## 4 Results and discussion
### Changes in Internal Forces of Culverts under the Effect of Dissolution  
The occurrence of dissolution damage in different parts of concrete will lead to changes in the internal forces of the concrete structure, which adversely affect the long-term operation of the project. Since the tensile strength of concrete is much lower than the compressive strength, the main tensile stress interval of concrete is studied. From the initial state of the maximum stress, shown in the Figure 11, separate zones can be seen in six parts of the obvious tensile stress concentration. The six zones are named as the I-VI regions, and both the sides and the central part of the obvious tensile stress area are not seen at this analysis site. Under different working conditions in each area of the culvert, with the deepening of the degree of dissolution, the culvert maximum tensile stress changes, as shown in Figure 12. The following law can be found. Figure 11: Initial state maximum tensile stress cloud. Figure 10: Relative error variation curve. Figure 9: Measured data distribution and numerical simulation settlement curve. 1. The maximum tensile stress area of the culvert is mainly distributed in the lower end of the culvert center wall, the top and bottom of the cavity, and near the corner of the bottom of the culvert. The maximum tensile stress value in the initial state is 1.16 MPa: 1.20 MPa in the A condition, 1.16 MPa in the B condition, 1.20 MPa in the C condition, 1.19 MPa in the D condition, 1.18 MPa in the E condition, and 1.16 MPa in the full dissolution condition. The standard tensile strength of C20 concrete is 1.50 MPa, and the design value of tensile strength is 1.10 MPa. Considering the deterioration caused by dissolution, the strength of the concrete is discounted. However, the maximum tensile stress value of each working condition in the dissolution cycle is still less than its standard value of tensile strength. 2. In the II and VI regions, under the E working condition, the culvert middle wall undergoes dissolution degradation, and the decrease in elastic modulus leads to an increase in the vertical deformation of the middle wall. The middle of the roof plate produces a larger vertical displacement under the action of soil pressure, self-weight, and other loads, which leads to a significant increase in tensile stress in the II and VI regions, with a peak value of 0.89 MPa. In the A and C working conditions, the culvert sidewalls undergo dissolution deterioration and the reduction in elastic modulus leads to an increase in sidewall deformation. The two ends of the top plate produce larger vertical displacement under the action of soil pressure, self-weight, and other loads, which leads to a reduction in tensile stress in the II and VI regions. In the B condition, the bottom plate of the culvert is degraded by dissolution, and the decrease in elastic modulus leads to an increase in vertical displacement of the sidewall. Additionally, the two ends of the top plate produce a larger vertical displacement under the action of soil pressure, self-weight, and other loads, which leads to the decrease in tensile stress in the II and VI regions. In the D working condition, the culvert top slab undergoes dissolution deterioration, and the reduction in elastic modulus causes the stress concentration to be released, and the tensile stresses in the II and VI regions show a small decrease. Under the full dissolution condition, the culvert as a whole undergoes dissolution deterioration, and the resulting effect is equivalent to the use of low-strength concrete in terms of mechanical properties, with a small change in stress distribution, as can be seen in Figure 12. Here, the maximum tensile stress in each region under the full dissolution condition undergoes a small change. 3. The tensile stress growth is larger and symmetrically distributed with a peak value of 1.20 MPa in the III and V regions under working conditions C and A. The tensile stress grows fastest in area I under working condition B, and the peak value can reach 1.13 MPa.