## 5 Example Verification and Mechanism Analysis
### Mechanism Analysis  
1. As the most important mining factor affecting and controlling the development of water-conducting fractures in the overlying strata of coal seams, mining height has been recognized by scholars at home and abroad [14; 15; 16]. The goal formed by mining height is actually the space of movement, deformation, and fracture of the coal seam overburden. The size of the mining height determines the size and size of this \"space\", which also profoundly affects the degree of movement and deformation of the overlying strata of the coal seam. Generally speaking, the mining height has a significant positive effect on the development of water-conducting fractures in overlying strata; that is, the larger the mining height is, the larger the size of the goat is, the larger the space for the movement and deformation of the overlying strata is, and the higher the development height of water-conducting fractures in overlying strata is [18; 19]. Under the same mining depth and overburden structure conditions, the maximum development height of overburden water-conducting fractures caused by 5 m mining height is greater than that of 3 m mining height, and the former is 1.1\(\sim\)1.2 times of the latter on average, which not only verifies the positive effect of mining height on the development of overburden water-conducting fractures but also is consistent with the research results of [PERSON] et al. [26] and [PERSON] et al. [39]. 2. As a typical geological occurrence factor of coal resources in Yushenfu mining area, the number of sandstone layers (sand layer coefficient) in overlying strata will also have an important impact on the development of water-flowing fractures in overlying strata of coal seams. Under the condition of equal burial depth, the larger the sand layer coefficient is, the more the number of sandstone layers in the overlying strata of the coal seam is, and the smaller the thickness of the single-layer sandstone is. This will produce the following two effects: First, the increase in the sand layer coefficient will not only lead to the increase in the number of sandstone layers in the overlying strata of the coal seam but also lead to the increase in the number of layers between the sandstones (the main structural plane or weak surface in the rock mass), which makes the overall stability and anti-interference ability of the overlying strata of the coal seam worse [28; 30] and produces a higher degree of failure response under the influence of the same mining activities. In addition, the latest research results show that [40] when the sand layer coefficient is large, that is, the number of sandstone layers is large, and the sandstone of each layer will lead to significant differences in the size, shape, and arrangement of internal particles due to differences in deposition time and environment. The particles between the sandstone layers are difficult to deform synergistically and produce relative displacement when subjected to external forces, so that the cracks are more likely to expand rapidly along the particle boundary, resulting in a greater development height, as shown in Figure 9a; when the sand layer coefficient is small, that is, the number of sandstone layers is small, the thickness of each layer of sandstone is large, and the internal particles are relatively uniform and dense, so that under the same external force, it is easier to block and limit the generation and expansion of cracks, which in turn restricts the development of cracks in the rock layer, as shown in Figure 9b. Second, the increase in the sand layer coefficient will lead to the decrease in the thickness of the stressed rock layer (such as sandstone) in the overburden of the coal seam, which will lead to the deterioration of the mechanical properties of the stressed rock layer [41]. Under the same load and mining activities, it is more likely to crack, break, and eventually lose the ability to support the load of the overlying rock mass [42] and the ability to block the development of the underlying mining cracks [22].