# Landslide-Tunnel Interactions and Control Countermeasures under an Orthogonal System
## 2 Evaluation of Landslide Effects on Tunnels
### Analysis of Three Positional Damage Patterns  
The relative positional relationship between the tunnel and the sliding surface determines the force mechanism and deformation characteristics of the tunnel, which are the main factors determining the interaction pattern between the tunnel and the landslide. Based on this spatial relationship, the stress mode and deformation characteristics of the  
Figure 1: The relative position of a landslide and a tunnel.  
various types can be analyzed, and the interaction laws of the tunnel-landslide system can be determined.  
1. The tunnel is located above the sliding surface.  
When a tunnel is located above the sliding surface, the main feature of the tunnel is longitudinal bending; its positional relationship and force analysis are shown in Figure 2. Under the influence of landslide pressure, the tunnel experiences an uneven distribution of loads. As the uneven load increases, both ends of the tunnel bear significant shear force, and the middle part bears a large amount of bending moment. Under the combined action of landslide pressure and stratum resistance, the failure mode manifests as shear cracks in the tunnel crown and tension cracks in the side wall and arch foot of the tunnel; thus, the strength of the lining decreases. If there are significant in situ stresses within the landslide, the tunnel will experience further damage under the action of ground pressure. The deformation pattern of the tunnel will also become more complex.  
2. The tunnel intersects with the sliding surface.  
When a tunnel crosses the sliding surface of the landslide mass, the lining is dominated by longitudinal cracks, and the deformation on the side of the mountain is serious. The force characteristics of the tunnel are shown in Figure 3. Among them, the blue arrows represents the direction of stress around the surrounding rock, and red dash lines represents the sliding zone area. The tunnel crown and sidewalls are subject to geotechnical pressure with weak shear resistance, and shear damage can easily occur at the junction of the tunnel and the sliding surface. The bending moment of the side wall and the tunnel crown will be the largest, and the mountainside deformation will be more serious. Tunnel excavation causes the sliding surface to slide, with the lining structure on the mountainside of the tunnel bearing and transmitting the thrust from the landslide. Owing to the influence of tunnel excavation, the tunnel easily forms a loose circle, loosening the surrounding rock and further inducing instability and cracking in the tunnel.  
Figure 3: The force analysis of the tunnel sliding surface.  
Figure 2: Schematic diagram of solution circulation.  
(3) The tunnel is located below the sliding surface.  
When a tunnel is excavated below the sliding surface, its main characteristics are crown deformation and side wall deformation on the mountainside. Figure 4 shows that the tunnel crown is subjected to the combined action of rock and soil pressure and landslide disturbance pressure. The transmission of these forces is related to the surrounding rock grade, structure, and other factors. The deformation characteristics mainly manifest as the relaxation of the rock mass at the top of the tunnel, and local collapse or extrusion deformation may occur. Given the uneven load, the axial tension or shear strain of the tunnel lining structure will be greater than its yield value, the crown will bend to the tunnel, and the bottom will be compressed, so the shear deformation of the tunnel near the sliding surface is the most obvious. When the tunnel is close to the slip zone, it has a greater impact on the stability of the landslide. Thus, the surrounding rock strength of the tunnel is related to the distance of the tunnel from the sliding surface.