Long-term water and salt transport patterns during soil reconstruction in coal mining subsidence areas using activated coal gangue

Coal mining not only generates large amounts of coal gangue but also causes surface subsidence, soil degradation, and other environmental issues. The utilization of coal gangue for the restoration of degraded soils in subsidence areas represents a crucial approach to simultaneously address the issues of solid waste emissions and soil degradation. In this study, taking degraded soil in the collapsed wind erosion mining area as an example, coal gangue activated by means of calcination and acid leaching was combined with fly ash to improve the soil. Two soil reconstruction schemes, namely single-layer improvement and double-layer improvement, were designed using the improved soil. With the assistance of HYDRUS-3D software, models for the soil reconstruction schemes were established, and continuous soil moisture infiltration experiments were conducted to verify the accuracy of the model. The results show that the R² values range from 0.89 to 0.98 and the root mean square error (RMSE) values range from 0.051 to 0.064. Finally, soil water and salt transport experiments were performed to analyze the water and salt transport characteristics in the three soil reconstruction schemes. The results suggest that the shallow soil moisture content in the single improved layer scheme is 26.02 % and 6.73 % higher than the other two schemes, demonstrating its better water retention. The peak content of salts that accumulate in the surface soil is 7.30 mg/cm³ in the double improved layer scheme, which is 29.3 % and 23.3 % lower than the other two schemes, highlighting its stronger salt isolation effect. The research findings are expected to provide a reference for ecologically utilizing coal-based solid waste and restoring degraded soil in mining areas.