## 7 Conclusions  
This study fully analyzed the impact of surrounding rock disturbance caused by double-roadway digging and verified it by theoretical analysis. By using numerical simulation and field monitoring, the results showed that a 16 m coal pillar could maintain roadway stability under the condition of improving the efficiency of the double-roadway digging and improving the utilization rate of the coal resources compared with the 20 m pillar. This provides a reliable reference for the optimization of large coal pillars under multiple disturbances in coal mines with similar working conditions in other countries around the world.  
1. For solving large coal pillar shortening difficulty under the disturbance of mining on both sides, this research adopts the method of theoretical analysis-numerical simulation-site monitoring, based on key stratum theory, builds the structural mechanics model, reasonably analyzes the displacement of the surrounding rock, comes up with the state of distribution of supporting pressure, and applies the method of limit equilibrium to obtain the theoretical width of the coal pillar is 16 m. The double roadway excavation is relatively small, and the position of the roadway is located in the high-stress peak area. Reasonably, reducing the coal pillar size is the best choice.
2. FLAC3D numerical simulation is used to verify the results, which show that when the coal pillar width is 16 m, the stress of the coal pillar is lower, and the range of the plastic zone is smaller under the condition of mining on one side, and the stress peak is reduced under the condition of mining on both sides, and there exists a stress buffer zone of 1-5 m, and the elastic zone width is large. Therefore, compared with the original 20 m coal pillar, the 16 m coal pillar can meet the requirements of safety and efficiency.
3. Combined with field monitoring results, it is concluded that the range of mining pressure manifestation is 30 m, and when the distance of the monitoring station from the working face is less than 20 m, the internal stress of the coal pillar increases sharply, and the peak stress of the 16 m deep borehole is less than 10 MPa, indicates the 16 m coal pillar's rationality.  
In summary, this study gradually deepens and advances from the above three aspects, verifies the feasibility of a 16 m small coal pillar, provides the theoretical basis and engineering support for the optimization of double-roadway way excavation large coal pillars, and provides reliable examples for coal mines with similar conditions. However, there are still shortcomings. Limited by geological conditions, the stratum and surrounding rock conditions of Jinjitan Coal Mine are good, and this study did not consider the complex soft rock geological conditions. The production conditions of Jinjitan Coal Mine are good, and it is less affected by gas and mine earthquakes. This coal pillar optimization does not include the possible gas explosion and mine earthquake in the research scope. So, there is still much room for improvement.  
Methodology, L.P.; software, M.H.; validation, L.P. and K.G.; formal analysis, K.G.; investigation, L.P.; data curation, K.G.; writing--review and editing, K.G.; supervision, M.H.; project administration, L.P.; funding acquisition, L.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (Grant Number 51674058).  
Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to the confidentiality of the project involved.  
**Acknowledgments:** We thank the anonymous reviewers for their constructive feedback.  
**Conflicts of Interest:** The authors declare no conflicts of interest.