## 4 Results and discussion
### Changes in Soil Pore Pressure Caused by Culvert Dissolution  
The deepening of the degree of dissolution damage leads to a substantial decrease in the permeability coefficient of concrete in the culverts, and then the phenomenon of leakage occurs, leading to changes in the hydraulic boundary conditions of the soil. This affects the changes in the pore pressure field of the surrounding soil. Through numerical simulation, the following features are found:  
1. As can be seen from the Figure 16, the dissolution damage at the bottom of the culvert (working condition B) reached a permeability coefficient of 8.354 \(\times\) 10\({}^{-8}\) m/s for the concrete in about 16 years. Furthermore, local leakage occurred, causing a significant increase in the pore pressure of the soil near the leakage location. The full dissolution condition reaches a concrete permeability coefficient of 6.957 \(\times\) 10\({}^{-8}\) m/s in about 13 years. Furthermore, local leakage occurs, causing a significant increase in the pore pressure of the soil near the leakage location.
2. Different locations along the culvert show dissolution damage, causing different locations where the increase in pore pressure of the surrounding soil occurs. When damage occurs at the top and bottom of the culvert, the pore pressure changes have a clear symmetry. When damage occurs in the lateral part, the pore pressure changed only in a unilateral range. This is consistent with the conclusion that the maximum ground settlement value occurs near the centerline of the culvert when dissolution damage occurs at the top and bottom of the culvert, while the maximum ground settlement value occurs on the side of the centerline of the culvert when dissolution damage occurs at the sidewalls of the culvert.
3. The range and shape of the increase in pore pressure of the surrounding soil caused by dissolution damage occurring at various locations along the culvert are different. The range of the increase in pore pressure of the soil caused by top dissolution (D working condition) is the smallest, and the influence range is approximately rectangular, at about 11 m in the horizontal direction and 1 m in the vertical direction. The increased range in soil pore pressure caused by lateral dissolution (A and C working conditions) is more concentrated, and the influence range is approximately triangular, at about 15 m in the horizontal direction and 7 m in the vertical direction. As can be seen from Figure 17, the increased range in pore pressure caused by the bottom dissolution (B condition) and the full dissolution conditions is approximately isosceles trapezoidal, where the increased range in pore pressure caused by the full dissolution condition is the largest, at about 25 m in the horizontal direction and 13 m in the vertical direction.
4. Under the full dissolution condition, when leakage occurs at the bottom and side of the culvert, the impact is the widest, the pore pressure changes the most, and the seepage pressure is the largest. For the soil body under the action of seepage pressure, the settlement value increases substantially, which is consistent with the conclusion that the surface settlement value is the largest under the full dissolution condition.  
Figure 15: Comparison of surface sedimentation maxima with the degree of dissolution.