## 3 Experimental Process of the Cutterhead System  
This experimental bench is composed of a proportional cutter head, a driving device, a loading device, a simulated soil box, a signal monitoring device, etc. The working steps of the tunneling experiment are as follows: First, the drive motor is started. The hydraulic pump transmits the hydraulic oil with power from the hydraulic oil tank to the hydraulic cylinder and motor. While the hydraulic cylinder pushes the motor base, the hydraulic motor also drives the rotating shaft of the cutter head to rotate. A formation simulation soil box is installed on the right side of the experimental bench to simulate sandy and pebble formation. In order to monitor the signals and directly observe the operating status of the test bench, the dimensions of the test bench frame are set to be 2800 mm in length, 800 mm in height, and 1250 mm in width. The simulation test bench is shown in Figure 8.  
The experimental bench is designed to simulate the function of the cutter head system of the earth pressure balance shield machine; both the diameter of the cutter head and the opening size have been reduced. During the experiment, particles with overly large diameters need to be processed to prevent damage to the cutter head in the same proportion. Figure 8: The experimental platform for the tunneling process. Figure 7: Comparison of the actual tool head torque and the simulated tool head torque in a certain ring. The equivalent substitution method, one of the methods for treating large-sized particles, is applied. The equal substitution method is used to replace the excess particle size part in the soil within the allowable range with 15 to 20 mm particles. The research results show that the coarse-grained part after substitution has some changes in the curvature coefficient and non-uniformity coefficient but still maintains the original particle content. For particles larger than the opening of the simulated cutter head, particles of the same volume are filled into the simulated soil box to ensure the integrity of the formation particle gradation. Figure 8 shows the partial screening particle diagram. In the screened soil used in the experiment, particles smaller than 10 mm were classified as sand soil particles, those ranging from 0 to 10 mm and 10 to 15 mm were classified as gravel sand particles, and those ranging from 15 to 20 mm were classified as pebble particles. After the soil filling is completed, the soil in the box is compacted and left to stand for 10 h before the start of each group of experiments. Two earth pressure gauges are set inside the soil box to monitor the pressure changes inside the box in real time. The model of the earth pressure gauge used is TMT-Y2000. The soil pressure in the simulated earthen box is set at 10 kPa and the simulated formation depth is 15 m. The wireless torque sensor measures the strain at the end of the cutter head drive shaft by connecting strain gauges. The strain value is measured by vertically arranging 120-3 AA strain gauges. Through the torque signal processing module in the dynamic signal acquisition system, parameters such as the diameter at the end of the shaft, elastic modulus, and Poisson's ratio are set. This module can convert the strain measured by the sensor into a torque value. The rotational speed of the cutter head is measured by using the DH5640 photoelectric rotational speed sensor in conjunction with the DH5905 rotational speed module, and the rotational speed of the cutter head is monitored through the dynamic signal acquisition system. Reflective patches are pasted on the drive shaft of the cutter head, and the sensor is fixed on the simulated shield body for collection. Sensors were used in tunneling experiments on five different types of formations to measure the torque, thrust, and rotational speed of the cutterhead. Two tunneling simulation experiments were conducted for each formation.