## 6 Conclusions  
This paper presented a comprehensive case study of the surrounding rock failure characteristics and the control techniques for the 21309 roadway at the Huoijitu coal mine through three research methods: theoretical calculations, field observations, and numerical modeling. The main conclusions of this study are as follows:  
1. The shorter the distance is from the working face, the larger is the developmental range of the broken rock zone; the range of the broken rock zone of the coal wall  
Figure 15: Rock strata fracture diagram: (**a**) traditional mining method; (**b**) roof cutting and pressure relief.  
side is larger than that of the coal pillar side. Through formula calculation and field observation, the maximum damage range in surrounding rock on both sides of the roadway can reach 1.8 m.
2. Under the influence of primary mining, the maximum principal stress of the roadway surrounding rock reaches the maximum value of 6.29 MPa at a distance of 170 m behind the working face. The ratio of the maximum principal stress to the minimum principal stress reaches the maximum value of 1.51 at a distance of 70 m behind the working face. Moreover, the plastic zone of the surrounding rock is less developed, and the surrounding rocks of the roof and floor are relatively complete.
3. Under the influence of secondary mining, the maximum principal stress of the roadway surrounding rock reaches the maximum value of 19.82 MPa at a distance of 70 m behind the working face. The ratio of the maximum principal stress to the minimum principal stress reaches the maximum value of 1.95 at a distance of 20 m behind the working face. The plastic zone of the surrounding rock is large, the plastic zone of the roof is small, the maximum depth is 0.3 m, the developmental ranges of the two sides are large, the maximum damage depth is 0.9 m, and the floor is relatively intact.
4. This study demonstrates that a combination of multiple research methods is needed for further comprehensive studies to avoid partial conclusions. The methods and results presented herein are expected to serve as a reference for the analysis of roadway surrounding rock states under similar conditions; optimized support design is also expected to guide field applications.  
Conceptualization, X.Y. and G.Y.; methodology, G.Y., R.H. and Y.W.; software, G.Y.; validation, R.H., Y.W. and J.L.; formal analysis, R.H. and J.L.; investigation, J.Z. and S.H.; resources, X.Y. and Y.W.; data curation, J.Z. and S.H.; writing--original draft preparation, G.Y.; writing--review and editing, R.H., Y.W. and J.L.; visualization, G.Y. and Y.W.; supervision, X.Y.; project administration, G.Y.; funding acquisition, X.Y. All authors have read and agreed to the published version of the manuscript.  
This work was funded by the National Natural Science Foundation of China, Grant No. 52074295, and the Fundamental Research Funds for the Central Universities, Grant No. 2021 YJSSB13.  
The authors appreciate the support of the School of Energy and Mining Engineering, China University of Mining and Technology-Beijing, and Huojitu coal mine of China Shenhua Shandong Coal Group Corporation Limited for field practice study.  
The authors declare no conflict of interest.