Abstract: Rock hardness is an important indicator reflecting the relative hardness, drillability, and blastability of rock formation. Accurate interpretation of the response of percussion drilling tools can provide new possibilities for in-situ, rapid, and quantitative evaluation of rock hardness. High-precision digital displacement, hydraulic pressure, and rotational speed sensors were used to monitor the key transmission parts of the percussion drill, and a digital monitoring system for the drilling process was then established. Rock hardness measurement and orthogonal tests of percussion drilling were parallelly carried out, and a standard database containing response data of the drill when drilling various types of rocks was established. Functional relationships between propelling pressure, percussion pressure, rotational speed, and impact energy dissipation were developed, and a novel method to quantitatively evaluate rock hardness based on impact energy dissipation index was proposed. The performed tests and analyses revealed that there is an inverse linear relationship between the propelling pressure and impact energy dissipation. The fitting curve of percussion pressure and drilling energy dissipation is an open upward parabola, and the curves for various rocks have the same symmetry axis but different curvature radii. The influence of rotational speed of drill rod on drilling energy dissipation is negligible. By dimensionless treatment of drilling energy dissipation per unit volume, the influence of mechanical parameters of percussion drilling is removed, and the impact energy dissipation index , which has low discreteness and a good correlation with rock hardness, was defined to characterize the rock hardness. The response data of the drilling process in conventional boreholes were obtained and interpreted by the digital sensing technology, and the obtained data were used to determine the rock hardness without additional survey or test, which puts forward a new way for direct evaluation of rock mass parameters on engineering sites.

Key words: rock hardness, percussion drill, impact energy dissipation index, propelling pressure, percussion pressure, rotational speed of drill rod