## 4 The Large-Scale Landslide Model Experiment and Bayesian Updating
### Experiment Setup  
The experiments have been carried out in a large-scale landslide model experiment at The Key Laboratory of Geological Hazards and the Ministry of Education of the Three Gorges Reservoir Area of the Three Gorges University (China); the setup is shown in Figure 3. The model test platform was 6 m long, 0.8 m wide, and 1.5 m high. The door at the right end of the test platform could control the rise and fall of the reservoir water level. The landslide model was connected to external water supply pipes and drainage pipes. The speed at which the water level of the reservoir changed was adjusted by setting a flow valve.  
Figure 2: Flowchart of the Bayesian updating procedure.  
According to the nature of the landslide body in the Three Gorges reservoir area, the material of the landslide body was designed. The material used in the landslide body was composed of soil and small stones, and the ratio was 7:3. The landslide model test was completed according to the principle of landslide model forming. Considering the size of the model and the need to embed sensors, it was decided to choose the tamping method to build the landslide model. The sensors were embedded in the model in advance. The moisture content sensors were arranged in four sections, with 3 sensors in each section. Then we increased the water level of the reservoir to monitor the change of its water content. The overall landslide model is shown in Figure 4. In this figure, instruments for displacement monitoring and high-density electrical methods are included (the results are not used in this article.) In order to obtain the material parameters of the landslide model, a triaxial test and a constant head permeability coefficient experiment were carried out. A pressure plate instrument was used to obtain the characteristic curve of unsaturated soil water, as shown in Figure 5a,b. In this figure, the pressure pump and pressure plate instruments are displayed.  
Figure 4: A picture of the landslide model built indoors, from a frontal view: the model was 1.5 m (height) \(*\) 0.8 m (width). The water content sensor is inside the landslide body (not visible; the actual water content sensor is shown in Figure 6a).  
Figure 3: The side view of the landslide model and configuration of instruments in the experiment. A drawing of the configuration of the experimental model, showing the bedrock region (within blue lines), the landslide body region (below the green line), and the embedded sensors to monitor the water content.  
Sensors were used to obtain water content data in real time. Figure 6a shows the water content sensor. The power supply voltage of the sensor was 5 V, and the output signal type was RS485. The monitoring data of the water content sensor were saved when the water level was from 0.3 to 1 m. Figure 6b shows the sensor data interface. Its function was to convert RS485 signals into USB signals. Based on the Modbus protocol, the data acquisition software was developed using C# to save the water content data to the database. All sensors conducted data sampling and recording every 10 s. Figure 7 is a histogram representation of moisture sensor monitoring data. In this figure, the abscissa represents different moisture content, and the ordinate represents its frequency. These water content data were used as observation samples in Bayesian updating (specifically, as shown in Figure 2).