The rock drilling is an important aspect of rock engineering. In view of the significance of drilling operation, the present investigation introduces Inherent Damage Factor (IDF) to analyse the influence of intrinsic parameters on penetration performance of drilling system. The drilling experiments were carried out on sandstones of Upper Kaimur Group, Vindhyan Supergroup, collected from upper and lower level of vertical structural litho-succession around Jhingura, Mirzapur, Uttar Pradesh, India. The velocities of primary wav (P wave) in sandstones were used to determine the IDF values. The geomechanical properties of sandstones from upper and lower levels show distinct difference. The penetration performance of drilling system is found maximum (74.58 cm/min) in sandstones having IDF 0.541 (sandstone from lower level). at thrust of 48.5 kg and operative air pressure of 6.5 kg/cm2. However, the sandstones of upper level showing IDF, 0.00 exhibit minimum penetration rate as 24.51 cm/min at the same thrust and operating air pressure.
Drilling of rock strata is vitally used in geological, civil and mining engineering projects such as hydropower project, road and bridge constructions, mining, petroleum and allied industries. Particularly in engineering geological projects, the drilling performance as well as the wear of the tool and equipment is decisive for the progress of excavation work (Thuro and Plinninger, 2003). Thus, an improved prediction of drill bit penetration and bit consumption are technoeconomic for progress of rock engineering projects. The progress of drilling is principally depend on type, geometry, applied thrust, operating air pressure, flushing out of debris, rock properties, geological conditions and geotechnical response. The parameters related to geoground condition are called as uncontrolled factors (Dubey, 2003). The parameters affecting the drilling process are quantified as penetration rate for specific geoground conditioner have been the subject matter of several drilling investigation (Protodyakonov, 1963, Hustrulid, 1968; Hawakes and Wright, 1968; Rabia, 1985; Paone et al., 1996; Kaharaman et. al., 2003). In addition to technical parameters the geological and geotechnical parameters are some of the critical parameters directly influencing the penetration response of drilling system. In the study of drilling performance to parameters have proved to be most significant namely penetration rate in meters per minute and the bit life span in meter span in meters per drilling bit. The wear of bit is principally dependent on rockmass conditions and petromechanical response of rocks. Thus, the penetration performance of rock excavators is one of the most important aspects for progress of engineering projects. However, limited studies are available on these important aspects till date. In view of possible correlation between textural parameters and mechanical properties Ehlich and Weinberg (1970) proposed a grain roughness coefficient for the some rocks. In the uncontrollable parameters the is the result of intrinsic components of rocks and rock mass and the geotechnical properties are basically dependent on these components. Thus, the geotechnical response is function of lithology (Donath and Fruth, 1971), mineral constituents (Pouya, 1991), textures and microstructures (Howarth and Rowland, 1987) of the rocks.
