Empirical relationship of characteristic impedance with rock drillability and cuttability

In rock and mining engineering, it is essential to predict rock cuttability and drillability for estimating drilling costs, selecting suitable drilling/cutting machine and tools, and achieving high productivity. To predict the drillability and cuttability, many destructive methods have been developed. However, they are often expensive and time-consuming. To explore a non-destructive method, this paper builds a series of empirical relationships between rock characteristic impedance and its drillability and cuttability indices by using a large quantity of measured data from various laboratory and field tests in previous publications. The relationships between rock’s UCS (uniaxial compressive strength) and its drillability and cuttability indices are also built for comparison. The results indicate that: (1) the penetration rates of both percussive drilling and rotary drilling depend on rock characteristic impedance, and they decrease with increasing impedance. (2) The specific energies in percussive drilling, rotary drilling and cutting all increase with increasing rock impedance. (3) Most of current drillability indices such as alfa, DRI, CLI and Shore hardness have a certain relationship with rock impedance. (4) Characteristic impedance has a more confident relation with drillability and cuttability than the UCS. Since determination of rock impedance does not necessarily require a destructive method, characteristic impedance has a great potential to be taken as an index to predict rock drillability and cuttability.