Statistical and geostatistical analysis of drilling parameters in the Brenner Base tunnel

This paper deals with the statistical and geostatistical analysis of drilling parameters for predicting the rock-mass quality ahead of the tunnel face. For this purpose hammer drillings equipped with data loggers (DAC tests) were performed ahead of the tunnel face in order to carry out a preliminary assessment of the rock-mass conditions before the excavation. The study presents an analysis and correlation study between the measured data and the rock mass quality, expressed by the Rock Mass Rating (RMR) index. A significant negative linear correlation was found between the average values of the rate of penetration ROP and RMR data collected at the same tunnel chainage, but irrespective of the different lithologies. A more sophisticated geostatistical study was then performed. By using all available data, a ROP-RMR co-regionalisation model was set-up for estimating by co-kriging the subsequent RMR values of the rock-mass ahead of the face. Very satisfactory results were obtained, making the procedure valuable for similar cases where ROP data are available.