## 6 Discussion  
Numerous studies have shown that the freeze-thaw effect is one of the significant factors affecting the mechanical properties of rock materials [31; 32; 33; 34]. The peak compressive strength and elastic modulus are not inherent properties of rock materials; rather, they are closely related to the properties of the rock and the external environment. After the water saturation treatment of sandstone specimens, water fills the original pores and cracks within the specimens, causing soluble minerals to dissolve, weakening the cementation between particles, and partially adhering to the particle surfaces, thereby reducing the friction between particles. During the freeze-thaw cycle, the particles within the rock undergo varying degrees of contraction due to the phase change of water to ice, while the freezing expansion force of pore water increases the volume of pores and cracks, weakening the cementation capacity between particles. After multiple freeze-thaw cycles, the internal microstructural pores of the specimens gradually decrease, while new cracks increase, further enlarging the original pores and cracks; this results in a gradual increase in the proportion of medium and large pores, a gradual decrease in the specimen strength, and  
Figure 13: Comparison between the predicted values and the experimental values. (**a**) Peak compressive strength; (**b**) elastic modulus.  
a transition of the mechanical properties from brittleness to ductility, leading to severe structural damage in the specimens. Consequently, the peak compressive strength and elastic modulus decrease gradually with the increase in freeze-thaw cycle number [35; 36]. [PERSON] [37] pointed out that freeze-thaw cycles facilitate the generation and propagation of internal cracks in specimens, with the effective porosity of the specimens increasing with the number of freeze-thaw cycles. [PERSON] [27] indicated that the cementation and friction between particles within the specimens can restrict the initiation and propagation of cracks; however, as the number of freeze-thaw cycles increases, the cementation between particles deteriorates, leading to a higher degree of damage and deterioration in the specimens, which is consistent with the findings of this study.  
Freezing temperature is also a crucial factor affecting the mechanical properties of water-saturated coal-measure sandstone. [PERSON] [9] demonstrated that, as the freezing temperature decreases, the failure mode of rock materials transitions from splitting failure to shear failure, with a significant increase in the number and extent of cracks. When the freezing temperature is \(-5\,^{\circ}\)C, the degree of damage to the specimens is relatively minor with fewer freeze-thaw cycles, exhibiting one or more independent cracks on the surface. However, when the freezing temperature is \(-10\,^{\circ}\)C or lower, the surface cracks develop and interconnect, forming conical fractures, significantly reducing the integrity of the specimens. The primary reason for this is that the decrease in freezing temperature leads to an increasing degree of contraction of the internal particles, significantly weakening the cementation between particles, resulting in the development of secondary cracks within the specimens and an increase in through-going cracks, which macroscopically manifests as an increase in the degree of damage to the specimens under uniaxial compression conditions.  
However, due to the triaxial stress state of the rock in its natural condition, the horizontal deformation of the rock is constrained. Therefore, the next phase of research should investigate the effects of freezing temperature and the number of freeze-thaw cycles on the mechanical properties of the rock under triaxial stress conditions. It is important to note that both the triaxial testing machine and the pressure medium (such as oil) must be cooled during the experimental process.