Prediction of Rock Properties and Specific Energy using Sound Levels Produced during Diamond Drilling

Abstract

Drilling is widely used in many engineering applications such as mining, geotechnical and petroleum industries. Drilling operations produce sound that can be used to estimate rock properties and specific energy. The conventional method of determining of rock properties and specific energy is expensive and time-consuming. In this study, a new technique was developed to estimate rock properties and specific energy (SE) using dominant frequencies and A-weighted equivalent sound pressure levels generated during diamond drilling operations. First, sound pressure level was recorded while performing rock drilling experiments on seven different types of rock samples using computer numerical control (CNC) drilling machine BMV 45 T20 and sound signals of these sound frequencies were analyzed using Fast Fourier transform (FFT). Using simple linear, multiple regression analysis and artificial neural networks, mathematical equations were developed for various rock properties, i.e. uniaxial compressive strength, Brazilian tensile strength, density, abrasivity, impact strength index using dominant frequencies of sound pressure levels. This study also reports the methods for prediction of SE, effect of physico-mechanical rock properties on SE and effect of operational variables on SE using A - weighted equivalent sound levels produced during diamond drilling operations. Initially SE was determined for all selected rock types and a correlation was developed between SE and physico-mechanical rock properties (PMRP) and operating variables. The developed prediction models were validated using determination coefficients (R2), t-test, F-test and performance predictions i.e. values account for (VAF), root mean square error (RMSE) and mean absolute percentage error (MAPE). For SE, the R2 values obtained a range from 75.58 % to 78.76 %, RMSE values obtained a range from 0.074411 to 0.578601, VAF values obtained a range from 72.826808 to 84.155813 and MAPE values obtained a range from 0.061218 to 2.321007 for selected rock samples and t and F values also obtained below the tabulated values (2.44). Concerning SE’s relation to PMRP, it was observed that SE increased with increasing uniaxial compressive strength, Brazilian tensile strength and dry density and decreased with increasing abrasivity. For PMRP, the R2 values obtained from 92.25 %, 90.99 %, 47.15 %, 93.39 %, corresponded to uniaxial compressive strength, Brazilian tensile strength, density and abrasivity. Similarly, regarding SE’s relation with operational variables, it was found that SE decreased with increasing drill bit diameter, penetration rate and drill bit speed. The developed models can be used to predict rock properties and specific energy at early stage of planning and design.