Techniques for coal resource conservation during the ecological restoration of alpine mining areas on plateaus

Objective The prolonged coal mining of the Muli coalfield, located in an alpine region in the eastern Qinghai-Tibet Plateau, has posed many ecological challenges, which especially include the presence of considerable quantities of disturbed coal resources in open-pit mining areas. This study aims to achieve scientific and effective coal resource conservation during the ecological restoration of coal mines.

Methods Focusing on the Jvhugeng mining area of the Muli coalfield, this study investigated the destruction characteristics of the coal resources in the open-pit mining area. From the perspective of geological mechanisms behind the destruction, this study artificially constructed the roofs of residual coal seams and their overlying protective layers using the method for constructing eco-geological layers. By fully leveraging geologic environments in the mining area while considering intensive resource utilization, economic viability, and coordination between resources and landscapes, this study integrated coal resource conservation into the ecological restoration of the mining area using countermeasures tailored to zones and categories based on local conditions. Accordingly, this study developed two techniques for coal measure resource conservation: the technique for constructing coal seam roofs using artificial frozen soil layers as eco-geological layers and the technique for coal resource conservation by replacing backfill with water. The former technology can be further divided into the conservation technique for slope coal seams, the technique for simulating frozen soil layers as the roofs of coal seams at the mining pit bottom, and the technique for managing and conserving coal seams subjected to spontaneous combustion.

Results and Conclusions  Field measurements of test pits reveal that 18 months after control, the artificially constructed coal resource conservation layers had progressively recovered and preliminarily formed frozen soil layers. During the melting season, the frozen soil layers exhibited melting depths ranging from 1.8 m to 2.3 m, leading to the formation of new coal seam conservation layers. Replacing backfill with water contributes to both coal seam conservation and landscape coordination while considering the economic viability, suggesting satisfactory application effects. This study, developing a novel philosophy for the coordination between coal resource conservation and ecological restoration in alpine mining areas through exploration, provides a reference for the ecological restoration and control of open-pit coal mines in similar regions.