ASTM D2936-20 PDF Download

The ASTM D2936-20 standard is titled "Standard Test Method for Direct Tensile Strength of Intact Rock Core Specimens." This test method is used to determine the tensile strength of rock by subjecting cylindrical rock specimens to direct tensile stress.

It is noted that rock is weaker in tension than in compression, so it is important to determine the tensile strength of rock when assessing the failure condition of a rock structure. Direct tensile testing involves applying stress to the specimen along its longitudinal axis. However, it should be recognized that the test may break at the weakest link, whether it is the rock substance itself or any discontinuity within the rock. Unless the purpose of the test is to assess the strength across discontinuities, the results are considered conservative and more representative of the tensile strength at the rock substance scale.

The standard specifies that the test is applicable to intact, isotropic cylindrical rock specimens at room temperature. Non-isotropic or transversely isotropic specimens are not covered. The specimens can be drill cores obtained from the field or rock blocks transported to the laboratory and then drilled into cylindrical shape. Other specimen shapes, such as dog bone-shaped, are not included in this standard.

The test specimens may be tested under constant load or deformation rate, providing flexibility in the testing approach. The standard also provides guidelines for significant digits and rounding of the observed and calculated values, referring to Practice D6026, unless superseded by this standard.