Calibrating a New Compressive-to-Tensile Load-Transferring Device for Determining the Direct Tensile Strength of Granite

The direct tensile strength of hard rocks such as granite was measured using hollow disk-type specimens in the form of rock rings. These specimens were placed in a novel apparatus that transferred the compressive load to the tensile load during the direct tensile test. Before performing the laboratory tests on the actual geomaterial specimens, the numerical modeling of the hollow disk specimens of granite (with five different hole diameters) was accomplished in the two-dimensional particle flow code (PFC2D). It was found that the best tensile loading condition is for the case of 15-cm-diameter specimens. Therefore, the experimental tests for the direct tensile testing apparatus using the compressive-to-tensile load-transferring (CTLT) device were carried out on the granite specimens with 15 cm holes. The indirect Brazilian tensile strength of granite was also measured in the laboratory to calibrate the numerical code and compare the indirect and direct values of the tensile strengths of the geomaterials. The indirect and direct tensile strength tests were simulated with PFC2D. The measured tensile strength values of the granite hollow disk specimens were compared with the corresponding numerical results. The numerical code was calibrated by adjusting the proper microparameters for the rock specimens. Additionally, the direct and indirect tensile testing results were compared, and a good correlation was made. These results showed that the direct tensile strength of granite obtained by the CTLT device is lower than that of the indirect one obtained from the Brazilian disk approach.