Experimental Investigations on Penetration Rate of Percussive Drill

In this paper, detailed studies were carried out to determine the influence of rock properties on the penetration rate during pneumatic drilling. Further investigation was also carried out on the effect of thrust, air pressure, and compressive strength on penetration rate. Rock properties, like compressive strength and abrasivity of various samples collected from the field were determined in the laboratory. Drilling experiments were carried out on ten different rock samples for varying thrust, air pressure values and bit diameter. It was observed that very low thrust results in low penetration rate. Even very high thrust does not produce high penetration rate at higher operating air pressures. With increase in thrust beyond the optimum level the penetration rate starts decreasing and causes the drill bit to ‘stall’. Results of the study show that penetration rate increases with increase in the thrust level. After reaching the maximum, they start decreasing despite the increase of thrust. The main purpose of the study is to develop a general prediction model and to investigate the relationships between penetration rate during drilling and physical properties such as uniaxial compressive strength and abrasivity of sedimentary rocks. The results were evaluated using the multiple regression analysis taking into account the interaction effects of predictor variables.