Assessment of Direct Tensile Strength Tests in Rock Through a Multi-laboratory Benchmark Experiment

• Published in: Rock mechanics and rock engineering 2024-05, Vol.57 (5), p.3617-3634
• Main Authors: Pérez-Rey, Ignacio, Muñiz-Menéndez, Mauro, Frühwirt, Thomas, Konietzky, Heinz, Jacobsson, Lars, Perras, Matthew A., Atefi-Monfared, Kamelia, Mas Ivars, Diego, Sánchez Juncal, Abel, Alejano, Leandro R.
• Format: Article
• Language: English
• Subjects: Benchmark; Civil Engineering; Deformability; Deformation; Direct tensile strength; Earth and Environmental Science; Earth Sciences; Formability; Geophysics/Geodesy; Granite; Laboratories; Loading rate; Measuring instruments; Methodology; Original Paper; Poisson's ratio; Repeatability; Reproducibility; Rock mechanics; Rocks; Sandstone; Sedimentary rocks; Sensitivity analysis; Stone; Strain measurement; Tensile strength; Test equipment
• ISSN: 0723-2632; 1434-453X; 1434-453X
• DOI: 10.1007/s00603-023-03751-z

This study aims to experimentally assess repeatability and reproducibility of direct tensile strength (DTS) tests with deformability measurements on two types of rocks: Blanco Mera granite (Spain) and Cotta sandstone (Germany). The tests were conducted in four rock mechanics laboratories located in different countries (Canada, Germany, Spain and Sweden). A total of 51 tests were performed on cylindrical specimens of the two rocks, using different test equipment and measuring devices. Mean and standard deviation DTS values were determined in the four laboratories for the granite (5.70 ± 0.32, 6.06 ± 0.11, 3.84 ± 0.50 and 6.76 ± 0.10 MPa) and for the sandstone (1.88 ± 0.07, 1.96 ± 0.06, 1.15 ± 0.32 and 1.74 ± 0.19 MPa), together with Young’s moduli and Poisson’s ratios in tension, being statistically analysed to evaluate the variability and compare the main results obtained from the participating laboratories. The findings indicate that the DTS test with deformability measurements on cylindrical rock specimens is operationally feasible. However, certain shortcomings have been identified during the course of the experiments with the existing methodologies, such as the one suggested by the ISRM for DTS tests. The results have also shown to be sensitive to appropriate test and strain measurement configurations. The objective of this study was to shed light on these issues and provide new insights for potential future improvements of the existing testing methods. Highlights An experimental assessment of reproducibility and repeatability of direct tensile strength tests was carried out. Tests were conducted on two rocks (granite, sandstone), in four laboratories located in Canada, Germany, Spain and Sweden. Direct tensile strength test with deformability measurements on cylindrical rock specimens was found operationally feasible. Some shortcomings in current methodologies have been found, such as inappropriate loading rates or no recommendations for deformability measurements. This work provides new insights for potential future improvements of the existing testing methods.