# Influence of a Landslide on a Tunnel in Loess-Bedrock Ground
## 1 Introduction  
Loess-bedrock landslides are one of the main types of landslides. The huge impulse generated during sliding and the large volume of such landslides are very likely to cause rock instability, which is highly hazardous [1]. The deformation of a loess-bedrock landslide is affected by many factors, and the deformation characteristics are different under different conditions. The bedrock layer in contact with the loess forms over a short term and is mainly composed of sedimentary rocks [2], which contain sandstone and mudstone. These rocks are susceptible to water ingress. Once the rock is softened, the anti-slide force of the interface between the loess and bedrock decreases and a slide occurs [3; 4; 5; 6]. In addition, water that permeates into the loess will make the soil self-weight increase, meaning the slide force increases. In addition, in the back edge of a slope, a series of tension cracks provide a path for water infiltration. Water in these back edge cracks will introduce pore water pressure and seepage pressure, which are key factors that induce slides. Furthermore, vibrational effects due to seismic or engineering activities can also induce some landslides [7; 8]. Landslides lead to stress conditions for tunnels, and the stress state and deformation characteristics of a tunnel-landslide system are different for each landslide. There are several kinds of factors that influence tunnel structures: the spatial relationship, the slide area behavior, the soil behavior, the tunnel structure parameters, etc. [9; 10; 11]. The model test and numerical simulation are regarded as the most effective methods to investigate the deformation characteristics of a Landslide-Tunnel System (LTS). Although numerical simulation offers an effective and low-cost method, it encounters difficulties in determining the material parameters. The parameters of the soil obtained from model tests or field tests or variation of the envelope parameters or parameter sensitivity analysis are usually used to determine the parameters for numerical simulations to study the impact of landslides on a tunnel [12; 13; 14]. The model test can provide the material parameters and the real deformation situation, so the two methods are usually combined to achieve this aim. Many model tests are employed in the context of LTS, including model box, vibrostand, and centrifuge systems. The stress and displacement of the slope during the tunnel excavation process have been studied, considering the creep of slip-face soil under water-softened conditions [15]. In addition, seismic activity is one of the key factors affecting the stability of the second lining in shallow-buried tunnels [16; 17]. The loess behavior and tunnel burial depth both have an impact on tunnel stability [18]. The spatial relationship between a tunnel and landslide has also been studied using a model box, where the tunnel axial was the same as the slope dip-direction [19; 20; 21]. What is more, the collapse of the foundation under a tunnel affects the tunnel stability [22]. There have also been a series of model experiments examining tunnels and slopes [23; 24; 25]. In most studies, the deformation and mechanical behavior are the primary focuses. In geological history, loess deposited on bedrock may have moved many times. Loess-bedrock landslides exhibit a special form of movement, which is called stick-slip. With the tunnel excavation, the loess is disturbed and moves again. This movement form is a potential threat to tunnel stability. Therefore, there are two key problems in LTS research: the stick-slip characteristics of the slope and mechanical behavior of the tunnel. In order to solve these problems, this paper developed a slip surface deformation monitoring method through model testing of LTS and monitored the lateral deformation of the slope surface through particle image velocimetry (PIV).