# Numerical Simulation on Dynamic Response of Drilling Parameters in Loaded Rock Mass
## 3 Establishment of Numerical Model
### Analysis of Drilling Parameters Under Different Thrust Conditions  
In order to compare and analyze the variation trend of the drilling rate and torque of each rock under different thrust conditions, in the numerical simulation, the revolution speed of the drill bit is fixed at 120 r/min. By changing the thrust, the time-drilling depth, time-drilling rate, and time-torque curves of drilling four kinds of rocks under different thrust levels are recorded, respectively, as well as the curves for the drilling rate and torque changing with thrust, as shown in Figures 14-18. Through the analysis of Figure 14b, Figure 15b, Figure 16b, and Figure 17b, it can be found that under the same thrust, due to the low strength of coal, mudstone, and sandy mudstone, even if the thrust is small, the drill bit can cut into the rock relatively easily. The siltstone has high strength and hardness, so it is difficult for the drill bit to cut into the rock effectively, and the drilling rate is very low. This is because when the thrust is at a low level, the contact pressure between the cutting edge of the drill bit and the rock is significantly lower than the compressive strength of the rock. Because the rock needs to overcome its own structural strength to break, when the thrust is small, the breaking of the rock is mainly due to the work accomplished by the contact friction between the cutting edge and the rock. This process is mainly to grind the rock, and the separated rock particles are extremely small, which leads to the drilling rate being not significant. When the thrust rises, the drill bit can be pushed relatively easily, and the drilling rate will rise rapidly with the increase in thrust. It can be seen from Figure 14a, Figure 15a, Figure 16a, Figure 17a, and Figure 18a that as the thrust continues to increase, the drilling rate of coal increases from 74.62 mm/s to 141.51 mm/s, the drilling rate of mudstone increases from 35.51 mm/s to 57.69 mm/s, and the drilling rate of sandy mudstone increases from 28.03 mm/s to 47.09 mm/s. The drilling rate of mudstone increases from 28.16 mm/s to 42.13 mm/s, and the drilling rate of all kinds of rocks will gradually increase accordingly, showing a significant positive correlation trend. Through the analysis of Figure 14c, Figure 15c, Figure 16c, and Figure 17c, it can be seen that the variation law of torque in the drilling process of four kinds of rocks is basically the same. Taking coal as an example, when the thrust is 3000 N, the average value of torque is 38.33 N\(\cdot\)m. At the initial moment of drilling, due to the small thrust, the initial pressure exerted by the drill bit on the rock surface is limited, and it is difficult to quickly break the initial resistance of the rock surface, making the torque close to 0. With the passage of time,  
Figure 17: Variation curves of drilling parameters of siltstone under different thrust conditions at 120 r/min. (**a**) Time–drilling depth variation curve; (**b**) time–drilling rate variation curve; (**c**) time–torque variation curve. Figure 18: Variation curves of torque and drilling rate with thrust. (**a**) Thrust–drilling rate variation curves of different rocks; (**b**) thrust–torque variation curves of different rocks. the drill bit gradually cuts into the rock. However, due to the lack of thrust, it is relatively difficult to overcome the cohesion and friction of the rock, and the torque will jump sharply to try to break through the obstacles, thus forming multiple peaks and valleys, and the fluctuation range is large. When the thrust increases to 5000 N, the average torque is 48.99 N\(\cdot\)m. In the initial stage of drilling, the torque rises from zero due to the need to overcome the static friction on the rock surface. With the deepening of drilling, the larger thrust makes the drill bit more powerfully cut into the rock. Compared with the low thrust, it can drill into the rock faster, so the torque rises faster in the early stage and reaches a higher peak value.