## 3 Analysis of Test Results
### Rock Mechanical Properties Under the Interaction of Multiple Factors
#### 3.3.2 Factor Interactions on Peak Stresses
However, under high confining pressure, the confining pressure effectively inhibits crack sliding, while the high-strength grouting material enhances the bonding force of the crack surface, and the synergistic effect of the two significantly improves the bearing capacity of the rock specimen. In addition, during the transition from low to high strength of the grouting material, the peak stress gain increased nonlinearly from 33.89 MPa to 49.96 MPa with increasing confining pressure, an increase of 1.47-times. The low-strength grouting material has a limited reinforcement effect on the fracture surface, and the increase in peak stress mainly depends on the confining pressure compacting the fracture; under the condition of high-strength grouting material, the increase in bearing capacity of the fracture surface and the confining effect of the confining pressure form a strong synergistic effect, which fully inhibits the slip and expansion of the fracture and greatly improves the overall strength of the rock mass. Interaction between fracture dip angle and roughness: As the inclination and roughness of the crack increase, there is a strong superposition effect on the peak stress. During the transition from a low to a high inclination angle, the gain in peak stress increases nonlinearly from 5.96 MPa to 15.43 MPa, an increase of 2.59-times, as the roughness increases. At low crack inclination angles, the angle between the crack surface and the principal stress direction is large, and the external force is mainly shear. However, an increase in roughness only slightly increases the frictional resistance and interlocking effect of the crack surface, resulting in a small increase in peak stress. At high crack inclination angles, the angle between the crack surface and the principal stress direction decreases, and the external force is more easily transmitted to the interior of the crack. The increase in roughness significantly enhances the anchoring effect and anti-slip ability between the fracture surfaces, thereby greatly increasing the peak stress. In addition, during the transition from low to high roughness, as the fracture inclination angle increases, the peak stress gain increases nonlinearly from 29.3 MPa to 38.77 MPa, an increase of 1.32-times. At low roughness conditions, the fracture surface is relatively smooth, it is less sensitive to changes in the fracture inclination angle, and changes in the fracture inclination angle have a limited effect on increasing the peak stress. However, at high roughness conditions, the concave-convex structure of the fracture surface not only disperses the stress more evenly and reduces the stress concentration effect but also relieves the stress accumulation at the fracture tip,  
Figure 10: Visualization of the interaction effect between fracture dip angle and roughness on peak stress. delaying the fracture propagation, so that the peak stress increases significantly with the increase in the fracture inclination angle. In summary, the nonlinear gain effect of peak stress is particularly obvious under the interactive effects of grouting material and roughness, grouting material and confining pressure, and fracture inclination angle and roughness. There is a significant interactive enhancement mechanism.