Complex hydrogeological conditions in China's coal mines have contributed to frequent mine water disasters. A simple and effective method to determine water inflow sources and paths is therefore essential. The Longmen Mine, located in Henan Province, in central China was used as a case study. A Piper diagram and cluster analysis were used to screen the characteristic values of 18 water samples from potential aquifers. A comprehensive fuzzy evaluation of the groundwater ions was carried out to determine the main source of the total mine inflow. Then, based on conservation of ionic masses, a matrix function was established to calculate the groundwater recharge composition. Finally, using measured water inflows for the Cambrian limestone aquifer, the calculated and observed results were compared. The results showed that the Carboniferous Taiyuan Formation limestone aquifer (the L 7 limestone aquifer) accounts for 60.8% of the total mine inflow, while the Cambrian limestone and roof sandstone aquifers account for 34.8 and 4.4% of the inflow, respectively. The normal mine inflow totals about 19,200 m 3 /day, of which 6,840 m 3 /day is from the Cambrian limestone aquifer. This agrees well with the calculated value of 6,720 m 3 /day. Thus, the method is feasible and reliable.

On 22 May 2017, a groundwater inrush accident occurred in the gob area of coal floor at Dongyu Coal Mine in Qingxu County, Shanxi Province, China. The water inrush accident caused great damage, among which six people died and the direct economic loss was about CNY 5.05 million. An elliptical permeable passage appeared at the floor of the water inrush point, and the lithology of the outburst is mainly fragmented sandy mudstone and siltstone of coal roof No.2 in the lower layer of coal seam No.3, which is currently being mined, with a peak inflow of 500 m3/h. The water inrush happened due to following reasons: There is an abandoned stagnant water-closed roadway in coal seam No.2, which is the lower mine group of coal seam No.3. The abandoned roadway of coal seam No.2 is an inclined roadway. The water level of the roadway far away from the accident point is higher than the floor elevation of coal seam No.3. Under the joint action of water pressure, mining disturbance, and weakening of goaf water immersion, the original equilibrium state was broken, resulting in the destruction of the only 7 m water-barrier rock pillar between coal seam No.3 and coal seam No.2. The water in the goaf led upward along the roof crack, gradually evolved from seepage to gushing water, and a large amount of goaf water poured into the roadway in the working face of the 03304 panel, finally leading to the occurrence of catastrophic water inrush. Technically, the miners did not implement the technical provisions of the coal mine water control regulations, leading to the accident. In addition, the failure to arrange evacuees to a safe location after apparent signs of water inrush also increased the catastrophic level of the accident.

No abstract

Goaf water in mining areas is widely found in China’s coal mines. To clarify the hydrogeochemical characteristics of goaf water and the influence mechanism of water–rock interaction and further reveal microbial action on the formation of goaf water quality, the goaf water in the Menkeqing coal mine was taken as the object, and physical modeling was used to simulate the process of the real goaf changing from an oxygen-sufficient environment to an anoxic environment with the rise of groundwater level in this work. The experimental results showed that the water–rock interaction in the goaf was mainly the dissolution–precipitation of minerals in the rocks of the caving zone and fracture zone, cation exchange, and oxidation of pyrite in the coal layer. The primary sources of Na+ and K+ in the goaf water were the dissolution and reverse ion exchange of silicate minerals such as albite and potassium feldspar, while Ca2+ and Mg2+ mainly from the dissolution of minerals such as calcium feldspar, calcite, and chlorite. The oxidation of pyrite in coal was the main reason for the increase in SO42− concentration, the enhancement of reduction, and the decrease in pH and DO (dissolved oxygen) in the goaf water. Relative abundance of sulfate-reducing bacteria (SRB) in goaf (e.g., Desulfosporosinus, Desulfobacterium, etc.) increased gradually, inhibiting the increase in SO42− concentration in goaf water through the devulcanization of SRB. The inverse hydrogeochemical modeling was performed using PHREEQC for two stages of the simulation experiment: 0–30 days and 30–300 days. The simulation results show that the water–rock action in the formation of goaf water mainly occurred in the simulation experiment’s early stage (0–30 days), and the mineral dissolution is dominant throughout the experimental stage. The results of the study provide a theoretical reference for the prediction of highly mineralized water pollution in goaf and its prevention and control.

After a water inrush disaster occurs in the mine production process, it is urgent to identify the source of water inrush and formulate corresponding countermeasures in the complex hydrogeological condition of coal mines. Therefore, accurate identification of mine groundwater source is one of the keys to prevent mine water disasters. According to the difference between the hydrochemical compositions of three aquifers in Chengjiao coal mine, six primary ions (Na++K+, Ca2+, Mg2+, SO42-, Cl,- and HCO3-) were selected as the indexes for groundwater source identification. On this basis, a mathematical model for groundwater source identification was established by combining the analytic hierarchy process- (AHP-) entropy weight method and the set pair analysis (SPA) theory. Next, this model was used to identify the sources of 10 sets of water samples from the mine, and then, the identification results were compared with the results of conventional models established using Fisher discriminant analysis (FDA) and Bayes discriminant analysis (BDA) methods. The results show that the SPA-based model performs better in identifying the groundwater sources. Furthermore, the model was used to identify the source of water inflow in the No. 21304 panel. The analysis on identification results reveals that the area close to the F20 normal fault tends to receive water supply from the Ordovician limestone aquifer and the Taiyuan Formation limestone aquifer, so it should be regarded as a key area for water inrush prevention and control.