## 2 Experimental Outline
### Analysis of Internal Force and Displacement of Lining Structure  
A total of 16 measurement sites were placed on the inner and outer surfaces of the liner model in order to track the internal force of the lining structure. Figure 7 illustrates the internal force imparted to the lining structure. Among these, compression produces a positive axial force, while tension on the lining's outer surface and compression on its inner surface provide a positive bending moment. The loading moment, midway moment, and end moment of the test are represented by the values of t = 0, 98, and 196 h, respectively. The lining's maximal axial force, 196.1 kN, is found at the left arch's waist. The lining's internal force is essentially spread symmetrically from left to right and up and  
Figure 5: Variation of radial stress of surrounding rock in horizontal direction at arch waist. **(a)** Left measurement point; **(b)** Right measurement point.  
down. The entire lining is under pressure. The top of the arch experiences the greatest bending moment, which is 25.0 kN\(\cdot\)m (absolute), whereas the upper and lower arch girdles experience essentially no bending. The outside surface of the lining is tensile at both sides of the arch girdle, and the bottom and top of the arch are pressured. The axial force increases from the middle moment to the ending moment and from the loading moment to the middle moment, respectively, and is stronger at all points along the lining at the ending moment than at the loading moment. Consequently, it suggests that the creep effect of the surrounding rock has a time-dependent characteristic that causes the internal force of the lining structure to change over time.  
Six measuring stations were positioned inside the lining structure to track its displacement; the displacement of the lining structure is depicted in Figure 8. The tunnel's inner lining deformation is seen as a positive direction of deformation. Over time, the displacement of every position in the lining structure primarily goes through two stages: deformation and stability. Every curve in the deformation stage mutates initially and then tends to stabilize, with the exception of the left and right arch waists, where the deformation protrudes outward; at all other points, the deformation occurs to the interior. The vault experienced the greatest displacement of 1.50 mm out of all the locations where the lining structure was present. While the displacements at the foot and bottom of the arch decreased over time as a result of the surrounding rocks settling, the displacements at the top of the arch and the left and right arch waists increased over time, but the growth rate eventu  
Figure 6: Variation of radial stress of surrounding rock in vertical direction. (**a**) Top measurement point; (**b**) Bottom measurement point.  
Figure 7: Internal force of lining structure. (**a**) Axial force; (**b**) Bending moment.  
ally slowed and reached a stable state. As the test came to a close, displacement varied at every site in comparison to the instantaneous displacement in the deformation stage, with the maximum displacement increment being 0.39 mm. This suggests that the lining displacement likewise possesses the time-dependent characteristic of changing over time.