An application of hydraulic tomography to a deep coal mine: Combining traditional pumping tests with water inrush incidents

Water inrush incidents threaten the safety of coal mining. Understanding of hydrogeologic parameter distributions is critical for preventing water-related hazards in coal mines. During the deep mining (>1000 m) under the North China Plain, water from water-bearing strata discharges into coal seams through geologic conduits (i.e. water inrush) due to the fractured zone under the floor of working faces. In this study, a water inrush incident was exploited as an active stimulus. A 3D groundwater flow model was built for the eighth member of the Middle Ordovician system in Xingdong coal mine. Using this model and an inverse approach, we first checked if the data from the incident and an independent pumping test carry non-redundant information about the heterogeneity of the mine. Afterward, we combined these datasets to conduct a large-scale (approximately 10 km) hydraulic tomography (HT) analysis. The estimated hydraulic conductivity distribution from the HT analysis is found consistent with the distribution of known geologic faults. That is, a cluster of faults is characterized as a high-conductivity zone. A high conductivity zone is identified at locations close to the water inrush location, which is the high cement consumption zone during the grouting project. Finally, results of this study promote exploiting the water inrush events as a HT survey for mapping geologic structures over a large area.