The drillability assessment of rocks using the different brittleness values

The brittleness is a fundamental rock property and effective in drilling and rock excavation. Knowing the relations between the drillability and the brittleness will help the rock engineers. For this reason, to investigate the relations between the drilling rate index (DRI) and the different brittleness values, 32 different rock types were tested in the laboratory. Uniaxial compressive strength and tensile strength were determined for the brittleness calculations. The brittleness of B3 (the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength), and the brittleness of B8 (the half of the product of compressive strength and tensile strength) were calculated from the test results. In addition, Sievers’ J-miniature drill test and the brittleness test were carried out and DRI values were calculated. Then, B3 and B8were correlated with DRI values. A good correlation between DRI and the brittleness of B3 could not be found. However, a strong exponential relation between DRI and the brittleness of B8 was found. Comparing the results with the literature showed that there was an agreement between this study and previous studies. It can be concluded that B8 can be used for the assessment of rock drillability.

Research highlights
► The relations between the two brittleness values (B3, B8) and the drilling rate index were analyzed.
► A strong exponential relation between the DRI and the brittleness of B8 was found.
► The brittleness B8 can be used for the assessment of rock drillability.