## 2 Experimental Outline
### Analysis of Contact Force between Surrounding Rock and lining Structure
(**a**) Axial force; (**b**) Bending moment. Figure 13: Variation of radial displacement of lining structure under different burial depths (Ac for arch crown, Ab for arch bottom, Aw\({}_{1}\) for left arch waist, Aw\({}_{r}\) for right arch waist, S\({}_{1}\) for left spandrel, Af\({}_{1}\) for left arch foot). Figures 15 and 16 illustrate how the surrounding rock stress changes under various lateral pressure coefficient circumstances. The surrounding rock stresses at all measurement points, with the exception of A1 and B1, increased significantly in the horizontal direction after the lateral pressure coefficient was changed from 0.3 to 0.5, while they slightly decreased at A1 and B1. The instantaneous stresses at measurement points A1, A2, A3, and A4 at a lateral pressure coefficient of 0.5 and a lateral pressure coefficient of 0.3 differ at the first moment of load application by \(-\)0.22, 2.24, 2.26, and 2.75, respectively, and at measurement points B1, B2, B3, and B4 by \(-\)0.32, 2.43, 2.17, and 2.53, respectively. The changes in the surrounding rock stress were minimal in the vertical direction. A range of stress-reduction zones forms near the tunnel's horizontal direction as a result of the surrounding rock's lower strength and larger compressive stress concentration. Using Figure 15a as an example, the monitoring point A1 is located in this zone, and as a result, its surrounding rock stress is lower than that of the monitoring points A2, A3, and A4. Figure 17 illustrates how the surrounding rock-lining contact force changes with varying lateral pressure coefficients. In accordance with the law of the contact force of surrounding rock and lining in Section 3.3, the lining structure is subjected to the pressure of surrounding rock in the following order when two different lateral pressure coefficients are used: left and right arch waist > left and right spandrel > left and right arch foot > arch crown > arch bottom. The pressure of the surrounding rock at the six measurement places  
Figure 16: Variation in the vertical direction of the radial stress in the tunnel surrounding rock at varying lateral pressure coefficients. (**a**) Top measurement point; (**b**) Bottom measurement point. Figure 15: Variations in the surrounding rock’s horizontal radial tension at the arch waist of the tunnel with varying lateral pressure coefficients. (**a**) Left measurement point; (**b**) Right measurement point. reduces with a change in the lateral pressure coefficient, and this also results in a drop in the pressure increment during the stabilization stage. It is evident that the lateral pressure coefficient lessens the force acting on the lining structure and has a significant impact on the lining force action. Figure 18 depicts the lining structure's radial displacement changes under various lateral pressure coefficients. The largest deformation happens at the arch crown when two distinct lateral pressure coefficients are utilized. The displacements of each measurement point decreased to varying degrees as the lateral pressure coefficient increased. This indicates that the lateral pressure coefficient plays a significant role in the tunnel structure's safety and that increasing the lateral pressure coefficient is beneficial for reducing the deformation of the tunnel lining structure. Figure 19 illustrates how the lining structure's internal force varies under various lateral pressure coefficients. When the lateral pressure coefficient is between 0.3 and 0.5 at a burial depth of 15 m, the incremental range of axial force at each position is 3-10 kN and 4-12 kN, respectively. This indicates that as the lateral pressure coefficient increases, the axial force of the lining increases as well, and the time-dependent characteristic of the axial force of the lining becomes more evident. Additionally, the bending moment change  
Figure 9:0 Variation of surrounding rock-lining contact force under different lateral pressure coefficients.