Abstract
Percussive-rotary drilling is widely used for excavation in hard rock massifs, yet it suffers from high energy consumption and low efficiency. This study presents a comprehensive assessment of energy consumption in percussive-rotary drilling based on specific fracture energy as the key metric. Laboratory experiments were conducted on granite, basalt, and quartzite using a controlled percussive-rotary drilling rig, with systematic variation of impact energy, rotary speed, and thrust force. Specific fracture energy w f , mechanical specific energy (MSE), rate of penetration (ROP), and energy efficiency were determined through direct measurements and energy balance calculations. Results revealed characteristic U-shaped relationships between specific fracture energy and drilling parameters, with minimum w f values corresponding to optimal chip formation regimes. Energy efficiency reached 38–52% under optimized conditions, while the percussive component accounted for 65–82% of total energy input. Strong linear correlation between w f and MSE confirmed the governing role of specific fracture energy in overall energy consumption. The findings enable clear identification of energy-efficient operating windows and provide practical recommendations for parameter optimization. This approach offers a physically grounded framework for reducing energy use, increasing penetration rate, and extending tool life in hard rock drilling operations.