In order to explore the potential effects of abandoned coal mines on the water quality of Ordovician limestone aquifers, water-rock interaction simulations were conducted. After the closure of the coal mine, the karst water in the goaf area and the waste gangue had a geochemical reaction, and the above-mentioned water-rock process was simulated by an indoor static immersion experiment to explore the differences in the effect of different types of karst water on the dissolution of gangue. The basic water quality parameters pH, EC (electrical conductance), and ORP (oxidation-reduction potential) showed different trends in karst hydro-immersion solution and ultra-pure hydro-immersion solution; pH and EC had greater fluctuations in two sets of ultrapure hydro-immersion solutions, while ORP fluctuated more widely in three groups of karst hydro-immersion solutions. In addition, gangue minerals dissolved more significantly in bodies of water where limestone was added. The results of chemical component clustering showed that TDS (total dissolved solids) and EC were homopolymerized in each immersion solution, and subsequent correlation analysis showed that TDS and EC clusters were more significantly affected by mineral properties in ultrapure water-immersion solutions, and more affected by dominant ions in karst water-immersion solutions.

In mining areas where gangue is used for infill mining, Ordovician limestone karst water is affected by discarded gangue, and the water quality changes significantly. In this study, the effects of gangue on water quality change under different immersion solution conditions were evaluated by Zhai Zhen Coal Mine, Hongqi Coal Mine Ordovician Limestone Karst Water, and Baizhuang Coal Mine. The results showed that the cations in each group of immersion solutions had similar trends, and the Na+ concentration fluctuations were greater in karst water immersion solutions with higher initial sodium ion concentrations, while the fluctuations of calcium and magnesium ions were more obvious in the early stage of immersion, and the fluctuations were gradually slowed down in the later stage. The anions in the immersion solution also have a similar fluctuation trend, but only in the early stage of immersion. By comparing the changes of the three indexes (pH, TDS, and ORP) in the immersion solution, it was found that highly mineralized karst water had a good buffering effect on the changes in the basic water quality index, while the ultrapure water quality index with low salinity had the greatest change. The 100% stacked columnar plot between the main water chemical ion changes shows the relative scale relationship of the water chemical components in the immersion solution at each period, and the water chemical components change significantly in the early immersion period (0–7 d), and then enter the fluctuation changes period, and the ion changes in the fluctuation changes period are mainly Na+ and SO42− ions. This study provides a theoretical basis for exploring the changes of gangue to the quality of karst water in Ordovician limestone and also provides theoretical guidance for the study of groundwater pollution mechanisms in closed coal mines.

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In order to study the seepage failure mechanism of roadway filling medium consisting of cohesive soil under complex hydrogeological conditions, a large-scale triaxial stress-seepage test system was utilized to investigate the influence of kaolin content and seepage loading rate on the seepage characteristics of filling medium. Through the analysis on the variation rules of sand loss and particle size distribution, the seepage characteristics and whole process of seepage instability of filling medium were explored in depth. It is concluded that (1) The seepage instability process of filling medium can be categorized into three stages: the initiation loss of fine clay, the accelerating loss of soil, and the stable status of soil loss. (2) The seepage failure process rate is proportional to the seepage loading rate and inversely proportional to the content of kaolin. (3) The kaolin and sand content of remaining mixture presented initial>bottom>middle>top status. The research results have guidance value for exploring the instability evolution mechanism of filling medium in deep roadway.