# Research on the Roof Failure Law of Downward Mining of Gently Inclined Coal Seams at Close Range
); [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (D.L. ); [EMAIL_ADDRESS] (J.D. ); [EMAIL_ADDRESS] (Y.Z.) Ji Z Zhang  
School of Energy and Mining Engineering, Xi'an University of Science and Technology, Xi'an 710054, China; [EMAIL_ADDRESS] (T.Y. ); [EMAIL_ADDRESS] (J.Z. ); [EMAIL_ADDRESS] (S.G.); [EMAIL_ADDRESS] (Y.H. ); [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (D.L. ); [EMAIL_ADDRESS] (J.  
properties of the overlying strata give rise to a range of significant issues [1; 2]. Multi-seam mining often leads to a series of safety hazards, such as secondary roof fracturing, interlayer separation-induced water hazards, and strong mine pressure [3]. These problems not only reduce mining efficiency but can also result in serious safety issues and accidents. As the cumulative mining thickness increases during multi-seam extraction, the water-conducting fracture zone in the roof progressively develops upward. Once it reaches an aquifer, it may channel water into the mine, potentially causing water intrushes or even mine flooding [4]. Therefore, studying the movement patterns of roof layers during multi-seam mining is of great theoretical significance for the prevention of water-related hazards and the assurance of safe coal production in the mines. The development height of the water-conducting fracture zone is one of the key factors leading to roof-related water hazards in coal mines; it is directly related to the safe operation of the mine and the protection of water resources. This zone refers to the fractured area in the overlying strata that, after coal seam extraction, forms through-going fractures under mining-induced stress, allowing connectivity with overlying aquifers or surface water. If the development height becomes excessive, it can connect the aquifer layers, potentially causing water inrush and mine flooding accidents. Therefore, scholars both at home and abroad have conducted long-term and in-depth theoretical investigations, field measurements, and modeling studies focusing on its development mechanisms, evolution patterns, and height prediction. These efforts have yielded abundant results and led to the development of various prediction methods. [PERSON] et al. [5] drew upon a systematic analysis of field observation data from numerous engineering cases to thoroughly summarize the dynamic development patterns of the caving zone and the water-conducting fracture zone in the overlying strata during coal seam mining. They found that the heights of the two zones are significantly correlated with mining height, lithological assemblage, and stratigraphic structure. On this basis, they developed empirical prediction formulas. [PERSON] [6] emphasized the significant controlling role of the internal structure of overlying strata on the initiation, propagation, and final morphology of the water-conducting fracture zone. He pointed out that factors such as the layering thickness of hard rock, the alternation of soft and hard rock layers, the presence of key strata, and their fracturing characteristics profoundly influence the development path, connectivity, and overall height of the fracture zone. His work advanced the study of the water-conducting fracture zone from a macro-level statistical perspective to a more refined analysis based on the mechanical structure of rock layers. [PERSON] [7] conducted research with a clear focus on engineering applications. By integrating detailed, measured data from multiple fully mechanized mining faces, he specifically analyzed the differential impacts of roof lithology--particularly the contrast between hard and soft rocks--on the development of the \"two zones\" (caving zone and water-conducting fracture zone). He distinguished between empirical formulas for hard-roof and soft-roof conditions, thereby enhancing the accuracy and relevance of fracture zone height prediction under varying geological conditions.