ASTM D7012 : 13

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

Standard Details

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 StandardDetails 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

where:
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 1—Elastic 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.