## 5 Conclusions  
In this paper, the adsorption characteristics of mixed coal (virgin coal and tectonic coal) and variations of specific surface areas before and after CH\({}_{4}\) adsorption were researched. The effect of different mass ratios of coal samples on the adsorption constants \(a\) and \(b\) and the change of the specific surface area before and after adsorption were studied. A mathematical model of the relationship between the strain after gas adsorption and the specific surface area change before and after adsorption was created. In addition, a mathematical model of the relationship between swelling stress and the specific surface area change before and after adsorption was deduced. The main conclusions are summarized below.  
1. Through the analysis of the test results of the specific surface area of the mixed coal sample, it was concluded that with the increasing proportion of the mass of the tectonic coal in the mixed coal sample, the difference of the proportion of the pore specific surface area before and after the adsorption of the coal sample showed a decreasing trend first and then increased and reached the minimum when the masses of tectonic coal and virgin coal were approximately equal. The change trend of the specific surface area of macro pores was opposite that of the specific surface area of micro pores.
2. By analyzing the experimental results, it was concluded that with an increase in the quality of the tectonic coal, the adsorption capacity of the mixed coal gradually increased. Under constant pressure, the amount of adsorbed gas changed with the mass ratio of the mixed coal, showing a downward parabola change characteristic. When the qualities of tectonic coal and virgin coal were approximately equal, the amount of gas adsorption, adsorption constant \(a\) value, and gas initial velocity of diffusion reached their maximums, but the adsorption constant \(b\) value reached its minimum.
3. On the basis of the gas adsorption test results of the mixed coal sample, the mathematical model of gas adsorption strain and pore specific surface area changes before and after adsorption in the mixed coal sample and the mathematical model of swelling stress and the variation of pore specific surface area before and after adsorption in the mixed coal sample were created. These models reflect the variation of the expansion strain and stress of the mixed coal sample after gas adsorption, and describe that when the mass ratio of virgin coal to tectonic coal was approximately equal, a large amount of gas is likely to push out after coal disturbance, providing a theoretical basis for the further study of coal and gas outburst mechanisms.  
In conclusion, the experimental study of the adsorption process in mixed coal in this paper provides a certain experimental scientific theory and lays a technical foundation for the further study of the gas adsorption characteristics near coal seams of mine structures. This information can help in effectively controlling the difficulties of coal dynamic disasters and studying the corresponding disaster prevention and control technology.  
Conceptualization, P.Z. and H.L. ([PERSON]); methodology, S.L.; validation, H.L. ([PERSON]); Y.J. and H.L. ([PERSON]); formal analysis, M.Y.; data curation, M.Y.; writing--original draft preparation, P.Z. and J.L.  
This research was funded by National Natural Science Foundation grants of China (51604219, 51674192, 51604220), the Basic Research on National Natural Science Foundation key project of China (51734007), and the Project of the Tian Shan Innovation Team (2018D14003). The authors wish to acknowledge the Tian Chi Coal Mine for providing the coal samples used in this study.  
The authors declare no conflict of interest.