## 3 Analysis of Test Results
### Mechanical Properties of Sandstone Under the Action of a Single Factor
The greatest shift occurs when the grouting material changes from ice to gypsum paste. This is because gypsum paste forms a strong crystalline structure during hydration, which better distributes external stress, enabling the rock specimen to withstand greater deformation. In contrast, ice has low strength and poor hardness, which limits its ability to provide continuous support. As a result, the increase in peak strain is minimal. Stage I: The compaction stage of the grouted rock specimen is shorter than that of the ungrouted sample. This suggests that the grouting material fills the micropores and microcracks in the sandstone, thereby increasing its density. Stage II: The slope of the curve is positively correlated with the strength of the grouting material. Compared to the ungrouted sample, the elastic modulus of the resin-injected rock specimen increases by 40.44%, indicating that the rigidity of the grouting material enhances the overall rigidity of the rock. Stage III: The stress-strain curves of the rock specimens show varying fluctuations. These fluctuations may result from the local destruction of filled cracks, causing stress redistribution. Stage IV: The peak stress is positively correlated with the strength of the grouting material. Compared to the ungrouted rock specimen, the peak stress of the resin-injected sample increases by 113.61%. The stress drop point shifts backward, and residual strength persists longer, indicating that the strong grouting material maintains bonding force even after the rock is damaged, continuing to provide support until final failure. Figure 6c shows the stress-strain curves of sandstone under different roughness conditions. Roughness enhances the anchoring effect of the slurry on the crack surface, improving stress distribution and transmission. This, in turn, slows crack propagation and enhances the rock specimen's stability, thereby improving its mechanical properties. As roughness increases, both the peak stress and peak strain of the rock specimen's stress-strain curve increase linearly, shifting the overall trend to the upper right. Stage I: The curves show no significant difference. Stage II: The slope of the curve increases with roughness intensity. Compared to the rock specimen without roughness, the elastic modulus of the rock with a JRC of 22 increases by 8.08%. This is due to the concave-convex structure of the rough fracture surface, which enhances the anchoring effect of the grouting material, making it more stable within the fracture. Phases III and IV: As roughness increases, both the peak strain and peak stress of the rock specimen gradually increase. Compared to the rock specimen without roughness, the peak stress of the rock with a JRC of 22 increases by 13.25%. This indicates that a rougher fracture surface disperses stress more evenly,  
reduces stress concentration, and delays the fracture propagation and instability of the rock specimen. Figure 6: Stress–strain curve of sandstone under the action of different factors. Figure 6d shows the stress-strain curve of sandstone under different crack inclinations. The crack inclination angle alters the angle between the crack plane and the direction of principal stress, promoting more efficient transmission of external stress to the rock's interior. This reduces the likelihood of slip and cracking on the fracture plane, optimizes stress distribution, and improves the rock's mechanical properties. As the fracture inclination increases, both the peak stress and peak strain of the rock specimen's stress-strain curve increase linearly, with the overall curve shifting notably to the upper right. Stage I: No significant difference is observed in the curves. Stage II: The slope of the curve increases with the fracture inclination angle. Compared to the rock specimen with a 15\({}^{\circ}\) inclination angle, the elastic modulus of the rock specimen with a 75\({}^{\circ}\) inclination increases by 27.25%.