Energy required to break rock by percussive drilling

Through tunnel boring has found a permanent place in rapid excavation and has given promising results. Percussive drilling and blasting, especially in hard rocks, is still the main excavating method. Advancements in this field are possible and probable. The use of energy in rock breaking is not wholly understood; the progress in this understanding leads to better control and improvements in the whole excavating process. The present study describes the way in which to use actual percussive drilling experiments for the determination of the specific energies in rock fracturing. It is concluded that the penetration rate depends primarily on the energy used to fracture the rock under the drill bit. Though the energy which is transmitted elastically to the rock is generally estimated to be negligible, in some rock types the elastic energy is a considerable amount of the total energy transferred to the rock.