## 3 Similarity Simulation Experimental Study on the Law of Overlying Strata Caving
### Characteristics of Overlying Strata Caving and Delamination Evolution  
Similar experiments have observed the caving characteristics of overlying strata after mining in the 8103 working face, and then analyzed the development of the water-conducting fracture zone by studying the caving process of overlying strata. Figure 3 shows the caving characteristics of the overlying rock after mining of the 8103 working face. After mining of the working face, overburden caving forms a breaking line and reaches a critical point, and the overburden migration height is 160 cm (320 m). The overburden rock of the 8103 working face was disturbed by mining, resulting in delamination and fractures, which led to the formation of a water-conducting fracture zone. During mining in the working face, the overburden separation layer mainly showed a change in shape and development height. As shown in Figure 4, the evolution of the mining separation layer in the 8103 working face shows the height of the water-conducting fracture zone in the working face reaches about 50 cm from the open cut, and the water-conducting fracture zone above the working face continues to develop after mining ends, stopping when the height reaches about 60 cm. With the advancing of the working face, the upper roof cannot completely fill the goat, and the upper strata of the goat move asynchronously, resulting in bed separation. With the advancing of the working face, the mined-out area is continuously filled, and the range of the height and length of the crack increases. The middle part of the broken rock mass is hinged, forming a \"triangular\" separation zone with the upper unbroken rock mass. Compared with the previous separation, the separation volume is obviously increased. As the working face continues to advance, the development height of the \"triangle\" separation zone extends to 73.4 cm, and begins to decrease gradually. As the hard main key layer plays a good supporting role, the separation layer does not continue to develop upwards, but develops into a \"basin\" at the bottom of the main key layer. At the bottom of the main key layer, the abscission layer experiences the evolution of \"emergence-development-closure\". The evolution of overlying strata caving is shown in Figure 5. The height and range of overlying strata caving are constantly expanding with periodic weighting, broken rock blocks are transformed into piled rock blocks, and undamaged rock strata form a new envelope of overlying strata caving. With development of the mining face, the range of the overlying strata caving envelope increases. When the working face advances to 51.8 cm, the caving height of overlying strata reaches 10.3 cm; when the working face advances to 73.4 cm, the overlying strata continue to develop upwards and collapse violently, and the development height of fissures reaches 43.8 cm. When the working face is 141.8 cm, the development height of the water-conducting fracture zone reaches the maximum, and does not continue to develop upwards, with a height of 73.4 cm. When full mining is achieved, the height of overburden fracture stability is 73.4 cm, which is similar to the height of abscission layer development shown in Figure 4.  
Figure 3: Caving characteristics of the overlying rock after mining of the 8103 working face. Location and Energy Characteristics of Microseismic Events in the Process of Overlying Strata Caving  
The microseismic monitoring system monitors microseismic events in the entire excavation process in real time and reveals the gestation process of the water channel through research on microseismic events and energy distribution. Figure 6 shows the microseismic events and the cloud image of energy distribution in the entire excavation process. As shown in Figure 6a, the dots represent microseismic events, and their colors represent the energy of the microseismic events. Cracks are continuously formed as mining takes place at the working face.