## 3 Analysis of Experimental Results  
### Stress-Strain Analysis  
The single triaxial reloading stress-strain curve of unloaded sandstone is illustrated in Figure 10. It is observed that under uniaxial loading conditions, there exists a negative correlation between the number of freeze-thaw cycles and the peak strength of sandstone.  
Figure 8: Stress path of unloaded sandstone subjected to freeze-thaw cyclic reloading.  
Figure 9: Test procedure for loading after freeze-thaw cycles.  
Specifically, an increase in the number of freeze-thaw cycles corresponds to a decrease in peak strength, while the rate of strength decay progressively diminishes.  
In the static water stage, sand is subjected to a target confining pressure to restore the state following the completion of stress redistribution after unloading. Subsequently, a constant confining pressure is applied alongside axial pressure until failure occurs. Within the triaxial reloading environment, a positive correlation exists between confining pressure and peak strength; specifically, as confining pressure increases, peak strength also increases. Conversely, under identical confining pressure conditions, a negative correlation is observed between the number of freeze-thaw cycles and peak strength; that is, an increase in the number of freeze-thaw cycles results in a decrease in peak strength. The analysis indicates that unloading damage leads to the formation of cracks and defects within the rock sample, as well as the expansion of pores. This phenomenon exerts a disruptive effect on the dense skeletal structure of the original rock sample. After the initial damage induced by unloading, the water present in the internal pores of the rock sample transitions from a liquid to a solid state during the process of saturation freezing. This transition results in a secondary expansion of the pores and further compromises the skeletal structure of the rock sample. Moreover, each freeze-thaw cycle compounds the damage incurred in the preceding cycles. As the frequency of freeze-thaw cycles escalates, the pressure-dense point progressively shifts to the right. This shift can be attributed to the loosening of the pores within the rock, which occurs as a result of the frost heave forces induced by multiple  
Figure 10: Single triaxial reloading stress–strain curve of unloaded sandstone.  
freeze-thaw cycles. This process leads to the expansion and potential interconnection of small cracks. Consequently, under both uniaxial and triaxial compression conditions, a greater increase in axial strain is required to achieve the compaction state. This effect becomes increasingly evident with a higher number of freeze-thaw cycles.  
The stress-strain relationship of rock samples subjected to varying freeze-thaw cycles exhibits distinct characteristics during the initial loading phase. Specifically, for a given partial force value during this phase, an increase in the degree of freeze-thaw erosion correlates with a greater axial strain response.  
The rock sample subjected to the combined effects of unloading damage and freeze-thaw erosion exhibits a heightened degree of internal fracture development and a more loosely structured skeleton. This condition leads to a more pronounced compaction process during the initial phase of reloading. The axial strain observed in rock samples under these combined influences is greater and shows a positive correlation with the extent of freeze-thaw erosion. Furthermore, this effect is particularly pronounced in environments characterized by low confining pressure (8 MPa). The findings indicate that the compaction efficacy of sand during the hydrostatic stage of preparing unloading sections in low confining pressure environments is inferior to that in high confining pressure settings, thereby creating ample pathways for subsequent freeze-thaw erosion. Consequently, the axial strain of rock samples in low confining pressure environments demonstrates heightened sensitivity to reloading tests.