Hydrogeological analysis and salvage of a deep coalmine after a groundwater inrush

This paper presents a case history of the permanent salvage of the Sanhejian Coalmine in China after a sudden groundwater inrush, which includes emergency responses, hydrogeological analyses, and design and performance of bulkheads. The inrush accident occurred in October 2002 in the mined-out area with a high water pressure of 7.6 MPa and a high water temperature of 51°C. The emergency response quickly followed up to provide the time required to perform a detailed hydrogeological analysis to identify the source and pathway of groundwater. The Sanhejian Coalmine is geologically located in the Tengxian anticline hydrogeological setting. The Sunshidian fault, the northern boundary of the mine, was assumed impermeable in the original hydrogeological report. After the accident and hydrogeological analysis, this assessment was revised and the fault was considered to be permeable. The Sunshidian fault connects the strata in the mine and the excellent water-productive Middle Ordovician Majiagou Formation in the core of the Tengxian anticline. It was concluded that the water inrush was from the underlying Ordovician karst aquifer and the pathway was a hidden tectonic structure in the strata overlying the aquifer. This assessment served as the guideline for salvaging the mine in this project. After a detailed technical and economic analysis, a concrete bulkhead design was selected from several alternatives including dewatering and surface grouting. The performance of the bulkheads has been sufficient for the last 6 years since their construction. This case history shows that the hydrogeological analysis plays an essential role in successfully salvaging the coalmine from the water inrush by identifying the source and pathway of groundwater.