Open-pit coal mining poses a severe threat to regional ecological security. Rapid and accurate monitoring of ecological quality changes is crucial for regional ecological restoration. In this study, taking the Wujiata open-pit coal mine as an example, the Red-Edge Normalized Difference Vegetation Index (RENDVI), Salinity Index (SI-T), WETness index (WET), Normalized Differential Built Soil Index (NDBSI), Land Surface Temperature (LST), and Desertification Index (DI) were used to construct the Open-pit Mine Remote Sensing Ecological Index (OM-RSEI) through Principal Component Analysis (PCA). The ecological quality and restoration conditions of typical mining areas in arid and semi-arid regions were monitored and evaluated. The results shown that: (1) The contribution rates and eigenvalues of OM-RSEI were higher than those of conventional RSEI, OM-RSEI was more applicable in open-pit mining areas. (2) From 2018 to 2023, the OM-RSEI of the Wujiata open-pit coal mine showed a 'V' shaped fluctuation that was damaged and then gradually recovered. (3) The degraded area of Wujiata open-pit coal mine and its 5 km buffer zone accounted for 78.02%, and the improved area accounted for 19.16%. (4) The average Moran's I index of OM-RSEI in the study area was 0.8189, and the high-high clustering corresponded to the 'good' and 'excellent' distributions, while the low-low clustering corresponded to the 'poor' and 'less-poor' distributions. The OM-RSEI provided a new indicator for monitoring and evaluation of ecological restoration in open-pit coal mines, which can provide theoretical support for ecological restoration in open-pit coal mining areas.

Non-technical summary To address the issues of declining groundwater levels and the degradation of soil ecological functions caused by open-pit coal mining in China. Based on theoretical analysis, laboratory experiments, on-site monitoring, mathematical modeling, and other means, the concept of coal ecological protection mining of 'damage reduction mining, three-dimensional protection, systematic restoration' is proposed. The mining concept has achieved remarkable ecological restoration effects, leading the scientific and technological progress of safe, efficient and green mining in open-pit coal mines. Technical summary The mechanism of damage propagation among 'rock-soil-water' ecological elements in open-pit coal mining was revealed. Adopting comprehensive damage-reducing mining technology throughout the entire stripping process, mining and drainage, shengli open-pit coal mine has doubled its production capacity, and reduced the land excavation and damage by 60 mu/year, reduced the mining area by 1,128 mu, and raised the groundwater level by 2.6-6 m, and the ecological restoration of the drainage field was advanced by more than 1 year. Adopting the three-dimensional water storage technology involves underground reservoirs, aquifer reconstruction, and near-surface distributed water storage units, baorixile open-pit mine has built the world's first open-pit underground water reservoir, with a water storage capacity of 1.22 million m(3), and the speed of groundwater level restoration has been increased by more than 70%. By adopting the systematic restoration technology of geomorphology-soil-vegetation in the discharge site, the soil water content in the demonstration area has been increased by 52%, the survival rate of plants has been increased by 34%, and the vegetation coverage has been increased by more than 40%. Social media summary Damage-reducing mining and systematic ecological restoration in open-pit coal mining are essential for the safe, efficient and green development of coal.

More than 80% of open-pit coal mines in China are located in northern regions, and the mechanical properties and stability of loose soil-rock mixtures in waste disposal sites are significantly affected by freeze-thaw effects. This article takes the external dumping site of the Baorixile open-pit coal mine in the northern high-altitude region of the Inner Mongolia Autonomous Region as the research object. Through on-site investigation and sampling, indoor triaxial tests (confining pressures of 100 KPa, 200 KPa, and 300 Kpa; moisture contents of 18%, 21%, and 24%), numerical simulation, and other methods, the mechanical properties of soil-rock mixtures in the dumping site under different freeze-thaw cycle conditions were tested to reveal the specific influence of the number of freeze-thaw cycles on the mechanical properties of soil-rock mixtures. Using the discrete element software PFC, the microstructural changes in soil-rock mixtures formed by freeze-thaw cycles were studied, and the deformation mechanism and slip mode of loose slopes in waste disposal sites under different freeze-thaw cycle conditions were explored. The relationship between the number of freeze-thaw cycles and slope stability was clarified. The following conclusions can be drawn: the compressive strength of soil-rock mixtures decreases as a quadratic function with increasing freeze-thaw cycles; as the number of freeze-thaw cycles increases, the internal cracks of the soil-rock mixture model increase exponentially; and as the number of freeze-thaw cycles increases, the stability of the slope in the dumping site decreases significantly, and this stability also decreases with an increase in dumping height.