## 3 Results and Discussion
Figure 5: The evolution of the cross-section over time under salt weathering (**a–c**) samples soaked into magnesium sulfate solution for 10, 40, 60 days; (**d–f**) samples soaked into sodium sulfate solution for 10, 40, 60 days. in the specimen increase in each group, indicating that frost and salt weathering have a significant impact on the development of internal pores in the tuff. To quantify the cross-section pore characteristics, we calculated the porosity of each cross-section of the tuff during the salt and frost weathering process (Figure 7). With an increase in erosion days and freeze-thaw cycles, the porosity of the entire tuff cross-section progressively increased. When the number of erosion days increased from 10 to 60, the maximal porosity change in all cross-sections in the sodium sulfate and magnesium sulfate groups was 3.42% and 5.54%, respectively. As the number of freeze-thaw cycles increased from 10 to 60, the greatest value of porosity change in the sodium sulfate and magnesium sulfate groups was 3.77% and 3.35%, respectively. The average porosity of all the cross-sections in the magnesium sulfate and sodium sulfate test groups increased by 6.59% and 4.14%, respectively, when the number of days of salt erosion was extended from 10 days to 60 days. The average porosity of all the cross-sections in the magnesium sulfate and sodium sulfate test groups increased by 2.25% and 2.18%, respectively, as the number of freeze-thaw cycles increased from 10 to 60. Figure 6: 3D Pore distribution of tuff (**a**) N2 group, (**b**) N3 group, (**c**) N5 group, and (**d**) N6 group. To examine and describe the variations in pore properties of the tuff, a statistical analysis was performed on the distribution of porosity obtained from the CT scanning images of three distinct cross-sections inside each sample. These cross-sections were selected for analysis because of their noticeable differences in porosity, as illustrated in Figures 8-11. Porosity is categorized into three distinct ranges: high porosity area, medium porosity area, and low porosity area, which correspond to values of 0.18-0.3, 0.06-0.18, and less than 0.06, respectively. As shown in Figure 8, after 10 days of erosion, the cross-sections at all three locations are dominated by areas with low porosity. The central local area of the cross-section at Z = 24 mm changed from a low porosity zone to an elongated high porosity zone band as the erosion days increased from 10 to 20. At Z = 46 mm and Z = 74 mm, there are numerous high porosity regions in the area to the lower right of the cross-section and in the area directly above the cross-section, respectively. As the number of erosion days increased from 10 to 60, the distribution of low porosity areas decreased significantly on the 24 mm, 46 mm, and 74 mm cross-sections, while the distribution of high porosity area increased significantly. The porosity of the section increased from 5.22%, 8.49%, and 8.96% to 8.14%, 11.05%, and 10.11%, respectively (Figure 8a). It showed that the saturated sodium sulfate solution corroded the tuff, destroyed its internal pore structure, and increased its porosity. Figure 7: Cross-section porosity (**a**) N2 group, (**b**) N3 group, (**c**) N5 group, and (**d**) N6 group. Figure 8: (**a**) Porosity of cross-sections and (**b**) porosity distribution on the cross-sections at \(Z=24\), 46, 74 mm with 10, 20, 40, 60 days in N2 group. Figure 10: (**a**) Porosity of cross-sections and (**b**) porosity distribution on the cross-sections at \(Z=10\), 38, 62 mm with 10, 20, 40, 60 days in N5 group. Figure 3:0 (**a**) Porosity of cross-sections and (**b**) porosity distribution on the cross-sections at \(Z=29\), 51, 76 mm with 10, 20, 40, 60 days in N3 group. Figure 9 shows that after 10 days of erosion, the cross-sections at Z = 29 mm and Z = 51 mm were predominantly medium porosity zone, while the cross-section at Z = 76 mm was mostly low porosity zone.