## 2 Similar Model Test Design
### Test Process  
The flowchart of the test, including the main steps, is shown in Figure 12 as follows. Figure 11: Gravel bedding. Figure 12: Test flowchart. Figure 10: Cement-soil-making process. 1. Sample preparation and test preparation In the process of the layered filling test model, each layer of the 10 cm soil layer was left standing for 24 h to ensure that each layer had initially settled fully under the action of its own weight, and then the next layer of soil sample was filled. Considering that the test model box was assembled using three layers of enclosure, when the soil layer was filled to a height of 50 cm, the rigid enclosure was removed, and green pushpins were used to make speckle. The pushpins were driven into the soil layer surface, and then the prepared plexiglass was installed on the model box; the next layer of the soil layer was filled by repeating the above steps. The final test model is shown in Figure 13. During the soil-filling process, we buried the prepared earth pressure box at a predetermined position according to the test plan, as shown in Figure 14. After the soil layer filling was completed, the prepared cement soil and gravel were filled on top of the soil sample, and the prepared test model is shown in Figure 15. After the scaled test model was prepared, the soil sample was transported to the indicated position using the trolley of the slope stability system, and the 2D full-field strain measurement system and earth pressure box were connected with the corresponding control hardware. All the test equipment was debugged, slope stability system loading and test data-monitoring performance were debugged under no-load conditions, and the loading path was set. Figure 16 shows the equipment layout of the tunnel scaling test site after the final debugging of data-monitoring performance and data-monitoring settings for the 2D full-field strain measurement system and earth pressure box. Figure 16: Tunnel scale test site equipment layout. Figure 15: Prepared test model. Shield and train vibration simulation  
In order to simulate the deformation and load of the tunnel face and overlying strata during shield tunneling without and with trains, two test conditions were determined in this scaled test: The first is the case of no train vibration load, meaning there is no load on the upper part of the test model, and only horizontal thrust is applied to the tunnel axis to simulate the influence of thrust during shield propulsion on tunnel face deformation and load distribution. The second is the case of train vibration load, meaning when simulated train vibration load is applied to the upper part of the test model, horizontal thrust is also applied to the tunnel axis, and the coupling effect of train vibration load and shield thrust on the tunnel face deformation and load distribution is simulated. In the first case, no rail model is arranged on the upper part of the test model, as shown in Figure 17a; in the second case, a rail model of similar proportions is arranged on the upper part of the test model according to the rail distribution of Xulan high-speed railway (on-site), as shown in Figure 17b. (3) Load path determination  
(1) Test condition 1: Loading path  
For condition 1, there was no train load in the upper part of the test model, and only the stratum dead weight acted on the tunnel face during shield tunneling. Therefore, only the influence of the thrust along the water level on the tunnel face during shield tunneling was considered during the test. In the test process, the hydraulic servo actuator of the slope stability system pushes the force transfer rod of the tunnel mold and then acts on the tunnel face, and the pressure and deformation characteristics of the tunnel face and the overlying ground layer during the process of the horizontal servo actuator are monitored using the earth pressure box and the 2D full-field strain measurement system.