# Influence of a Landslide on a Tunnel in Loess-Bedrock Ground
## 4 Discussion  
The sliding zone of a loess-bedrock landslide is located on the contact surface between the loess and bedrock. At the contact surface of relatively flat sedimentary rock, the main deformation mode is friction sliding, and the friction law dictates the deformation process. This movement characteristic determines that this type of landslide will have periodic sliding, namely stick-slip, which is a process of energy accumulation and release. When the deformation is stable, the soil compacts gradually from the back to the front. When the compactness reaches a certain degree, the accumulated potential energy in the soil reaches a critical value, and the potential energy is transformed into kinetic energy, so that the soil slides. This process is short and rapid. When a certain amount of potential energy is released, the potential energy of the soil and the potential energy generated by friction are balanced, and the soil reaches a static state again and begins to accumulate energy. Because soil is a porous elastoplastic media, compaction, elastic deformation, plastic deformation, and whole slip occur during the process of deformation, in which both elastic deformation and plastic deformation occur simultaneously. The soil stress decreases gradually with the increase in depth, and the tunnel affects the stress transfer and changes the stress state of the soil, and further influences the movement mode of the landslide. The  
Figure 14: Deformation characteristics of the slope at the end of the test loading. Figure 13: Deformation contour of slope surface and vertical section calculated by the numerical simulation. essence of the shear stress in soil lies in the friction force and bite force between soil particles. After multiple cyclic shearing, the soil particles in the sliding zone, which were originally arranged in order during the consolidation stage, re-interlock with each other. Hence the shear strength of the first shearing is the greatest. As the particles are gradually arranged in order during the repeated shear process, the shear stress displayed by the particles gradually decreases, and the shear stress tends to a constant value after the completion of the particle arrangement, which is the shear residual stage. The spatial relationship between a landslide and a tunnel will show different deformation and failure forms. According to the landslide characteristics and tunnel distribution, there are seven different types (Figure 15). Among them, c and d are tunnels through bedrock, and their stability is not affected by landslides. Type a and f cross the slide body in different directions, and the tunnel structure is completely located within the slide body. During slope sliding, whole deformation of these two kinds of tunnels will occur along with the soil mass. The deformation characteristics of these two kinds of tunnels can be determined by using the beam model of elastic foundation [26, 27, 28, 29, 30, 31, 32]. In the loess area, the deformation of the shallow surface is the main form of landslide, playing a large role in slope collapse [33, 34]. A shallow surface landslide changes the stress characteristics of the tunnel. For an f-type tunnel, on the one hand, it will produce a bias voltage, and on the other hand, it will produce a friction effect between the soil and the tunnel structure. For a g-type tunnel, due to the change in the earth pressure behind the wall, wall cracking often occurs, and sometimes the tunnel is buried by a mud flow. The e-type tunnel is an extreme case, in which the sliding zone passes through the tunnel structure under shear action, leaving it prone to deformation and failure. Faults or structural planes pass through tunnels in similar ways within the rock mass. This kind of tunnel does not appear in engineering in general, and is analyzed and discussed as a theoretical model. In this paper, type b was taken as the study object. In this case, the tunnel is partly embedded in the bedrock and partly in the loess.