## 5 Conclusions and Discussion  
The model test of surrounding rock and lining structure stress and deformation time-dependent characteristics was conducted based on the creep effect of weak surrounding rock medium. The stress and deformation time-dependent characteristics of operational tunnels under various burial depths and lateral pressure coefficients were examined. The following are the paper's conclusions and discussion:  
1. By examining the stress and deformation of the surrounding rock and lining structure over time, one can observe that, as long as the load remains constant, the surrounding rock's stress, the lining structure's internal force and displacement, and the contact force between the lining and surrounding rock all increase over time and eventually tend to stabilize. It suggests that the surrounding rock and lining structure's stress and deformation have an evolutionary characteristic that changes with time;
2. When the radial distance increases in a vertical direction, the surrounding rock stress reduces, whereas, in a horizontal direction, the surrounding rock stress increases and then declines. The stress size and pattern of change on both sides of the tunnel are nearly the same, regardless of whether the orientation of the forces is vertical or horizontal. With the exception of the left and right arch waists, where the deformation protrudes outward, the lining structure deforms quickly under pressure. All other positions experience internal distortion, with the arch top experiencing the greatest amount of deformation. In accordance with the lining structure's surrounding rock pressure, which goes from large to small order: Left and right arch waist > left and right spandrel > left and right arch foot > arch top > arch bottom;
3. The surrounding rock stress, lining structure internal force, and surrounding rock and lining structure contact force all increase as tunnel burial depth increases, making the time-dependent characteristics of the change more evident. Burial depth also has a significant impact on the lining deformation of the time-dependent changes, with the arch top consistently experiencing the greatest deformation;
4. Increases in the lateral pressure coefficient have a significant effect on the surrounding rock stress in the horizontal direction while having little effect on the vertical direction. Additionally, the lateral pressure coefficient has a significant influence on the axial  
Figure 19: Internal force of lining structure under different lateral pressure coefficients. (**a**) Axial force; (**b**) Bending moment. force of the lining structure, the bending moment and displacement of the lining, and the contact force between the surrounding rock and the lining, all of which experience varying degrees of reduction. These findings suggest that the lateral pressure coefficient plays a critical role in the long-term safety of the tunnel structure and that an increase in the lateral pressure coefficient is beneficial to the control of the stress and deformation of the tunnel lining structure;
* The stress and deformation evolution of the surrounding rock and lining during long-term tunnel operation and maintenance has been obtained in this study, which can offer theoretical references for the identification of the operational tunnels' service state as well as for the prediction, prevention and control of diseases. However, the monitoring period of the model tests should be extended in subsequent studies in order to obtain more comprehensive experimental data on the long-term behavior of the surrounding rock and lining structure. This will allow for the detection of trends and evolutionary patterns that may be missed in shorter monitoring periods, which could serve as a foundation for a more robust and reliable tunnel design approach. Conceptualization, P.W. and X.M. ; methodology, L.Y. ; validation, L.Y., X.S. and X.W. ; investigation, P.W. ; resources, L.Y. ; data curation, X.M. ; writing--original draft preparation, P.W. ; writing--review and editing, X.M. and L.Y.