Rock-Breaking Characteristics and Specific Energy Evolution of High-Prestressed Granite During Rock Drilling Using MATDEM Simulation

To investigate the working state of hydraulic rock drills in deep rock mass mining and to improve their working efficiency, this paper uses the MATDEM 1.75 discrete element software to carry out numerical simulation experiments on highly pre-stressed rock under different impact frequencies and impact energies, and conducts a preliminary analysis of crack generation, energy variation, rock-breaking speed, and the specific energy of rock breaking during the fragmentation process. The results show that the number of cracks exhibits a stepwise increasing trend over time, and the bit displacement is basically consistent with the generation trends of the various types of cracks. Both the elastic potential energy of the overall cemented bonds and that of the uncemented bonds gradually decrease with the impact process, whereas the elastic potential energy stored per cemented bond gradually increases with the impact process. Both the impact energy and the impact frequency affect the rock-breaking speed: a greater impact energy results in a faster rock-breaking speed, exhibiting a con-cave-shaped (nonlinear) relationship, while a higher impact frequency results in a faster rock-breaking speed, though the growth in the latter half is not pronounced, exhibiting a convex-shaped (nonlinear) relationship. Neither the impact energy nor the impact frequency has a monotonic relationship with the specific energy of rock breaking; both relationships appear as V-shaped (piecewise linear) trends. In other words, under a given set of working conditions there exists an optimal impact energy and impact frequency at which the hydraulic rock drill consumes the least energy to break a unit volume of rock. The rock fragmentation rate is also sensitive to these two parameters. Within the tested range, the specific energy reaches its minimum near 300 J and 50 Hz, providing a preferred operating condition for balancing energy consumption and breaking efficiency.