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

Importancia y uso:

4.1 The dimensional, shape, and surface tolerances of rock core test specimens are important for determining rock properties of intact specimens. This is especially true for strong rocks, greater than 7250 psi (50 MPa) and for rock specimens that will be tested in stiff testing load frames without a spherical seat where non-uniform loading could occur. Dimensional and surface tolerance checks are required in the test methods listed in Section 2.1. To simplify test procedures in laboratories, the parts of those procedures that are common to the test methods in Section 2.1 are given in this standard.

4.2 This procedure is applicable to all the standards listed in Section 2.1; however, specimens for Test Method D2936 do not need to be machined or to meet the specified tolerances for flatness and parallelism.

4.3 The moisture condition of the specimen at the time of the sample preparation can have a significant effect upon the strength and deformation characteristics of the rock. Good practice generally dictates that laboratory tests be made upon a specimens’ representative of field conditions. Thus, it follows that the field moisture condition of the specimen should be preserved until the time of the test. In some instances, however, there may be reasons for testing specimens at other moisture contents, from saturation to dry. In any case, the moisture content of the test specimen should be tailored to the problem at hand.

Note 3: Discussions on moisture content are common in many rock testing standards but professional judgement will be needed to both handle and report this issue. For example, when obtaining the samples or preparing the specimens, water or some other cooling agent may be required or used. Therefore, the moisture in the specimen or samples may not be what it was in situ; this applies to both water chemistry and quantity of fluids. This issue should be addressed, and a plan put in place for each step from the sampling to the testing phase in a manner that records/reports what steps were advised to successfully prepare testable samples. Usually a compromise between preserving in-situ conditions, costs, conditions outside the control of the laboratory and obtaining testable specimens is required. For example, loss of moisture that leads to the samples or specimens falling apart may be of greater concern than testing with in situ water or at the in situ water content or both.

4.4 Excess moisture will affect the adhesion of resistance strain gages, if used, and the accuracy of their performance. Adhesives used to bond the rock to steel end caps and fixtures for attaching specimens to actuators and crosshead of the load frame in the direct tension test (D2936) will also be affected adversely by excess moisture.

Note 4: The quality of the result produced by these practices is dependent upon 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 and sampling. Users of these practices are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.

Subcomité:

D18.12

Referida por:

C0170_C0170M-24A, D2936-20, C0170_C0170M-24A, D7070-16, D7012-23, D7012-23

Volúmen:

04.08

Número ICS:

93.020 (Earthworks. Excavations. Foundation construction. Underground works)

Palabras clave:

conformance; core; diameter; dimensional tolerances; dimensions; length; rock; specimen preparation (for testing); specimen shape; specimen size;