## 5 Conclusions  
This paper utilized a damaged coal rock body seepage test system to conduct repeated loading and unloading seepage tests on coal rock body samples from three overburden zones. The tests revealed the seepage characteristics of coal rock bodies in these zones under multi-protection layer mining in high-gas coal seam groups. The main conclusions are as follows:  
1. The permeability of the broken coal sample during the first loading seepage process is significantly higher than during the subsequent loading processes. Permeability during the loading stage is consistently greater than during the unloading stage in each cycle. As the number of loading and unloading cycles increases, the permeability decreases as each cycle gradually diminishes.
2. The permeability of broken coal rock bodies decreases with stress, increases with larger particle sizes, and rises with a higher proportion of rock in the coal rock samples. The permeability distribution in the mining area follows an \"O\"-shaped pattern, gradually increasing from the center to the outer areas.
3. When the protected layer is located within the fracture zone of protective layer mining, and the first mining stage has already resulted in significant stress relief and permeability improvement, the effect of the second protective layer mining on stress release and permeability enhancement becomes less pronounced. In contrast, if the first mining stage did not sufficiently relieve stress or enhance permeability, the second mining stage has a more substantial effect.
4. When the protected layer is located within the curved subsidence zone of protective layer mining, the mining process is ineffective in relieving stress and improving permeability, even when multiple layers are mined. Therefore, in protective layer mining practices, it is recommended to select a protected layer within the fracture zone and avoid positioning it in the curved subsidence zone to achieve the best results for stress release and permeability improvement. Additionally, gas extraction drill  
Figure 11: Vertical stress and permeability distribution in the goat: (**a**) vertical stress distribution in the goat and (**b**) permeability distribution in the goat.  
holes should be positioned along the outer rim of the goaf, particularly at the four corners of it, to enhance drilling efficiency.  
Conceptualization, B.L.; methodology, J.Z. and B.L.; investigation, J.Z. and B.L.; writing--original draft preparation, J.Z. and B.L.; writing--review and editing, J.Z.; funding acquisition, J.Z. and B.L. All authors have read and agreed to the published version of the manuscript.  
This paper is financially supported by the National Natural Science Foundation of China (52204132 and 42304085), the Jiangsu Funding Program for Excellent Postdoctoral Talent (2023 ZB154), the Natural Science Foundation of Jiangsu Province (BK20231086), the Hunan Provincial Natural Science Foundation of China (2023 JJ40285), and the Scientific Research Foundation of Hunan Provincial Education Department (22B0469).  
Not applicable.  
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.