Trend of water inrush at depth in the Puyang coal mine, karst basin area, southeastern Yunnan plateau

The Puyang coal mine, southeastern Yunnan lies in shallow Neogene strata of a fault-depression, encompassed by three kinds of hydrogeologic boundaries. The elevation of coal seams is lower than the outlet of an underground river by 100-230 m. Surroundings and basin basement all host karst aquifers, of which the confined water head is higher than the coal-bed bottom by 67-268 m, and the average confined water head at the estimated lowest mining elevation is about 260 m. To solve the inrush threat of groundwater in the mine, it is required to monitor the amount of water inflow and outflow of the Puyang river, and establish a long-term drainage scheme. Investigations show that the karst in the mine area is of clear vertical zoning. The karst aquifer beneath the coal-bed bottom is dominated by weak karst zones. In the mine area, 93% of underground water drainages through the underground Puyang river. Besides, confined beds of some thickness exist below the coal seam, thus local water inrush may occur when mining at depth. But the amount of such water inrush is not big, with the maximum only equivalent to the volume of underground water runoff to the Puyang river in the natural state. Combining the control factors of pit water filling and dynamic analysis of underground water, it is considered convenient and feasible to estimate amount of water inrush using the water balance method.