Uniaxial Compressive Strength (UCS), also known as unconfined compressive strength, is a key rock property which influences multiple steps along the mining value chain including drilling, blasting and comminution operations. UCS is usually measured on drill cores in the laboratory, a process that is both time consuming and expensive, while offering very limited sampling of the overall volume of rock to be extracted. We have developed a novel accelerometer-based measurement acquired while drilling which can determine the UCS of the rock being drilled from the vibrations induced in the drillstring. The fundamental response measured is a time delay, not a force or torque, and so does not suffer from the calibration and consistency issues that plague attempted application of Measurement while drilling (MWD) data to rock parameter determination. In addition, the measurement is insensitive to bit condition and driller actions, resulting in a significantly more robust evaluation of the subsurface than available through MWD analysis. The measured delay correlates strongly with UCS, so when acquired during blasthole drilling the measurement provides high resolution UCS data with fine spatial sampling, providing a rich, statistically-significant dataset for determination of the distribution of rock strength. This information feeds into drilling, blasting and comminution optimization. Drilling through the current bench and sampling the next bench down expands the application of this measurement to drill pattern planning based on the measured mechanical properties of the next bench. Survey hardware, deployment and processing is presented along with an example application to a copper porphyry mine.

Open-Access Online Publication: May 22, 2023