A significant amount of open-pit-mine broken sandstone (OMBS) is produced during open-pit mining. The mechanical strength of the loose sandstone is critical for ensuring dump slope stability and sustainable mine construction. This study investigates the modification of OMBS using artemisia sphaerocephala krasch (ASK) gum to enhance its engineering properties. Unconfined compressive strength, shear strength and permeability tests were conducted to quantitatively analyze the modification effect. And the stability was evaluated using FLAC3D simulation methods. The modification mechanism was characterized through SEM, FT-IR, XRD. The results demonstrated that the addition of 2 % ASK gum significantly improved OMBS mechanical performance and reduced permeability. Meanwhile, the failure mode of OMBS changed with the ASK gum content increasing. The simulation result indicated the stability of modified dump slope was better under the drying-wetting cycle. From the perspective of microstructure and chemical characteristics, the addition of ASK gum created new hydrogen bonds through intermolecular interactions with the hydrophilic groups between OMBS particles and formed a dense and stable structure through three reinforcement modes: surface encapsulation, pore filling, and bonding connection. This study provides a new idea for resource saving and environmentally friendly mining area development.

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.

An ancient landslide located in Xichang, China, that was reactivated by mining excavation and rainfall was investigated in this study. The volume of the reactivated landslide was approximately 1200 x 104 m3, thus posing a major threat to the mining area's safety. Field surveys, drilling, on-site monitoring, laboratory studies, and numerical analyses were performed to investigate the landslide deformation characteristics and reactivation mechanism. The reactivated landslide was divided into four zones: the leading-edge collapse, the sliding, the uplifting, and the traction sliding zones. X-ray diffraction and ring shear tests indicate that the sliding zone soil exhibits significant strength-weakening characteristics when exposed to water, and the residual cohesion and internal friction angle decrease by 26.9% and 28.9%, respectively, as the moisture content increases from 15 to 24%. Additionally, a three-dimensional numerical simulation was conducted to quantitatively analyze the stability evolution of the landslide. The results showed that the topographic, stratigraphic lithology, and sliding zone soil properties provided the basic conditions for landslide formation, while mining excavation and concentrated rainfall triggered landslide reactivation. Furthermore, a conceptual model characterizing the reactivation process was constructed, and the reactivation process was divided into five stages: leading-edge collapse, sliding, extrusion and bulging, deformation expansion, and accelerated creep deformation. This study provides a basis for understanding the reactivation mechanism of ancient open-pit mine landslides.

Intense precipitation infiltration and intricate excavation processes are crucial factors that impact the stability and security of towering and steep rock slopes within mining sites. The primary aim of this research was to investigate the progression of cumulative failure within a cracked rock formation, considering the combined effects of precipitation and excavation activities. The study was conducted in the Huangniuqian eastern mining area of the Dexing Copper Mine in Jiangxi Province, China. An engineering geological investigation was conducted, a physical model experiment was performed, numerical calculations and theoretical analysis were conducted using the matrix discrete element method (MatDEM), and the deformation characteristics and the effect of the slope angle of a fractured rock mass under different scenarios were examined. The failure and instability mechanisms of the fractured rock mass under three slope angle models were analyzed. The experimental results indicate that as the slope angle increases, the combined effect of rainfall infiltration and excavation unloading is reduced. A novel approach to simulating unsaturated seepage in a rock mass, based on the van Genuchten model (VGM), has been developed. Compared to the vertical displacement observed in a similar physical experiment, the average relative errors associated with the slope angles of 45 degrees, 50 degrees, and 55 degrees were 2.094%, 1.916%, and 2.328%, respectively. Accordingly, the combined effect of rainfall and excavation was determined using the proposed method. Moreover, the accuracy of the numerical simulation was validated. The findings contribute to the seepage field in a meaningful way, offering insight that can inform and enhance existing methods and theories for research on the underlying mechanism of ultra-high and steep rock slope instability, which can inform the development of more effective risk management strategies. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Open-pit mining seriously damages the original vegetation community and soil layer and disturbs the carbon cycle of vegetation and soil, causing instability in the mining ecosystem and decrease in the carbon sequestration capacity of the mining area. With the deepening of environmental awareness and the influence of related policies, the ecological restoration of open-pit mines has been promoted. The mining ecosystem is distinct owing to the disperse distribution of mines and small scale of single mines. However, the carbon sequestration capability of mines after ecological restoration has not been clearly evaluated. Therefore, this study evaluated the carbon sequestration capacity of restoration mines, taking the mines of the Yangtze River Basin in Jurong City, Jiangsu Province as the research objects. Firstly, the visual effects of the vegetation and soil in their current status were determined through field investigation, the methods for sampling and data collection for the vegetation and soil were selected, and the specific laboratory tests such as the vegetation carbon content and soil organic carbon were clarified. Meanwhile, the evaluation system consisting of three aspects and nine evaluation indexes was established by using the analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE). The process of evaluation included the following: the establishment of the judgment matrix, calculation of the index weight, determination of the membership function, and establishment of the fuzzy membership matrix. Finally, the evaluation results of the restoration mines were determined with the 'excellent, good, normal and poor' grade classification according to the evaluation standards for each index proposed considering the data of the field investigation and laboratory tests. The results indicated that (1) the evaluation results of the mines' carbon sequestration capacity were of excellent and good grade at a proportion of 62.5% and 37.5%, which was in line with the field investigation results and demonstrated the carbon sequestration capacity of all the restored mines was effectively improved; and (2) the weights of the criterion layer were ranked as system stability > vegetation > soil with the largest value of 0.547, indicating the stability of the system is the main factor in the carbon sequestration capacity of the mines and the sustainability of the vegetation community and the stability of soil fixation on the slope. The proposed evaluation system effectively evaluates the short-term carbon sequestration capability of the restoration mining system according to the visual effects and the laboratory testing results, objectively reflecting the carbon sequestration capacity via qualitative assessment and quantitative analysis. The evaluation method is relatively applicable and reliable for restoration mines and can provide a reference for similar ecological restoration engineering.

