## 4 Conclusions  
This study investigates the changes in the mechanical properties of sandstone under the independent and interactive effects of five factors, utilizing experimental methods such as indoor freeze-thaw cycles, triaxial compression testing, and acoustic emission monitoring. This study uncovers the interactive mechanisms influencing the mechanical properties of rock in complex environmental conditions. The following conclusions were primarily drawn:  
1. The degree of influence of each factor on the peak stress of sandstone under the action of each factor is ranked as follows: confining pressure > fracture dip angle > grouting material > number of freeze-thaw cycles > roughness. The degree of influence on the elastic modulus is ranked as follows: number of freeze-thaw cycles > confining pressure > grouting material > fracture dip angle > roughness. Freeze-thaw cycles lead to the expansion of microfractures and the deterioration of the pore structure, which is expressed as a weakening effect. Grouting materials have a strengthening effect by improving the adhesion and support of the rock, the dip of the fissures improves the efficiency of stress transmission, roughness enhances the anchoring effect of the grout, and confining pressure improves the compactness of the rock specimen and limits deformation. 2. Under the interactive effect of grouting materials and roughness, high-strength grouting materials and high-roughness fissure surfaces form a strong anchoring system, which can effectively disperse external stress and reduce the stress concentration, resulting in a significant gain in peak stress. Under the interactive effect of grouting material and confining pressure, confining pressure effectively inhibits crack sliding, and grouting material enhances the bonding force of the crack surface, and the synergistic effect of the two significantly increases the peak stress of the rock specimen. Under the interactive effect of crack inclination and roughness, high crack inclination and high roughness enhance the anchoring effect and anti-sliding ability of the crack surface, relieve the stress accumulation at the crack tip, and result in a significant increase in peak stress. By making reasonable use of the above-mentioned interactive enhancement mechanism, the bearing capacity of the rock mass can be effectively improved. 3. Under the interactive effect of confining pressure and fracture dip angle, high confining pressure and high fracture dip angle promote the reconstruction of the fracture network, the microfractures are fully compacted, the contact area of the particles increases, and the external stress is more effectively transmitted through the particle contact surface, resulting in a significant increase in the elastic modulus of the rock specimen. Under the interactive effect of grouting material and roughness, high-strength grouting material effectively reinforces the cracks, while high roughness provides more anchor points, further significantly increasing the elastic modulus of the rock specimen; under the interactive effect of confining pressure and roughness, high confining pressure and high roughness work together to compact the cracks and enhance the frictional resistance, significantly increasing the elastic modulus of the rock specimen. By reasonably utilizing the aforementioned interactive enhancement mechanisms, the deformation resistance of the rock mass can be effectively improved. 4. Under the interactive effect of grouting material and the number of freeze-thaw cycles, and the number of freeze-thaw cycles and confining pressure, both high levels of grouting material and confining pressure can reduce the impact of freeze-thaw cycles on peak stress. However, a high level of freeze-thaw cycles inhibits the reinforcing effect of grouting material and the strengthening effect of confining pressure, and there is an interactive inhibition mechanism for peak stress.