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  Assessment of drilling deviations in underground construction

  Besides gathering information of the drill/rock interaction, the drill monitoring system commonly known as MWD (Measurement While Drilling) gives measures of the collaring and, from the length and the drill angles, the theoretical end position of the blasthole. Since the trajectory of the drill is not measured, deviations are not accounted with the result that the actual spatial position of the blasthole is unknown. The quality of the drilling in underground blasting operations is investigated with a view to quantify the error of the MWD system with respect to the real end position of the blasthole logged. For that, a Pulsar Micro Probe Mk3 has been used to measure the actual trajectory of five production blastholes, drilled in semi-automatic mode, by measuring inclination and azimuth values at every 1 m. The results indicate significant deviations between the actual end position of the blastholes and the end position given by the MWD system. This brings undesired variations of charge concentration at depth resulting in poor or excessive rock breakage and under- or overexcavation. It outliers the need of quantifying the drilling deviation Drilling deviation, MWD, Tunnelling, Blasting.

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