## 3 Numerical Simulation Analysis of Deformation Mechanism of Tunnel-Landslide Orthogonal System
### Numerical Simulation Program Design  
There are many factors affecting the occurrence of landslides in actual engineering conditions, mainly due to the weakening of the shear strength index of the slope geotechnical body as a result of natural weathering, rainfall scouring, seismic vibration, etc. [19]. The strength reduction method in FLAC3D focuses on the analysis of the results of the change in stress-strain in the destructive process of the geotechnical body during the computation process, rather than the process of the reasons that lead to changes in stress-strain [20]. Therefore, in this study, the influence of rainfall, groundwater, and earthquakes is not considered, but the shear strength index of the slope geotechnical body is directly discounted. The values of shear strength index \(c\) and \(\varphi\) of the slope geotechnical body are simultaneously divided by the folding multiplier, i.e., the folding coefficient \(F_{s}\), to obtain the folded shear strength index \(c^{\prime}\) and \(\varphi^{\prime}\). Then, \(c^{\prime}\), \(\varphi^{\prime}\) as the new shear strength index is brought into the FLAC3D programming language to re-test the calculation when the slope soil body meets the stability determination conditions. \(F_{s}\) can be called the minimum stability coefficient of the slope.  
\[F_{s}=\frac{c}{c^{\prime}},\;F_{s}=\frac{\tan\varphi}{\tan\varphi^{\prime}} \tag{1}\]  
Figure 11: Sliding belt model contact surface establishment.  
Figure 12: Model boundary constraint condition setting.  
where \(c\) is the cohesion of the original slope geotechnical body; \(c^{\prime}\) is the cohesion of the discounted slope geotechnical body; \(\varphi\) is the internal friction angle of the original slope geotechnical body; and \(\varphi^{\prime}\) is the internal friction angle of the discounted slope geotechnical body.  
This paper adopts the strength reduction method and combines the FLAC3D 6.0 software to calculate the stability of engineering examples and takes the following three points as the judgment of slope stability: whether the static equilibrium calculation is convergent, the displacement of the sudden change in the characteristic point, and the penetration of the plastic zone of the slope, and combines the three points of judgment to comprehensively judge the overall stability of the slope.  
This tunnel is an existing tunnel; to study the force and deformation characteristics of the tunnel under the action of upper landslide thrust in the tunnel-landslide system and the change in axial force of NPR constant-resistance large deformation anchors, the strength reduction method is used to reduce the shear strength parameter of rock and soil bodies in the slip zone. By reducing the angle of internal friction and cohesion, the landslide thrust is simulated to be generated by the landslide body sliding under the water softening and an earthquake occurring. Comparative analysis was carried out using the original scheme (without discounting) and four different discounting schemes, which are shown in Tables 2-4 below.  
Plan 1 is the original plan, where the friction angle and cohesion in the slide belt take the actual value according to Tables 2-4, and Plan 2 to Plan 5 take different discount coefficients to discount the friction angle and cohesion in the slide belt to increase the landslide downward force and compare and analyze this with the original plan.