# Numerical Simulation on Dynamic Response of Drilling Parameters in Loaded Rock Mass
## 3 Establishment of Numerical Model
### Numerical Simulation Experiment Scheme  
In order to further explore the dynamic response mechanism in the drilling process of a coal mine roadway, this study will systematically change the key parameters in the drilling process, including the thrust, the revolution speed of the drill bit, and the stress state of the rock, so as to study the variation law of the dynamic response characteristics of coal mine roadway drilling under different drilling parameters and different confining pressure conditions. The drilling simulation experiment scheme under different thrust speed conditions is shown in Table 3.  
In order to further explore the influence of confining pressure conditions on the drilling parameters of coal in the drilling process, this experiment applied pressure on the surface of the rock in the x and y directions as shown in Figure 5, and the variation in parameters while drilling in the process of coal drilling under confining pressure is studied. The specific experimental scheme is shown in Table 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Rock Type** & **Coal** & **Mudstone** &
\begin{tabular}{c} **Sandy** \\ **Mudstone** \\ \end{tabular} & **Silstone** \\ \hline Density & 1.35 & 2.66 & 2.61 & 2.88 \\ Elastic Modulus/GPa & 2.80 & 9.50 & 10.00 & 31.60 \\ Poisson Ratio & 0.23 & 0.26 & 0.27 & 0.30 \\ Uniaxial Compressive & 21.30 & 38.20 & 48.00 & 83.00 \\ Strength/MPa & 28.00 & 38.00 & 48.00 & 29.90 \\ Angle of Friction & 28.00 & 38.00 & 48.00 & 29.90 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Main physical properties of rock. Figure 4: Numerical simulation verification curve. is a complex contact-separation-recontact dynamic process between the bit and the rock during the drilling process. In the microscopic process of rock drilling, the fluctuation in the torque and drilling rate is closely related to the function of the 'life and death unit' used in meshing. When the cutting teeth break the rock, each unit in the model will bear different degrees of stress. If a unit fails because the stress it bears exceeds its limit, the unit will be removed from the model according to the setting of the 'life and death unit'. According to the principle of  
Figure 8: Time–drilling rate curve. Figure 6: Time–drilling depth curve. Figure 7: Time–torque curve. interaction in mechanics, at the moment of unit failure, the contact between the cutting teeth and the rock will be suddenly interrupted, which will lead to a sharp decline in the reaction force and moment. As the drill bit continues to rotate, the cutting teeth establish contact with the new rock unit. At this time, the reaction force and torque will rise rapidly. This process directly causes severe fluctuations in the torque and drilling rate. During the whole drilling process, this contact-failure cycle is repeated continuously, so that the force on the drill bit is always in a certain state of change. The drilling performance of different rock types under the same thrust and revolution speed is further compared, and the parameters such as the drilling time, drilling rate, and torque are analyzed in detail. When drilling the same displacement, the shortest time required for drilling coal is 3.01 s, followed by mudstone at 6.22 s, sandy mudstone at 7.27 s, and the longest time required for drilling is for siltstone at 10.65 s. From the change in the drilling rate and torque, under the same drilling depth, the average drilling rate and average torque of different rocks show significant differences. The average drilling rate of coal is 99.83 mm/s, and the average torque is 48.95 N\(\cdot\)m; the average drilling rate of mudstone is 48.21 mm/s, and the average torque is 51.85 N\(\cdot\)m; the average drilling rate of sandy mudstone is 41.49 mm/s, and the average torque is 63.04 N\(\cdot\)m; the average drilling rate of siltstone is 28.2 mm/s, and the average torque is 67.47 N\(\cdot\)m. In-depth exploration of its internal mechanism shows that there is a significant correlation between rock strength and drilling characteristics.