## Case Study
### Results and Discussion  
(1) Influence of surrounding rock Poisson's ratio  
From Figure 8, we note that with the increase in the reduction rate of surrounding rock Poisson's ratio, tunnel perimeter displacements increase with time, but they are only slightly changed. In general, the curvature of the curve of the vault settlement versus time (Figure 8b) is larger than that of the displacement of the side wall versus time (Figure 8a). Figure 8: _Cont._  
(2) Influence of surrounding rock internal friction angle  
From Figure 9, we note that with the increase in the reduction rate of the surrounding rock internal friction angle, tunnel perimeter displacements increase with time, but there is a big change. With the increase in the reduction rate of the surrounding rock internal friction angle, both the curvature of the curve of the displacements of the side wall versus time (Figure 9a) and that of the vault settlement versus time (Figure 9b) decrease. Figure 8: Variation of perimeter displacement with Poisson’s ratio. (**a**) D3 monitoring point. (**b**) D6 monitoring point. Figure 9: _Cont._  
(3) Influence of the surrounding rock elastic modulus  
From Figure 10, we note that with the increase in the reduction rate of the surrounding rock elastic modulus, tunnel perimeter displacements increase with time, but there is a big change. With the increase in the reduction rate of the surrounding rock elastic modulus, both the curvature of the curve of the displacements of the side wall versus time (Figure 10a) and that of the vault settlement versus time (Figure 10b) increase. (4) Influence of the lateral pressure coefficient  
From Figure 11, we note that with the increase in the reduction rate of the lateral pressure coefficient, tunnel perimeter displacements increase with time. However, for the reduction rate of 10% among the lateral pressure coefficient, the curvature of the curve of the perimeter displacement increases with time and its variation is the largest. In general, for the reduction rate of 10-30% among the lateral pressure coefficient, the curvature of the curve of the perimeter displacement and lateral pressure coefficient increases with time. The curvature of the curve corresponding to the other reduction rates are only slightly changed. (5) Influence of the elastic modulus of primary support  
From Figure 12, we note that with the increase in the reduction rate of the elastic modulus of primary support, tunnel perimeter displacements increase with time. In general, the curvature variation of the curve of the displacements of the side wall versus time is only slightly changed (Figure 12a). However, with the increase in the reduction rate of the elastic modulus of primary support, the curvature of the curve of the vault settlement versus time (Figure 12b) has a relatively large change. That is to say, the initial support stiffness has a greater influence on the vault settlement than the side wall displacement. (6) Non-stationary parameter creep large deformation mechanism  
In the following, we use the proposed method to investigate the large deformation mechanism of Section K3 + 038-040 of the tunnel. Figure 9: Variation of perimeter displacement with internal friction angle. (**a**) D3 monitoring point. (**b**) D6 monitoring point. Figure 11: _Cont._  
Figure 10: Variation of perimeter displacement with elastic modulus. (**a**) D3 monitoring point. (**b**) D6 monitoring point. Figure 11: Variation of perimeter displacement with lateral pressure coefficient. (**a**) D3 monitoring point. (**b**) D6 monitoring point. Figure 12: Variation of perimeter displacement with elastic modulus of primary support. (**a**) D3 monitoring point. (**b**) D6 monitoring point. We use the proposed back analysis method to inversely analyze the mechanical parameters of surrounding rock according to the displacement monitoring data of monitoring points D4 and D6 of Section K3 + 040 from 1 to 24 h of rheology time. Then, the obtained mechanical parameters are substituted into the model for calculation.