## 3 Results and Discussion
The cross-sections of the three sites exhibited a tendency toward steady increases in high porosity area and decreases in low porosity area as the erosion days rose from 10 to 20. After 60 days of erosion, the majority of the cross-section's medium porosity zones at Z = 29 mm and Z = 51 mm progressively merged and evolved into the high porosity zone, covering practically the whole section with only sporadic low porosity patches. From bottom to top, the cross-sectional porosity of the three places increased from 6.73%, 6.63%, and 2.49%, to 12.27%, 11.9%, and 8.09%, respectively. It showed that the saturated magnesium sulfate solution had a severe corrosive impact on tuff, gradually expanding the microscopic pores within the rock and increasing porosity. As shown in Figure 10, after 10 freeze-thaw cycles, the majority of the Z = 10 mm and Z = 38 mm cross-sections consist of low and medium porosity regions, with only a few regions containing high porosity parts. In the Z = 62 mm cross-section, the lower right area had almost entirely high porosity areas, while the other regions are dominated by medium porosity areas. When the number of freeze-thaw cycles increases from 10 to 60, the upper left region of the cross-section at Z = 10 mm transforms from a low porosity region to an elongated band of high porosity. At Z = 38 mm, the middle and upper regions of the cross-section become labyrinthine high porosity regions. At Z = 62 mm, the central and lower regions of the cross-section are occupied with zones of high porosity. The porosity of the three cross-sections increased from 3.15%, 5.26%, and 11.4%, respectively, to 7.57%, 9.63%, and 15.24%, respectively. It demonstrates that the porosity of the tuff progressively increased as the number of freeze-thaw cycles increased. This is due to the volume enlargement caused by the phase transition of ice water during the freeze-thaw cycle, which expanded the pores within the rock. When the number of freeze-thaw cycles increased from 40 to 60, there was little change in the porosity distribution of the specimen's cross-section, indicating that freeze-thaw erosion tended to be stable. Concurrently, a fraction of the saline solution infiltrated the sample by pore seepage [30; 31], resulting in the deposition of salt crystals that have the potential to obstruct certain pores and fortify the pore space within the tuff during successive freeze-thaw cycles. Figure 11 shows that after 10 freeze-thaw cycles, punctate high porosity plaques emerge on the lower left border of the cross-section at Z = 35 mm; the majority of the remaining regions are low and medium porosity regions. At Z = 51 mm, a large high porosity zone appeared in the left part of the cross-section, and a definite band-like high porosity region appeared in the middle region. The lower right of the cross-section at Z = 87 mm shows lumpy areas of high porosity, whereas the middle and upper sections  
Figure 3:1 (**a**) Porosity of cross-sections and (**b**) porosity distribution on the cross-sections at Z = 35, 51, 87 mm with 10, 20, 40, 60 days in N6 group. have punctate areas of high porosity. The lower left part of the cross-section at Z = 35 mm evolved from a low porosity zone to a punctate high porosity region as the freeze-thaw cycle increases from 10 to 60. The high porosity zone on the left side of the cross-section at Z = 51 mm gradually expanded, and a punctate high porosity region appears below; the high pore zone on the lower right of the cross-section at Z = 87 mm marginally increased. It demonstrates that freeze-thaw cycles have an influence on the interior pores of twff. The porosity of the three cross-sections increased from 5.26%, 8.05%, and 7.26% to 7.66%, 10.89%, and 9.24%, respectively. Frost and salt weathering are two of the primary causes of pore expansion, weathering, and rock deterioration [32,33].