Drilling parameter acquisition and rock strength determination on rotary-percussive drilling for drill-and-blast excavation

Drill-and-blast excavation design requires a comprehensive understanding of the strength properties of the surrounding rock mass in the blast area. However, due to the absence of reliable methods for determining rock strength in situ, blast designs commonly rely on laboratory test results derived from limited core samples. To address this limitation, this study proposes a novel method for estimating in situ rock compressive and tensile strengths using drilling monitoring data. Drilling monitoring is a technique that interprets the properties of the drilled medium through recorded drilling parameters. A rotary-percussive drilling test system was developed for this purpose, incorporating an actual rotary-percussive drill from a blasthole drill rig along with integrated monitoring systems. Importantly, a complete procedure for acquiring five key drilling parameters, including thrust force, rotation speed, torque, drilling rate, and percussive pressure are described. These parameters were used to calculate the drilling work done, defined as the energy required to excavate a unit volume of rock. The results indicate a nonlinear correlation between drilling work done and percussive pressure, which corresponds to the compressive and tensile strengths of the tested rocks. Furthermore, applying confining stress to rock samples was found to increase the drilling work done, reflecting a higher energy demand for drilling under confined conditions. This observation is consistent with rock mechanics principles, wherein rock strength increases under confining pressure. Thus, this study demonstrates that drilling monitoring tests can effectively indicate rock strength under in situ stress conditions. The findings offer practical implications for real-time in situ rock strength assessment, thereby bridging the gap between drilling monitoring research and rock mechanics applications.