## 6 Conclusions  
1. According to the key stratum theory, the determination of the separation development position is as follows: between the first layer, Yan'an Formation carbonaceous mudstone, and the second layer, Yan'an Formation coarse sandstone; between the third layer, Zhiluo Formation siltstone, and the fourth layer Zhiluo Formation medium-grain sandstone; between the sixth layer, Anding Formation sandy mudstone, and the seventh layer Anding Formation mudstone; and between the eighth layer, Anding Formation sandy mudstone, and the ninth layer Yijun Formation conglomerate. Based on the estimated height of the developed aquifer fracture zone, we can observe that the main concentration of overlying strata water separation development in coal mining is between the Yijun Formation conglomerate layer and the Anding Formation sandy mudstone. The main aquifer in the Yijun and Luohe groups at the 9 th level can serve as a replenishment water source for the aquifer, so, with the disturbance of mining, there is a high possibility of aquifer water inrush between the 8 th and 9 th levels
2. Through a similar experimental method, the evolution process of the overlying strata under mining action was studied, revealing the gradual development of horizontal stratified space from bottom to top along the mining process in the stope. As the working face advances, the horizontally stratified space formed in the early stage andthe vertical fissures will gradually compact and form closed zones as the overlying strata collapse. On the side closer to the working face, a new fissure zone will form, while the asynchrony of overlying strata movement promotes the development of vertical fissures, thereby creating conditions for sudden water inrush disasters induced by water storage space. When the working face advances to 240 m, the stratified space develops to about 248 m above the coal seam roof, between the 8 th and 9 th layers, with a space height of about 0.8 m and a length of about 22 m. At this point, the water-conducting fissure zone has not yet developed into the stratified space and remains relatively stable with subsequent mining. The water-storing stratified space, as surrounding water continuously converges into it, generates a certain static water pressure, exerting pore pressure and load on the underlying rock layers. The pore pressure disrupts the rock structure at the bottom of the stratified space, reducing the effective thickness of the aquiclude. The water load on the strata causes an increase in the height of the fissure zone at the bottom of the strata, potentially leading to water breakthrough in the aquiclude due to the formation of water-conducting fissures. 3. Using numerical simulation techniques, we studied the development of the off-layer position and water-conducting fracture height during the mining of the 1304 working face of Guojiahe coal mine. When excavating to 220 m, the first off-layer appears between the 8 th sandy mudstone layer and the 9 th conglomerate layer, with a width of about 22 m and a height of about 0.9 m. The water-conducting fracture zone jumps to 175 m. When excavating to 240 m, the second off-layer appears, and the first off-layer gradually compacts, with the water-conducting fracture zone height increasing to 202 m. After that, the height of the water-conducting fracture zone does not continue to increase. When excavating to 280 m, the space of the second off-layer reaches its maximum, with a width of about 19 m and a height of about 1.2 m. This off-layer is a water-storing off-layer, and at this point, the water storage capacity of the off-layer has reached its maximum. Methodology, T.Y. and J.S. ; data curation, J.Z., J.W. and J.D. ; manuscript writing, J.S. ; similar simulation experiments, H.L., R.B. and Y.Z. ; writing--review and correction, T.Y. All authors have read and agreed to the published version of the manuscript. This study was supported by the National Natural Science Foundation of China (NO. 52004200), The agency's funding is gratefully acknowledged. Not applicable.