PurposeOver the past three decades, open-pit mining has been expanding in arid and semi-arid areas of China.Open-pit mining profoundly changes the soil environment and has a profound impact on the circulation of soil water in the aeration zone.Therefore, this research explores the impacts of open-pit coal mining on soil moisture processes in the semi-arid grasslands of Eastern Inner Mongolia Autonomous Region, China.Materials and methodsSoil samples were collected from depths of 0-500 cm at Shengli No. 1 open-pit mine's inner dump and a nearby natural grassland. These soil samples were analyzed for stable isotope characteristics (delta 2H,delta 18O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta 2 H, \delta {18} O}$$\end{document}) and moisture content. Collection of underground water samples inside and outside the mining area for conductivity analysis.Results and discussionSoil evaporation loss in the mine's inner dump was significantly higher than in the grassland, with rates of 22.26% for delta 18O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta {18} O}$$\end{document} and 6.61% for delta 2H\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\delta 2 H}$$\end{document}. The limiting depth of soil evaporation at the mine was found to be 260 cm, compared to 200 cm in the grassland. The increased underground water conductivity in the mine area was linked to heightened soil evaporation loss. Isotopic profiling of the soil indicated that the open-pit mining led to deeper preferential flow infiltration during heavy precipitation, reaching 280 cm in the mine area versus 220 cm in the grassland.ConclusionsThe surface soil moisture content (SMC) increased due to mining activities intensified water-heat exchanges with the atmosphere, leading to more frequent and severe wet-dry cycles. This study provides a comprehensive understanding of open-pit mining's impact on SMC, evaporation, and infiltration in semi-arid areas, offering critical insights for ecological reclamation and sustainable mine construction.

There are many factors affecting the stability of open-pit mine slopes, among which slopes with soft interlayers have become an important factor inducing deformation and instability due to their poor mechanical properties. In this paper, for the destabilization of a slope with soft interlayer under rainfall infiltration in an open-pit mine in Zhejiang Province of China during the rainy season, a sudden change of displacement at the monitoring point and the formation of a continuous plastic deformation of the slope are proposed as the criteria for slope destabilization through the establishment of a rainwater seepage-stress coupling model combined with the strength reduction method, and by using COMSOL Multiphysics finite element numerical simulation software to establish a three-dimensional numerical model based on the actual mining slope conditions. The safety principle is introduced through the strength reduction method to analyze the stability of the slope with soft interlayer under the coupling effect of seepage and stress. The safety coefficients of the slope with soft interlayer are calculated by using Numerical methods under the coupling effect of seepage and stress. The influence of rainfall intensity and duration on the stability or safety factor of the slope with soft interlayers was studied through analysis of stress, saturation, displacement, and pore pressure evolution. The mechanism of rainfall affecting slope stability was investigated, and the findings were validated using an engineering case study of a slope with a soft interlayer. The findings show that rainfall intensity is the main factor affecting slope stability in the open-pit mine slope with soft interlayer. The higher the rainfall intensity, the faster the shallow soil forms a saturation zone, whereas soft interlayers speed up the process and endanger slope stability. The slope prevention and control technology of the prestressed anchor cable (rod) framework was proposed based on the slope management construction conditions of the mine, and the effectiveness of the measure was verified through on-site industrial tests. The research findings provide a reference for preventing and controlling slope with soft interlayers in open-pit mines under similar conditions.

The collapse of open-pit coal mine slopes is a kind of severe geological hazard that may cause resource waste, economic loss, and casualties. On 22 February 2023, a large-scale collapse occurred at the Xinjing Open-Pit Mine in Inner Mongolia, China, leading to the loss of 53 lives. Thus, monitoring of the slope stability is important for preventing similar potential damage. It is difficult to fully obtain the temporal and spatial information of the whole mining area using conventional ground monitoring technologies. Therefore, in this study, multi-source remote sensing methods, combined with local geological conditions, are employed to monitor the open-pit mine and analyze the causes of the accident. Firstly, based on GF-2 data, remote sensing interpretation methods are used to locate and analyze the collapse area. The results indicate that high-resolution remote sensing can delineate the collapse boundary, supporting the post-disaster rescue. Subsequently, multi-temporal Radarsat-2 and Sentinel-1A satellite data, covering the period from mining to collapse, are integrated with D-InSAR and DS-InSAR technologies to monitor the deformation of both the collapse areas and the potential risk to dump slopes. The D-InSAR result suggests that high-intensity open-pit mining may be the dominant factor affecting deformation. Furthermore, the boundary between the collapse trailing edge and the non-collapse area could be found in the DS-InSAR result. Moreover, various data sources, including DEM and geological data, are combined to analyze the causes and trends of the deformation. The results suggest that the dump slopes are stable. Meanwhile, the deformation trends of the collapse slope indicate that there may be faults or joint surfaces of the collapse trailing edge boundary. The slope angle exceeding the designed value during the mining is the main cause of the collapse. In addition, the thawing of soil moisture caused by the increase in temperature and the reduction in the mechanical properties of the rock and soil due to underground voids and coal fires also contributed to the accident. This study demonstrates that multi-source remote sensing technologies can quickly and accurately identify potential high-risk areas, which is of great significance for pre-disaster warning and post-disaster rescue.