**6. Future Prospects and Possible Research Directions**

Underground reservoirs in coal mines are an effective means to develop China's coal mining in the direction of environmental protection. They not only reduce the waste of water resources and carbon dioxide emissions, but also save costs and improve the economic benefits of coal mines. In this paper, one of the factors affecting the stability of coal pillar dams in underground reservoirs of coal mines has been discussed: that is, the development and the evolution law of fissures, and some useful suggestions on the size of coal pillars, have been put forward. Future research on underground reservoirs in coal mines may be directed toward the following topics:


**Author Contributions:** Conceptualization, B.Z.; Methodology, B.Z. and W.N.; Investigation, B.Z. and X.H.; Writing—original draft, B.Z., W.N. and H.L.; Formal analysis, B.Z., H.L. and Y.S.; Writing review and editing, B.Z. and H.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding author upon request.

**Conflicts of Interest:** The authors declare no conflict of interest.
