Optimization study on transverse mining zoning during the capacity expansion stage of nearly horizontal open-pit coal mines

To address key challenges during the capacity expansion of the Baoqing Chaoyang Open-Pit Coal Mine from 7 to 11 Mt/a—such as insufficient working-line length, excessive advancing intensity, poor coordination between mining zones, elevated internal dump slope risks, and constrained dumping capacity—this study develops a zoning optimization method based on Unascertained Measure Theory (UMT). A working-line optimization model, constructed from coal seam thickness, density, production targets, and advancing dynamics, indicates a rational length range of 1350–2050 m at 11 Mt/a. Guided by coal seam occurrence and the original layout, the initial longitudinal-mining area is reorganized into four transverse primary zones. An eight-dimensional evaluation index system is established, covering geological, geotechnical, hydrogeological, topographic, engineering, economic, environmental, and social factors. Combined weighting using the Analytic Hierarchy Process and the Entropy Weight Method, together with multiplicative normalization, yields a hybrid subjective–objective weighting set. On this basis, four-level UMT evaluation functions and an evaluation matrix are constructed, and comprehensive assessments are performed using a confidence recognition criterion. The results show that Scheme II achieves the best overall performance in terms of economic efficiency, transportation, safety, and resource utilization, with a V₁-level confidence of 0.7058, significantly higher than the other schemes. Under Scheme II, the four zones provide 971.2 Mt of recoverable raw coal, an average stripping ratio of 5.8, and a maximum service life of 34.3 years. The proposed integrated framework of working-line design, mining-zone zoning, and uncertainty-based evaluation offers a practical decision-support tool for capacity expansion planning in large-scale open-pit coal mines.