# Motion Characteristics of Collapse Body during the Process of Expanding a Rescue Channel
## 2 Expansion Test of Rescue Channel
### Expansion Test Scheme of Rescue Channel  
(1) Design of physical model for expansion test  
In the physical experiment, the experimental platform is supported by a similar simulator stand and is completed by building a collapse body, a base plate, an expansion device, and a marked particle. Figure 2 shows that the collapse body has an equal proportion of granular particles made of coal from the roof and floor of the actual roadway and is mixed and arranged according to the particle size proportion of the field investigation and statistics; the base plate is a model constructed by pouring with a strength similar to that of the field floor, which is used to limit the vertical displacement of the collapse body; the expansion device is a jack embedded in the base plate, which can slowly lift the collapse bodies above to simulate the expansion test of the rescue channel (as shown in Figure 3). The marked particles are collapse bodies marked by the color calibration method. They are arranged in layers with a spacing of 0.1 m for the purpose of the overall monitoring of the collapse profile displacement, but they cannot be perfectly arranged in a straight line due to certain differences among the particle sizes. Therefore, by recording and comparing the way of marking the particle positions before and after the expansion test, the law of the collapse body is studied when the rescue channel is constructed by means of expansion. Figure 1: Schematic diagram of rescue channel expansion in collapse body. As this test aims to study the motion law of the collapse body, the geometric parameter similarity ratio is taken as the main similarity ratio parameter. The main influencing parameters considered in the simulation device are the width of the expanded channel and the particle size of the collapse body. Therefore, the length similarity ratio of 10:1 and the area similarity ratio of 100:1 are used to meet the requirements of the channel expansion test. In the test, the expansion channel was designed with three different sizes: 0.8 m, 1 m, and 1.2 m. The collapse body can be divided into three particle sizes: 5-10 cm, 10-20 cm, and \(\geq\)20 cm, with a ratio of 2:2:1, according to the site survey statistics. In addition, since the collapse body materials prepared in the experiment are the same, the comparative test for the materials of the collapse bodies is not designed in the physical experiment. According to the similarity ratio, the specific parameters of the simulation device can be calculated as shown in Table 1.  
(2) Design of numerical model for expansion test  
With reference to similar simulated tests, the numerical model constructed in PFC (particle flow code) is also composed of the expansion device, the boundary of collapse body, and the collapse body (as shown in Figure 4). The model uses the actual size of 10 m \(\times\) 4 m; the expansion device and the boundary of the collapse body are simulated by the wall element, and the collapse body is simulated by the rigid block model; the contact model between the blocks and the block and wall element is a linear parallel bond model. In addition, with reference to the mechanical properties of the actual coal rock, the numerical model parameters of the collapse body (rigid block) and the boundary (wall) of the collapse body are shown in Table 2. For the collapse body shown in Figure 4, the model generates the collapse body by randomly generating irregular shapes based on  
Figure 3: Particle expansion process. Figure 2: Similar simulation device and collapse body sample. the Gaussian function so that there is sufficient internal locking force among the particles of the collapse body. At the same time, the collapse particles are generated according to different particle sizes, and the ratio of the three collapse bodies with different particle sizes is 2:2:1. In order to restore the natural accumulation of collapse bodies, the collapse body is generated at a height of 2 m from the bottom with a relatively sparse density, and it falls and accumulates by gravity.