# Influences of Different Factors and Sensitivity Analysis of Permeability of Gassy Coal
## 6 Conclusions  
The seepage test system for damaged coal and rock mass was used to carry out seepage tests on gassy coal under different factors (axial pressure, confining pressure, and gas pressure). The influence of these factors on the permeability of gassy coal and the sensitivity of permeability to each factor were analyzed. The following main conclusions are drawn:  
1. The relationship between permeability and axial pressure in gassy coal follows a quadratic polynomial function under constant confining pressure, while the relationship between permeability and confining pressure is described by a power function under constant axial pressure. During axial seepage, gassy coal's permeability is significantly more sensitive to confining pressure than axial pressure, with the sensitivity to confining pressure being approximately 8.5 times greater. Therefore, reducing vertical stress in the protected layer has a more pronounced pressure-relief and permeability-enhancing effect compared to decreasing horizontal stress in protective layer mining;
2. At constant axial and confining pressures (same stress), the permeability of gassy coal initially decreases and then increases, following a V-shaped pattern as gas pressure increases. There is a turning point in the seepage tests, that is, the critical gas pressure, which is the boundary between the slippage effect and effective stress. When the gas pressure is lower than the critical value, the slippage effect plays the leading role, and the lower the stress and gas pressure are, the more significant the influence of the slippage effect on the permeability; on the contrary, the effective stress plays a dominant role in the variation of permeability of coal when the gas pressure exceeds the critical value;
3. Under a non-isobaric deviatoric stress state, the permeability of gassy coal is primarily influenced by confining pressure, followed by gas pressure and axial pressure in decreasing order of sensitivity.  
Data curation, B.L.; Funding acquisition, B.L. and Y.L.; Methodology, Y.Y.; Validation, Z.Q.; Writing--original draft, B.L.; Writing--review and editing, Y.L. and Y.Y. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Natural Science Foundation of China (52204132 and 52174166), the Independent research project of State Key Laboratory for Fine Exploration and Intelligent Development of Coal Resources, CUMT (SKLCRSM24X002), Hunan Provincial Natural  
Figure 11: Influence trends of various factors on the permeability. (**a**) Orthogonal experiment Table 1, (**b**) orthogonal experiment Table 2.  
Science Foundation of China (2023)[J40285], Scientific Research Foundation of Hunan Provincial Education Department (22B0469).  
Not applicable.  
**Data Availability Statement**: The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding authors.  
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.