Investigation of the Rock-Breaking Mechanism of Drilling under Different Conditions Using Numerical Simulation

The interaction between the drill bit and rock is a complex dynamic problem in the process of drilling and breaking rock. In this paper, the dynamic process of drilling and breaking rock is analyzed using ABAQUS software. The rock-breaking mechanism of drilling is revealed according to the stress–strain state of the rock and the force of the drill bit. The effect of the size of the drill bit and the characteristics of the rock mass on the drilling parameters is studied during the drilling process. The results show that both thrust force and torque show a linear increase with the increasing drilling speed under each fixed rotational speed. The drill bit size has minimal impact on the correlation coefficient of the relationship curves between thrust force, torque, and rotation speed. The drilling results in a soft–hard interlayered rock formation show that there are significant differences in thrust force and torque during the drilling process of different rock types. Whether transitioning from a soft rock layer to a hard rock layer or vice versa, the relationship between thrust force and torque is distinctly manifested whenever there is a change in rock quality. The thrust force and torque increase correspondingly with the increase in confining pressure. When subjected to lateral pressure, thrust force and torque gradually increase with the rising confining pressure. Vertical drilling exhibits a larger increase in thrust force and torque compared to horizontal drilling. The thrust force and torque increase more significantly with the rise in confining pressure compared to lateral pressure.