Underground space utilization of coalmines in China: A review of underground water reservoir construction

•Underground water reservoirs provides basis for water and geothermal utilization.•Coal pillar dam stability is important for underground water reservoirs operation.•Ecologic and economic evaluation should be studied ahead reservoirs construction.•Underground water reservoirs in operational and abandoned mines are prospected. A large number of abandoned mines with sizeable underground space resources were formed in China. Meanwhile, for an operational mine, the protection and utilization of mine water resources are increasingly important for ecological environment construction. The coal industry faces difficulties regarding safe and efficient utilization of abandoned mine resources and protection of the ecological environment in the operational mines. As a solution to these problems, underground water reservoirs (UWRs) technology were proposed and implemented. There are three underground space utilization modes based on UWRs: storage and filtration of mine water, pumped hydroelectric storage plants system and geothermal utilization model. This paper provides a review of existing research literature and thought on the UWRs design, construction and operation. The main underground space for UWRs in China is the caving zone formed by longwall mining. Compared with previous UWRs that utilized the tunnel as the main space, the storage capacity is larger and the gangue in the caving zone can be used to purify the mine water. However, the stress environment of the UWRs in the caving zone is more complex, and the stability of the surrounding rock is relatively poor. Therefore, there are many key elements in UWRs construction and operation. Storage capacity calculation, coal pillar dam stability, water quality evolution are the principal issues. Additionally, the feasibility analysis including ecological environment effects and economic evaluation should be carried out before UWRs construction in coal mines. Based on the current development of UWRs and the future utilization of underground space in China, the prospects for UWRs in operational and abandoned mines are presented.