Digital drilling-based determination of rock anisotropy and anisotropic effect on cutter wear

Anisotropy affects the mechanical behaviours of rock, especially in the application of rock engineering. In this study, a digital drilling method is proposed to evaluate the mechanical anisotropy of rock and the anisotropic effect on cutter wear. In considering critical friction, the cutting efficiency and contact stress were determined from the revised drilling model in order to characterize the drilling process. For six types of rock, a series of drilling tests were conducted on three axial directions using a coring bit. The anisotropy of the rock strength was obtained from point load tests to compare with the anisotropy of the drilling characteristics. Correspondingly, an anisotropy criterion was established. A critical point was identified in the evolution of contact stress and in the plot of drilling parameters, corresponding to the critical friction. Results indicate that the evolution of contact stress with inclination angle suggests similar elastic and plastic stages (inclination angles of 5 degrees and 12 degrees, respectively). The typical evolution was also confirmed by the critical depth of the friction point. Moreover, the cutting efficiency and contact stress at the critical point showed the evident anisotropic characteristic. A comparison of two kinds of anisotropy indices, A(1) and A(2), was conducted to determine the anisotropy index of the drilling characteristics. The contact stress gave the anisotropy sequence to be shale (22.45) > gneiss (14.21) > schist 302 (10.74) and blue sandstone (10.07) > granite (7.29) > red sandstone (5.09). An examination of consistency with strength anisotropy index suggested that the contact stress has a fitting correlation with an accuracy of 91%. In summary, the digital drilling-based method provides a reliable evaluation of rock anisotropy, showing potential for a practical application.