ABSTRACT
This paper assesses the use of measurement while drilling (MWD) to predict the potential over- and under-excavated zones created in the contour of a tunnel developed by drill and blasting. Scanner profiles of the excavated sections have been compared with the position of contour blastholes to develop an excavated mean distance value (EMD), which may be considered as a macroscopic damage measure. A thorough normalization of the MWD data gathered has been carried to minimize external influences that may hide the actual response of the rig to rock mass. 54 blasts, which comprise around 1700 contour blastholes, have been compared with more than 2200 excavated sections. A non-linear multiple-variable power-form model has been developed to predict the excavated mean distance as function of the normalized penetration rate, hammer pressure, rotation speed, rotation pressure and water flow parameters, and the lookout distance. This combines the rotational, hydraulic and percussive mechanisms of the drill, and the confinement of the rock mass by depth. The model has a determination coefficient of 0.74, with the coefficients of the model strongly significant.
