*2.1. Experimental Model*

The two-dimensional similar material simulation experiment platform was often used to simulate the deformation, damage and failure laws of overlying strata in the process of mining [18,19]. The size of similar material simulation experiment platform was 1800 × 160 × 1100 mm in the lab. The multi-layer combined coal and rock mass was composed of five layers, each with a thickness of 200 mm; from top to bottom, they were fine sandstone, medium sandstone, coal, coarse sandstone and mudstone. The similarity density constant of rock mass is 1.6, and that of coal is 1; the composition and ratio of similar materials of each layer in coal and rock mass can be seen in Table 1. The vibration amplitude was measured by magnetoelectric speed sensors (2D001) with a size of 63 × 63 × 63 mm. The distributed network dynamic signal test system (DH5981) was used for data acquisition and analysis, as shown in Figure 1.



**Figure 1.** Experimental model and data acquisition system.
