Cutting energy characteristics for brittleness evaluation of rock using digital drilling method

The reliable evaluation of rock brittleness is essential in engineering geology for various applications, such as water conservancy, hydropower, transportation, energy exploration, and underground engineering development. This study proposes a new method for evaluating rock brittleness using a digital drilling approach. A cutting model was established to describe the relationship between the energy characteristics and mechanical parameters of the rock during the drilling process, accounting for the effects of friction and drilling fluid. Furthermore, a drilling-based index, the brittleness evaluation index ( BEI ), was developed to evaluate rock brittleness based on energy dissipation. We conducted drilling tests to investigate energy evolution, including cutting energy, friction energy, and liquid energy. The results indicated that cutting energy has a linear correlation with the strength parameters of rock, with a significant correlation coefficient. With increasing drilling depth, cutting energy and liquid energy exhibit a similar increasing trend, which initially remains constant and then increases linearly after a critical depth is reached. Friction energy rapidly increases with drilling depth at the beginning, and the growth rate decreases after reaching the critical point. Compared with the laboratory-determined brittleness index, our proposed method provides a reliable evaluation of rock brittleness. In summary, our study offers a practical approach to evaluating rock brittleness that could benefit various engineering applications.