# Research on the Roof Failure Law of Downward Mining of Gently Inclined Coal Seams at Close Range
## 2 Overview of the Mining Area
### Hydrogeology  
The aquifer within the well field consists of the Quaternary aquifer, which receives the most precipitation recharge. The lithology here is primarily loess, with good vertical permeability, and water is mainly stored at the bottom of the Quaternary formation. The unit water inflow is 0.003 L/(s\(\cdot\)m) and the permeability coefficient is 0.014 m/d, indicating very weak aquifer water content. There is no significant impermeable layer between the Paleogene aquifer section and the Quaternary aquifer section. The Paleogene aquifer, which is located above the red clay, is considered part of the same aquifer as the Quaternary one, with weak water-bearing properties. The lower part of the Anding Formation contains relatively thick coarse sandstone, which is loosely cemented and has developed fractures and voids. The simple hydrological observation data indicate that the unit water inflow of this aquifer is 0.81 L/(s\(\cdot\)m), and the permeability coefficient is 0.412 m/d, suggesting a moderate water-bearing capacity. According to the BK1 drilling data, the coarse-grained sandstone in the Zhi Luo Formation accounts for nearly 50% of the aquifer, with a strong  
Figure 2: Geological profile of the 11 th mining area of Yündongou Coal Mine. water-bearing capacity. However, according to lithological analysis, there are impermeable layers of claystone interbedded within the coarse-grained sandstone, which hinders hydraulic connectivity between the aquifers, thus leading to noticeable heterogeneity in the water-bearing capacity of the Zhi Luo Formation. The Yan'an Formation aquifer section is divided into three segments, based on sedimentary cycles: the water-bearing section above Coal Seam 5, the water-bearing section between Coal Seams 5 and 12, and the water-bearing section below Coal Seam 12. Coal Seam 4 is currently being mined and is affected by the water-bearing section above Coal Seam 5, which is influenced by coal seams and impermeable lithologies such as mudstone and siltstone. The hydraulic connectivity of the aquifer is weak, vertically, and the water-bearing capacity is also weak. The impermeable layer within the wellfield consists of impermeable Paleogene sandy claystone layers. The lithology mainly includes purple-red sandy clay, silt, and gravel, with an average thickness of around 40 m, and is relatively stable. This stratum exhibits good impermeability and stability, serving as a stable barrier between the unconsolidated rock layers and the bedrock aquifer within the wellfield. The impermeable siltstone and mudstone layers in the central part of the Zhiluo Formation are composed of light gray and gray-green siltstone and mudstone, with a relatively large and stable thickness averaging around 30 m. This is also a stable impermeable layer. The impermeable layers in various sections of the Yan'an Formation consist of intercalated siltstone, mudstone, and coal layers, including the coal seams themselves, as well as the interbedded sandy mudstone layers at the top and bottom. The lithology primarily consists of coal, dark gray mudstone, and siltstone interlayers, with a dense structure. The distribution within the wellfield is relatively stable, and the impermeability is relatively good. The geological column diagram is shown in Figure 3.  
Figure 3: Geological bar chart of the Yindonggoul Coal Mine. Theoretical Analysis of the Roof Failure Law in the Downward Mining of Gently Inclined Coal Seam Groups  
The research on the development height laws of the collapse zone and fracture zone in a single coal seam is currently mature and is theoretically guided by the three-lower coal mining code. However, there is no clear prediction method to determine the development height of the fall zone and fracture zone during the mining of close-range coal seams. [PERSON], [PERSON], et al.