of the problem under consideration will require the effective stress or drained parameters be determined.

    5.2 Uniaxial compressive strength (Method C) of rock is used in many design formulas and is sometimes used as an index property to select the appropriate excavation technique. Deformation and strength of rock are known to be functions of confining pressure. The triaxial compression test (Method A) is commonly used to simulate the stress conditions under which most underground rock masses exist. The elastic constants (Methods B and D) are used to calculate the stress and deformation in rock structures.

    5.3 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 2Notwithstanding the statements on precision and bias contained in this test method; the measures of precision of these test methods are dependent on the competence of the personnel performing them, and on 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 for evaluating some of those factors.

    1. Scope

    1.1 These test methods cover the determination of the strength of intact rock core specimens in uniaxial and triaxial compression. The tests provide data in determining the strength of rock, namely: the uniaxial strength, shear strengths at different pressures and different elevated temperatures, angle of internal friction, (angle of shearing resistance), and cohesion intercept. The test methods specify the apparatus, instrumentation, and procedures for determining the stress-axial strain and the stress-lateral strain curves, as well as Young's modulus, E, and Poisson's ratio, υ. It should be observed that these methods make no provision for pore pressure measurements and specimens are undrained (platens are not vented). Thus the strength values determined are in terms of total stress, that is, are not corrected for pore pressures. These test methods do not include the procedures necessary to obtain a stress-strain curve beyond the ultimate strength.

    1.2 This standard replaces and combines the following Standard Test Methods: D2664 Triaxial Compressive Strength of Undrained Rock Core Specimens Without Pore Pressure Measurements; D5407 Elastic Moduli of Undrained Rock Core Specimens in Triaxial Compression Without Pore Pressure Measurements; D2938 Unconfined Compressive Strength of Intact Rock Core Specimens; and D3148 Elastic Moduli of Intact Rock Core Specimens in Uniaxial Compression. The original four standards are now referred to as Methods in this standard.

    1.2.1 Method A: Triaxial Compressive Strength of Undrained Rock Core Specimens Without Pore Pressure Measurements.

    1.2.2 Method B: Elastic Moduli of Undrained Rock Core Specimens in Triaxial Compression Without Pore Pressure Measurements.

    1.2.3 Method C: Uniaxial Compressive Strength of Intact Rock Core Specimens.

    1.2.4 Method D: Elastic Moduli of Intact Rock Core Specimens in Uniaxial Compression.

    1.2.5 Option A: Elevated Temperatures.

    1.3 For an isotropic material in Test Methods B and D, the relation between the shear and bulk moduli and Young's modulus and Poisson's ratio are:

    Equation D7012-13_1

    Equation D7012-13_2

    G   =   shear modulus,
    K   =   bulk modulus,
    E   =   Young's modulus, and
    υ   =   Poisson's ratio.

    1.3.1 The engineering applicability of these equations decreases with increasing anisotropy of the rock. It is desirable to conduct tests in the plane of foliation, cleavage or bedding and at right angles to it to determine the degree of anisotropy. It is noted that equations developed for isotropic materials may give only approximate calculated results if the difference in elastic moduli in two orthogonal directions is greater than 10 % for a given stress level.

    Note 1Elastic moduli measured by sonic methods (Test Method D2845) may often be employed as a preliminary measure of anisotropy.

    1.4 Test Methods B and D for determining the elastic constants do not apply to rocks that undergo significant inelastic strains during the test, such as potash and salt. The elastic moduli for such rocks should be determined from unload-reload cycles, that are not covered by this test method.

    1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

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

    1.7 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.

    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D653 Terminology Relating to Soil, Rock, and Contained Fluids

    D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass

    D2845 Test Method for Laboratory Determination of Pulse Velocities and Ultrasonic Elastic Constants of Rock

    D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction

    D4543 Practices for Preparing Rock Core as Cylindrical Test Specimens and Verifying Conformance to Dimensional and Shape Tolerances

    D6026 Practice for Using Significant Digits in Geotechnical Data

    E4 Practices for Force Verification of Testing Machines

    E122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process

    ASTM Adjunct


    ICS Code

    ICS Number Code 13.080.20 (Physical properties of soil)

    UNSPSC Code

    UNSPSC Code

    DOI: 10.1520/D7012

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    ASTM D7012

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