Drillability of Granitic Rocks After Thermal Loading

Abstract

Balmoral Red granite and Kuru Grey granite were exposed to heat shock using a stationary flame torch and a moving plasma gun. The effect of the heat shock on the drillability was quantified using the Sievers J-miniature drill test. The samples were also investigated using X-ray micro-computed tomography and scanning electron microscopy. The flame torch created mainly surface porosity in the Kuru Grey granite, but the drillability did not increase. A larger number of cracks were found in the flame torched Balmoral Red granite, and here the drillability increased significantly where the heat input was greatest. The plasma gun caused spallation of the surface in both granite types, and an increase in drillability in a damage layer 100-200 µm thick.