## 3 Results
### Variation Laws of Surface Mechanical Properties Under Different Corrosion Mechanisms
#### 3.2.2 Variation Laws of Surface Longitudinal Wave Velocity Under Different Corrosion Mechanisms  
P-wave velocity is a reliable indicator of pore and micro-fissure development within the rock, as well as the degree of specimen damage [22]. To compare changes in surface acoustic wave distribution under different dissolution conditions, acoustic wave contour maps for dynamic and static dissolution are presented in Figures 13 and 14. Figure 14: Evolution of P–wave velocity contour maps with static immersion time (**a**) Static dissolution for 240 h, (**b**) static dissolution for 480 h, (**c**) static dissolution for 720 h.  
Figure 13: Evolution of P–wave velocity contour maps with dynamic cyclic time. (**a**) Undissolved, (**b**) dynamic dissolution for 24 h, (**c**) dynamic dissolution for 48 h, (**d**) dynamic dissolution for 72 h, (**e**) dynamic dissolution for 96 h, (**f**) dynamic dissolution for 120 h, (**g**) dynamic dissolution for 144 h, (**h**) dynamic dissolution for 168 h, (**i**) dynamic dissolution for 192 h.  
The aforementioned studies (Figures 13 and 14) show that surface P-wave velocity under different dissolution methods gradually decreases as corrosion progresses. However, the specific patterns of change differ significantly, as described below:  
(1) Dynamic Cyclic Dissolution:  
As shown in Figure 13, overall P-wave velocity gradually decreases with increasing dissolution time. Analysis shows that minimum P-wave velocity values become more concentrated and their distribution range becomes more defined. Maximum P-wave velocity values remain largely unchanged in position, consistently concentrated in the central region, but their distribution range gradually expands. The areas where minimum P-wave velocity occurs follow a sequence: periphery (Figure 13a) \(\rightarrow\) upper right (Figure 13b,c) \(\rightarrow\) upper left (Figure 13d) \(\rightarrow\) upper right (Figure 13e) \(\rightarrow\) upper left (Figure 13f,g) \(\rightarrow\) lower right (Figure 13h) \(\rightarrow\) upper left (Figure 13i), indicating significant fluctuations in the locations of minimum values. This suggests that dynamic cyclic dissolution induces fluctuating changes in the rock's internal pore structure, attributed to the staged evolution of porosity. (2) Static Immersion Dissolution:  
As shown in Figure 14, overall P-wave velocity also decreases gradually with increasing immersion time. Maximum P-wave velocity values remain relatively concentrated in the central region, with no significant positional changes, but their distribution range gradually expands. Minimum P-wave velocity values consistently appear around the edges of the rock slab. To further elucidate the differential impacts of static and dynamic dissolution on surface acoustic waves, area proportions of P-wave velocity distribution (relative to the non-corroded state) were calculated from P-wave velocity contour maps and are summarized in Table 4. Figure 15 illustrates changes in the area distribution proportions of different wave-velocity ratios over dissolution time. These analyses reveal distinct variation patterns of surface P-wave velocity under static and dynamic dissolution, highlighting the non-uniformity of acoustic wave distribution during weathering. These insights are crucial for understanding sandstone degradation mechanisms and developing targeted conservation strategies for sandstone-based cultural heritage.