Mechanism and field validation of fly-ash grouting for mitigating mining-induced surface subsidence

The extensive extraction of global coal resources has induced severe surface subsidence in goaf areas, posing signif-icant threats to the surrounding environment and infrastructure. This study investigates the application and mechanisms of overburden separation grouting technology for controlling surface subsidence, using the 2311 working face of Changcun Coal Mine in China as a case study. A grouting process was designed utilizing fly ash as the primary material, incorporating an optimized borehole layout, dynamic adjustment of grouting parameters, and scientific selection of grouting timing. A visual compression-flow experimental system was employed to sys-tematically analyze the compressive stress-deformation relationship and bleeding characteristics of the fly ash slurry, providing critical evidence for determining grouting process parameters. Combined with long-term surface deformation monitoring data, the significant effectiveness of the grouting technology in mitigating surface subsid-ence was confirmed. The key transferable contributions of this research are: (i) a quantitative method to determine the optimal grout-ing-production ratio (≈ 0.5) for effective subsidence control; (ii) a dynamic pressure adjustment strategy based on real-time subsidence monitoring; and (iii) an integrated laboratory-field validation framework linking slurry rhe-ology to field performance. These findings provide a process-level basis for engineering practices in coal mines with comparable geological and mining conditions, offering both methodological innovation and practical guidance. .