## 3 Results and Discussion
### Influence of the Confining Pressure on the Cutting Performance of Cutting Head  
Figure 10 shows the comparisons of cutting forces between no confining pressure and confining pressure of 5.0 MPa. From the respective cutting forces in the \(x\)-, \(y\)-, and \(z\)-directions, whether there is confining pressure or not, the cutting forces in the \(y\)-direction are the largest, followed by the cutting forces in the \(z\)-direction, and the forces in the \(x\)-direction are the smallest. In order to further explore the impact of confining pressure on the cutting force, the mean cutting forces under different confining pressures can be found in Figure 11.  
According to Figure 11, if there is not any confining pressure on the rock mass and the top side (Plane A) of the rock mass is totally constrained, the cutting force in the \(y\)-direction is about 2000 kN. Confining pressure is applied on the top side and if it is 0.5 MPa, the cutting force in the \(y\)-direction significantly increases to about 2100 kN. If the confining pressure continues to increase to 1.0 MPa, the cutting force in the \(y\)-direction drops a little in comparison with that under the confining pressure of 0.5 MPa. However, the force under the confining pressure is still larger than that without any confining pressure on plane A; When the confining pressure increases to 2.0 MPa, the cutting force in the \(y\)-direction is close to that without confining pressure. Afterward, as the confining pressure increases, the decreasing trend of cutting force can be found in the paper. According to [PERSON] et al. [21], under high uniaxial-confining pressure, the high elastic energy stored in rock mass would convert into kinetic energy and rock mass would be broken easily by a smaller cutting  
Figure 11: Cutting force in the \(y\)-direction under different confining pressures. Figure 10: Rock cutting force on the cutting head in different directions. (**a**) cutting force in the \(x\)-direction; (**b**) cutting force in the \(y\)-direction; (**c**) cutting force in the \(z\)-direction. force. According to the results, it is helpful to reduce the cutting force on the shearer drum under a certain confining pressure. However, the confining pressure is not always good for improvement of cutting performance. According to [PERSON] et al. [22], severe rock robustness would happen under higher uniaxial confining pressure, which might lead to disaster underground. Figure 12 shows the deformation of rock mass in the \(y\)-direction under different confining pressures. According to the figure, when the confining pressure on plane A is 0 MPa, there is no deformation of rock mass in the \(y\)-direction until cutting happens. After rock cutting happens, deformation of rock mass in the \(y\)-direction occurs and increases from 0 mm to 4 mm; When the confining pressure on the plane A is 0.5 MPa, deformation of rock mass occurred in the \(y\)-direction even if rock cutting did not happen. Then rock cutting happens and under the influence of cutting force and confining pressure, the deformation of rock mass in the \(y\)-direction increased from \(-0.5\) mm to 0 mm and then continued to increase to 5 mm. Therefore, it could be found that the deformation of rock mass in the \(y\)-direction firstly decreases under the confining pressure and cutting force, and then increases in reverse. When the confining pressure applied on plane A reached 5.0 MPa, the deformation of rock mass showed with different characteristics. Under the confining pressure, the deformation of rock mass before rock cutting happens (0-4 s in Figure 12) showed the same regularity as those shown under a confining pressure of 0.5 MPa. However, after the 4 th second, the regularity of rock deformation in the \(y\)-direction seemed to be different, and the deformation in the \(y\)-direction began to decrease to 0 mm gradually. Afterward, it started to increase in the opposite direction along the \(y\)-direction.