# Influence of a Landslide on a Tunnel in Loess-Bedrock Ground
## 3 Results  
### Mechanical Behaviors and Displacements  
In this study, five repeated loading tests were conducted, with each loading test conducted for 20 minutes unloading. Figure 5 shows the load-displacement and displacement-time curves of the MTS. There are five curves in Figure 5a, which represent two different deformation modes: a long \"S\" shaped curve (o-a), and a short \"S\" shaped curve (a-b, b-c, c-d, d-e). The change curve has three stages: the compaction stage, the deformation accumulation stage, and the sliding stage. The difference between the two modes lies in the compaction stage. In the curve o-a, compaction is maintained for a long time, the porosity in the soil decreases, and the soil becomes consolidated. After compaction, the interface between loess and bedrock is affected by friction. The soil slides along the interface when the friction reaches the maximum static friction force (60 kN). The first inflection point appears on the displacement-time curve. When unloading, the displacement remains unchanged. In curve a-e, the compaction time is greatly reduced, and the deformation of soil is mainly due to slippage. The maximum force of each curve is close to 45 kN and the maximum displacement is 18 mm. According to the displacement-time curve, the soil shows complete plastic behavior. Figure 4: Numerical modeling of the test model at a 1:1 ratio. Therefore, we assume that the loading method was displacement controlled. The residual curve appeared under continuous loading conditions with a value of 60 kN. In this experiment, the peak force decreased after repeated loading. This result indicates that the maximum static friction force was 45 kN. The first peak force contains the cohesive force between the soil particles, as well as the resistance caused by the tunnel. In conclusion, the initial slip had the largest force, and once the slope had slipped, the next slip occurred easily. The tunnel moved as the slope slipped. The laser cross site at different time points was used to reflect the tunnel deformation \"\(l\)\". The original site was regarded as the zero point, and the tunnel photo was measured every 30 min. The tunnel deformation characteristics are shown in Figure 6. In the first 300 min of the test, the image showed a minimum pulsating deformation, and the displacement in the y direction was about 1 cm. After 300 min, the soil deformed, resulting in an obvious deformation of the tunnel. The tunnel displacement increased with the increase in load, and then rebounded after unloading. With the increase in time, the tunnel rebound deformation decreased gradually. There are three forces that determine the tunnel's resistance to the landslide: the pressure upon the soil, the support force of the underlying soil, and the embedded force of  
Figure 5: MTS data measured during the loading process. Figure 6: Tunnel deformation reflected by the site change of laser cross site. the bedrock. The test results show that the supporting force of the lower soil increased with the decrease in the influence of the embedded force. A series of annular cracks developed in the tunnel structure. In order to compare the soil pressure changes at different slope heights, the earth pressure cells along the axle wire (1-2, 2-2, 2-5, 2-8, 3-1, 3-2) were regarded as the objects. There were three zones, as illustrated in Figure 7: A is the soil upon the tunnel, B is the tunnel, and C is the soil below the tunnel. The soil pressure was zero in the B zone. There were four measurement points at heights of 80, 50, 30, and 10 cm. The soil pressure was 400 kPa at 80 cm, which is equal to the MTS's force. The soil pressure was 268 kPa at 50 cm, 110 kPa at 30 cm, and 60 kPa at the bottom of the slope. The soil pressure of uniformly distributed soil calculated based on the self-weight of soil is shown in the solid line in Figure 7. The theoretical calculated value is the soil pressure of homogeneous soil, while the experimental and numerical calculated values are the soil pressure in the presence of the tunnel structure soil.