# Study on the Damage Process and Numerical Simulation of Tunnel Excavation in Water-Rich Soft Rock
## 5 Validation of the Simulation Method Based on Dual Softening Effect
### Comparison of Numerical Simulation and Field Monitoring Results
#### 5.4.1 Tunnel Vault Settlement and Convergence Displacement Analysis  
The monitoring data and simulation results of the vault settlement and horizontal convergence of section K14 + 885 of the Xujiadi tunnel are shown in Figures 20 and 21. The time history curves of vault settlement and horizontal convergence are both showing the trend of \"rapid rise-gradual stabilization-rise again-final stabilization\", which is related to the bench construction on site. The surrounding rock converges rapidly after the unloading softening of the upper and lower bench excavation, which shows a rapid linear rise in the curve, and then under the softening of groundwater, the surrounding rock deforms slowly until it stabilizes, showing a slow rise after a rapid rise. The final vault settlement is 60.7 mm and the horizontal convergence is 42.7 mm.  
According to the comparison of different curves in Figures 20 and 21, when the flow-solid coupling without considering the effects of softening and time is used, the calculated vault settlement and horizontal convergence are 47.5 mm and 33.8 mm, which are smaller than the monitoring results by about 21.7% and 20.8%, respectively. When the calculation model only considers the softening of excavation unloading, the calculated vault settlement and horizontal convergence are 52.5 mm and 36.6 mm, which are smaller than the monitoring results by about 13.5% and 14.3%, separately, which are closer to the field monitoring value than the fluid-solid coupling without considering softening effect. When the simulation simultaneously considers the dual damage of excavation unloading and water-softening without time, the final calculated vault settlement and horizontal convergence are 56.9 mm and 39.9 mm, which are smaller than the monitoring results by about 6.3% and 6.6%, respectively. However, if the simulation does not involve the time variation, then the calculated deformation of surrounding rock only occurs at the excavation moment, which means the surrounding rock deformation is only related to the construction steps and has nothing to do with time. Although the model can calculate the final vault settlement and horizontal convergence more accurately, it cannot reflect the variation of surrounding rock displacement with time during the construction, nor can it predict the appropriate support time during the design and construction. So, when the simulation considers excavation unloading, water-softening and time effect at the same time, the calculated vault settlement and horizontal convergence are 58.3 mm and 40.8 mm, which are about 4.0% and 4.4% different from the monitoring results, respectively, and the error is minimum compared with other cases. The calculated results considering time effect are not greatly different from the results without time effect, but the deformation curve of the surrounding rock calculated by the time-effect model has an obvious trend of \"rapid rise-slow growth-rise again-final stabilization\", which matches well with the development of the site monitoring data and provides a good reference for the site construction.