The influence of drilling technology on the qualitative assessment of the rock mass

A comparison of rock quality designation (RQD) parameters obtained from drill core analysis and the RQD determined from the walls of boreholes are presented in various type of rock mass. The borehole-walls imaging were carried out on the basis of optical and acoustic televiewer records evaluation. A comparison of the RQD calculated from the drill core and the RQD from the optical and acoustic televiewer records shows that the RQD values from the drill core are on average 30% lower. Significant differences were recorded particularly near the surface, or near mine excavations. The RQD parameter for rocks of the borehole walls boreholes was determined according to used methodology for each meter of the evauated borehole length separately. Open fractures identified by acoustic and optical televiewer were included in the RQD and frequency of dislocations calculation. Results show the impact of drilling technology on the the qualitative classification of the rock mass.