Investigation of a Comprehensive Methodology for Overburden Delamination Grouting to Mitigate Longwall Mining Surface Subsidence

Underground mining-induced surface subsidence poses significant risks to overlying structures, infrastructure, and the environment. Overburden delamination grouting has emerged as an effective technique to mitigate subsidence, but its design requires a comprehensive understanding of fractured-zone development, grouting-layer placement, isolation-layer stability, and grout material performance. This study developed an integrated methodology for overburden delamination grouting in longwall mining by combining fractured- and bending-zone analysis, grouting-layer design, isolation-layer stability evaluation, grout material strength design, and surface-subsidence monitoring for performance assessment. The mechanical properties of grout materials were systematically evaluated through laboratory testing, including compressive behavior and stress–strain response. Results indicate that ternary mixtures exhibit the best compressive stability, with a fly ash–coal gangue–slag powder ratio of 4:3:3 achieving a compressive ratio of 8.2%. The proposed workflow and selected materials were validated through three representative engineering case studies, demonstrating practical applicability under varied geological and mining conditions. Surface-subsidence monitoring results show that grouting effectively reduces subsidence and supports the continued safe performance of overlying structures. This study offers both theoretical guidance and practical solutions for sustainable subsidence control in underground mining.