## 2 Experimental Outline
### Analysis of Contact Force between Surrounding Rock and lining Structure
When compared to the force at the same location at a burial depth of 30 m, the surrounding rock-lining contact force at the left arch girdle increased significantly at 45 m. Similarly, the force at the right arch waist increased significantly by approximately 4.7 kPa, and the pressure increment at the remaining locations increased as the burial depth increased. Figure 10: Variations in the surrounding rock’s horizontal radial tension at the arch waist of the tunnel with varying burial depths. (**a**) Left measurement point; (**b**) Right measurement point. Based on the aforementioned analysis, the loading method of grading three times is used to simulate the change in tunnel depth. As a result, there are three stages of changes in the surrounding rock stress and the surrounding rock-lining contact force, and each stage has growth and stabilization stages of the stress. The growth stage is the process of the curve increasing steeply after loading to the point where the curve shows a convex process. The curve initially changes dramatically upon loading, which is caused by the surrounding rock producing stress and rapid growth during the loading moment. Afterward, the curve tends to convex and stabilize, bringing the surrounding rock stress into the stabilization stage. This demonstrates that both the surrounding rock stress and the surrounding rock-lining contact force have the time-dependent characteristic of changing with time due to the creep effect of the surrounding rock. Additionally, as burial depth increases, not only does the stress increase, but its time-dependent characteristic becomes more evident. Figure 13 illustrates how the lining's displacement changes depending on the burial depth. At each stage, there was an abrupt change in the displacements, which later increased over time, but the growth rate slowed down and eventually reached the steady creep stage. The left and right arch waists exhibit the least amount of deformation, while the arch crown experiences the most deformation. At a burial depth of 30 m, the arch crown exhibits 3.81 mm of deformation, and at a depth of 45 m, this location experiences 6.29 mm of deformation. These findings demonstrate the significant impact of burial depth on the time-dependent variation of the lining displacement, leading to a continuously fluctuating deformation over time. Figure 11: Variation in the vertical direction of the radial stress in the tunnel surrounding rock at varying burial depths. (**a**) Top measurement point; (**b**) Bottom measurement point. Figure 12: Variation of surrounding rock-lining contact force under different burial depths. Figure 14 illustrates how the internal force of the lining structure varies at various burial depths. At 15 and 30 m below ground, the axial force increment ranges are 3-10 kN and 6-13 kN, respectively, and the absolute value of the bending moment increment at the arch crown is 0.60 kN\(\cdot\)m and 0.98 kN\(\cdot\)m, respectively. These results demonstrate that as tunnel depth increases, so does the internal force of the lining, and the time-dependent characteristics of these changes become more apparent. At the arch foot and spandrel, the bending moment is nearly zero, and the variation is negligible. Influence of Lateral Pressure Coefficient on Time-Dependent Characteristics of Stress and Deformation in Surrounding Rock and Lining Structure  
The stress and deformation of the surrounding rock and lining are significantly influenced by the lateral pressure coefficient (\(c_{\rm lp}\)), and the time-dependent characteristics of the stress and deformation of the surrounding rock and lining may differ depending on the lateral pressure coefficient. In this model test, the impact of changing the loads loaded in the horizontal direction by setting up conditions 4 and 5 based on conditions 1 and 2 was realized by altering the surrounding rock stress, internal force and displacement of the lining structure, and surrounding rock-lining contact force. Figure 14: Internal force of lining structure under different burial depths.